Light Measuring Device

Abstract

To provide an optical measuring device with which it is possible to solve at least one of the stated problems.SOLUTION: A light source device 200 generates wavelength sweep light L1. An irradiation optical system 310 irradiates an object with the wavelength sweep light L1. A pulse light source 210 generates pulse light that includes a continuous spectrum. A divider 222 spatially divides the pulse light into n beams (n≥2) in accordance with a wavelength. N fibers FB give different delays to the n beams. A coupler 226 is a bundle fiber FB or a multi-core fiber that multiplexes the n beams outputted from the n fibers FB. A rod integrator 228 has its incidence end connected to an emission end of the coupler 226. A critical illumination system 312 projects the light source image of an emission end of the rod integrator 228 to the object 2.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present disclosure relates to a light measurement device. [Background technology]

[0002] Spectroscopic analysis is widely used for the component analysis and inspection of objects. In spectroscopic analysis, an object is irradiated with irradiating light and the spectrum of the resulting object light is measured. Then, based on the relationship between the spectrum of the object light and the spectrum of the irradiating light, optical characteristics such as reflectance characteristics (wavelength dependence) or transmittance characteristics can be obtained.

[0003] Wavelength-swept spectroscopy is known as one of the methods for measuring optical properties. A wavelength-swept spectrometer generates wavelength-swept light, whose wavelength changes over time, and irradiates the test object. The wavelength-swept light is a pulse or pulse train in which time and wavelength have a one-to-one relationship. The time waveform of the light obtained by irradiating the test object with the wavelength-swept light is then detected by a photodetector. The output waveform of the photodetector represents a spectrum in which the time axis corresponds to the wavelength.

[0004] 1 is a diagram showing a wavelength sweep type spectroscopic device 10. The spectroscopic device 10 includes a light source device 20, a spectroscopic head 30, and a processing unit 40.

[0005] The light source device 20 generates wavelength-swept light L1. The wavelength-swept light L1 is guided to the spectroscopic head 30. The irradiation optical system 31 of the spectroscopic head 30 irradiates the wavelength-swept light L1 onto the sample 2. The first photodetector 32 detects light (object light) L2 obtained as a result of irradiating the sample 2 with the wavelength-swept light L1. The object light L2 can be reflected light or transmitted light from the sample 2.

[0006] In the irradiation optical system 31, a part of the wavelength swept light L1 is branched off as a reference light L3. A second light receiver 33 measures the reference light L3.

[0007] The first detection signal S1 generated by the first photodetector 32 and the second detection signal S2 generated by the second photodetector 33 are supplied to the arithmetic processing device 40. The object light L2 and the reference light L3 inherit the one-to-one time-wavelength correspondence of the wavelength-swept light L1. Therefore, the time waveform of the first detection signal S1 can be converted into the spectrum of the object light L2 by converting the time axis into wavelength. Similarly, the time waveform of the second detection signal S2 can be converted into the spectrum of the reference light L3 by converting the time axis into wavelength. The arithmetic processing device 40 calculates the ratio of each corresponding wavelength of the object light L2 to the reference light L3 and measures the spectral characteristics (reflectance and transmittance) of the sample 2.

[0008] 2 is a diagram showing a light source device 20 that generates wavelength swept light. The light source device 20 includes a pulsed light source 21, a wavelength selection filter 22, a splitter 23, a delay line 24, and a coupler 25.

[0009] The pulse light source 21 generates pulsed light having a continuous spectrum. The wavelength-selecting filter 22 selects a wavelength band to be used for spectroscopic analysis from among the spectral components contained in the pulsed light. The splitter 23 is an arrayed waveguide grating (AWG) that splits the pulsed light into multiple n paths according to wavelength. The delay line 24 imparts different delays to the light (split light) on the multiple paths. For example, the delay line 24 includes multiple fibers FB1 to FBn of different lengths. The coupler 25 is a multicore fiber or a bundle fiber that spatially recombines the light output from the multiple fibers FB1 to FBn. The recombined light is output as wavelength-swept light L1.

[0010] Patent Document 2 discloses an optical system that irradiates an object with light emitted from a coupler 25 that is a multicore fiber or a bundle fiber. Each beam emitted from a multicore fiber or a bundle fiber has a Gaussian intensity distribution, and the irradiation optical system of Patent Document 2 irradiates the beam onto the object while maintaining the Gaussian intensity distribution. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Publication No. 2020-159973 [Patent Document 2] Japanese Patent Publication No. 2022-42444 [Patent Document 3] US Patent Application Publication No. 2017 / 0122806 Summary of the Invention [Problem to be solved by the invention]

[0012] The present inventors have studied the wavelength swept light source device 20 shown in FIG. 2 and have come to recognize the following problem.

