Pulse Spectrometer

Abstract

To reduce the effect of dead time in an AD converter so that the excellent characteristics of high speed, high resolution, and high signal-to-noise ratio are not lost.SOLUTION: Light from a pulsed light source 1A is irradiated onto an object S, with a pulse width of the light being elongated by an elongation element 2 so that an elapsed time in a pulse corresponds one-to-one to a wavelength of the light. An output of a photodetector 4, which receives the light from the object S, is digitized by an AD converter 6 and supplied to calculation means 5. A trigger signal generated by a trigger signal generation unit 7 upon a rise of the pulsed light is delayed by a trigger delay unit 74 and is supplied to the AD converter 6 so that the trigger signal is input after end of a dead time T3.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The invention of this application relates to a pulsed spectroscopic device that performs spectroscopic measurement by utilizing the correspondence between time and wavelength in pulsed light. [Background technology]

[0002] A typical pulsed light source is a pulsed laser (pulse laser). In recent years, there has been active research into broadening the wavelength of pulsed lasers, and a typical example of this is the generation of supercontinuum light (hereinafter referred to as SC light) using nonlinear optical effects. SC light is light obtained by passing light from a pulsed laser through a nonlinear element such as a fiber and broadening the wavelength using nonlinear optical effects such as self-phase modulation and optical soliton. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-205390 Summary of the Invention [Problem to be solved by the invention]

[0004] Although the wavelength range of the broadband pulsed light described above is significantly expanded, its pulse width (time width) remains close to that of the input pulse used to generate the SC light. However, the pulse width can also be expanded by utilizing the group delay in a transmission element such as a fiber. In this case, by selecting an element with appropriate chromatic dispersion characteristics, the pulse can be expanded with a one-to-one correspondence between the time (elapsed time) within the pulse and the wavelength.

[0005] The correspondence between time and wavelength in broadband pulsed light whose pulse has been stretched in this way (hereinafter referred to as broadband stretched pulsed light) can be effectively utilized in spectroscopic measurement. When broadband stretched pulsed light is received by a photodetector, the temporal change in light intensity detected by the photodetector corresponds to the light intensity of each wavelength, i.e., a spectrum. Therefore, the temporal change in the output data of the photodetector can be converted into a spectrum, making spectroscopic measurement possible without using a special dispersive element such as a diffraction grating. In other words, by irradiating a target with broadband stretched pulsed light, receiving the light from the target with a photodetector, and measuring the temporal change, the spectral characteristics of the target (e.g., spectral transmittance) can be determined.

[0006] Spectroscopic measurement utilizing this correspondence between time and wavelength in pulsed light (hereafter referred to as pulse spectroscopy) involves simply irradiating an object with several pulses (theoretically, even one pulse is possible) and receiving the light from the object with a photodetector. This allows for extremely fast spectroscopic measurement, and it is expected that, for example, real-time 100% inspection of products on an inspection line will be possible using spectroscopic measurement. Furthermore, wavelength resolution can be increased by optimizing pulse stretching to reduce Δλ / Δt. Furthermore, it is also possible to achieve measurements with a high signal-to-noise ratio by irradiating multiple pulses and averaging (or integrating) the output from the photodetector.

[0007] However, despite the expected advantages of pulse spectroscopy, it has become clear that it also has its own unique challenges. One of these is the problem of data reading. When performing pulse spectroscopy, a high-speed photodetector, such as a high-speed photodiode with a frequency of around 1 GHz to 10 GHz, is used to convert the elapsed time of the pulse into wavelength. In this case, the output data must be digitized at an equally high speed for processing, and the output (analog signal) of the photodetector is converted to a digital signal by a high-speed AD converter.

[0008] High-speed AD converters that can be used for such applications start sampling when a trigger signal is input, and digitize the analog signal that has been captured at an acquisition period that is longer than the sampling period. During the digitization process, new trigger signals are not accepted, and no analog signals are input during this time, and the analog signal is not digitized during this time. The period when analog input is not possible after the end of an acquisition period until the next acquisition becomes possible (until the start of the next acquisition period) is called dead time. High-speed AD converters have a high sampling rate (sampling frequency) and digitize many samples, so the dead time tends to be very long.

[0009] Dead time also occurs in oscilloscopes (digital oscilloscopes), which can be broadly considered AD converters. After data is acquired at a certain acquisition period longer than the sampling period, digitized, and converted into a waveform, there is a period of time before the next data can be acquired, known as dead time. High-end, high-speed digital oscilloscopes also tend to have longer dead times.

