Optical measuring device and optical measuring method

Abstract

To provide an optical measurement device and optical measurement method that can accurately identify at which timing a detected optical pulse is a reflection optical pulse corresponding to the optical pulse radiated even if an order of the optical pulse is replaced or the optical pulse overlaps with each other during a period of time until detection of the optical pulse from radiation thereof.SOLUTION: A plurality of optical pulses different in a time waveform from each other, and different in a center wavelength from each other are made incident upon a measurement object with the optical pulse spatially separated from each other every center wavelength, and a time waveform signal of the plurality of optical pulses is obtained by multiplexing and receiving the plurality of optical pulses reflected by the measurement object. An individual optical pulse appearing in the time waveform signal can be identified with each other based on respective time waveforms.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to an optical measurement device and an optical measurement method.

Background Art

[0002] Non-Patent Document 1 discloses a technique in which a plurality of optical pulses having different wavelengths are spatially separated from a broadband optical pulse including a plurality of wavelength components using a spectroscopic element, and each of the plurality of optical pulses is radiated at different timings toward each of a plurality of positions on a subject, and the optical pulses reflected at each of the plurality of positions on the subject are detected by a single light receiving element to perform distance measurement for each of the plurality of positions on the subject.

Prior Art Document

Non-Patent Document

[0003]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the technique disclosed in Non-Patent Document 1, since each of a plurality of optical pulses having different wavelengths is radiated toward each of a plurality of positions on the subject, the wavelengths of the optical pulses radiated toward the subject are different for each position on the subject, but the temporal waveforms of the optical pulses are the same for any position on the subject. Therefore, it is impossible to distinguish from each other a plurality of optical pulses reflected by the subject and detected by one light receiving element. For this reason, even if the order of the optical pulses is switched or the optical pulses overlap each other between the radiation of the optical pulses toward each of the plurality of positions on the subject and the detection of the optical pulses reflected at each of the plurality of positions on the subject, it is impossible to recognize this. Therefore, it is impossible to correctly identify which timing of the radiated optical pulses the detected optical pulse corresponds to as the reflected optical pulse. As a result, there is a problem that distance measurement cannot be correctly performed for each of the plurality of positions on the subject.

[0005] An object of the present disclosure is to provide an optical measurement apparatus and an optical measurement method capable of correctly identifying which timing of the radiated optical pulses the detected optical pulse corresponds to as the reflected optical pulse, even if the order of the optical pulses is switched or the optical pulses overlap each other between the radiation of the optical pulses and the detection thereof.

Means for Solving the Problems

[0006] The optical measurement apparatus according to the present disclosure includes a measurement optical pulse light source that outputs a plurality of measurement optical pulses having different temporal waveforms and different center wavelengths, a spectroscopic unit that spatially separates the plurality of measurement optical pulses from each other for each center wavelength and makes them incident on a measurement target, a multiplexing unit that multiplexes a plurality of measurement optical pulses reflected by the measurement target or transmitted through the measurement target and outputs them on one optical path, a light detection unit that receives the plurality of measurement optical pulses emitted from the multiplexing unit and outputs temporal waveform signals of the plurality of measurement optical pulses, and a measurement unit that measures the timing at which each of the plurality of measurement optical pulses is received by the light detection unit or the difference in the timing based on the temporal waveform signals.

[0007] Furthermore, the optical measurement method according to this disclosure comprises the steps of: outputting a plurality of measurement light pulses having different time waveforms and different central wavelengths; spatially separating the plurality of measurement light pulses according to their central wavelengths and causing them to be incident on a measurement target; combining the plurality of measurement light pulses that have been reflected by or transmitted through the measurement target and emitting them onto a single optical path; receiving the plurality of measurement light pulses emitted onto a single optical path and outputting time waveform signals of the plurality of measurement light pulses; and measuring the timing at which each of the plurality of measurement light pulses was received or the difference in such timings based on the time waveform signals. [Effects of the Invention]

[0008] According to the optical measuring device and optical measuring method described herein, even if the order of measurement light pulses is changed or the measurement light pulses overlap between the time the measurement light pulses are emitted and the time they are detected, it is possible to correctly identify which measurement light pulse corresponds to which time the detected measurement light pulse was emitted. Therefore, measurements using measurement light pulses can be performed correctly. [Brief explanation of the drawing]

[0009] [Figure 1] This figure shows an example of the configuration of a distance measuring device according to the first embodiment. [Figure 2] This figure shows an example of the configuration of the pulse formation section of the distance measuring device according to the first embodiment. [Figure 3] This figure shows the modulation surface of the spatial light modulator (SLM) of the distance measuring device according to the first embodiment. [Figure 4] This figure schematically shows an example of the time waveforms of multiple reflected light pulses measured by the distance measuring device according to the first embodiment. [Figure 5] This figure schematically shows an example of the time waveforms of multiple reflected light pulses measured by the distance measuring device relating to the comparative example. [Figure 6] This figure shows a part of the configuration of a distance measuring device according to the first embodiment. [Figure 7] This figure schematically shows an example of the time waveforms of multiple reflected light pulses measured by the distance measuring device according to the first embodiment. [Figure 8] (a) The spectral waveform of a single-pulse broadband measurement light pulse is shown. (b) The time intensity waveform of the same broadband measurement light pulse is shown. [Figure 9] (a) The spectral waveform of the output light from the pulse generation unit when rectangular wave phase spectral modulation is applied in the SLM is shown. (b) The time intensity waveform of the output light is shown. [Figure 10] This figure shows the procedure for calculating the phase spectrum using the iterative Fourier transform. [Figure 11] This figure shows the procedure for calculating the phase spectral function. [Figure 12] This figure shows the procedure for calculating spectral intensity. [Figure 13] This figure shows an example of the procedure for generating a target spectrogram. [Figure 14] This figure shows an example of the procedure for calculating the intensity spectral function. [Figure 15] (a) This figure shows the spectrogram SGIFTA(ω,t). (b) This figure shows the target spectrogram TargetSG0(ω,t) which is a modified version of the spectrogram SGIFTA(ω,t). [Figure 16] This figure shows an example of the configuration of a surface roughness measuring device according to the second embodiment. [Figure 17] This figure schematically shows an example of the time waveforms of multiple measurement light pulses and multiple reflected light pulses measured by the surface roughness measuring device according to the second embodiment. [Figure 18] This figure shows an example of the configuration of a two-dimensional spectrometer in a distance measuring device according to a first modification of the first embodiment. [Figure 19] This is a side view showing the structure of the VIPA plate of a distance measuring device according to a first modification of the first embodiment. [Figure 20] This figure shows an example of the configuration of a distance measuring device according to a second modification of the first embodiment. [Figure 21] This figure shows an example of the configuration of a distance measuring device according to a third modification of the first embodiment. [Figure 22] This figure shows an example of the configuration of a distance measuring device according to a fourth modification of the first embodiment. [Figure 23] This figure shows an example of the configuration of the pulse formation section of a distance measuring device according to a fourth modification of the first embodiment. [Figure 24] This figure shows an example of a time waveform of a pulse train consisting of multiple pulses with different time waveforms. [Figure 25] This figure shows an example of a spectrum obtained by performing a Fourier transform on an example of the time waveform of a pulse train consisting of multiple pulses with different time waveforms. [Modes for carrying out the invention]

[0010] The optical measuring device according to this disclosure comprises: a measuring light pulse light source that outputs a plurality of measuring light pulses having different time waveforms and different central wavelengths; a spectroscopic unit that spatially separates the plurality of measuring light pulses according to their central wavelengths and causes them to be incident on a target for measurement; a multiplexing unit that combines the plurality of measuring light pulses reflected by or transmitted through the target for measurement and emits them onto a single optical path; a photodetector that receives the plurality of measuring light pulses emitted from the multiplexing unit and outputs time waveform signals of the plurality of measuring light pulses; and a measuring unit that measures the timing at which each of the plurality of measuring light pulses is received by the photodetector or the difference in such timings based on the time waveform signals.

[0011] Furthermore, the optical measurement method according to this disclosure comprises the steps of: outputting a plurality of measurement light pulses having different time waveforms and different central wavelengths; spatially separating the plurality of measurement light pulses according to their central wavelengths and causing them to be incident on a measurement target; combining the plurality of measurement light pulses that have been reflected by or transmitted through the measurement target and emitting them onto a single optical path; receiving the plurality of measurement light pulses emitted onto a single optical path and outputting time waveform signals of the plurality of measurement light pulses; and measuring the timing at which each of the plurality of measurement light pulses was received or the difference in such timings based on the time waveform signals.

[0012] The optical measuring apparatus and optical measuring method according to this disclosure involve injecting a plurality of measurement light pulses, each having a different time waveform, into the object to be measured. Therefore, the individual measurement light pulses appearing in the time waveform signal obtained by receiving the plurality of measurement light pulses reflected by or transmitted through the object to be measured can be identified from each other regardless of the order in which they appear. Consequently, even if the order of the measurement light pulses changes or the measurement light pulses overlap between the time they are emitted and the time they are detected, it is possible to correctly identify which measurement light pulse corresponds to which time, thereby enabling accurate measurement using the measurement light pulses.

[0013] In the above-described optical measuring device, multiple measurement light pulses that are incident on the object to be measured may have a time interval between them and constitute a measurement light pulse train. In this case, multiple measurement light pulses can be easily formed.

[0014] In the above-described optical measuring device, the measurement light pulse light source may include a plurality of pulsed laser light sources that output light pulses with different time waveforms and different center wavelengths, and a multiplexing optical system that combines the light pulses output by each of the plurality of pulsed laser light sources and outputs them as a plurality of measurement light pulses. In this case, a plurality of measurement light pulses with different time waveforms and different center wavelengths can be easily formed using a general pulsed laser light source.

[0015] In the above-described optical measurement device, the multiple pulsed laser light sources are multiple semiconductor laser light sources with different emission wavelengths, and the drive current supplied to each of the multiple semiconductor laser light sources may be different from each other so that the time waveforms of the optical pulses output by each of the multiple semiconductor laser light sources are different from each other. In this case, multiple measurement optical pulses with different time waveforms and different center wavelengths can be easily formed using semiconductor laser light sources, which are general-purpose laser light sources. Furthermore, the time waveforms of the multiple measurement optical pulses can be easily measured by general-purpose photodetectors such as photodiodes and photomultiplier tubes.

[0016] In the above-described optical measuring device, the measurement light pulse light source may include a pulsed laser light source that outputs a broadband light pulse having multiple wavelength components, and a pulse forming unit that forms multiple measurement light pulses from the broadband light pulse. In this case, multiple measurement light pulses having a full width at half maximum on the order of femtoseconds can be easily formed, thereby improving the measurement resolution.

[0017] In the above-described optical measuring device, the pulse formation unit may include: a spectroscopic element that spatially separates multiple wavelength components contained in a broadband optical pulse according to wavelength; a spatial light modulator that modulates at least one of the phase and intensity of each of the multiple wavelength components spatially separated according to wavelength such that when the multiple wavelength components are combined, multiple optical pulses with different time waveforms and center wavelengths are formed; and a multiplexing optical system that combines the multiple wavelength components, with at least one of the phase and intensity modulated, and outputs them as multiple measurement optical pulses. In this case, since the phase and intensity of the multiple wavelength components contained in the broadband optical pulse can be accurately modulated, multiple measurement optical pulses with different time waveforms and different center wavelengths can be easily formed.

[0018] In the above-described optical measuring device, the photodetector includes a correlation optical system that receives multiple measurement light pulses emitted from a multiplexer and a reference light pulse, and outputs correlated light including the cross-correlation between the two, and a photodetector that receives the correlated light and outputs a correlation signal. The correlation optical system outputs correlated light by superimposing multiple measurement light pulses and a reference light pulse while changing the time delay amount of the reference light pulse relative to the multiple measurement light pulses, and the photodetector may generate and output a time waveform signal from the correlation signal obtained for each time delay amount. In this case, by utilizing the cross-correlation between multiple measurement light pulses and a reference light pulse, the time waveforms of multiple measurement light pulses having a full width at half maximum on the order of femtoseconds can be measured, and the measurement resolution can be improved by using multiple measurement light pulses having a full width at half maximum on the order of femtoseconds.

[0019] In the above-described optical measurement device, the correlation optical system may include a beam splitter that branches off a portion of the broadband optical pulse output by a pulsed laser light source to form a reference optical pulse, a moving reflector that changes the time delay amount of the reference optical pulse, and an optical element that generates correlated light by superimposing multiple measurement optical pulses and reference optical pulses. In this case, since the reference optical pulse can be easily obtained, correlated light including the cross-correlation between multiple measurement optical pulses and reference optical pulses can be easily obtained.

[0020] In the above-described optical measuring device, the optical element may include a nonlinear optical crystal. In this case, correlation light, which includes the cross-correlation between multiple measurement light pulses and a reference light pulse, can be easily obtained by utilizing the second harmonic generated in the nonlinear optical crystal.

[0021] In the above-described optical measuring device, the pulsed laser light source may be an optical frequency comb light source. In this case, precise measurements using the optical frequency comb become possible.