[0013] (Task 1) Figure 3 is a diagram illustrating one of the problems (referred to as Problem 1) of wavelength-swept spectrometers. The wavelength-swept light L1 beam is a pulse that is repeatedly irradiated onto a predetermined position, and the object (sample) OBJ is transported by a transport means so as to cross the irradiation position of the wavelength-swept light L1. Figure 3 shows the relative positional relationship between the object OBJ and the wavelength-swept light L1 beam.

[0014] When the wavelength swept light L1 has a Gaussian-shaped illuminance distribution, the tail of the Gaussian distribution (for example, 1 / e 2 Therefore, when inspecting the entire object OBJ, including the edges, the intensity distribution of the wavelength swept light L1 is 1 / e as shown in the upper part of Figure 3. 2 The lower part (hatched) extends beyond the object OBJ. If the extended light becomes stray light and enters the receiver, the measurement accuracy will decrease. Furthermore, since the stray light does not pass through the object OBJ and is not attenuated, it is highly intense, and if it enters the receiver, it may have a negative effect on the receiver's reliability.

[0015] As shown in the lower part of Figure 3, stray light can be reduced by offsetting the relative positions of the beams irradiated on both ends of the object OBJ inward so that the tails of the beams are contained within the object OBJ. However, in this case, both ends of the object OBJ cannot be inspected, narrowing the measurable range. Furthermore, while the S / N ratio is improved by √N times by accumulating the spectra for N irradiations, in the state of the lower part of Figure 3, the number of irradiations of pulses of wavelength swept light L1 on one object OBJ is reduced compared to the state of the upper part, resulting in a lower S / N ratio.

[0016] (Task 2) Figure 4 is a diagram explaining another issue (referred to as issue 2) of wavelength-swept spectrometers. Figure 4 shows the intensity distribution of multiple beams of different wavelengths on the surface (sample surface) of an object OBJ. The thickness d of the object OBJ may vary depending on the irradiation position. As shown in Figure 4, when beams of wavelengths λ1 and λ2 are irradiated at different positions, the perceived thicknesses d1 and d2 will differ for each wavelength. The following Beer-Lambert law generally holds between the intensity I0 of the incident light and the intensity I of the transmitted light. -log(I / I0)=ε·c·d Here, -log(I / I0) is the absorbance, ε is the extinction coefficient, and d is the optical path length. If the optical path length, i.e., the thickness of the object, is constant, the absorbance is proportional to the concentration, so the concentration of the target substance can be determined by measuring the absorbance. However, as shown in Figure 4, if the thickness of the object OBJ is not uniform and the beam is irradiated at different positions depending on the wavelength, the thickness of the object will differ at each wavelength, and the absorbance will be affected not only by the extinction coefficient ε of the substance contained in the object OBJ but also by the optical path length d, resulting in the problem of not being able to accurately measure the absorbance spectrum.

[0017] To solve this problem, it is necessary to disclose an irradiation optical system that irradiates the same position with a plurality of beams having different wavelengths, and a special optical system such as that disclosed in Patent Document 2 is required.

[0018] These problems should not be considered as common knowledge among those skilled in the art, but rather have been independently recognized by the present inventors.

[0019] The present disclosure has been made in light of the above-mentioned circumstances, and one exemplary purpose of an embodiment thereof is to provide a light measurement device that can solve at least one of the above-mentioned problems. [Means for solving the problem]

[0020] One aspect of the present disclosure relates to a light measurement device. The light measurement device includes a light source device that generates wavelength-swept light and an optical system that irradiates an object with the wavelength-swept light. The light source device includes a pulsed light source that generates pulsed light having a continuous spectrum, a splitter that spatially splits the pulsed light into multiple n (n≧2) beams according to wavelength, multiple n fibers that impart different delays to the n beams, a coupler that is a bundle fiber or multicore fiber that combines the n beams output from the n fibers, and a rod integrator whose input end is coupled to the output end of the coupler. The optical system includes a critical illumination system that projects a light source image at the output end of the rod integrator onto the object.

[0021] Any combination of the above elements, or mutual substitution of elements or expressions between methods, devices, systems, etc., are also valid aspects of the present invention or the present disclosure. Furthermore, the description in this section (Means for Solving the Problems) does not explain all essential features of the present invention, and therefore, subcombinations of the described features may also constitute the present invention. [Effects of the Invention]