[0010] The problem of long dead time as described above can be a problem that impairs the excellent properties of pulse spectroscopy, such as high speed, high resolution, and high S / N ratio. The present invention was made to solve this problem, and aims to reduce the effects of dead time in a pulse spectroscopy device that obtains results by digitizing an analog signal from a photodetector using an AD converter, thereby preventing the excellent properties, such as high speed, high resolution, and high S / N ratio, from being impaired. [Means for solving the problem]

[0011] In order to solve the above problems, the pulse spectroscopy device of the present invention comprises: a pulsed light source; an expansion element that expands the pulse width of light from a pulsed light source so that the elapsed time within the pulse corresponds one-to-one to the wavelength of the light; a light receiver that receives light from an object illuminated with light from the elongation element; a computing means for processing the output from the photoreceiver to obtain a measurement result; an AD converter that converts the analog signal output from the photodetector into a digital signal and supplies it to a calculation means; A pulse spectroscopy device comprising: a trigger signal generating unit that generates a trigger signal in response to a rise of pulsed light from the pulsed light source; a trigger supply unit that supplies the trigger signal generated by the trigger signal generation unit to the AD converter; The AD converter is a converter that starts to capture the analog signal from the receiver when a trigger signal is supplied. The trigger supply unit includes a trigger delay unit that delays the trigger signal. The delay amount in the trigger delay element is a delay amount that ensures that the trigger signal is input to the AD converter before the rising edge of the pulse signal that is output from the photodetector and input to the AD converter when the pulsed light that generated the trigger signal is irradiated onto the target. In order to solve the above problems, the pulse spectroscopy device comprises: the pulse light source includes an ultrashort pulse laser and a nonlinear element that generates a nonlinear optical effect in the laser light emitted from the ultrashort pulse laser to broaden the bandwidth; The trigger signal generating section may be configured to generate a trigger signal by extracting and detecting a portion of the laser light emitted from the ultrashort pulse laser and before it enters the nonlinear element. In order to solve the above problems, the pulse spectroscopy device comprises: the trigger signal is an electrical signal, the trigger supply unit is a cable connecting the trigger signal generation unit and the AD converter, and this cable has a surplus portion that is longer than the length required for connection due to the spatial separation between the trigger signal generation unit and the AD converter; The trigger delay section may have the configuration of being a surplus section of the cable. In order to solve the above problem, the pulse spectroscopy device may be provided with a temperature adjustment mechanism that adjusts the temperature of the excess portion. In order to solve the above problems, the pulse spectroscopy device comprises: a splitting element that splits the light from the elongation element so that one of the split light beams is directed to the object; a reference light receiver provided at a position where the other light split by the splitting element is incident without passing through the object; and a reference AD ​​converter that converts the analog signal output from the reference photoreceiver into a digital signal. The trigger supply unit may be configured to supply a trigger signal to the reference AD ​​converter as well, and the trigger delay unit may be configured to delay the trigger signal supplied to the reference AD ​​converter in the same manner as the trigger signal supplied to the AD converter. In order to solve the above problem, the pulse spectrometer may be provided with a synchronization means for synchronizing the sampling in the AD converter with the sampling in the reference AD ​​converter. In order to solve the above problem, the pulse spectrometer may be configured to include an arrayed-waveguide grating that divides light from a pulsed light source into light of each wavelength, and an elongated fiber as an elongation element that transmits each of the light beams divided by the arrayed-waveguide grating into each wavelength. In order to solve the above problem, the pulse spectroscopy device may have a dead time, which is a period of time after the AD converter has finished capturing an analog signal and during which it is possible to capture the next analog signal, and the pulse repetition period of the pulse light source is such that the interval between each pulse after being stretched by the stretching element is longer than the dead time. In order to solve the above problems, a pulse spectroscopy device according to another aspect of the present invention comprises: a pulsed light source; an expansion element that expands the pulse width of light from a pulsed light source so that the elapsed time within the pulse corresponds one-to-one to the wavelength of the light; a light receiver that receives light from an object illuminated with light from the elongation element; a computing means for processing the output from the photoreceiver to obtain a measurement result; an AD converter that converts the analog signal output from the photodetector into a digital signal and supplies it to a calculation means; A pulse spectroscopy device comprising: a trigger signal generating unit that generates a trigger signal in response to a rising edge of pulsed light from a pulsed light source (excluding a rising edge of the pulsed light when the target is pulsed light); The trigger signal generating unit includes a trigger supply unit that supplies the trigger signal generated by the trigger signal generating unit to the AD converter. The AD converter starts to receive an analog signal from the optical receiver when a trigger signal is supplied, and the dead time is the period from when the analog signal reception is completed until the next analog signal reception is possible. T3 It has The pulse repetition period of a pulsed light source is When the acquisition delay, which is the difference between the timing of the rise of the pulsed light from the pulsed light source and the timing of the light receiving device receiving the pulsed light, is T2, The interval between each pulse after being stretched by the stretcher is Longer than the sum of T2 and T3 The repetition period is: [Effects of the Invention]