[0022] In the above-described optical measuring device, the photodetector includes a correlation optical system that receives multiple measurement light pulses emitted from the multiplexer and a reference light pulse, and outputs correlated light including the cross-correlation between the two, and a photodetector that receives the correlated light and outputs a correlation signal. The correlation optical system includes a second pulsed laser light source that outputs a reference light pulse, and the second pulsed laser light source may be an optical frequency comb light source whose phase is synchronized with the pulsed laser light source and whose period for outputting light pulses is different from that of the pulsed laser light source. In this case, by utilizing the cross-correlation between multiple measurement light pulses and a reference light pulse, the time waveforms of multiple measurement light pulses having a full width at half maximum on the order of femtoseconds can be measured, thereby improving the measurement resolution using multiple measurement light pulses having a full width at half maximum on the order of femtoseconds. Furthermore, precise measurements using dual-comb spectroscopy technology become possible. In addition, since a moving mirror that changes the time delay amount of the reference light pulse is not required, the dynamic range of measurement can be expanded and the time required for measurement can be shortened.

[0023] In the above-described optical measuring device, the pulse forming unit includes an array waveguide diffraction grating that spatially separates multiple wavelength components contained in a broadband optical pulse according to wavelength, multiple optical fibers that transmit each of the multiple wavelength components that have been spatially separated according to wavelength, and an array waveguide diffraction grating that combines the multiple wavelength components transmitted by the multiple optical fibers and outputs them as the multiple measurement optical pulses. The multiple optical fibers may have different lengths and refractive indices. In this case, the pulse forming unit can be miniaturized. Furthermore, since there are no moving parts, the pulse forming unit can be made robust, and multiple measurement optical pulses can be stably formed.

[0024] In the above-described optical measurement device, the pulsed laser light source may include a continuous-wave laser light source that outputs continuous-wave laser light and a microring resonator that receives the continuous-wave laser light, converts it into broadband optical pulses, and outputs them. In this case, multiple measurement optical pulses having a full width at half maximum on the order of femtoseconds can be stably formed, thereby improving the measurement resolution.

[0025] In the above-described optical measuring device, the photodetector may include a microring resonator that receives multiple measurement light pulses and outputs correlated light including autocorrelation. In this case, by utilizing the autocorrelation of multiple measurement light pulses, the time waveforms of multiple measurement light pulses having a full width at half maximum on the order of femtoseconds can be measured, thereby improving the measurement resolution using multiple measurement light pulses having a full width at half maximum on the order of femtoseconds. Furthermore, precise measurements using dual-comb spectroscopy techniques become possible. In addition, only one pulsed laser light source is required, and a moving mirror that changes the time delay amount of the reference light pulse is unnecessary, thus expanding the dynamic range of measurement and shortening the time required for measurement.

[0026] In the above-described optical measuring device, the light detection unit may include a photodiode or a photomultiplier tube. In this case, measurements can be performed using a photodiode or photomultiplier tube, which are common photodetectors.

[0027] In the above-described optical measuring device, the measurement unit may include a Fourier analysis unit that performs Fourier analysis on a time waveform signal, and a calculation unit that, based on the results of the Fourier analysis, measures the timing at which each of the multiple measurement light pulses is received from the time waveform signal, or the difference between those timings. In this case, the timing at which each of the multiple measurement light pulses is received by the photodetector, or the difference between those timings, can be measured without identifying each of the multiple measurement light pulses on the time axis.

[0028] In the above-described optical measuring device, the spectroscopic section may include a diffraction grating, and the multiplexing section may also include a diffraction grating. In this case, the spectroscopic section or the multiplexing section can be easily constructed using a diffraction grating, which is a common spectroscopic element.

[0029] In the above-described optical measuring device, the multiplexing unit combines multiple measurement light pulses reflected by the object to be measured and emits them onto a single optical path. The multiplexing unit may also serve as the spectral unit. In this case, the number of optical elements constituting the optical measuring device can be reduced.

[0030] In the above-described optical measurement device, the spectroscopic unit may spatially separate multiple measurement light pulses along two directions. In this case, two-dimensional measurement becomes possible.

[0031] In the above-described optical measuring device, the measurement unit may calculate at least one of the following based on the timing at which each of the multiple measurement light pulses is received by the photodetector, or the difference in such timings: the distance to the object to be measured, the thickness of the object to be measured, the thickness and refractive index of a film formed on the surface of the object to be measured, and the surface roughness of the object to be measured. According to the optical measuring device of this disclosure, these physical quantities can be measured correctly.

[0032] Embodiments of the optical measuring apparatus and optical measuring method relating to this disclosure will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described below. The technical scope of the present invention is determined based on the claims. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant descriptions are omitted.

[0033] Figure 1 shows an example of the configuration of a distance measuring device 1A according to a first embodiment of the optical measuring device of the present disclosure. The distance measuring device 1A comprises a pulsed laser light source 2, a beam splitter 3, a pulse forming unit 4, a beam splitter 5, a diffraction grating 6, a lens 7, a moving mirror 8, fixed mirrors 9a and 9b, a lens 10, an optical element 11, a photodetector 12, and a signal processing device 13, and measures the distance to an object 100 to be measured.

[0034] The pulsed laser light source 2 outputs a broadband optical pulse P. The pulsed laser light source 2 is, for example, a femtosecond laser light source. The pulsed laser light source 2 is, for example, a solid-state laser light source, and in one example, an LD-directly excited Yb:YAG pulsed laser light source. The time waveform of the broadband optical pulse P is, for example, a Gaussian function shape, and the full width at half maximum (FWHM) of the broadband optical pulse P is, for example, 10 fs or more and 10000 fs or less, and in one example, 100 fs. That is, the broadband optical pulse P is a so-called femtosecond optical pulse. The broadband optical pulse P is an optical pulse with a certain wavelength bandwidth and contains multiple consecutive wavelength components. The bandwidth of the broadband optical pulse P is, for example, 10 nm, and the center wavelength of the broadband optical pulse P is, for example, 1030 nm.

[0035] A portion of the broadband light pulse P is reflected by the beam splitter 3 to become a broadband measurement light pulse Ps, which is then incident on the pulse formation unit 4. The remaining portion of the broadband light pulse P is branched off from the broadband light pulse P by passing through the beam splitter 3 to become a reference light pulse Pr.

[0036] The pulse formation unit 4 forms multiple measurement light pulses Pa from a broadband measurement light pulse Ps. The multiple measurement light pulses Pa are a group of single pulses generated by dividing the wavelength band of the broadband measurement light pulse Ps into multiple wavelength bands and using each wavelength band. The multiple wavelength bands may have overlapping portions near their respective boundaries. The multiple measurement light pulses Pa are femtosecond light pulses, similar to the broadband light pulse P. The multiple measurement light pulses Pa have different time waveforms and different center wavelengths.

[0037] The pulsed laser light source 2, beam splitter 3, and pulse formation unit 4 constitute a measurement light pulse light source that outputs multiple measurement light pulses Pa, each having a different time waveform and a different center wavelength.

[0038] Figure 1 shows only three measurement light pulses, Pa1, Pa2, and Pa3, as individual measurement light pulses contained within multiple measurement light pulses Pa. However, the number of individual measurement light pulses contained within multiple measurement light pulses Pa is not limited to three, but can be any number (for example, 20).

[0039] Furthermore, Figure 1 schematically shows examples of time waveforms for individual measurement light pulses Pa1, Pa2, and Pa3 contained in multiple measurement light pulses Pa, including a rectangular wave shape, a Gaussian function shape, and a triangular wave shape. However, the time waveforms of individual measurement light pulses Pa1, Pa2, and Pa3 are not limited to these and can be any shape (e.g., sawtooth wave shape, multiple peak shape, etc.). Alternatively, a group of pulses consisting of multiple single pulses having a suitable time waveform (e.g., a Gaussian function shape) can be considered as a single pulse, and by varying the number of single pulses in each pulse group, multiple pulses with different time waveforms can be formed. For example, pulses with different time waveforms may include pulses consisting of two consecutive single pulses (double pulse), three consecutive single pulses (triple pulse), four consecutive single pulses (quadruple pulse), etc.

[0040] Multiple measurement light pulses Pa may have time intervals between them, as shown in Figure 1. In this case, the multiple measurement light pulses Pa constitute a measurement light pulse train. Alternatively, multiple measurement light pulses Pa do not have to have time intervals between them. In this case, the multiple measurement light pulses Pa overlap each other. When multiple measurement light pulses Pa have time intervals between them, these time intervals may all be the same, as shown in Figure 1, or they may be different.

[0041] Figure 2 shows an example of the configuration of the pulse formation unit 4. The pulse formation unit 4 includes a diffraction grating 41, a lens 42, a spatial light modulator (SLM) 43, a lens 44, and a diffraction grating 45.

[0042] The diffraction grating 41 is a spectroscopic element and is optically coupled to the pulsed laser light source 2 via the beam splitter 3. The diffraction grating 41 spatially separates multiple wavelength components contained in the broadband measurement light pulse Ps, wavelength by wavelength. Other spectroscopic elements, such as a prism, may be used instead of the diffraction grating 41. The lens 42 collects the light P1 containing multiple wavelength components, wavelength by wavelength, and images it onto the modulation plane of the SLM 43. A concave mirror may be used instead of the lens 42.

[0043] The SLM43 is optically coupled to the diffraction grating 41 via a lens 42. The SLM43 shifts the phases of multiple wavelength components emitted from the diffraction grating 41 to convert a broadband measurement light pulse Ps into multiple measurement light pulses Pa. To this end, the SLM43 receives a control signal from a control unit (not shown) and simultaneously performs phase modulation and intensity modulation of the light P1 containing multiple wavelength components. The SLM43 may perform only phase modulation or only intensity modulation. The SLM43 is, for example, a phase-modulating type, and in one example, an LCOS (liquid crystal on silicon) type. The SLM43 may be a transmission type or a reflection type, as shown in Figure 2.

[0044] Figure 3 shows the modulation surface 46 of the SLM43. As shown in Figure 3, the modulation surface 46 has multiple modulation regions 46a arranged along direction AA, and each of the multiple modulation regions 46a extends in direction AB, which intersects direction AA. Direction AA is the spectral direction by the diffraction grating 41. The modulation surface 46 acts as a Fourier transform surface, and the corresponding wavelength components after spectral analysis are incident on each of the multiple modulation regions 46a. In each of the multiple modulation regions 46a, the SLM43 modulates the phase and intensity of each incident wavelength component independently of the other wavelength components. Since the SLM43 in this embodiment is a phase-modulated type, intensity modulation is realized by the phase pattern (phase image) presented on the modulation surface 46. Details of the modulation method in the SLM43 will be described later.

[0045] Returning to Figure 2, the lens 44 focuses each wavelength component of the modulated light P2, modulated by the SLM 43, onto a single point on the diffraction grating 45. The lens 44 functions as a focusing optical system that concentrates the modulated light P2. The diffraction grating 45 functions as a multiplexing optical system, combining each wavelength component of the modulated light P2. That is, the lens 44 and the diffraction grating 45 focus and combine multiple wavelength components of the modulated light P2 to form multiple measurement light pulses Pa. A concave mirror may be used instead of the lens 44. Other spectroscopic elements such as a prism may be used instead of the diffraction grating 45.

[0046] Returning to Figure 1, the multiple measurement light pulses Pa formed by the pulse formation unit 4 pass through the beam splitter 5 and are incident on the diffraction grating 6.

[0047] The diffraction grating 6 is a spectroscopic element that spatially separates the individual measurement light pulses Pa1, Pa2, and Pa3 contained in the multiple incident measurement light pulses Pa, according to their wavelengths. Since the individual measurement light pulses Pa1, Pa2, and Pa3 have different central wavelengths, they are diffracted in different directions by the diffraction grating 6 and spatially separated from each other. The lens 7 focuses the spatially separated individual measurement light pulses Pa1, Pa2, and Pa3 and irradiates them at different positions on the surface of the object 100. The diffraction grating 6 and lens 7 constitute a spectroscopic section that spatially separates the individual measurement light pulses Pa1, Pa2, and Pa3 contained in the multiple measurement light pulses Pa according to their central wavelengths and irradiates them onto the object 100. Other spectroscopic elements such as a prism may be used instead of the diffraction grating 6. A concave mirror may be used instead of the lens 7.

[0048] At least a portion of the individual measurement light pulses Pa1, Pa2, and Pa3 irradiated at different positions on the surface of object 100 are reflected by the surface of object 100, becoming individual reflected light pulses Pb1, Pb2, and Pb3, respectively.

[0049] Lens 7 focuses the individual reflected light pulses Pb1, Pb2, and Pb3 to a single point on the diffraction grating 6. Lens 7 functions as a focusing optical system that concentrates the individual reflected light pulses Pb1, Pb2, and Pb3. The diffraction grating 6 functions as a multiplexing optical system. The diffraction grating 6 combines the individual reflected light pulses Pb1, Pb2, and Pb3 and emits them as multiple reflected light pulses Pb toward the beam splitter 5. Lens 7 and diffraction grating 6 constitute a multiplexing section that focuses and combines the individual reflected light pulses Pb1, Pb2, and Pb3 toward each other and emits them as multiple reflected light pulses Pb toward the beam splitter 5.

[0050] Since multiple measurement light pulses Pa are femtosecond light pulses, multiple reflected light pulses Pb are also generally femtosecond light pulses. Furthermore, since multiple measurement light pulses Pa have different time waveforms and different center wavelengths, multiple reflected light pulses Pb also have different time waveforms and different center wavelengths.