[0022] According to an aspect of the present disclosure, at least one of the above-mentioned problems can be solved. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 is a diagram showing a wavelength sweep type spectroscopic device. [Figure 2]FIG. 1 is a diagram illustrating a light source device that generates wavelength swept light. [Figure 3] FIG. 1 is a diagram illustrating one of the problems of a wavelength sweeping spectroscopic device. [Figure 4] FIG. 10 is a diagram illustrating another problem of a wavelength sweeping spectroscopic device. [Figure 5] 1 is a diagram illustrating a light measurement device according to an embodiment. [Figure 6] FIG. 2 is a perspective view showing a coupler and a rod integrator. [Figure 7] FIG. 2 is a cross-sectional view of a coupler and a rod integrator. [Figure 8] 10A and 10B are diagrams illustrating profile conversion by a rod integrator. [Figure 9] FIG. 1 is a diagram illustrating wavelength swept light. [Figure 10] 6 is a diagram illustrating spectroscopy by the light measurement device of FIG. 5. FIG. [Figure 11] 1 is a diagram illustrating the intensity distribution of wavelength swept light irradiated onto the surface of a sample. FIG. [Figure 12] FIG. 10 is a diagram illustrating a first effect of the light measurement device. [Figure 13] FIG. 10 is a diagram illustrating a second effect of the light measurement device. [Figure 14] FIG. 10 is a diagram illustrating a top-hat beam profile. [Figure 15] 10A and 10B are diagrams showing measurement results of the beam profile of irradiation light generated by the light measurement device according to the embodiment. [Figure 16] 10A and 10B are diagrams illustrating a beam profile smoothing process. [Figure 17] FIG. 10 is a diagram showing profiles of multiple beams with different wavelengths. [Figure 18] FIG. 10 is a diagram showing a beam profile obtained by a rod integrator having a hexagonal cross section. [Figure 19] FIG. 2 is a cross-sectional view of a rod integrator. [Figure 20] FIG. 10 is a diagram showing a beam profile obtained by a rod integrator with a circular cross section. [Figure 21] FIG. 10 shows a beam profile obtained by a rod integrator with a triangular cross section. [Figure 22] FIG. 10 is a diagram showing a beam profile obtained by a rod integrator having a square cross section. [Figure 23] FIG. 10 is a diagram showing a beam profile obtained by a rod integrator with a pentagonal cross section. DETAILED DESCRIPTION OF THE INVENTION

[0024] (Outline of the embodiment) A summary of some exemplary embodiments of the present disclosure is provided. This summary is intended to provide a simplified overview of some concepts of one or more embodiments in order to provide a basic understanding of the embodiments as a prelude to the more detailed description that follows. It is not intended to limit the scope of the invention or disclosure. Furthermore, this summary is not an exhaustive overview of all possible embodiments, nor does it limit essential elements of the embodiments. For convenience, the term "one embodiment" may refer to one embodiment (example or variant) or multiple embodiments (examples or variants) disclosed herein.

[0025] An optical measurement device according to one embodiment includes a light source device that generates wavelength-swept light and an optical system that irradiates an object with the wavelength-swept light. The light source device includes a pulsed light source that generates pulsed light having a continuous spectrum, a splitter that spatially splits the pulsed light into multiple n (n≧2) beams according to wavelengths, multiple n fibers that impart different delays to the n beams, a coupler that is a bundle fiber or a multicore fiber that combines the n beams output from the n fibers, and a rod integrator whose input end is coupled to the output end of the coupler. The optical system includes a critical illumination system that projects a light source image at the output end of the rod integrator onto the object.

[0026] Multiple beams with a Gaussian intensity distribution are emitted from the coupler. As these multiple beams pass through the rod integrator, each beam has a top-hat beam profile at the output end of the rod integrator, which is flatter than a Gaussian distribution. Therefore, a light source image is generated at the output end of the rod integrator, in which multiple beams of different wavelengths are superimposed with a uniform intensity distribution. By irradiating this light source image directly onto the surface of the target (sample surface) using the critical illumination system, multiple wavelengths are irradiated at the same location and in the same range with a uniform illuminance distribution. Because the energy of the top-hat beam is smaller in the tail portion than in a Gaussian beam, stray light can be suppressed even if the beam irradiation position is moved closer to the edge of the target.

[0027] In this specification, the term "top-hat beam profile" does not mean a complete top-hat profile, but may include a profile similar to a top-hat profile. A top-hat beam profile has two characteristics: a steep edge and a flat peak. In relation to Problem 1, the steep edge is important, and in relation to Problem 2, the flat peak is important.

[0028] For example, if the target object is flat, only problem 1 can be focused on. In this case, the intensity distribution at the output end of the rod integrator only needs to have a steep tail, and such a beam profile is also included in the category of a top-hat beam profile.

[0029] Alternatively, in the case of an apparatus in which sufficient measures have been taken to prevent stray light, only Problem 2 can be addressed, and the intensity distribution at the output end of the rod integrator only needs to have a flat peak, and such a beam profile is also included in the category of a top-hat beam profile.

[0030] In one embodiment, a top-hat beam profile may refer to an edge steepness of 0.2 or less and a flatness of 25% or less.

[0031] The steepness is defined as follows using the beam width corresponding to 40% intensity (40% width) and the beam width corresponding to 10% intensity (10% width) when the peak of the intensity distribution is normalized to 100%: Steepness = (10% width - 40% width) / 10% width

[0032] The flatness is defined as the CV value (Coefficient of Variation) in a range where the intensity is 40% or more (within a 40% width).