[0012] As will be explained below, according to the invention of the pulse spectroscopy device of the present application, the trigger signal delayed by the trigger delay unit is supplied to the AD converter, which has the effect of reducing pulse loss and preventing the unnecessary consumption of time and resources, thereby improving the overall efficiency of measurements. Furthermore, in a configuration in which a trigger signal is generated by extracting and detecting a portion of the light emitted from an ultrashort pulse laser before it enters a nonlinear element, the trigger signal is generated by capturing a sharply rising pulse, making it easy to generate a trigger signal stably and with good reproducibility. This also enables the digitization process in the AD converter to be performed stably and with good reproducibility, improving the reliability of the device. Furthermore, if the trigger supply unit is a cable connecting the trigger signal generating unit and the AD converter, and the trigger delay unit is the excess part of this cable, the effect of increasing the stability of the delay amount and increasing the degree of freedom in changing the delay amount can be obtained. Furthermore, if a temperature control mechanism is provided to adjust the temperature around the excess portion, it is possible to suppress fluctuations in the delay amount due to temperature and to easily change the delay amount intentionally. Furthermore, if a reference photoreceiver is provided and reference spectrum data can be obtained in real time, and the trigger signal is also supplied to the reference AD ​​converter, highly accurate spectroscopic measurements can be performed at all times without being affected by external disturbances, and the effects of reducing pulse loss and improving the overall measurement efficiency can be achieved. Furthermore, if a synchronization means is provided to synchronize the sampling in the AD converter with the sampling in the reference AD ​​converter, the problem of a decrease in the reliability of the measurement results due to a sampling deviation can be eliminated. Furthermore, in a configuration that includes an arrayed-waveguide grating that divides light from a pulsed light source into light of each wavelength and an elongation fiber as an elongation element that transmits each of the light beams divided by the arrayed-waveguide grating into each wavelength, it is possible to optimize the group delay for each wavelength and achieve optimal pulse elongation. In this configuration, the delay of light incident on the photodetector tends to be large, and therefore reducing pulse dropouts and unnecessary data acquisition periods is extremely significant. Furthermore, if the repetition period of the pulses in the pulse light source is such that the interval between each pulse after being stretched by the stretching element is longer than the dead time in the AD converter, it is possible to reduce pulse dropout to zero, which is preferable in this respect. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a schematic diagram of a pulse spectroscopy device according to an embodiment. [Figure 2] FIG. 1 is a schematic diagram illustrating pulse stretching by a stretching element. [Figure 3] FIG. 2 is a diagram illustrating a main part of an example of a measurement program provided in the pulse spectrometer. [Figure 4] 10 is a schematic diagram illustrating the significance of a trigger delay unit in the pulse spectroscopy device of the embodiment. FIG. [Figure 5] 1 is a schematic diagram of a pulse spectroscopy device according to a second embodiment; [Figure 6] FIG. 10 is a schematic diagram of a pulse spectroscopy device according to a third embodiment. [Figure 7] FIG. 10 is a schematic diagram of a pulse spectroscopy device according to a fourth embodiment using an arrayed waveguide grating. [Figure 8] FIG. 1 is a planar schematic diagram of an arrayed waveguide grating used as a dividing element. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, modes (embodiments) for carrying out the invention of this application will be described. Fig. 1 is a schematic diagram of a pulse spectroscopy device according to an embodiment. The pulse spectroscopy device shown in Fig. 1 includes a pulse light source 1 and an expander element 2 that expands the pulse width of light from the pulse light source 1. The pulse light emitted from the expander element 2 has a one-to-one correspondence between the elapsed time within the pulse and the wavelength, and the device performs spectroscopic measurement by utilizing this correspondence.