[0051] As mentioned above, multiple measurement light pulses Pa may constitute a measurement light pulse train or they may overlap with each other. The same applies to multiple reflected light pulses Pb, but generally, each individual reflected light pulse Pb1, Pb2, and Pb3 is a pulse reflected by the surface of object 100 at a different timing, and therefore, multiple reflected light pulses Pb have a time interval between them and constitute a reflected light pulse train.

[0052] Multiple reflected light pulses Pb are reflected by the beam splitter 5 and incident on the lens 10.

[0053] In the distance measuring device 1A, the individual measurement light pulses Pa1, Pa2, Pa3 and their corresponding individual reflected light pulses Pb1, Pb2, Pb3 are configured to travel along the same optical path in opposite directions. The diffraction grating 6 and lens 7 are shared in both the spectral section, which spatially separates the individual measurement light pulses Pa1, Pa2, Pa3 contained in the multiple measurement light pulses Pa and irradiates them onto the object 100, and the multiplexing section, which focuses and combines the individual reflected light pulses Pb1, Pb2, Pb3 to emit multiple reflected light pulses Pb toward the beam splitter 5. However, the individual measurement light pulses Pa1, Pa2, Pa3 and their corresponding individual reflected light pulses Pb1, Pb2, Pb3 may be configured to travel along different optical paths, and the spectral section and the multiplexing section may be configured separately.

[0054] The reference light pulse Pr is sequentially reflected by the moving mirror 8 and the fixed mirrors 9a and 9b before entering the lens 10. At least some of the multiple mirrors 8, 9a, and 9b (the moving mirror 8 in the example shown in Figure 1) are mounted on a moving stage (not shown) and are movable in the optical axis direction indicated by the arrow L in Figure 1. This makes the optical path length of the reference light pulse Pr variable.

[0055] The lens 10 focuses each of the multiple reflected light pulses Pb and the reference light pulse Pr toward the optical element 11, and in the optical element 11, the optical axes of the multiple reflected light pulses Pb and the optical axis of the reference light pulse Pr intersect each other at a predetermined angle.

[0056] The optical element 11 includes, for example, a nonlinear optical crystal that generates second harmonics (SHG). Examples of nonlinear optical crystals include KTP (KTiOPO4) crystals, LBO (LiB3O5) crystals, and BBO (β-BaB2O4) crystals.

[0057] In the optical element 11, which includes a nonlinear optical crystal, the optical axes of multiple reflected light pulses Pb and the optical axis of a reference light pulse Pr intersect each other at a predetermined angle. Therefore, when multiple reflected light pulses Pb and reference light pulse Pr are incident on the optical element 11, a second harmonic Pc is generated starting from the intersection of their optical axes. This second harmonic Pc is correlated light that includes the cross-correlation between the multiple reflected light pulses Pb and the reference light pulse Pr. The moving mirror 8, the fixed mirrors 9a and 9b, the lens 10, and the optical element 11 constitute a correlated optical system that outputs correlated light that includes the cross-correlation between the multiple reflected light pulses Pb and the reference light pulse Pr.

[0058] The second harmonic Pc generated in the optical element 11 is parallelized or focused by a lens (not shown) and then incident on the photodetector 12. The photodetector 12 receives the second harmonic Pc, converts it into an electrical signal, and outputs it. The photodetector 12 is, for example, a photodiode or a photomultiplier tube.

[0059] In the optical element 11, which includes a nonlinear optical crystal, a second harmonic is generated when both multiple reflected light pulses Pb and a reference light pulse Pr are incident on the optical element 11. Therefore, the second harmonic Pc generated in the optical element 11 corresponds to an optical signal obtained by sampling the time waveform of the multiple reflected light pulses Pb at the timing when the reference light pulse Pr is incident on the optical element 11.

[0060] In the distance measuring device 1A, the optical path length of the reference light pulse Pr is variable, so that a difference can be created in the timing at which each of the multiple reflected light pulses Pb and the reference light pulse Pr enters the optical element 11, and this difference can be changed. Therefore, by repeatedly outputting a broadband light pulse P from the pulse laser light source 2 at a constant period to repeatedly generate multiple reflected light pulses Pb at a constant period, and setting the optical path length of the reference light pulse Pr to a predetermined length, the second harmonic Pc generated at a predetermined timing during one period in the optical element 11 can be received by the photodetector 12, converted into an electrical signal, and output. Thus, by repeatedly detecting the second harmonic Pc generated in the optical element 11 with the photodetector 12 while changing the optical path length of the reference light pulse Pr, electrical signals corresponding to optical signals sampled at different timings of the time waveforms of multiple reflected light pulses Pb can be sequentially acquired. The signal processing device 13 measures the time waveforms of multiple reflected light pulses Pb by processing the electrical signals acquired in this manner.

[0061] Normally, the time waveform of an optical pulse can be measured based on the time waveform of the electrical signal output by a photodetector (e.g., a photodiode, photomultiplier tube, etc.) that directly receives the optical pulse. However, because there is a limit to the response speed of the photodetector, as the pulse width of the optical pulse narrows, the time waveform of the electrical signal output by the photodetector no longer faithfully reflects the time waveform of the optical pulse. Therefore, depending on the time waveform of the electrical signal output by the photodetector that directly receives the optical pulse, it may not be possible to accurately measure the time waveform of an optical pulse with a narrow pulse width (e.g., a femtosecond optical pulse). For this reason, in the distance measuring device 1A, as described above, the time waveform of the optical pulse is measured using optical sampling technology with a correlation optical system.

[0062] The correlation optical system, composed of a moving mirror 8, fixed mirrors 9a and 9b, a lens 10, and an optical element 11, along with the photodetector 12 and the signal processing device 13, constitutes a photodetection unit that receives multiple reflected light pulses Pb and outputs their time waveform signals. The signal processing device 13 also constitutes a measurement unit that measures the timing at which multiple reflected light pulses Pb are received or the difference in those timings based on the time waveform signals of the multiple reflected light pulses Pb.

[0063] Since the individual reflected light pulses Pb1, Pb2, and Pb3 contained in the multiple reflected light pulses Pb have different time waveforms, it is possible to identify the individual reflected light pulses Pb1, Pb2, and Pb3 from the time waveforms of the multiple reflected light pulses Pb. Therefore, even if the order of the individual reflected light pulses Pb1, Pb2, and Pb3 is changed or the individual reflected light pulses Pb1, Pb2, and Pb3 overlap with each other before the multiple reflected light pulses Pb are incident on the optical element 11, it is possible to identify that the individual reflected light pulses Pb1, Pb2, and Pb3 correspond to the individual measured light pulses Pa1, Pa2, and Pa3.

[0064] The following describes an example of a procedure for measuring the distance to object 100 using the distance measuring device 1A, with reference to Figures 1 and 4. Figure 4 is a schematic diagram showing an example of the time waveforms of multiple reflected light pulses Pb measured by the distance measuring device 1A.

[0065] First, a reference object is prepared. For example, a flat plate with a flat surface can be used as the reference object. Furthermore, the distance to the reference object is assumed to be known.

[0066] Next, the distance measuring device 1A irradiates a reference object with multiple measurement light pulses Pa and measures the time waveforms of multiple reflected light pulses Pb. An example of the time waveforms of multiple reflected light pulses Pb obtained from the reference object is schematically shown in Figure 4(a). Since the time waveforms of each reflected light pulse Pb1, Pb2, and Pb3 are different from each other, the individual reflected light pulses Pb1, Pb2, and Pb3 can be identified from the time waveforms of the multiple reflected light pulses Pb.

[0067] As shown in Figure 1, if multiple measurement light pulses Pa constitute a measurement light pulse train, and the individual measurement light pulses Pa1, Pa2, and Pa3 are arranged in this order, then each measurement light pulse Pa1, Pa2, and Pa3 is incident on the surface of the reference object at different positions in this order. Since the reference object is a flat plate with a flat surface, each measurement light pulse Pa1, Pa2, and Pa3 is reflected in the order of incident, becoming individual reflected light pulses Pb1, Pb2, and Pb3. Thus, multiple reflected light pulses Pb constitute a reflected light pulse train, and each reflected light pulse Pb1, Pb2, and Pb3 is always arranged in this order. Therefore, when the time waveforms of multiple reflected light pulses Pb are measured, for example, as schematically shown in Figure 4(a), the time waveform of reflected light pulse Pb1 appears first, followed by the time waveforms of reflected light pulse Pb2 and reflected light pulse Pb3 in sequence. In other words, if the reference object is a flat plate with a flat surface, the time waveforms of individual reflected light pulses Pb1, Pb2, and Pb3 can also be identified based on the order in which they appear.

[0068] Next, the distance measuring device 1A irradiates the object 100 to be measured with multiple measurement light pulses Pa and measures the time waveforms of multiple reflected light pulses Pb. An example of the time waveforms of multiple reflected light pulses Pb obtained from object 100 is schematically shown in Figure 4(b).

[0069] For example, if the distance to object 100 is less than the distance to a reference object, the timing at which the time waveforms of multiple reflected light pulses Pb appear will be earlier compared to the reference object. Furthermore, as shown in Figure 1, if object 100 is not a flat plate with a flat surface, and the distance to object 100 varies depending on the position on the surface of object 100, the degree to which the timing of the appearance of the time waveforms of individual reflected light pulses Pb1, Pb2, and Pb3 appear will differ from one another. This is because each reflected light pulse Pb1, Pb2, and Pb3 is produced when individual measurement light pulses Pa1, Pa2, and Pa3, which are irradiated at different positions (i.e., at different distances from each other) on the surface of object 100, are reflected by the surface of object 100. For example, in the example shown in Figure 1, measurement light pulse Pa3 is located at the end of a train of measurement light pulses composed of multiple measurement light pulses Pa, but because it is irradiated at the position with the shortest distance on the surface of object 100, it may be reflected at an earlier timing than the other measurement light pulses and become reflected light pulse Pb3. In that case, the reflected light pulse Pb3 will be located at the beginning of the reflected light pulse train composed of multiple reflected light pulses Pb. Therefore, when measuring the time waveforms of multiple reflected light pulses Pb, for example, as schematically shown in Figure 4(b), the time waveforms of the multiple reflected light pulses Pb will appear at an earlier timing overall than the time waveform schematically shown in Figure 4(a). Moreover, the order in which the time waveforms of the individual reflected light pulses Pb1, Pb2, and Pb3 appear may differ from the order in which the individual measured light pulses Pa1, Pa2, and Pa3 that produced each individual reflected light pulse Pb1, Pb2, and Pb3 appeared.

[0070] Since the time waveforms of each reflected light pulse Pb1, Pb2, and Pb3 are different from each other, it is possible to identify each reflected light pulse Pb1, Pb2, and Pb3 from the time waveforms of multiple reflected light pulses Pb, regardless of whether the order in which each reflected light pulse Pb1, Pb2, and Pb3 appear in the time waveform matches or differs from the order in which each measured light pulse Pa1, Pa2, and Pa3 appear. Therefore, by comparing the time waveforms of multiple reflected light pulses Pb obtained from a reference object with the time waveforms of multiple reflected light pulses Pb obtained from object 100, it is possible to measure how much the timing of the appearance of a particular reflected light pulse (e.g., reflected light pulse Pb3) differs between the reference object and object 100. For example, as shown in Figure 4, if the timing at which the time waveform of reflected light pulse Pb3 appears in the time waveforms of multiple reflected light pulses Pb obtained from object 100 is Δt earlier than the timing at which the time waveform of reflected light pulse Pb3 appears in the time waveforms of multiple reflected light pulses Pb obtained from a reference object, then Δt corresponds to the difference obtained by subtracting the distance to object 100 at the same position from the distance to the reference object at the position where the measurement light pulse Pa3 was incident. The distance to the reference object is known. Also, since the reference object is a flat plate with a flat surface, the distance to the reference object is the same regardless of the position on the surface of the reference object. Therefore, the distance to object 100 at that position can be calculated based on Δt.

[0071] Furthermore, if the distance to object 100 is greater than the distance to the reference object, the timing of the appearance of the reflected light pulse Pb3 will not be advanced by Δt, but rather delayed. In this case, Δt will correspond to the difference obtained by subtracting the distance to the reference object from the distance to object 100. Therefore, it remains possible to calculate the distance to object 100 based on Δt.

[0072] Figure 5 schematically shows an example of the time waveforms of multiple reflected light pulses Pb measured by the distance measuring device according to the comparative example.

[0073] The configuration of the distance measuring device according to the comparative example is the same as the configuration of the distance measuring device 1A according to the first embodiment, except that the time waveforms of the multiple measurement light pulses Pa are identical to each other (for example, all have a Gaussian function shape). In the distance measuring device according to the comparative example, since the time waveforms of the multiple measurement light pulses Pa are identical to each other, the time waveforms of the multiple reflected light pulses Pb are also identical to each other (for example, all have a Gaussian function shape). An example of the time waveforms of the multiple reflected light pulses Pb obtained from a reference object by the distance measuring device according to the comparative example is schematically shown in Figure 5(a), and an example of the time waveforms of the multiple reflected light pulses Pb obtained from object 100 is schematically shown in Figure 5(b).