[0033] In one embodiment, the cross section of the rod integrator may be polygonal. The closer the rod integrator is to a circle, the longer the rod length required to obtain a top-hat beam profile. Conversely, a triangular or rectangular cross section can shorten the rod length required to obtain the same top-hat beam profile, but requires high precision in alignment with the coupler. Considering the balance between these factors, a pentagonal to octagonal cross section is preferable.

[0034] In one embodiment, the rod integrator may have a hexagonal cross section, which reduces the rod length required to achieve a top-hat beam profile while relaxing the required alignment accuracy with the coupler.

[0035] In one embodiment, the length of the rod integrator may be greater than 100 mm, which allows for a sufficiently flat beam profile.

[0036] In one embodiment, the length of the rod integrator may be shorter than 500 mm. For example, if a circular rod integrator is used to achieve a beam profile on the top hat side, a rod length exceeding 500 mm is required. However, such a long rod integrator poses a problem of bending loss due to its own weight, and it is not easy to position and support a long rod integrator with high precision. If the length of the rod integrator is set to 500 mm, preferably 200 mm or less, bending due to its own weight can be suppressed and it becomes easy to position and support a long rod integrator with high precision.

[0037] (Embodiment) The present disclosure will be described below based on preferred embodiments with reference to the drawings. The same or equivalent components, parts, and processes shown in each drawing are designated by the same reference numerals, and redundant descriptions will be omitted where appropriate. Furthermore, the embodiments are illustrative and do not limit the disclosure, and all features and combinations thereof described in the embodiments are not necessarily essential to the disclosure.

[0038] The dimensions (thickness, length, width, etc.) of each component shown in the drawings may be enlarged or reduced as appropriate for ease of understanding. Furthermore, the dimensions of multiple components do not necessarily represent their relative sizes. Even if a component A is drawn thicker than another component B in the drawings, it is possible that component A is thinner than component B.

[0039] 5 is a diagram showing a light measurement device 100 according to an embodiment. The light measurement device 100 includes a light source device 200, an irradiation optical system 310, a light receiving device 320, and a calculation processing device 400.

[0040] Light source device 200 generates wavelength swept light L1 whose wavelength changes over time. The wavelength swept light L1 has a one-to-one correspondence between time and wavelength. This means that the wavelength swept light L1 "has a unique wavelength."

[0041] The light source device 200 includes a pulsed light source 210 and a pulse stretcher 220 .

[0042] The pulsed light source 210 emits broadband pulsed light L1a having a broad, continuous spectrum. The spectrum of the broadband pulsed light L1a is continuous over a wavelength range of at least 10 nm, preferably 50 nm, and more preferably 100 nm, for example, in the range of 900 nm to 1300 nm. The width of the wavelength range of the broadband pulsed light L1a needs only to cover the wavelength range required for spectroscopy.

[0043] For example, the pulsed light source 210 may include an ultrashort pulse laser and a nonlinear element. Examples of the ultrashort pulse laser include a gain-switched laser, a microchip laser, and a fiber laser.

[0044] Nonlinear elements use nonlinear phenomena to further broaden the spectral width of the ultrashort pulses generated by ultrashort pulse lasers. Fibers are suitable as nonlinear elements, and photonic crystal fibers and other nonlinear fibers can be used. Single-mode fibers are preferred, but multi-mode fibers can also be used as long as they exhibit sufficient nonlinearity.

[0045] As the pulsed light source 210, other broadband pulsed light sources such as an SLD (Superluminescent Diode) light source may also be used.

[0046] The broadband pulsed light L1a output from the nonlinear element has a pulse width on the order of femtoseconds to nanoseconds.

[0047] The pulse stretcher 220 stretches the pulse width of the broadband pulsed light L1a and outputs the wavelength-swept light L1. The pulse stretcher 220 includes a splitter 222, a delay line 224, a coupler 226, and a rod integrator 228.

[0048] The splitter 222 splits the broadband pulsed light L1a into multiple n beams (n≧2) according to the wavelengths. The configuration of the splitter 222 is not particularly limited, but can be configured, for example, by an arrayed waveguide grating (AWG).

[0049] The delay line 224 includes a plurality of n fibers FB1 to FBn, which have different lengths and impart different delays to the plurality of beams split by the splitter 222.

[0050] Assume that the broadband pulsed light L1a before splitting is a positive chirp pulse (up-chirp pulse) whose frequency increases (wavelength shortens) over time. In this case, the leading edge of the pulse contains a component with the longest wavelength λ1, and the trailing edge of the pulse contains a component with the shortest wavelength λ1. n Contains the ingredients:

[0051] The multiple fibers FB1 to FBn have different lengths l1 to l n λ1 is the longest wavelength, λ n is the shortest wavelength, in order to make the wavelength swept light L1 a positive chirped pulse like the broadband pulse light L1a, <l2<…<l n As an example, when n=20, the lengths l1 to l1 of the 20 fibers FB are 20 may be increased in 1m increments from 1m to 20m.