[0015] The pulse light source 1 is a light source that emits pulsed light with a continuous spectrum. In this embodiment, for example, the light source emits light with a continuous spectrum over a wavelength width of at least 10 nm in the range of 900 nm to 1300 nm. The phrase "a continuous spectrum over a wavelength width of at least 10 nm in the range of 900 nm to 1300 nm" refers to any continuous wavelength width of at least 10 nm in the range of 900 to 1300 nm. For example, the spectrum may be continuous over a wavelength width of 900 to 910 nm or 990 to 1000 nm. It is more preferable that the spectrum be continuous over a wavelength width of 50 nm or more, and even more preferable that the spectrum be continuous over a wavelength width of 100 nm or more. Furthermore, "a continuous spectrum" means that the spectrum includes a continuous spectrum over a certain wavelength width. This does not necessarily mean that the spectrum of the pulsed light is continuous over the entire spectrum, but may also be partially continuous.

[0016] The reason for specifying the range from 900 nm to 1300 nm is that the pulse spectroscopy device of this embodiment is intended for spectroscopy in this wavelength range. Light with a continuous spectrum over a wavelength width of at least 10 nm is typically SC light. Therefore, in this embodiment, the pulse light source 1 is an SC light source. However, a broadband pulse light source other than an SC light source may also be used.

[0017] The pulse light source 1, which is an SC light source, includes an ultrashort pulse laser 11 and a nonlinear element 12. In this embodiment, a fiber laser including a seed laser 110 and a pumping laser 111 is used as the ultrashort pulse laser 11. A laser medium (fiber) sandwiched between a pair of high-reflection / low-reflection resonator mirrors such as an FBG is excited by pumping laser light (continuous wave light) from the pumping laser 111 via a coupling element 112 such as a fiber coupler, and seed laser light (pulsed light) from the seed laser 110 is introduced thereto. This causes stimulated emission in the laser medium, emitting ultrashort pulse laser light. Alternatively, a gain-switched laser, a microchip laser, or the like can be used as the ultrashort pulse laser 11.

[0018] Fiber is often used as the nonlinear element 12. For example, photonic crystal fiber or other nonlinear fibers can be used as the nonlinear element 12. Although the fiber is often single-mode, multi-mode fibers can also be used as the nonlinear element 12 as long as they exhibit sufficient nonlinearity.

[0019] As described above, the stretcher element 2 stretches the pulse so that the relationship between the time and the wavelength of the light after stretching is one to one. This point will be explained using Figure 2. Figure 2 is a schematic diagram showing pulse stretching by the stretcher element. When SC light L1, which has a continuous spectrum in a certain wavelength range, is passed through a group delay fiber 20 that has positive dispersion characteristics in that wavelength range, the pulse width is effectively extended. As shown in Figure 2, although the SC light L1 is an ultrashort pulse, the longest wavelength λ1 exists at the beginning of the pulse, and as time passes, light with gradually shorter wavelengths appears, and at the end of the pulse, the shortest wavelength λ n When this light is passed through a normal dispersion group delay fiber 20, the shorter the wavelength of light, the more delayed it propagates through the normal dispersion group delay fiber 20, so the time difference within one pulse is increased, and when it is output from the group delay fiber 20, the shorter wavelength light is delayed further than the longer wavelength light. As a result, the output SC light L2 is light whose pulse width is extended while the uniqueness of time versus wavelength is ensured. That is, as shown in the lower part of Figure 2, n is the wavelength λ1 to λ n The pulses are stretched in a one-to-one correspondence with each other.

[0020] It is also possible to use an anomalous dispersion fiber as the group delay fiber 20 for pulse stretching. In this case, the SC light is dispersed in such a way that the long-wavelength light present at the beginning of the pulse is delayed and the short-wavelength light present at a later time is advanced. This reverses the temporal relationship within a pulse, and the pulse is stretched in such a way that the short-wavelength light is present at the beginning of the pulse and the long-wavelength light is present as time passes. However, compared to normal dispersion, this often requires a longer propagation distance for pulse stretching, which tends to result in larger losses. Therefore, normal dispersion is preferable in this respect.

[0021] 1, the pulsed light stretched by the stretching element 2 is irradiated onto an object S by an irradiation optical system 3. A holding member for holding the object S is provided at the irradiation position. In this embodiment, since the pulsed light is irradiated from above, the holding member is a receiving plate 30. Furthermore, since the device in this embodiment is a device for measuring the spectral transmittance characteristics of the object S, the receiving plate 30 is translucent, and a light receiver 4 is provided at a position for receiving the transmitted light.