[0074] Even when using the distance measuring device according to the comparative example, if the reference object is a flat plate with a flat surface, it is possible to distinguish the individual reflected light pulses Pb1, Pb2, and Pb3 contained within the multiple reflected light pulses Pb obtained from the reference object. As mentioned above, as shown in Figure 1, if multiple measurement light pulses Pa constitute a measurement light pulse train, and the individual measurement light pulses Pa1, Pa2, and Pa3 are arranged in this order, then the individual measurement light pulses Pa1, Pa2, and Pa3 are incident on each other at different positions on the surface of the reference object in this order and reflected in this order to become the individual reflected light pulses Pb1, Pb2, and Pb3. Therefore, the individual reflected light pulses Pb1, Pb2, and Pb3 contained within the multiple reflected light pulses Pb are always arranged in this order. That is, as schematically shown in Figure 5(a), the time waveforms of the individual reflected light pulses Pb1, Pb2, and Pb3 appear in this order in the time waveforms of the multiple reflected light pulses Pb. Therefore, even if the time waveforms of multiple reflected light pulses Pb are identical to each other, the time waveforms of individual reflected light pulses Pb1, Pb2, and Pb3 can be identified based on the order in which they appear.

[0075] In contrast, with respect to the multiple reflected light pulses Pb obtained from object 100, it is not possible to distinguish between the individual reflected light pulses Pb1, Pb2, and Pb3 contained within them. Generally, the surface of object 100 is not flat, and individual measurement light pulses Pa1, Pa2, and Pa3 are reflected at different positions and at different timings on the surface of object 100 to become individual reflected light pulses Pb1, Pb2, and Pb3. Therefore, even if multiple measurement light pulses Pa constitute a measurement light pulse train, and the individual measurement light pulses Pa1, Pa2, and Pa3 are arranged in this order, the order in which the time waveforms of the individual reflected light pulses Pb1, Pb2, and Pb3 appear may differ from the order in which the individual measurement light pulses Pa1, Pa2, and Pa3 that produced each individual reflected light pulse Pb1, Pb2, and Pb3 appeared. In such cases, as schematically shown in Figure 5(b), the individual reflected light pulses Pb1, Pb2, and Pb3 cannot be distinguished from each other based on their time waveforms, nor can they be identified from each other based on the order in which they appear.

[0076] As described above, the distance measuring device 1A according to the first embodiment incidents a plurality of measurement light pulses Pa, each having a different time waveform and a different center wavelength, onto the object 100 to be measured. Therefore, even if the order of the individual reflected light pulses Pb1, Pb2, and Pb3 included in the plurality of reflected light pulses Pb is changed, or if the individual reflected light pulses Pb1, Pb2, and Pb3 overlap with each other, the individual reflected light pulses Pb1, Pb2, and Pb3 can be correctly identified. Consequently, the distance to the object 100 can be measured correctly.

[0077] In the above explanation, we first measured the time waveforms of multiple reflected light pulses Pb from the reference object, and then measured the time waveforms of multiple reflected light pulses Pb from object 100. However, it is also possible to measure the time waveforms of the reflected light pulses from both the reference object and object 100 simultaneously. That is, since the multiple measurement light pulses Pa irradiated by the distance measuring device 1A are spatially separated from each other, it is possible to simultaneously irradiate the reference object with a portion of the individual measurement light pulses included in the multiple measurement light pulses Pa (for example, measurement light pulse Pa1) and object 100 with the remainder (for example, measurement light pulses Pa2 and Pa3). In that case, the distance to object 100 can be measured based on the time difference between the timing at which the time waveform of the reflected light pulse Pb1 from the reference object appears and the timing at which the time waveforms of the reflected light pulses Pb2 and Pb3 from object 100 appear.

[0078] The distance measuring device 1A according to the first embodiment can also be used to measure the thickness of an object 100. Below, an example of the procedure for measuring the thickness of an object 100 using the distance measuring device 1A will be described with reference to Figures 1 and 4.

[0079] First, a reference object with a known thickness is prepared and placed on a sample stage, for example. A flat plate with a known uniform thickness can be used as the reference object. In the following explanation, the reference object will be described as a flat plate with a known uniform thickness, but it is not limited to this. Even an object with a non-uniform thickness can be used as a reference object if the thickness is known at each location on the object's surface.

[0080] Next, the distance measuring device 1A irradiates the reference object with multiple measurement light pulses Pa and measures the time waveforms of multiple reflected light pulses Pb. An example of the time waveforms of multiple reflected light pulses Pb obtained from the reference object is schematically shown in Figure 4(a).

[0081] Next, instead of the reference object, the object to be measured 100 is placed on the sample stage, and the distance measuring device 1A irradiates the object 100 with multiple measurement light pulses Pa, and measures the time waveforms of multiple reflected light pulses Pb. An example of the time waveforms of multiple reflected light pulses Pb obtained from object 100 is schematically shown in Figure 4(b).

[0082] For example, if the thickness of object 100 is greater than the thickness of the reference object, the timing at which the time waveforms of multiple reflected light pulses Pb appear will be earlier compared to the reference object. Furthermore, for example, if the thickness of object 100 differs at different positions on the surface of object 100, as shown in Figure 1, the degree to which the timing of the appearance of the time waveforms of individual reflected light pulses Pb1, Pb2, and Pb3 appear will differ from one another. Therefore, when measuring the time waveforms of multiple reflected light pulses Pb, for example, as schematically shown in Figure 4(b), the time waveforms of the multiple reflected light pulses Pb will generally appear earlier than the time waveform schematically shown in Figure 4(a), and moreover, the order in which the time waveforms of individual reflected light pulses Pb1, Pb2, and Pb3 appear may differ from the order in which the individual measured light pulses Pa1, Pa2, and Pa3 that produced each individual reflected light pulse Pb1, Pb2, and Pb3 appeared.

[0083] From this point onward, the procedure is the same as for distance measurement. That is, the time waveforms of multiple reflected light pulses Pb obtained from the reference object are compared with the time waveforms of multiple reflected light pulses Pb obtained from object 100 to measure how much the timing at which the time waveform of a specific reflected light pulse (for example, reflected light pulse Pb3) appears differs between the reference object and object 100. For example, as shown in Figure 4, if the timing at which the time waveform of reflected light pulse Pb3 appears in the time waveforms of multiple reflected light pulses Pb obtained from object 100 is earlier by Δt than the timing at which the time waveform of reflected light pulse Pb3 appears in the time waveforms of multiple reflected light pulses Pb obtained from the reference object, then Δt corresponds to the difference obtained by subtracting the thickness of the reference object at the same position from the thickness of object 100 at the position where the measurement light pulse Pa3 is incident. Since the thickness of the reference object at that position is known, the thickness of object 100 at that position can be calculated based on Δt.

[0084] Furthermore, if the thickness of object 100 is less than the thickness of the reference object, the timing at which the time waveform of the reflected light pulse Pb3 appears will not be advanced by Δt, but rather delayed. Even in that case, however, it is still possible to calculate the thickness of object 100 based on Δt.

[0085] The distance measuring device 1A according to the first embodiment can also be used to measure film thickness. Below, an example of a procedure for measuring film thickness using the distance measuring device 1A will be described with reference to Figures 6 and 7. Figure 6 is a diagram showing a part of the configuration of the distance measuring device 1A shown in Figure 1. Figure 7 is a schematic diagram showing an example of the time waveforms of multiple reflected light pulses Pb measured by the distance measuring device 1A.

[0086] As shown in Figure 6, the distance measuring device 1A irradiates the multilayer film structure 200, which is the object to be measured, with multiple measurement light pulses Pa, and measures the time waveforms of multiple reflected light pulses Pb.

[0087] The multilayer structure 200 includes a thin film 201, which is formed on the surface of a substrate 202. The substrate 202 is, for example, a flat plate with a uniform thickness, but is not limited to this. The thickness of the thin film 201 may be uniform, or it may vary at different positions on the surface of the thin film 201, as shown in Figure 6. In the multilayer structure 200 shown in Figure 6, only one layer of thin film 201 is formed on the surface of the substrate 202. However, the number of layers of thin film 201 is not limited to one, but can be any number.

[0088] Individual measurement light pulses Pa1, Pa2, and Pa3, irradiated at different positions on the surface of the multilayer film structure 200, are not only reflected by the surface of the thin film 201, but also penetrate the thin film 201 to the surface of the substrate 202, where they are reflected again. That is, multiple reflected light pulses are generated from each of the multiple measurement light pulses Pa irradiated onto the multilayer film structure 200. For example, as schematically shown in Figure 7(b), a portion of the measurement light pulse Pa3 is reflected by the surface of the thin film 201 to become the first reflected light pulse Pb31, and a further portion of the remaining portion is reflected by the surface of the substrate 202 after penetrating the thin film 201 to become the second reflected light pulse Pb32. Although not shown in Figure 7(b), similarly, the first and second reflected light pulses are generated from the measurement light pulses Pa1 and Pa2, respectively.

[0089] Figure 7(a) is an example of the time waveforms of multiple reflected light pulses Pb obtained from a reference object (a flat plate with a known uniform thickness), and is the same as Figure 4(a), so no explanation is provided.

[0090] Generally, when a light pulse is irradiated onto a multilayer film structure composed of a substrate and multiple layers of thin films formed on the substrate, it is reflected not only by the surface of the uppermost thin film and the surface of the substrate, but also by the interfaces between the thin films. Therefore, if the number of thin film layers is N, then N+1 reflected light pulses are generated. Accordingly, by irradiating each of the multiple measurement light pulses Pa at different positions on the surface of the multilayer film structure 200 and counting the number of reflected light pulses (e.g., the first reflected light pulse Pb31, the second reflected light pulse Pb32) generated from the measurement light pulse (e.g., measurement light pulse Pa3) irradiated at a certain position, the number of layers of the thin film 201 at that position can be determined.

[0091] Furthermore, based on the time waveforms of multiple reflected light pulses Pb, the thickness of the thin film 201 at the position where the measurement light pulse Pa3 was incident can be calculated based on the difference Δt in the timing of the appearance of the time waveforms of the first reflected light pulse Pb31 (light pulse reflected by the surface of the thin film 201) and the second reflected light pulse Pb32 (light pulse reflected by the surface of the substrate 202), and the known refractive index of the thin film 201.

[0092] Furthermore, if the thickness of the thin film 201 is known, the refractive index of the thin film 201 can be calculated based on the timing difference Δt. In other words, the distance measuring device 1A according to the first embodiment can also be used to measure the refractive index.

[0093] Here, we will explain in detail the modulation method used in the SLM43 of the pulse formation unit 4 shown in Figure 2 to convert a single broadband measurement light pulse Ps into multiple measurement light pulses Pa. The region in front of the lens 44 (spectral domain) and the region behind the diffraction grating 45 (time domain) are in a Fourier transform relationship with each other, and phase modulation in the spectral domain affects the time intensity waveform in the time domain. Therefore, the output light from the pulse formation unit 4 can have various time intensity waveforms different from the broadband measurement light pulse Ps, depending on the modulation pattern of the SLM43.

[0094] Figure 8(a) shows, as an example, the spectral waveform (spectral phase G11 and spectral intensity G12) of a single-pulse broadband measurement light pulse Ps, and Figure 8(b) shows the time intensity waveform of the same broadband measurement light pulse Ps. Figure 9(a) shows, as an example, the spectral waveform (spectral phase G21 and spectral intensity G22) of the output light from the pulse formation unit 4 when a rectangular wave-shaped phase spectral modulation is applied to the SLM43, and Figure 9(b) shows the time intensity waveform of the output light. In Figures 8(a) and 9(a), the horizontal axis represents wavelength (nm), the left vertical axis represents the intensity value of the intensity spectrum (arbitrary unit), and the right vertical axis represents the phase value of the phase spectrum (rad). In Figures 8(b) and 9(b), the horizontal axis represents time (femtoseconds), and the vertical axis represents light intensity (arbitrary unit).

[0095] In this example, a single pulse of the broadband measurement light pulse Ps is converted into a double pulse accompanied by higher-order light by applying a rectangular wave-shaped phase spectrum waveform to the output light. Note that the spectrum and waveform shown in Figure 9 are just examples, and the time-intensity waveform of the output light from the pulse formation unit 4 can be shaped into various forms by various combinations of phase spectra and intensity spectra.

[0096] The phase modulation pattern for bringing the time intensity waveform of the output light of the pulse formation unit 4 closer to a desired waveform is configured as data for controlling the SLM43, i.e., data including a table of the intensity of the complex amplitude distribution or the intensity of the phase distribution. The modulation pattern is, for example, a computer-generated hologram (CGH). In this embodiment, the SLM43 is made to present a phase pattern that includes a phase modulation phase pattern that provides the output light with a phase spectrum to obtain the desired waveform, and an intensity modulation phase pattern that provides the output light with an intensity spectrum to obtain the desired waveform.

[0097] Here, the desired time-intensity waveform is expressed as a function of the time domain, and the phase spectrum is expressed as a function of the frequency domain. Therefore, the phase spectrum corresponding to the desired time-intensity waveform can be obtained, for example, by an iterative Fourier transform based on the desired time-intensity waveform. Figure 10 shows the procedure for calculating the phase spectrum using the iterative Fourier transform method.