[0052] The fibers FB1 to FBn do not need to have different group delay characteristics for each wavelength, and the same fiber (fibers with the same core / clad material) can be used. In this sense, the fiber FB can be a multimode fiber, which is advantageous in that unintended nonlinear optical effects can be prevented.

[0053] The coupler 226 recombines the multiple beams to which different delays have been imparted by the delay line 224. For example, the coupler 226 is a bundle fiber or a multi-core fiber that combines n beams.

[0054] The input end of the rod integrator 228 is optically coupled to the output end of the coupler 226, and functions as a homogenizer that smooths the beam profile.

[0055] 6 is a perspective view showing coupler 226 and rod integrator 228. Coupler 226 includes multiple fibers 227, each of which transmits a different wavelength λ1, λ2, ... λ n The beams propagate in a single transverse mode (single mode) within each fiber 227, and the profile of each beam has a Gaussian distribution at the output end of fiber 227. The beams of each wavelength are incident on different positions at the input end of rod integrator 228.

[0056] 7 is a cross-sectional view of coupler 226 and rod integrator 228. In this example, coupler 226 includes 60 fibers 227 that are distributed across the cross-section of rod integrator 228.

[0057] Fig. 8 is a diagram illustrating profile conversion by rod integrator 228. Fig. 8 shows only beams BMi and BMj of the ith wavelength λi and the jth wavelength λj. The Gaussian beam output from fiber 227 propagates within rod integrator 228. When propagating through rod integrator 228, the beam becomes multimode, and the beam size increases to the cross-sectional size of rod integrator 228 at output end 229 of rod integrator 228. The profile of each beam BMi and BMj at the output end approaches a top hat shape.

[0058] The above is the configuration of the light source device 200.

[0059] 9 is a diagram showing the wavelength swept light L1. The upper part of FIG. 9 shows the intensity (time waveform) I WSThe lower part shows the time variation of the wavelength λ of the wavelength swept light L1. In this example, the wavelength swept light L1 is a single pulse light, and its dominant wavelength is λ1 at its leading edge and λ2 at its trailing edge. n and the wavelength changes from λ1 to λ n In this example, the wavelength swept light L1 is a positive chirp pulse (λ1>λ) whose frequency increases with time, in other words, whose wavelength shortens with time. n ) The wavelength swept light L1 may be a negative chirp pulse whose wavelength increases with time (λ1<λ n As will be described later, the wavelength swept light L1 may be a pulse train consisting of pulses (wave packets) isolated in time for each wavelength.

[0060] Returning to Figure 5, the illumination optical system 310 includes a critical illumination system 312, a beam splitter 314, and a mirror 316.

[0061] The critical illumination system 312 projects a light source image at the exit end 229 of the rod integrator 228 onto the surface of the sample 2 (sample surface).

[0062] The beam splitter 314 directs a portion of the wavelength swept light L1 toward the sample 2. The beam splitter 314 also extracts a portion of the wavelength swept light L1 as a reference light L3. The mirror 316 directs the reference light L3 toward the light receiving device 320.

[0063] The light receiving device 320 includes a first light receiver 322, a second light receiver 324, and A / D converters 326 and 328. The first light receiver 322 detects object light L2 obtained by irradiating the wavelength swept light L1 onto the sample 2. The object light L2 may be reflected light or transmitted light.

[0064] The A / D converter 326 converts the output signal S1 of the first photodetector 322 into a digital signal D1. The second photodetector 324 detects the reference light L3. The A / D converter 328 converts the output signal S2 of the second photodetector 324 into a digital signal D2. The time waveform I of the object light L2 indicated by the digital signal D1 is OBJ(t) and the time waveform I of the reference light L3 indicated by the digital signal D2 REF (t) is input to the processor 400.

[0065] In wavelength-swept spectroscopy, there is a one-to-one correspondence between time and wavelength in the wavelength-swept light L1. This correspondence is naturally also held by the reference light L3, and is also inherited by the object light L2. Using this correspondence between time and wavelength, the arithmetic processing device 400 calculates the time waveform I of the object light L2. OBJ (t) is the frequency domain spectrum I OBJ (λ). The arithmetic processing device 400 also converts the time waveform I REF (t) is converted to a spectrum and scaled appropriately to obtain the reference spectrum I REF Calculate (λ).

[0066] The processing of the arithmetic processing device 400 is not particularly limited. For example, the arithmetic processing device 400 may REF (λ) and the spectrum of the object light L2 OBJ Based on (λ), the transmittance T(λ) or reflectance R(λ) of the object OBJ can be calculated. T(λ)=I OBJ (λ) / I REF (λ) R(λ)=I OBJ (λ) / I REF (λ)

[0067] 10 is a diagram illustrating the spectroscopy by the optical measurement device 100 of FIG. 5. As described above, the wavelength swept light L1 has a one-to-one correspondence between time t and wavelength λ, and therefore its time waveform I REF (t) is the frequency domain spectrum I REF (λ).