[0022] The device is equipped with a calculation means 5 as a means for processing the output of the photoreceiver 4 to obtain spectroscopic measurement results. In this embodiment, a general-purpose PC is used as the calculation means 5. Furthermore, an AD converter 6 is provided between the photoreceiver 4 and the calculation means 5, and the output of the photoreceiver 4 is input to the calculation means 5 via the AD converter 6. The calculation means 5 includes a processor 51 and a storage unit (hard disk, memory, etc.) 52. A measurement program 53 that processes output data from the photodetector 4 to calculate a spectrum and other necessary programs are installed in the storage unit 52. Fig. 3 is a diagram showing a schematic diagram of the main parts of an example of a measurement program included in the pulse spectroscopy device.

[0023] The example in Figure 3 shows an example of a program in which the measurement program 53 measures an absorption spectrum (spectral absorptance). Reference spectral data is used to calculate the absorption spectrum. The reference spectral data is a value for each wavelength that serves as a reference for calculating the absorption spectrum. The reference spectral data is acquired by irradiating light from the expander element 2 onto the photodetector 4 without passing through the object S. That is, light is irradiated onto the photodetector 4 without the object S being placed, and the output of the photodetector 4 is input to the calculation means 5 via the AD converter 6 to acquire values ​​for each time resolution Δt. Each value is stored as a reference intensity (V1, V2, V3, . . .) for each time Δt (t1, t2, t3, . . .). The time resolution Δt is a quantity that depends on the response speed (signal output period) of the photodetector 4, and refers to the time interval at which a signal is output.

[0024] The reference intensities V1, V2, V3, at each time t1, t2, t3, are the intensities (spectrum) of the corresponding wavelengths λ1, λ2, λ3,. The relationship between the times t1, t2, t3, and wavelengths within one pulse is examined in advance, and the values ​​V1, V2, V3, at each time are treated as the values ​​of λ1, λ2, λ3,. When light that has passed through the target object S is incident on the photodetector 4, the output from the photodetector 4 passes through the AD converter 6 and is similarly stored in memory as values ​​(measured values) at each time t1, t2, t3, ... (v1, v2, v3, ...). Each measured value is compared with the reference spectrum data (v1 / V1, v2 / V2, v3 / V3, ...), and the result is the absorption spectrum (taking the logarithm of the reciprocal if necessary). The measurement program 53 is programmed to perform the above-mentioned calculations.

[0025] The AD converter 6 that digitizes the analog signal from the photodetector 4 and inputs it to the calculation means 5 that performs such processing will be described in more detail below. As mentioned above, a high-speed AD converter is used as the AD converter 6. For example, a high-speed (or ultra-high-speed) AD converter with a sampling rate of about 1000 MSPS to 10 GSPS is suitable. MSPS is a unit that expresses the number of samples per second in mega, and GSPS is a unit that expresses the number of samples per second in giga.

[0026] As described above, a trigger signal is required to provide the AD converter 6 with the timing to start capturing the analog signal. For this reason, the device of the embodiment includes a trigger signal generating unit 7. As mentioned above, the processing in the calculation means 5 calculates the light intensity at each wavelength using the correspondence between time and wavelength in the pulse, so the digitization processing in the AD converter 6 also needs to be performed for each pulse. In other words, although an analog signal is constantly output from the photodetector 4, the output is essentially zero during times when no pulses are being received, so there is no point in digitizing this. Therefore, a trigger signal accompanying pulse generation needs to be supplied to the AD converter 6, which then triggers the AD converter 6 to digitize the pulse amplitude (output value of the photodetector 4) at each sampling period.

[0027] For this reason, a trigger signal generating unit 7 is provided that generates a trigger signal in response to the rising edge of the pulsed light from the pulsed light source 1. In this embodiment, the trigger signal generating unit 7 is provided inside the pulsed light source 1. The reason for this is from the viewpoint of the sharpness of pulse generation. The trigger signal generator 7 may be provided on the output side of the pulse light source 1, or, for example, on the output side of the stretcher 2. However, as shown in Figure 2, it is inevitable that the waveform of the stretched pulse will have a gradual rise. In the case of a pulse with such a gradual rise, it becomes unclear at what point the pulse was generated, making it difficult to generate a trigger signal stably and reproducibly. Therefore, it is preferable to capture pulse generation at a stage before pulse stretching.

[0028] From this perspective, in this embodiment, a trigger signal generating unit 7 is provided within the pulse light source 1. More specifically, in this embodiment, a portion of the output from the ultrashort pulse laser 11 is extracted by a beam splitter 71 and detected by a detector 72 to generate a trigger signal. In other words, the trigger signal generating unit 7 is made up of the beam splitter 71 that extracts a portion of the output from the ultrashort pulse laser 11 and the detector 72 that detects the extracted light.