[0098] First, we prepare the initial intensity spectral function A0(ω) and phase spectral function Ψ0(ω), which are functions of frequency ω (process number (1) in the figure). In one example, these intensity spectral function A0(ω) and phase spectral function Ψ0(ω) represent the spectral intensity and spectral phase of the input light, respectively. Next, we prepare the intensity spectral function A0(ω) and phase spectral function Ψ n Prepare a frequency-domain waveform function (a) that includes (ω) (process number (2) in the figure).

number

[0099] Next, a Fourier transform from the frequency domain to the time domain is performed on the above function (a) (arrow A1 in the figure). This gives the time intensity waveform function b n (t) and time-phase waveform function Θ n The time-domain waveform function (b) including (t) is obtained (process number (3) in the figure).

number

[0100] Next, the time-intensity waveform function b included in the above function (b) n Replace (t) with a time-intensity waveform function Target0(t) based on the desired waveform (e.g., time interval and number of light pulses) (process numbers (4) and (5) in the figure). [Number] [Number]

[0101] Subsequently, an inverse Fourier transform from the time domain to the frequency domain is performed on the above function (d) (arrow A2 in the figure). As a result, a waveform function (e) in the frequency domain including the intensity spectrum function B n (ω) and the phase spectrum function Ψ n (ω) is obtained (processing number (6) in the figure). [Number]

[0102] Subsequently, in order to constrain the intensity spectrum function B n (ω) included in the above function (e), it is replaced with the initial intensity spectrum function A0(ω) (processing number (7) in the figure). [Number]

[0103] Thereafter, by repeatedly performing the above processes (2) to (7) a plurality of times, the phase spectrum shape represented by the phase spectrum function Ψ n (ω) in the waveform function can be made closer to the phase spectrum shape corresponding to the desired time-intensity waveform. Based on the finally obtained phase spectrum function Ψ IFTA (ω), a modulation pattern for obtaining the desired time-intensity waveform, that is, a plurality of measurement light pulses Pa including two or more optical pulses, is created.

[0104] While the iterative Fourier method described above can control the time-intensity waveform, it cannot control the frequency components (band wavelengths) that constitute the time-intensity waveform. Therefore, when the center wavelengths of two or more optical pulses constituting multiple measurement optical pulses Pa are to be different from each other, the phase spectral function and intensity spectral function that form the basis of the modulation pattern are calculated using the calculation method described below. Figure 11 shows the calculation procedure for the phase spectral function.

[0105] First, we prepare the initial intensity spectral function A0(ω) and phase spectral function Φ0(ω), which are functions of frequency ω (process number (1) in the figure). In one example, these intensity spectral function A0(ω) and phase spectral function Φ0(ω) represent the spectral intensity and spectral phase of the input light, respectively. Next, we prepare the first waveform function (g) in the frequency domain, which includes the intensity spectral function A0(ω) and phase spectral function Φ0(ω) (process number (2-a)). Here, i is the imaginary unit.

number

[0106] Next, a Fourier transform from the frequency domain to the time domain is performed on the above function (g) (arrow A3 in the figure). This yields a second time domain waveform function (h) that includes the time intensity waveform function a0(t) and the time phase waveform function φ0(t) (process number (3)).

number

[0107] Next, as shown in the following equation (i), the time-intensity waveform function Target0(t), which is based on the desired waveform (e.g., the time interval and number of light pulses), is substituted into the time-intensity waveform function b0(t) (process number (4-a)).

number

[0108] Next, as shown in the following equation (j), the time-intensity waveform function a0(t) is replaced with the time-intensity waveform function b0(t). That is, the time-intensity waveform function a0(t) included in the above function (h) is replaced with the time-intensity waveform function Target0(t) based on the desired waveform (e.g., the time interval and number of light pulses) (process number (5)).

number

[0109] Next, the second waveform function (j) is modified so that its spectrogram approaches the pre-generated target spectrogram according to the desired wavelength band. First, a time-frequency transformation is applied to the second waveform function (j) to obtain the spectrogram SG. 0,k Convert to (ω,t) (process number (5-a) in the diagram). The subscript k represents the kth conversion process.

[0110] Here, time-frequency conversion refers to the process of applying frequency filtering or numerical calculation (a process that derives a spectrum for each time point by multiplying while shifting a window function) to a composite signal such as a time waveform, and converting it into three-dimensional information consisting of time, frequency, and the strength of the signal components (spectral intensity). In this embodiment, the conversion result (time, frequency, spectral intensity) is defined as a "spectrogram". Examples of time-frequency conversions include the Short-Time Fourier Transform (STFT) and wavelet transforms (Haar wavelet transform, Gabor wavelet transform, Mexican hat wavelet transform, Morlay wavelet transform).

[0111] Furthermore, a pre-generated target spectrogram, TargetSG0(ω,t), is obtained according to the desired wavelength band. This target spectrogram, TargetSG0(ω,t), is approximately equivalent to the target time waveform (time intensity waveform and its constituent frequency components) and is generated using the target spectrogram function of process number (5-b).

[0112] Next, Spectrogram SG 0,k Pattern matching is performed between (ω,t) and the target spectrogram TargetSG0(ω,t) to check the similarity (how well they match). In this embodiment, an evaluation value is calculated as an index representing the similarity. Then, in the subsequent process number (5-c), it is determined whether the obtained evaluation value satisfies a predetermined termination condition. If the condition is met, the process proceeds to process number (6); otherwise, the process proceeds to process number (5-d). In process number (5-d), the time-phase waveform function φ0(t) included in the second waveform function is changed to an arbitrary time-phase waveform function φ 0,k Change to (t). The second waveform function, after changing the time-phase waveform function, is converted back into a spectrogram using a time-frequency converter such as STFT.

[0113] Subsequently, the above-mentioned processing steps (5-a) to (5-d) are repeated. In this way, the spectrogram SG is formed. 0,k The second waveform function is modified so that (ω,t) gradually approaches the target spectrogram TargetSG0(ω,t). Then, an inverse Fourier transform is performed on the modified second waveform function (arrow A4 in the figure) to generate the third waveform function (k) in the frequency domain (process number (6)).

number

[0114] Figure 12 shows the procedure for calculating spectral intensity. Note that the procedure from process number (1) to process number (5-c) is the same as the spectral phase calculation procedure described above, so the explanation is omitted.

[0115] Spectrogram SG 0,k If the evaluation value indicating the similarity between (ω,t) and the target spectrogram TargetSG0(ω,t) does not satisfy the predetermined termination condition, the time-phase waveform function φ0(t) included in the second waveform function is constrained to its initial value, while the time-intensity waveform function b0(t) is set to an arbitrary time-intensity waveform function b 0,k Change to (t) (process number (5-e)). The second waveform function, after changing the time intensity waveform function, is converted back into a spectrogram by a time-frequency conversion such as STFT.

[0116] Subsequently, processing numbers (5-a) to (5-c) are repeated. In this way, the spectrogram SG is formed. 0,k The second waveform function is modified so that (ω,t) gradually approaches the target spectrogram TargetSG0(ω,t). Then, an inverse Fourier transform is performed on the modified second waveform function (arrow A4 in the figure) to generate the third waveform function (m) in the frequency domain (process number (6)).

number

[0117] Next, in processing number (7-b), the intensity spectral function B included in the third waveform function (m) is analyzed. 0,k A filter is applied to (ω) based on the intensity spectrum of the input light. Specifically, the intensity spectral function B 0,k The intensity spectrum obtained by multiplying (ω) by the coefficient α is used, and the portion exceeding the cutoff intensity for each wavelength determined based on the intensity spectrum of the input light is cut off. The intensity spectral function αB is used across all wavelength ranges. 0,k This is to ensure that (ω) does not exceed the spectral intensity of the input light.

[0118] In one example, the cutoff intensity for each wavelength is set to match the intensity spectrum of the input light (in this embodiment, the initial intensity spectral function A0(ω)). In that case, the intensity spectral function αB is as shown in the following equation (n). 0,k At frequencies where (ω) is greater than the intensity spectral function A0(ω), the intensity spectral function A TWC-TFD The value of the intensity spectral function A0(ω) is taken as the value of (ω). Also, the intensity spectral function αB 0,k At frequencies where (ω) is less than or equal to the intensity spectral function A0(ω), the intensity spectral function A TWC-TFD The intensity spectral function αB is used as the value of (ω). 0,k The value of (ω) is incorporated (process number (7-b) in the diagram).

number

[0119] And the phase spectral function Φ TWC-TFD The spectral phase shown by (ω) and the intensity spectral function A TWC-TFD A phase modulation pattern (e.g., a computer-generated hologram) is calculated to impart the spectral intensity indicated by (ω) to the output light. Figure 13 shows an example of the procedure for generating the target spectrogram TargetSG0(ω,t). Since the target spectrogram TargetSG0(ω,t) shows the target time waveform (time intensity waveform and the frequency components (wavelength band components) that constitute it), creating the target spectrogram is an extremely important step for controlling the frequency components (wavelength band components).

[0120] As shown in Figure 13, first, the spectral waveform (initial intensity spectral function A0(ω) and initial phase spectral function Φ0(ω)) and the desired time intensity waveform function Target0(t) are input. Also, a time function p0(t) containing the desired frequency (wavelength) band information is input (process number (1)). Next, for example, using the iterative Fourier transform method shown in Figure 10, the phase spectral function Φ0(ω) is used to realize the time intensity waveform function Target0(t). IFTA Calculate (ω) (process number (2)). Next, the previously obtained phase spectral function Φ IFTA The intensity spectral function A is obtained by the iterative Fourier transform method using (ω) to realize the time-intensity waveform function Target0(t). IFTA Calculate (ω) (process number (3)). Here, Figure 14 shows the intensity spectral function A IFTA This figure shows an example of the procedure for calculating (ω).

[0121] First, the initial intensity spectral function A k=0 Prepare (ω) and the phase spectral function Ψ0(ω) (process number (1) in the figure). Next, prepare the intensity spectral function A k Prepare a frequency-domain waveform function (o) that includes (ω) and the phase spectral function Ψ0(ω) (process number (2) in the figure).

number

[0122] Next, a Fourier transform from the frequency domain to the time domain is performed on the above function (o) (arrow A5 in the figure). This gives the time intensity waveform function b k The time-domain waveform function (p) including (t) is obtained (process number (3) in the figure).

number

[0123] Next, the time-intensity waveform function b included in the above function (p) k Replace (t) with a time-intensity waveform function Target0(t) based on the desired waveform (e.g., time interval and number of light pulses) (process numbers (4) and (5) in the figure).

number

number

[0124] Next, an inverse Fourier transform from the time domain to the frequency domain is performed on the above function (r) (arrow A6 in the figure). This gives the intensity spectral function C k (ω) and phase spectral function Ψ k The frequency-domain waveform function (s) containing (ω) is obtained (process number (6) in the figure).

number

[0125] Next, the phase spectral function Ψ included in the above function (s) k To constrain (ω), we replace it with the initial phase spectral function Ψ0(ω) (process number (7-a) in the figure).

number

[0126] Furthermore, the intensity spectral function C in the frequency domain after the inverse Fourier transform. k A filter is applied to (ω) based on the intensity spectrum of the input light. Specifically, the intensity spectral function C k The portion of the intensity spectrum represented by (ω) that exceeds the cutoff intensity for each wavelength determined based on the intensity spectrum of the input light is cut off.

[0127] For example, the cutoff intensity for each wavelength is the intensity spectrum of the input light (e.g., the initial intensity spectral function A). k=0 It is set to match (ω). In that case, the intensity spectral function C is as shown in the following equation (u). k (ω) is the intensity spectral function A k=0 At frequencies greater than (ω), the intensity spectral function A k The intensity spectral function A is the value of (ω). k=0 The value of (ω) is incorporated. Also, the intensity spectral function C k (ω) is the intensity spectral function A k=0 At frequencies below (ω), the intensity spectral function A k The intensity spectral function C is used as the value of (ω). k The value of (ω) is incorporated (process number (7-b) in the diagram).

number

[0128] Subsequently, by repeatedly performing the above processes (2) to (7-b), the intensity spectral function A in the waveform function is obtained. k The intensity spectral shape represented by (ω) can be made to approximate the intensity spectral shape corresponding to the desired time intensity waveform. Ultimately, the intensity spectral function A IFTA (ω) is obtained.

[0129] Refer to Figure 13 again. Phase spectral function Φ in processing numbers (2) and (3) described above. IFTA (ω) and intensity spectral function A IFTA By calculating (ω), a third waveform function (v) in the frequency domain, which includes these functions, is obtained (process number (4)).

number

[0130] Next, we perform a Fourier transform on the waveform function (v) above. This yields the fourth waveform function (w) in the time domain (process number (5)).

number

[0131] Next, the fourth waveform function (w) is converted to a spectrogram SG using time-frequency conversion. IFTA Convert to (ω,t) (process number (6)). Then, in process number (7), a spectrogram SG is created based on the time function p0(t) containing the desired frequency (wavelength) band information. IFTA By modifying (ω,t), the target spectrogram TargetSG0(ω,t) is generated. For example, a spectrogram SG composed of two-dimensional data. IFTA We partially extract characteristic patterns appearing at (ω,t) and manipulate the frequency components of those parts based on the time function p0(t). A specific example of this is explained in detail below.

[0132] For example, consider the case where the desired time-intensity waveform function Target0(t) is set to a triple pulse with a time interval of 2 picoseconds. In this case, the spectrogram SG IFTA The result for (ω,t) is shown in Figure 15(a). In Figure 15(a), the horizontal axis represents time (unit: femtoseconds), and the vertical axis represents wavelength (unit: nm). The spectrogram values ​​are indicated by the brightness of the figure, with brighter values ​​indicating larger spectrogram values. This spectrogram SG IFTA At (ω,t), the triple pulse appears as domains D1, D2, and D3 separated on the time axis at 2 picosecond intervals. The center (peak) wavelength of domains D1, D2, and D3 is 800 nm.