[0068] Time waveform I of object light L2 OBJ In the case of (t), the time t and the wavelength λ correspond one-to-one. OBJ (t) is the spectrum I of the object light L2 OBJ(λ).

[0069] The processing unit 400 calculates the two spectra I OBJ (λ) and I REF (λ) ratio I OBJ (λ) / I REF Based on (λ), the transmission spectrum T(λ) of the object OBJ can be calculated.

[0070] The relationship between the wavelength λ of the wavelength swept light L1 and time t is expressed as a function λ = f(t). In the simplest terms, the wavelength λ changes linearly with respect to time t according to a linear function. The time waveform I of the object light L2 OBJ (t) is the time t x When the transmission spectrum T(λ) decreases at wavelength λ x =f(t x ) means that it has an absorption spectrum.

[0071] The processing in the arithmetic processing unit 400 is not limited to this. OBJ (t) and I REF (t) ratio T(t)=I OBJ (t) / I REF After calculating (t), the variable t of this time waveform T(t) may be converted to λ to calculate the transmission spectrum T(λ).

[0072] Next, the advantages of the light measurement device 100 will be described.

[0073] 11 is a diagram illustrating the intensity distribution of the wavelength swept light L1 irradiated onto the surface of the sample 2. As described above, at the output end 229 of the rod integrator 228, the beams BM1 to BMn having wavelengths λ1 to λn each have a top-hat profile, forming a light source image at the output end 229. The critical illumination system 312 projects this light source image onto the surface of the sample 2 while maintaining its intensity distribution. Note that the critical illumination system 312 may have a magnification according to the size of the output end 229 and the size of the sample 2, and therefore may perform enlarged or reduced projection. The surface of the sample 2 is sequentially irradiated with multiple beams of different wavelengths, each having a top-hat illuminance distribution, as the wavelength swept light L1.

[0074] FIG. 12 is a diagram illustrating a first effect of the light measurement device 100. The first effect corresponds to Problem 1. FIG. 12 shows the relative positional relationship between the object OBJ and the beam of wavelength swept light L1. As described above, the wavelength swept light L1 is irradiated multiple times while the object OBJ is being moved. Because the beam irradiated onto the surface of the object OBJ has a top-hat intensity distribution, the energy of stray light is small even when the beam is irradiated close to the edge of the object OBJ. Therefore, the above-mentioned Problem 1 caused by stray light can be solved.

[0075] FIG. 13 is a diagram illustrating a second effect of the optical measurement device 100. The second effect corresponds to Problem 2. In this embodiment, the critical illumination system 312 is used to project the illumination image of the exit end 229 of the rod integrator 228 directly onto the surface of the object OBJ. Therefore, beams of multiple wavelengths are irradiated with a top-hat intensity distribution at substantially the same location. As a result, beams of different wavelengths are perceived as having the same thickness, thereby solving the above-mentioned Problem 2.

[0076] Next, we will explain the design of rod integrator 228. As described above, rod integrator 228 is designed so that beams of multiple wavelengths have a top-hat beam profile at output end 229. Therefore, we will explain the top-hat beam profile.

[0077] 14 is a diagram illustrating a top-hat beam profile. In this embodiment, the top-hat beam profile can be defined from two perspectives: the steepness of the edge and the flatness of the top.

[0078] A "top-hat beam profile" does not mean a perfect top-hat shape, but can include a profile similar to a top-hat shape as shown in Figure 14. A top-hat beam profile can be understood from two characteristics: the steepness of the edge and the flatness of the peak. In relation to issue 1, the steepness of the edge is important, and in relation to issue 2, the flatness of the peak is important.

[0079] For example, if the target object is flat, only problem 1 can be focused on. In this case, the intensity distribution at the output end of the rod integrator only needs to have a steep tail, and such a beam profile is also included in the category of a top-hat beam profile.

[0080] Alternatively, in the case of an apparatus in which sufficient measures have been taken to prevent stray light, only Problem 2 can be addressed, and the intensity distribution at the output end of the rod integrator only needs to have a flat peak, and such a beam profile is also included in the category of a top-hat beam profile.

[0081] The steepness is defined as follows using the beam width corresponding to 40% intensity (40% width) and the beam width corresponding to 10% intensity (10% width) when the peak of the intensity distribution is normalized to 100%: Steepness = (10% width - 40% width) / 10% width

[0082] In order to solve Problem 1, it is preferable that the edge steepness is 0.2 or less. In other words, in this embodiment, a top-hat beam profile refers to one in which the edge steepness is 0.2 or less.