[0029] The ultrashort pulse laser light before entering the nonlinear element 12 has a very steep rise time, making it suitable for generating a trigger signal. Alternatively, a part of the seed laser light from the seed laser 110 may be extracted and detected to generate a trigger signal. Furthermore, in a configuration in which the seed laser 110 is not used and the laser medium is excited by a pulsed excitation laser to output ultrashort pulse laser light, the trigger signal may be generated by extracting a part of the output of the excitation laser.

[0030] Alternatively, a trigger signal may be generated by extracting and detecting a portion of the output of the nonlinear element 12. However, since the rise of the pulse may be slowed when the nonlinear element 12 broadens the bandwidth due to the nonlinear optical effect, it is preferable to extract light from the output side of the ultrashort pulse 11 (the input side of the nonlinear element 12).

[0031] 1, such a trigger signal generating unit 7 is connected to the AD converter 6 by a cable 73, and supplies a trigger signal to the AD converter 6. A major feature of this embodiment is that the trigger supplying unit that supplies such a trigger signal to the AD converter 6 is provided with a trigger delay unit 74 that delays the trigger signal.

[0032] The trigger supply unit is a cable (hereinafter referred to as a TrADC cable) 73 that connects the trigger signal generating unit 7 and the AD converter 6. As shown in FIG. 1 , in this embodiment, the trigger delay unit 74 is a surplus portion 731 of the TrADC cable 73. The "surplus portion" refers to a portion whose length exceeds the length necessary for connecting the trigger signal generating unit 7 and the AD converter 6 in terms of spatial separation. Therefore, the trigger delay unit 74 in this example is a portion that provides a delay that exceeds the delay that inevitably occurs in the length necessary to connect the trigger signal generating unit 7 and the AD converter 6. Strictly speaking, the TrADC cable 73 is a cable that connects the detector 72 of the trigger signal generating unit 7 and the AD converter 6.

[0033] For example, a coaxial cable is used as the TrADC cable 73. If, for example, 1 meter is sufficient to connect the trigger signal generator 7 and the AD converter 6, the portion exceeding 1 meter becomes the trigger delay unit 74. The total length of the TrADC cable 73 is, for example, 41 meters, and therefore the 40 meter portion becomes the trigger delay unit 74. In this case, the delay amount per meter is about 4.5 to 5.5 nanoseconds, so the total delay amount is about 180 to 220 nanoseconds.

[0034] The provision of such a trigger delay unit 74 is based on research conducted by the inventors to reduce the effects of dead time in the AD converter 6. This point will be explained below with reference to Fig. 4. Fig. 4 is a schematic diagram showing the significance of the trigger delay unit in the pulse spectroscopy device of the embodiment. Fig. 4(1) shows the digitization process in the AD converter 6 when the trigger delay unit 74 is not provided, and Fig. 4(2) shows the digitization process in the AD converter 6 when the trigger delay unit 74 is provided.

[0035] In Figure 4(1), the upper part shows the analog input (output of the photoreceiver 4) input to the AD converter 6, and the lower part shows the trigger signal generated by the trigger signal generator 7. Because the trigger signal is generated with the rising edge of a pulse, the trigger period basically matches the pulse period. T1 is the time length of the analog signal to be converted into a digital signal (the so-called data recording length). T0 is the period from when a trigger signal is accepted until the next trigger signal can be accepted. In other words, analog signal acquisition is performed for a length of T1 every T0 period. In the following explanation, T1 will be referred to as the acquisition period.

[0036] As shown in Figure 4(1), the rising edge of the pulse in the analog input does not coincide with the start of the acquisition period T1. In other words, the analog pulse signal is acquired with a delay from the start of T1. This delay is called T2. The delay T2 corresponds to the time lag until the pulsed light generated by the pulsed light source 1 is finally captured by the photodetector 4. Assume that the pulsed light source 1 generates and emits a pulsed light that rises at time t1. As shown in Figure 4(1), the timing of the trigger signal is time t1. This pulsed light passes through the expander 2 and the target S and reaches the photodetector 4, and an analog signal is input to the AD converter 6, but the rising time of the pulse at that input is t2, which is delayed by T2.