[0133] If you only want to control the time intensity waveform of the output light (simply to obtain a triple pulse), you do not need to manipulate domains D1, D2, and D3. However, if you want to control the frequency (wavelength) band of each pulse, you need to manipulate domains D1, D2, and D3. That is, as shown in Figure 15(b), moving each domain D1, D2, and D3 independently in the direction along the wavelength axis (vertical axis) means changing the constituent frequency (wavelength band) of each pulse. Such changes to the constituent frequency (wavelength band) of each pulse are made based on the time function p0(t).

[0134] For example, if we describe the time function p0(t) such that the peak wavelength of domain D2 is kept at 800 nm, and the peak wavelengths of domains D1 and D3 are shifted by -2 nm and +2 nm respectively, then the spectrogram SG IFTA (ω,t) changes to the target spectrogram TargetSG0(ω,t) shown in Figure 15(b). For example, by applying such processing to a spectrogram, it is possible to create a target spectrogram in which the constituent frequencies (wavelength bands) of each pulse are arbitrarily controlled without changing the shape of the time-intensity waveform.

[0135] Figure 16 shows an example of the configuration of a surface roughness measuring device 1B according to a second embodiment of the optical measuring device of the present disclosure. The configuration of the surface roughness measuring device 1B is the same as that of the distance measuring device 1A according to the first embodiment shown in Figures 1 to 3, except that a configuration for measuring the time waveforms of multiple measurement light pulses Pa has been added. Although not shown in Figure 16, the surface roughness measuring device 1B also includes a correlation optical system and a signal processing device similar to that of the distance measuring device 1A. The surface roughness measuring device 1B measures the surface roughness of an object 300 to be measured.

[0136] In the surface roughness measuring device 1B, the multiple measurement light pulses Pa formed by the pulse formation unit 4 pass through the beam splitter 5 and are incident on the surface of the object 300 to be measured. The multiple measurement light pulses Pa are then reflected by the surface of the object 300 to become multiple reflected light pulses Pb. The multiple reflected light pulses Pb, together with the reference light pulse Pr, are incident on a correlation optical system (not shown), and the correlated light, which includes the correlation between the two, is incident on the photodetector 12. The time waveforms of the multiple reflected light pulses Pb are then measured using an optical sampling technique with a correlation optical system, but the procedure is the same as in the distance measuring device 1A, so a detailed explanation is omitted.

[0137] Meanwhile, multiple measurement light pulses Pa are reflected by the beam splitter 5 and, together with the reference light pulse Pr, are incident on a correlation optical system (not shown), becoming correlated light that includes the correlation between the two, and are then incident on the photodetector 14. The time waveforms of the multiple measurement light pulses Pa are also measured using optical sampling techniques with the correlation optical system.

[0138] Figure 17 schematically shows an example of the time waveforms of multiple measurement light pulses Pa and multiple reflected light pulses Pb measured by the surface roughness measuring device 1B according to the second embodiment.

[0139] In the surface roughness measuring device 1B, multiple measurement light pulses Pa have time intervals between them, as schematically shown in Figure 17(a), and constitute a measurement light pulse train. The time intervals of the multiple measurement light pulses Pa are all the same, for example, Δt. In contrast, the time intervals of the multiple reflected light pulses Pb change from Δt to Δt1 and Δt2, as schematically shown in Figure 17(b), and are different from each other.

[0140] If the surface of object 300 is an ideal plane (a perfectly flat surface), the time interval between multiple reflected light pulses Pb will not change and will be the same as the time interval between multiple measurement light pulses Pa. The difference between the time interval between the multiple reflected light pulses Pb and the time interval between the multiple measurement light pulses Pa is a quantity that indicates the surface roughness of object 300, so by measuring this, the surface roughness of object 300 can be measured.

[0141] In Figure 17(a), the time intervals between the multiple measurement light pulses Pa are assumed to be the same. However, to measure the surface roughness of object 300, it is sufficient to know the difference between the time intervals of the multiple reflected light pulses Pb. Therefore, at least two of the time intervals between the multiple measurement light pulses Pa do not need to be the same.

[0142] The distance measuring device 1A according to the first embodiment and the surface roughness measuring device 1B according to the second embodiment of the optical measuring device of this disclosure are not limited to the specific examples described in detail above, and various modifications are possible.

[0143] Figure 18 shows an example of the configuration of a two-dimensional spectrometer 6A used in place of the diffraction grating 6 in a distance measuring device according to a first modification of the first embodiment. The two-dimensional spectrometer 6A includes a cylindrical lens 61, a VIPA (Virtually Imaged Phased Array) plate 62, a lens 63, and a diffraction grating 64. An echelon grating (stepped grating) may be used instead of the VIPA plate 62.

[0144] Multiple measurement light pulses Pa formed by the pulse formation unit 4 pass through the beam splitter 5 (Figure 1) and are incident on the cylindrical lens 61. The cylindrical lens 61 focuses the multiple measurement light pulses Pa and directs them onto the VIPA plate 62. The spatial shape of the multiple measurement light pulses Pa focused by the cylindrical lens 61 is a straight line extending along the direction x of the generatrix of the cylindrical lens 61.

[0145] Figure 19 is a side view showing the structure of the VIPA plate 62. The VIPA plate 62 has a glass substrate 62a with one surface and the other surface parallel to each other, a fully reflective film 62b formed on one surface of the glass substrate 62a, and a partially reflective film 62c formed on the other surface of the glass substrate 62a. The reflectance of the fully reflective film 62b is 100%, and the reflectance of the partially reflective film 62c is less than 100% (e.g., 99%). On one surface of the glass substrate 62a, a light incident region 62d is provided along one edge of the glass substrate 62a where the fully reflective film 62b is not formed.

[0146] Returning to Figure 18, the multiple measurement light pulses Pa focused by the cylindrical lens 61 are incident on the VIPA plate 62 in the light incident region 62d and undergo multiple reflections between the fully reflective film 62b and the partially reflective film 62c. As a result of the interference of light that occurs during the multiple reflections, the multiple measurement light pulses Pa are spectrally separated along a direction y perpendicular to the direction in which the straight line of its spatial shape extends (the direction x of the generatrix of the cylindrical lens), and are transmitted through the partially reflective film 61c and emitted from the VIPA plate 62. The light emitted from the VIPA plate 62 contains multiple wavelength components, and the frequency interval of these multiple wavelength components is determined by the emission direction and the thickness of the glass substrate 62a (the distance between the fully reflective film 62b and the partially reflective film 62c).

[0147] Lens 63 focuses the multiple measurement light pulses Pa spectrally separated by the VIPA plate 62 and directs them onto the diffraction grating 64. The diffraction grating 64 spectrally separates the multiple measurement light pulses Pa along the direction x of the generator of the cylindrical lens 61 and directs them onto lens 7 (Figure 1). Thus, the multiple measurement light pulses Pa are spatially separated along two directions: the direction x of the generator of the cylindrical lens 61 and the direction y perpendicular to it. Lens 7 focuses the individual measurement light pulses Pa1, Pa2, and Pa3, which are spatially separated from each other along the two directions, and irradiates them onto different positions on the surface of object 100. The two-dimensional spectrometer 6A and lens 7 constitute a spectral section that spatially separates the individual measurement light pulses Pa1, Pa2, and Pa3 contained in the multiple measurement light pulses Pa according to their central wavelength and directs them onto object 100.

[0148] In the distance measuring device 1A according to the first embodiment, the diffraction grating 6 and lens 7 are used in both the spectral section, which spatially separates the individual measurement light pulses Pa1, Pa2, and Pa3 contained in a plurality of measurement light pulses Pa and irradiates them onto the object 100, and the multiplexing section, which focuses and combines the individual reflected light pulses Pb1, Pb2, and Pb3 from each other and emits them as a plurality of reflected light pulses Pb toward the beam splitter 5. However, when the spectral section is configured with a two-dimensional spectrometer 6A and lens 7, it is necessary to configure the individual measurement light pulses Pa1, Pa2, and Pa3 and their corresponding individual reflected light pulses Pb1, Pb2, and Pb3 to travel along different optical paths, and to provide a multiplexing section separate from the spectral section configured with the two-dimensional spectrometer 6A and lens 7.

[0149] In the distance measuring device 1A according to the first embodiment, a diffraction grating 6 is used to spatially separate multiple measurement light pulses Pa according to their wavelengths, so that the multiple measurement light pulses Pa are separated one-dimensionally along the spectral direction of the diffraction grating 6. Therefore, it is possible to measure the one-dimensional distribution of distance.

[0150] In contrast, in the distance measuring device according to the first modified example using the two-dimensional spectrometer 6A, multiple measurement light pulses Pa are separated two-dimensionally along two mutually orthogonal directions x and y, making it possible to measure the two-dimensional distribution of distance.

[0151] Similar to the distance measuring device 1A according to the first embodiment, the distance measuring device according to the first modified example using a two-dimensional spectrometer 6A can also be used to measure the thickness of an object, the film thickness, and the refractive index of a film. In this case, it is possible to measure the two-dimensional distribution of the thickness of an object, the film thickness, and the refractive index of a film.

[0152] In the surface roughness measuring device 1B according to the second embodiment, by using a two-dimensional spectrometer 6A instead of a diffraction grating 6, it becomes possible to measure the two-dimensional distribution of surface roughness.

[0153] Figure 20 shows an example of the configuration of a distance measuring device 1C according to a second modification of the first embodiment. The distance measuring device 1C comprises a plurality of semiconductor laser light sources 21, 22, 23 with different emission wavelengths, a multiplexing optical system 24, a beam splitter 5, a diffraction grating 6, a lens 7, a photodetector 12, and a signal processing device 13, and measures the distance to an object 100 to be measured.

[0154] Multiple semiconductor laser light sources 21, 22, and 23 each output measurement light pulses Pa1, Pa2, and Pa3, respectively, at different timings and with different time waveforms. The output timing and time waveform of the measurement light pulses Pa1, Pa2, and Pa3 are controlled by controlling the drive current supplied to each of the multiple semiconductor laser light sources 21, 22, and 23. The multiplexing optical system 24 combines the measurement light pulses Pa1, Pa2, and Pa3 and emits them as multiple measurement light pulses Pa toward the beam splitter 5. The multiplexing optical system 24 can be composed of spectroscopic elements such as diffraction gratings and prisms. Alternatively, the multiplexing optical system 24 can be composed of dichroic mirrors or the like. The multiple semiconductor laser light sources 21, 22, and 23 and the multiplexing optical system 24 constitute a measurement light pulse source that outputs multiple measurement light pulses Pa with different time waveforms and different center wavelengths. The pulse width of the multiple measurement light pulses Pa is between 10 ns and 10,000 ns, and in one example it is 100 ns. In other words, the multiple measurement light pulses Pa are so-called nanosecond light pulses.

[0155] Multiple measurement light pulses Pa pass through the beam splitter 5 and are incident on the diffraction grating 6. The diffraction grating 6 spatially separates the individual measurement light pulses Pa1, Pa2, and Pa3 contained in the multiple incident measurement light pulses Pa according to their wavelength. The lens 7 focuses the spatially separated individual measurement light pulses Pa1, Pa2, and Pa3 and irradiates them at different positions on the surface of the object 100. The diffraction grating 6 and lens 7 constitute a spectroscopic unit that spatially separates the individual measurement light pulses Pa1, Pa2, and Pa3 contained in the multiple measurement light pulses Pa according to their central wavelength and incident them on the object 100. Other spectroscopic elements such as prisms may be used instead of the diffraction grating 6. A concave mirror may be used instead of the lens 7.

[0156] At least a portion of the individual measurement light pulses Pa1, Pa2, and Pa3, which are irradiated at different positions on the surface of object 100, are reflected by the surface of object 100, becoming individual reflected light pulses Pb1, Pb2, and Pb3, respectively. The multiple reflected light pulses Pb are also nanosecond light pulses.

[0157] Lens 7 focuses the individual reflected light pulses Pb1, Pb2, and Pb3 to a single point on the diffraction grating 6. Lens 7 functions as a focusing optical system that concentrates the individual reflected light pulses Pb1, Pb2, and Pb3. The diffraction grating 6 functions as a multiplexing optical system. The diffraction grating 6 combines the individual reflected light pulses Pb1, Pb2, and Pb3 and emits them as multiple reflected light pulses Pb toward the beam splitter 5. Lens 7 and diffraction grating 6 constitute a multiplexing section that focuses and combines the individual reflected light pulses Pb1, Pb2, and Pb3 toward each other and emits them as multiple reflected light pulses Pb toward the beam splitter 5.