[0083] The flatness is defined as the CV value (Coefficient of Variation) in a range where the intensity is 40% or more (within a 40% width).

[0084] In order to solve Problem 2, it is preferable that the flatness of the peak is 25% or less. In other words, in this embodiment, a top-hat beam profile has a flatness of 25% or less.

[0085] Next, a specific example of beam profile evaluation will be described. Fig. 15 is a diagram showing the measurement results of the beam profile of irradiated light generated by light measurement device 100 according to the embodiment. Rod integrator 228 has a regular hexagonal cross section circumscribing a 0.69 mm circle and is 100 mm long. Critical illumination system 312 is composed of two lenses with a focal length of 750 mm, and projects an illumination image at output end 229 of rod integrator 228 onto the imaging surface of the image sensor at 1x magnification.

[0086] As described above, because light propagates in multiple modes within the rod integrator 228, speckles occur in the illumination image at the exit end 229. Therefore, the profile of the imaging surface (i.e., the sample surface) on which the image is formed also has a mottled pattern. Therefore, when evaluating whether the beam has a top-hat profile, it is necessary to remove the effects of this speckle by smoothing.

[0087] The method of smoothing processing is not particularly limited, but an example will be described below.

[0088] 16 is a diagram illustrating the beam profile smoothing process. In step S100, the size (full width) Δ of the speckle in the original data before processing is obtained. In this example, as shown in the right diagram of step S100, one speckle spreads over approximately five pixels.

[0089] In step S102, the original data, data obtained by shifting the original data by Δ pixels in the positive direction, and data obtained by shifting the original data by Δ pixels in the negative direction are averaged. At this time, a weighted average may be calculated.

[0090] In step S104, a moving average is calculated using a window with a width of 2Δ. In this example, Δ=5 pixels, so a moving average of 10 pixels is calculated. Then, in step S106, the peak is normalized to 1 (100%).

[0091] The above is an example of the beam profile smoothing process. Those skilled in the art will understand that the smoothing method is not limited to this. For example, processes S102 and S104 may be interchanged. Furthermore, for final normalization, process S102 may be a simple addition.

[0092] Another method of smoothing is to convert the image data into frequency domain information and filter it, or to estimate the beam profile using an image sensor with a pixel pitch larger than the speckle width.

[0093] Next, the results of examining rod integrators 228 with different cross-sectional shapes and lengths will be described.

[0094] Figure 17 shows the profiles of multiple beams with different wavelengths. Measurements were performed under the same conditions as those described in Figure 15. The channel numbers correspond to the numbers indicating the positions of the fibers in Figure 7, and show the channels on the periphery where uniformity is difficult. The left figure for each channel shows the profile before smoothing, and the right figure shows the profile after smoothing.

[0095] The profile after smoothing was evaluated for edge steepness and peak flatness, and the results are as follows:

[0096] CH01 X direction steepness 0.08 Y-direction steepness 0.07 X direction flatness 15.5% Y direction flatness 16.0%

[0097] CH02 X direction steepness 0.108 Y-direction steepness 0.067 X direction flatness 15.3% Y direction flatness 16.9%

[0098] CH03 X direction steepness 0.090 Y-direction steepness 0.105 X direction flatness 15.8% Y direction flatness 16.0%

[0099] CH04 X direction steepness 0.090 Y-direction steepness 0.080 X direction flatness 20.6% Y direction flatness 20.6%

[0100] Next, the dependency of the profile transformation by the rod integrator 228 on the length will be described.

[0101] 18 is a diagram showing the beam profile obtained by rod integrator 228 with a hexagonal cross section. The length of rod integrator 228 was changed to 50 mm, 100 mm, and 150 mm, and the beam profile at output end 229 was simulated. Since the simulation cannot take multimode into account, the intensity distribution does not have a mottled shape with multiple peaks as in the actual measurement, but the trend is in good agreement with the actual measurement.

[0102] In the rod integrator with a hexagonal cross section, asymmetry is observed in the peak portion when the length is 50 mm, but it can be said that it is sufficiently flat for practical purposes.

[0103] Next, we will explain the results of examining rod integrators 228 with various cross-sectional shapes. Circles, triangles, squares, and pentagons were examined.

[0104] Figure 19 is a cross-sectional view of rod integrator 228. In the figure, the beam profile at the output end was calculated by simulation for beams that combine at the positions of channels CH03 and CH05 at the input end. The lengths of rod integrator 228 were set to 50 mm, 100 mm, and 150 mm.

[0105] 20 is a diagram showing the beam profile obtained by a rod integrator 228 with a circular cross section. The length required for uniformization of the circular rod integrator 228 is longer than that of a hexagonal or other shape. Even if the length is increased to 150 mm, the central portion remains doughnut-shaped with weak strength, and the flatness is inferior to that of other shapes of the same length.