[0037] This delay T2 is a delay in capturing the pulse signal caused by a delay in the light as it passes through the expander element 2 and the target object S. Hereinafter, this delay T2 will be referred to as the pulse capturing delay. In this embodiment, the trigger signal is a portion of the output of the seed laser 110, so strictly speaking, the pulse capturing delay T2 also includes the delay in the ultrashort pulse laser 11 and the delay in the nonlinear element 12. Because of this pulse capture delay T2, when capture begins, only an analog signal of essentially zero is captured initially, and after T2 has passed, capture of the analog signal for the actual pulse begins. After capture ends at the length of T1, the time until the next trigger signal can be received, i.e., the dead time, begins. In Figure 4(1), the dead time period is indicated by T3.

[0038] The capture cycle T1 is set as long as possible, so that multiple pulses of analog signals exist within the time period T1. In this example, two pulses are captured in one T1, but in reality, many more pulses are often captured, and sometimes several tens to 100 pulses are captured. When an analog signal consisting of multiple pulses is captured, after a trigger signal is generated and the capture of the analog signal begins, the trigger signal generated by the next pulse is ignored by the AD converter 6. That is, trigger signals are ignored not only during the time period T3 but also during the time period after the start of T1. The ignored trigger signals are indicated by dashed lines in Figure 4(1). The length of the capture cycle T1 is determined according to the number of pulses to be captured. For example, if five pulses are to be captured, the length is five pulses plus four intervals between each pulse. However, as shown in Figure 4, there is a pulse capture delay T2, so the time T2 is added to this.

[0039] As can be seen from the above explanation and Figure 4(1), even after data acquisition in the acquisition cycle T1 is completed, there is a further period of time during which the trigger signal is ignored, the dead time T3. Therefore, as shown in Figure 4(1), even if a trigger signal is input during this dead time T3, acquisition does not start, and acquisition starts from the next trigger signal (i.e., the next pulse). In other words, the pulse corresponding to the trigger signal that is ignored during the T3 period is not converted to a digital signal and is dropped from the output of the AD converter 6. In other words, the dead time T3 causes pulses to be dropped. In Figure 4(1), the dropped pulses are indicated by dashed lines.

[0040] On the other hand, in a configuration provided with a trigger delay unit 74, the trigger signal is delayed before being input to the AD converter 6, as shown in Figure 4(2). The delay amount is set to be slightly shorter than T2 in Figure 4(1). In Figure 4(2), the delay amount is indicated by T4. In this case, the pulse capture delay T2 that occurred in the past becomes very short or becomes almost zero. In other words, the delay in light itself does not change, so the timing t2 at which the beginning of the pulse is captured in the AD converter 6 does not change, but the trigger signal is also delayed in accordance with the delay in light (i.e., t1 becomes a later time), so as a result, the pulse capture delay T2 is shortened. Since the capture cycle T1 is long enough to capture the desired number of pulses, the shortened amount of T2 (delay amount T4) can be subtracted. In other words, T1' = T1 - T4.

[0041] On the other hand, the dead time T3 itself does not change. In other words, it is a fixed length of time that begins at the end of T1' and continues until the next trigger signal can be received. In this case, the trigger signal corresponding to the pulse following the pulse captured during the T1' period is also delayed by T4. As a result, this trigger signal is input after the end of dead time T3 and is effectively received. Therefore, the pulse corresponding to this trigger signal is also digitized and is not missed.

[0042] In this way, the trigger delay unit 74 in the embodiment delays the trigger signal by an amount corresponding to the pulse capture delay T2 before inputting it to the AD converter 6, thereby making it possible to input the trigger signal after the end of the dead time T3. Therefore, the amount of delay is determined by the difference between the time of the trigger signal occurring during the dead time T3 and the end of the dead time T3 (see FIG. 4( 2 ) is shown as δt. That is, the delay time T4 of the trigger signal must be equal to or greater than δt (or longer than δt).

[0043] However, if the delay time T4 exceeds the pulse capture delay T2 when no delay is applied (i.e., if T2 becomes negative), even though the pulse is actually incident on the photodetector 4, the trigger signal corresponding to that pulse will not be input to the AD converter 6, resulting in a situation where the initial pulse data will be missing. Therefore, the delay time T4 must be equal to or less than T2 when no delay is applied (or shorter than T2).

[0044] As can be seen from the above explanation, the trigger delay unit 74 in the device of the embodiment can also be said to ensure that the dead time T3 in the AD converter 6 ends during the pulse interval. Therefore, it is preferable to also optimize the pulse repetition period of the pulse light source 1. That is, in the device of the embodiment, the pulse is stretched by the stretcher element 2, so that the interval of the pulse light when it enters the photodetector 4 is shorter than the interval when it is emitted from the pulse light source 1. In this case, if the length of the interval is shorter than the dead time T3, it is not possible to eliminate missing pulses even if the trigger signal is delayed by the trigger delay unit 74.