[0158] Multiple reflected light pulses Pb are reflected by the beam splitter 5 and incident on the photodetector 12. The photodetector 12 is, for example, a photodiode or a photomultiplier tube. Since the multiple reflected light pulses Pb are nanosecond pulses, the time change of their light intensity is slower than that of femtosecond pulses, and can be tracked even with the response speed of a typical photodetector (e.g., a photodiode or photomultiplier tube). Therefore, the time waveform of the multiple reflected light pulses Pb can be directly measured by the time waveform of the electrical signal output by the photodetector 12, such as a photodiode or photomultiplier tube. However, in order to accurately evaluate the time waveform of nanosecond light pulses, it is desirable that the response frequency of the photodetector 12 be 1 GHz or higher. The photodetector 12 constitutes a photodetector that receives multiple reflected light pulses Pb and outputs their time waveform signals. The signal processing device 13 constitutes a measurement unit that measures the timing at which the multiple reflected light pulses Pb were received or the difference in those timings based on the time waveform signals of the multiple reflected light pulses Pb.

[0159] In the distance measuring device 1C according to the second modification of the first embodiment, nanosecond light pulses are used as multiple measurement light pulses Pa. Therefore, it is possible to measure the time waveforms of multiple reflected light pulses Pb by the photodetector 12 without using light sampling techniques using a correlation optical system. Consequently, although the distance resolution decreases due to the wider pulse width of the measurement light pulses Pa, the configuration of the device is simplified because there is no need to provide a correlation optical system. Furthermore, since there is no need to repeat light sampling to measure the time waveform, the time required for distance measurement can be shortened.

[0160] Figure 21 shows an example of the configuration of a distance measuring device 1D according to a third modification of the first embodiment. The distance measuring device 1D differs from the distance measuring device 1A according to the first embodiment in that it utilizes dual-comb spectroscopy technology. The distance measuring device 1D comprises a first pulsed laser light source 2A, a second pulsed laser light source 2B, a pulse forming unit 4, a beam splitter 5, a diffraction grating 6, a lens 7, a reflecting mirror 15, a beam splitter 16, a photodetector 12, and a signal processing device 13, and measures the distance to an object 100 to be measured.

[0161] The first pulsed laser light source 2A and the second pulsed laser light source 2B are both optical frequency comb light sources with stabilized pulse period and offset frequency, and periodically output femtosecond optical pulses consisting of a group of modes (comb mode group) arranged at equal frequency intervals. The first pulsed laser light source 2A and the second pulsed laser light source 2B are phase-synchronized with each other, and their periods of outputting femtosecond optical pulses differ slightly. The first pulsed laser light source 2A outputs a broadband measurement optical pulse Ps, and the second pulsed laser light source 2B outputs a reference optical pulse Pr.

[0162] The broadband measurement light pulse Ps output by the first pulsed laser light source 2A is incident on the pulse formation unit 4. The pulse formation unit 4 forms a plurality of measurement light pulses Pa from the broadband measurement light pulse Ps. The plurality of measurement light pulses Pa have different time waveforms and different center wavelengths. The configuration of the pulse formation unit 4 is the same as that of the distance measuring device 1A according to the first embodiment, so a description is omitted. The first pulsed laser light source 2A and the pulse formation unit 4 constitute a measurement light pulse source that outputs a plurality of measurement light pulses Pa that have different time waveforms and different center wavelengths.

[0163] Multiple measurement light pulses Pa pass through the beam splitter 5 and are incident on the diffraction grating. The diffraction grating spatially separates the individual measurement light pulses Pa1, Pa2, and Pa3 contained in the multiple incident measurement light pulses Pa. Lens 7 focuses each of the individual measurement light pulses Pa1, Pa2, and Pa3 and irradiates them at different positions on the surface of object 100. The diffraction grating 6 and lens 7 constitute a spectroscopic unit that spatially separates the individual measurement light pulses Pa1, Pa2, and Pa3 contained in the multiple measurement light pulses Pa according to their central wavelength and incidents them on object 100.

[0164] At least a portion of the individual measurement light pulses Pa1, Pa2, and Pa3 irradiated at different positions on the surface of object 100 are reflected by the surface of object 100, becoming individual reflected light pulses Pb1, Pb2, and Pb3, respectively.

[0165] Lens 7 focuses the individual reflected light pulses Pb1, Pb2, and Pb3 to a single point on the diffraction grating 6. Lens 7 functions as a focusing optical system that concentrates the individual reflected light pulses Pb1, Pb2, and Pb3. The diffraction grating 6 functions as a multiplexing optical system. The diffraction grating 6 combines the individual reflected light pulses Pb1, Pb2, and Pb3 and emits them as multiple reflected light pulses Pb toward the beam splitter 5. Lens 7 and diffraction grating 6 constitute a multiplexing section that focuses and combines the individual reflected light pulses Pb1, Pb2, and Pb3 toward each other and emits them as multiple reflected light pulses Pb toward the beam splitter 5.

[0166] Multiple reflected light pulses Pb are reflected by the beam splitter 5 and the reflector 15 and incident on the beam splitter 16. Meanwhile, the reference light pulse Pr output by the second pulsed laser light source 2B also incident on the beam splitter 16. The multiple reflected light pulses Pb are reflected by the beam splitter 16, and the reference light pulse Pr passes through the beam splitter 16. Both are focused by a lens (not shown) and incident on the photodetector 12. At this time, the multiple reflected light pulses Pb and the reference light pulse Pr interfere to form interference light, which the photodetector 12 receives, converts into an electrical signal, and outputs. The interference light of the multiple reflected light pulses Pb and the reference light pulse Pr is correlated light, which includes the cross-correlation between the two. The reflector 15 and the beam splitter 16 constitute a correlated optical system that outputs correlated light, which includes the cross-correlation between the multiple reflected light pulses Pb and the reference light pulse Pr.

[0167] Here, both the first pulsed laser light source 2A and the second pulsed laser light source 2B periodically output femtosecond light pulses, and their periods are slightly different. As a result, there is a difference in the timing at which multiple reflected light pulses Pb and reference light pulse Pr are incident on the beam splitter 16, and this difference changes over time. Therefore, the photodetector 12 sequentially outputs an electrical signal representing the intensity of the correlated light, including the cross-correlation between the multiple reflected light pulses Pb and reference light pulse Pr, while changing the time delay of the reference light pulse Pr relative to the multiple reflected light pulses Pb. This makes it possible to sequentially acquire electrical signals corresponding to optical signals sampled at different timings for the time waveforms of the multiple reflected light pulses Pb. The signal processing device 13 measures the time waveforms of the multiple reflected light pulses Pb by processing the electrical signals acquired in this manner.

[0168] The correlation optical system, comprised of the reflector 15 and beam splitter 16, the photodetector 12, and the signal processing device 13, constitute a photodetection unit that receives multiple reflected light pulses Pb and outputs their time waveform signals. The signal processing device 13 also constitutes a measurement unit that measures the timing at which multiple reflected light pulses Pb are received or the difference in those timings, based on the time waveform signals of the multiple reflected light pulses Pb.

[0169] In the distance measuring device 1A according to the first embodiment, in order to sample the time waveforms of multiple reflected light pulses Pb, it is necessary to move the moving reflector 8 mounted on the moving stage to change the optical path length (i.e., time delay) of the reference light pulse Pr. Since there are limits to the amount and speed of movement of the moving reflector 8, there are also limits to the dynamic range of distance measurement and the time required for distance measurement.

[0170] In contrast, the distance measuring device 1D according to the third modification of the first embodiment does not use a moving reflector, so the dynamic range of distance measurement can be expanded and the time required for distance measurement can be shortened compared to the distance measuring device 1A.

[0171] Figure 22 shows an example of the configuration of a distance measuring device 1E according to a fourth modification of the first embodiment. The distance measuring device 1E comprises a continuous wave laser light source 20, a microring resonator 25, a pulse forming unit 4A, a beam splitter 5, a diffraction grating 6, a lens 7, a microring resonator 17, a photodetector 12, and a signal processing device 13, and measures the distance to an object 100 to be measured.

[0172] The continuous-wave laser light source 20 outputs continuous-wave laser light (CW). By passing the continuous-wave laser light (CW) output by the continuous-wave laser light source 20 through the microring resonator 25, pulsed laser light can be generated. The resulting pulsed laser light is, for example, a femtosecond optical pulse. The microring resonator 25 periodically outputs the femtosecond optical pulse generated in this way as a broadband optical pulse P and directs it into the pulse formation unit 4A. The pulse formation unit 4A forms multiple measurement optical pulses Pa from the broadband optical pulse P. The multiple measurement optical pulses Pa have different time waveforms and different center wavelengths. The continuous-wave laser light source 20, the microring resonator 25, and the pulse formation unit 4A constitute a measurement optical pulse light source that outputs multiple measurement optical pulses Pa that have different time waveforms and different center wavelengths.

[0173] Figure 23 shows an example of the configuration of the pulse formation unit 4A. The pulse formation unit 4A includes an array waveguide diffraction grating 41A, a plurality of optical fibers 43A, and an array waveguide diffraction grating 45A. The array waveguide diffraction grating 41A is a spectroscopic element and is optically coupled to the microring resonator 25. The array waveguide diffraction grating 41A spatially separates the plurality of wavelength components contained in the broadband optical pulse P according to wavelength, and causes each wavelength component to be incident on each of the plurality of optical fibers 43A. Note that in Figure 23, only three optical fibers 43a, 43b, and 43c are shown as the plurality of optical fibers 43A. However, the number of plurality of optical fibers is not limited to three and can be any number.

[0174] Multiple optical fibers 43A differ from each other in at least one of their length and refractive index. Each wavelength component is delayed by a different amount depending on the difference in length of the multiple optical fibers 43A. In addition, the pulse shape of each wavelength component changes as it propagates through each of the multiple optical fibers 43A. Since the multiple optical fibers 43A have different refractive indices, the dispersion of light propagating through each of the multiple optical fibers 43A is also different. Therefore, the change in pulse shape that occurs as each wavelength component propagates through each of the multiple optical fibers 43A is also different. By utilizing the fact that multiple wavelength components emitted from the array waveguide diffraction grating 41A are delayed by different amounts and that the change in pulse shape of each wavelength component is different, a broadband optical pulse P can be converted into multiple measurement optical pulses Pa. The multiple optical fibers 43A are, for example, dispersion-compensated fibers or photonic crystal fibers.

[0175] Each wavelength component that has passed through each of the multiple optical fibers 43A is incident on the array waveguide diffraction grating 45A. The array waveguide diffraction grating 45A combines each wavelength component that has passed through each of the multiple optical fibers 43A and emits it as multiple measurement light pulses Pa.

[0176] The continuous-wave laser light source 20, the microring resonator 25, and the pulse formation unit 4A constitute a measurement light pulse light source that outputs a plurality of measurement light pulses Pa having different time wavelengths and different center wavelengths.

[0177] Returning to Figure 22, the multiple measurement light pulses Pa formed by the pulse formation unit 4A pass through the beam splitter 5 and are incident on the diffraction grating 6. The diffraction grating 6 spatially separates the individual measurement light pulses Pa1, Pa2, and Pa3 contained in the multiple incident measurement light pulses Pa according to their wavelength. The lens 7 focuses the spatially separated individual measurement light pulses Pa1, Pa2, and Pa3 and irradiates them at different positions on the surface of the object 100. The diffraction grating 6 and lens 7 constitute a spectroscopic unit that spatially separates the individual measurement light pulses Pa1, Pa2, and Pa3 contained in the multiple measurement light pulses Pa according to their central wavelength and incidents them on the object 100.

[0178] At least a portion of the individual measurement light pulses Pa1, Pa2, and Pa3 irradiated at different positions on the surface of object 100 are reflected by the surface of object 100, becoming individual reflected light pulses Pb1, Pb2, and Pb3, respectively.

[0179] Lens 7 focuses the individual reflected light pulses Pb1, Pb2, and Pb3 to a single point on the diffraction grating 6. Lens 7 functions as a focusing optical system that concentrates the individual reflected light pulses Pb1, Pb2, and Pb3. The diffraction grating 6 functions as a multiplexing optical system. The diffraction grating 6 combines the individual reflected light pulses Pb1, Pb2, and Pb3 and emits them as multiple reflected light pulses Pb toward the beam splitter 5. Lens 7 and diffraction grating 6 constitute a multiplexing section that focuses and combines the individual reflected light pulses Pb1, Pb2, and Pb3 toward each other and emits them as multiple reflected light pulses Pb toward the beam splitter 5.

[0180] Multiple reflected light pulses Pb are reflected by the beam splitter 5 and incident on the microring resonator 17. The multiple reflected light pulses Pb interfere with each other within the microring resonator 17, and the resulting interference light is emitted from the microring resonator 17. The photodetector 12 receives this interference light, converts it into an electrical signal, and outputs it. The interference light of the multiple reflected light pulses Pb is correlated light that includes the autocorrelation of the multiple reflected light pulses Pb, and the microring resonator 17 constitutes a correlated optical system that outputs correlated light that includes the autocorrelation of the multiple reflected light pulses Pb.

[0181] The time waveform of the electrical signal output by the photodetector 12 is the time waveform of correlated light, which includes the autocorrelation of multiple reflected light pulses Pb. The signal processing device 13 measures the time waveforms of the multiple reflected light pulses Pb based on the time waveform of the electrical signal output by the photodetector 12.

[0182] The microring resonator 17, the photodetector 12, and the signal processing device 13 constitute a photodetection unit that receives multiple reflected light pulses Pb and outputs their time waveform signals. The signal processing device 13 also constitutes a measurement unit that measures the timing at which multiple reflected light pulses Pb are received or the difference in those timings based on the time waveform signals of the multiple reflected light pulses Pb.