[0106] 21 is a diagram showing a beam profile obtained by a rod integrator 228 with a triangular cross section. In the case of a triangular cross section, flattening is possible with a short length. However, since it is very sensitive to positional misalignment (misalignment between the center positions of the coupler 226 and the rod integrator 228) and directional misalignment (rotational misalignment) between the coupler 226 and the rod integrator 228, strict restrictions on the misalignment are required. Furthermore, to contain a circular bundle fiber, a triangle with a length of one side equal to the bundle diameter x √3 is required, which requires a large optical system.

[0107] 22 shows the beam profile obtained by a rod integrator 228 with a square cross section. Like a triangle, a square can also be flattened in a short length. However, like a triangle, a square is also significantly affected by misalignment in position and direction.

[0108] 23 shows the beam profile obtained by rod integrator 228 with a pentagonal cross section. In the case of a pentagon, the length required for homogenization is longer than that of a triangle or a rectangle, but shorter than that of a circle. Compared to a triangle or a rectangle, it can be said that positional and directional misalignment have less effect on the beam profile.

[0109] In summary, the closer the cross section is to a circle, the longer the length of the rod integrator 228 required to obtain a flat profile; the closer the cross section is to a triangle, the shorter the rod integrator 228 required.

[0110] Circles are least susceptible to misalignment and misdirection, and the closer they are to triangles, the more severe the effects of misalignment and misdirection. This is because triangles are not point-symmetric, and quadrilaterals also have large differences in the lengths of their diagonals and the lines connecting their midpoints.

[0111] Therefore, when a triangular or rectangular rod integrator 228 is used, deviations in the transport of the sample 2, specifically positional deviations (deviations perpendicular to the transport direction) and angular deviations (deviations in the transport direction), can cause differences in the travel distances of each beam within the sample 2, potentially affecting measurement reproducibility. This effect is particularly pronounced when irradiating the sample 2 with a relatively large irradiation diameter relative to its shape and unevenness.

[0112] From this point of view, the more circular the cross section of the rod integrator 228 is, the less the influence of the above-mentioned conveyance deviation will be. However, a circle requires a long length for uniformity, and uniformity of about 100 mm is insufficient.

[0113] On the other hand, with a pentagon or hexagon, uniformity can be achieved to some extent even at 100 mm. In particular, a hexagon is suitable as a cross section of the rod integrator 228 because it is line-symmetric, point-symmetric, and close to a circle.

[0114] In particular, it is not practically easy to hold thin rods with a diameter of 1 mm or less, or long rods of several hundred mm or more. Such rods bend due to their own weight, resulting in loss. To reduce bending, it is necessary to increase the number of support parts, but this requires holding them with adhesives or the like that have a higher refractive index than glass, which causes the problem of light leakage at the support parts and increased loss. From this perspective, in practice, the rod integrator 228 should be no longer than 500 mm, preferably no longer than 200 mm. With a hexagonal rod integrator 228, a beam profile that can withstand practical use can be obtained with a length of 50 mm to 100 mm, so the loss caused by adding the rod integrator 228 can be suppressed.

[0115] Although the embodiments of the present disclosure have been described using specific terms, this description is merely an example to facilitate understanding and does not limit the scope of the present disclosure or the claims. The scope of the present invention is defined by the claims, and therefore, embodiments, examples, and modifications not described herein are also included in the scope of the present invention. [Explanation of symbols]

[0116] L1 wavelength swept light L1a broadband pulsed light L2 object light 2. Sample L3 reference beam 100 Light measuring device 200 Light source device 210 Pulsed Light Source 220 Pulse Stretcher 222 Divider FB fiber 224 Delay Line 226 Coupler 228 Rod Integrator 229 Output end 310 Irradiation optical system 312 Critical Lighting System 314 Beam Splitter 316 Mirror 320 Photodetector 322 1st receiver 324 2nd receiver 326,328 A / D converters 400 Processing Unit

Claims

1. a light source device that generates wavelength swept light; an optical system that irradiates an object with the wavelength swept light; Equipped with The light source device is a pulsed light source that generates pulsed light having a continuous spectrum; a splitter that spatially splits the pulsed light into a plurality of n beams (n≧2) according to wavelength; a plurality of n fibers for providing different delays to the n beams; a coupler which is a bundle fiber or a multi-core fiber that combines the n beams output from the n fibers; a rod integrator whose input end is coupled to the output end of the coupler; Including, The optical measurement device according to claim 1, wherein the optical system includes a critical illumination system that projects a light source image at the exit end of the rod integrator onto the object.

2. 2. The optical measurement device according to claim 1, wherein the rod integrator has a polygonal cross section.

3. 2. The optical measurement device according to claim 1, wherein the rod integrator has a hexagonal cross section.

4. 4. The optical measurement device according to claim 1, wherein the length of the rod integrator is greater than 100 mm.

5. 4. The optical measurement device according to claim 1, wherein the length of the rod integrator is shorter than 500 mm.

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