[0183] In the distance measuring device 1E according to the fourth modification of the first embodiment, as with the distance measuring device 1D according to the third modification, a moving reflector is not used, so the dynamic range of distance measurement can be expanded compared to the distance measuring device 1A, and the time required for distance measurement can be shortened. In addition, in the distance measuring device 1E according to the fourth modification, although dual-comb spectroscopy technology is used, unlike the distance measuring device 1D according to the third modification, complex operations such as phase-synchronizing the two pulsed laser light sources or slightly differentiating the periods of femtosecond light pulses periodically output by each pulsed laser light source are not required.

[0184] In the optical measuring device of this disclosure, individual reflected light pulses Pb1, Pb2, and Pb3 contained in a plurality of reflected light pulses Pb are identified based on their respective time waveforms. For example, if the characteristic points of individual measurement light pulses Pa1, Pa2, and Pa3 contained in a plurality of measurement light pulses Pa are extracted in advance, the time waveforms of individual reflected light pulses Pb1, Pb2, and Pb3 appearing in the time waveform of the plurality of reflected light pulses Pb can be identified based on these characteristic points.

[0185] Thus, in the optical measuring device of this disclosure, by identifying each pulse on the time axis, the timing at which each pulse is received or the difference in those timings can be measured.

[0186] Separately, the timing at which each pulse is received, or the difference in those timings, can also be measured from the spectrum obtained by Fourier transforming the time waveforms of multiple reflected light pulses Pb.

[0187] Figure 24 shows an example of the time waveform of a pulse train consisting of multiple pulses with different time waveforms. Figure 24 shows a pulse train consisting of multiple pulses with different time waveforms, each containing multiple single pulses, and consisting of three pulses (double pulse, triple pulse, and quadruple pulse) with different numbers of consecutive single pulses. Figure 24(a) shows an example of the time waveform of individual measurement light pulses Pa1, Pa2, and Pa3, which are included in multiple measurement light pulses Pa, and Figure 24(b) shows individual reflected light pulses Pb1, Pb2, and Pa3, which are included in multiple reflected light pulses Pb. The spacing between each pulse Pb1, Pb2, and Pb3 included in multiple reflected light pulses Pb is narrower than the spacing between each pulse Pa1, Pa2, and Pa3 included in multiple measurement light pulses Pa.

[0188] Figure 25 shows an example of a spectrum obtained by Fourier transforming the time waveform shown in Figure 24. Curve Ca is the spectrum of the time waveforms of multiple measurement light pulses Pa, and curve Cb is the spectrum of the time waveforms of multiple reflected light pulses Pb. A difference arises between the two curves Ca and Cb, reflecting that the intervals between each pulse in the multiple reflected light pulses Pb are narrower than the intervals between each pulse in the multiple measurement light pulses Pa. Therefore, by measuring the time waveforms of multiple measurement light pulses Pa and multiple reflected light pulses Pb and comparing the spectra obtained by Fourier transforming each, it is possible to calculate the changes in the order and intervals of individual pulses that occurred between the multiple measurement light pulses Pa and multiple reflected light pulses Pb. [Explanation of symbols]

[0189] 1A, 1C, 1D, 1E… Distance measuring device, 1B… Surface roughness measuring device, 2, 2A, 2B… Pulsed laser light source, 20… Continuous wave laser light source, 21, 22… Semiconductor laser light source, 24… Multiplexing optical system, 25… Microring resonator, 4, 4A… Pulse formation unit, 41, 45… Diffraction grating, 41A, 45A… Array waveguide diffraction grating, 43… Spatial light modulator (SLM), 43A, 43a, 43b, 43c… Optical fiber 6...diffraction grating, 6A...two-dimensional spectrometer, 62...VIPA plate, 64...diffraction grating, 8...moving mirror, 11...optical element, 12,14...photodetector, 17...microring resonator, 100...object, 200...multilayer structure, 300...object, CW...continuous wave laser light, P...broadband optical pulse, Pa, Pa1, Pa2, Pa3...measurement optical pulse, Pb, Pb1, Pb2, Pb3...reflected optical pulse, Pr...reference optical pulse.

Claims

1. A measurement light pulse light source that outputs multiple measurement light pulses having different time waveforms and different center wavelengths, A spectrometer or spectrometer that spatially separates the plurality of measurement light pulses according to their central wavelengths and directs them onto the object to be measured, A multiplexing unit that combines the plurality of measurement light pulses reflected by or transmitted through the object to be measured and emits them onto a single optical path, A photodetector that receives the plurality of measurement light pulses emitted from the wave multiplexer and outputs a time waveform signal of the plurality of measurement light pulses, The system includes a measurement unit that measures the timing at which each of the plurality of measurement light pulses is received by the photodetector, or the difference in those timings, based on the time waveform signal. The aforementioned measurement light pulse light source is A pulsed laser light source that outputs broadband optical pulses having multiple wavelength components, It includes a pulse forming unit that forms the plurality of measurement light pulses from the broadband light pulse, The pulse forming unit is A spectroscopic element that spatially separates multiple wavelength components contained in the broadband optical pulse according to wavelength, A spatial light modulator modulates at least one of the phase and intensity of each of the plurality of wavelength components spatially separated for each wavelength, such that when the plurality of wavelength components are combined, a plurality of light pulses are formed in which the time waveform and center wavelength are different from each other. A multiplexing optical system that combines the plurality of wavelength components, each having at least one of its phase and intensity modulated, to output the plurality of measurement light pulses, The spatial light modulator is an optical measuring device that modulates at least one of the phase and intensity of each of the plurality of wavelength components such that each of the plurality of measurement light pulses, which are femtosecond light pulses, becomes a single pulse whose time waveform is different from that of the other measurement light pulses.

2. A measurement light pulse light source that outputs multiple measurement light pulses having different time waveforms and different center wavelengths, A spectrometer or spectrometer that spatially separates the plurality of measurement light pulses according to their central wavelengths and directs them onto the object to be measured, A multiplexing unit that combines the plurality of measurement light pulses reflected by or transmitted through the object to be measured and emits them onto a single optical path, A photodetector that receives the plurality of measurement light pulses emitted from the wave multiplexer and outputs a time waveform signal of the plurality of measurement light pulses, The system includes a measurement unit that measures the timing at which each of the plurality of measurement light pulses is received by the photodetector, or the difference in those timings, based on the time waveform signal. The aforementioned measurement light pulse light source is A pulsed laser light source that outputs broadband optical pulses having multiple wavelength components, It includes a pulse forming unit that forms the plurality of measurement light pulses from the broadband light pulse, The pulse forming unit is An array waveguide diffraction grating that spatially separates multiple wavelength components contained in the broadband optical pulse according to wavelength, Multiple optical fibers that transmit each of the multiple wavelength components spatially separated by wavelength, The array waveguide diffraction grating includes a component that combines the multiple wavelength components transmitted by the multiple optical fibers and outputs them as multiple measurement light pulses, An optical measuring device in which, because the refractive indices of the plurality of optical fibers are different from each other, each of the plurality of measurement light pulses, which are femtosecond light pulses, is a single pulse whose time waveform is different from that of the other measurement light pulses.

3. The plurality of measurement light pulses, before being incident on the object to be measured, have a time interval between them and constitute a train of measurement light pulses. The light measuring device according to claim 1 or 2.

4. The aforementioned light detection unit is A correlation optical system that receives the plurality of measurement light pulses emitted from the multiplexing section and a reference light pulse, and outputs correlation light including the cross-correlation between the two, The system includes a photodetector that receives the aforementioned correlated light and outputs a correlated signal, The correlation optical system outputs the correlation light by superimposing the multiple measurement light pulses and the reference light pulse while changing the time delay amount of the reference light pulse relative to the multiple measurement light pulses. The light detection unit generates and outputs the time waveform signal from the correlation signal obtained for each time delay amount. The light measuring device according to claim 1.

5. The correlation optical system is A beam splitter that branches off a portion of the broadband optical pulse output by the pulsed laser light source from the broadband optical pulse to form the reference optical pulse, A moving reflector that changes the time delay amount of the reference light pulse, The optical element includes a plurality of measurement light pulses and a reference light pulse that superimposes the correlation light, The optical measuring device according to claim 4.

6. The optical element includes a nonlinear optical crystal. The optical measuring device according to claim 5.

7. The pulsed laser light source is an optical frequency comb light source. The optical measuring device according to claim 4.

8. The aforementioned light detection unit is A correlation optical system that receives the plurality of measurement light pulses emitted from the multiplexing section and a reference light pulse, and outputs correlation light including the cross-correlation between the two, The system includes a photodetector that receives the aforementioned correlated light and outputs a correlated signal, The correlation optical system is It includes a second pulsed laser light source that outputs a reference light pulse, The second pulsed laser light source is an optical frequency comb light source whose phase is synchronized with the pulsed laser light source and whose period for outputting optical pulses is different from that of the pulsed laser light source. The optical measuring device according to claim 7.

9. The pulsed laser light source is A continuous wave laser light source that outputs continuous wave laser light, A microring resonator that receives the continuous-wave laser light and converts it into a broadband optical pulse for output, is included. The optical measuring device according to claim 2.

10. The aforementioned light detection unit is The system includes a microring resonator that receives the aforementioned multiple measurement light pulses and outputs correlated light including autocorrelation, The optical measuring device according to claim 9.

11. The light detection unit includes a photodiode or a photomultiplier tube. The light measuring device according to any one of claims 1 to 10.

12. The aforementioned measuring unit is A Fourier analysis unit that performs Fourier analysis on the aforementioned time waveform signal, A calculation unit that, based on the results of the Fourier analysis, measures the timing at which each of the plurality of measurement light pulses is received by the photodetector, or the difference in those timings, from the time waveform signal, The light measuring device according to any one of claims 1 to 11.

13. The spectroscopic element or spectrometer includes a diffraction grating. The light measuring device according to any one of claims 1 to 12.

14. The multiplexing section includes a diffraction grating. The light measuring device according to any one of claims 1 to 13.

15. The wave-combining unit combines the plurality of measurement light pulses reflected by the object to be measured and emits them onto a single optical path. The wave multiplexing section also serves as the spectroscopic element or the spectrometer. The light measuring device according to any one of claims 1 to 14.

16. The optical measuring apparatus according to any one of claims 1 to 14, wherein the spectroscopic element or spectrometer spatially separates the plurality of measurement light pulses along two directions.

17. The measuring unit calculates at least one of the following based on the timing or the difference: the distance to the object to be measured, the thickness of the object to be measured, the thickness and refractive index of the film formed on the surface of the object to be measured, and the surface roughness of the object to be measured. A light measuring device according to any one of claims 1 to 16.

18. A step of outputting multiple measurement light pulses, each having a different time waveform and different center wavelengths. The steps include spatially separating the plurality of measurement light pulses according to their central wavelengths and directing them onto the object to be measured, The steps include combining the plurality of measurement light pulses that have been reflected by or transmitted through the object to be measured and emitting them onto a single optical path, The steps include receiving the plurality of measurement light pulses emitted on the single optical path and outputting time waveform signals of the plurality of measurement light pulses, The process includes measuring the timing at which each of the plurality of measurement light pulses is received, or the difference between those timings, based on the time waveform signal. The step of outputting the measurement light pulse is: The steps include outputting a broadband optical pulse having multiple wavelength components, The step of forming the plurality of measurement light pulses from the broadband light pulse includes, The step of forming the measurement light pulse is: The steps include spatially separating multiple wavelength components contained in the broadband optical pulse according to their wavelengths, The steps include: modulating at least one of the phase and intensity of each of the plurality of wavelength components spatially separated for each wavelength such that when the plurality of wavelength components are combined, a plurality of optical pulses are formed in which the time waveform and center wavelength are different from each other; The process includes the step of combining the plurality of wavelength components, each having at least one of its phase and intensity modulated, to output the plurality of measurement light pulses, A method for measuring light, wherein in the modulation step, at least one of the phase and intensity of each of the plurality of wavelength components is modulated such that each of the plurality of measurement light pulses, which are femtosecond light pulses, becomes a single pulse whose time waveform is different from that of the other measurement light pulses.

19. A step of outputting multiple measurement light pulses, each having a different time waveform and different center wavelengths. The steps include spatially separating the plurality of measurement light pulses according to their central wavelengths and directing them onto the object to be measured, The steps include combining the plurality of measurement light pulses that have been reflected by or transmitted through the object to be measured and emitting them onto a single optical path, The steps include receiving the plurality of measurement light pulses emitted on the single optical path and outputting time waveform signals of the plurality of measurement light pulses, The process includes measuring the timing at which each of the plurality of measurement light pulses is received, or the difference between those timings, based on the time waveform signal. The step of outputting the measurement light pulse is: The steps include outputting a broadband optical pulse having multiple wavelength components, The step of forming the plurality of measurement light pulses from the broadband light pulse includes, The step of forming the measurement light pulse is: The steps include spatially separating multiple wavelength components contained in the broadband optical pulse according to their wavelengths, A step of transmitting each of the plurality of wavelength components spatially separated by wavelength into a plurality of optical fibers, The step includes combining the plurality of wavelength components transmitted by the plurality of optical fibers and outputting them as the plurality of measurement light pulses, An optical measurement method in which, because the refractive indices of the plurality of optical fibers are different from each other, each of the plurality of measurement optical pulses, which are femtosecond optical pulses, is a single pulse whose time waveform is different from that of the other measurement optical pulses.

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