[0045] If the interval is longer than the dead time, the trigger signal can be appropriately delayed and an appropriate capture period T1 can be set to eliminate pulse dropouts. Therefore, it is preferable to set the pulse repetition period and the stretched pulse width so that the pulse interval in the photodetector 4 is longer than the dead time T3. Specifically, for example, it is possible to adjust the pulse oscillation period in the seed laser 110 depending on the amount of stretching in the stretching element 2.

[0046] Since pulse elongation in the target S can be ignored, it is also possible to set the pulse interval at the time of emission from the expander element 2 to be longer than the dead time T3. This interval can be determined by placing a photodetector immediately after the expander element 2 and measuring it. This configuration of making the pulse interval longer than the dead time can be effective even when the trigger signal is not delayed. That is, if the interval is equal to or longer than the pulse acquisition delay T2 + dead time T3 when the trigger signal is not delayed, then the trigger delay is unnecessary.

[0047] However, even if the interval is shorter than the dead time T3, there is still value in delaying the trigger signal. That is, the time period T2 is a time period during which analog signal acquisition has started but no pulse signal (the actual measurement signal) is being acquired, wasting time and resources. Therefore, eliminating or shortening this time will lead to overall measurement efficiency improvements. Furthermore, if multiple trigger signals fall within the dead time T3 when the trigger signal is not delayed, this means that multiple pulses will be missed, but delaying the trigger signal can reduce this. In other words, the trigger delay unit 74 is significant in that it can reduce, if not eliminate, the number of missed pulses.

[0048] In this way, in the pulse spectroscopy device of the embodiment, the input trigger signal is delayed in the AD converter 6 that digitizes the analog signal output from the photodetector 4, thereby reducing missed pulses and reducing wasted time and resources, thereby improving measurement efficiency. To give a more specific example, if the pulse light source 1 emits broadband pulsed light in the range of about 900 to 1300 nm, the pulse width after stretching by the stretching element 2 is about 1 to 150 nanoseconds. In this case, the light delay (pulse acquisition delay T2 when no delay is applied) is about 50 to 200 nanoseconds. The delay time T4 is set to, for example, 90% of T2, which in this example is about 45 to 180 nanoseconds. When a coaxial cable is used, a delay time T4 of this order can be achieved by ensuring that the length of the surplus portion 731 is about 9 to 36 m.

[0049] In practice, adjustments are made by appropriately adjusting the delay time T4 while observing the output of the AD converter 6 with an oscilloscope (or observing the output of the photodetector 4 with an oscilloscope built into the AD converter 6). That is, the longest possible value for T4 that does not cause missing of the leading portion of the pulse is determined and selected. More specifically, the TrADC cable 73 is set to a certain length. Initially, pulses are dropped because the delay time T4 is too long. The TrADC cable 73 is then gradually shortened by cutting it until the length at which no pulses are dropped is reached. The TrADC cable 73 is used at that length (including the surplus portion 731). Note that if there is significant loss in the TrADC cable 73, an amplifier may be provided to amplify the signal before transmitting it.

[0050] Next, a pulse spectroscopic device according to a second embodiment will be described. 5 is a schematic diagram of a pulse spectroscopy device according to the second embodiment. In the second embodiment, a trigger delay unit 74 is also provided, and a delayed trigger signal is input to the AD converter 6. The trigger delay unit 74 is also a surplus portion 731 of the TrADC cable 73. In this embodiment, a temperature adjustment mechanism 75 is provided for the trigger delay unit 74. A thermostatic bath with airtight insertion and removal holes for the TrADC cable 73 can be used as the temperature adjustment mechanism 75. In other words, the temperature adjustment mechanism 75 is a mechanism that keeps the temperature of the trigger delay unit 74 constant so that it does not change.

[0051] The impedance of the TrADC cable 73, which may be a coaxial cable or the like, changes with temperature. Even a slight change in impedance can cause significant fluctuations in the delay time T4 because the TrADC cable 73 includes a long surplus portion 731. The temperature adjustment mechanism 75 is intended to prevent this problem. In other words, it is intended to suppress fluctuations in the delay time T4, supply the trigger signal to the AD converter 6 with stable timing, and consistently achieve effects such as reduced pulse dropout.

[0052] In addition, the temperature adjustment mechanism 75 may maintain a constant temperature, or may actively set a different temperature and maintain it constant. For example, after a pulse spectroscopy device is manufactured and shipped, some factor may cause a change in the amount of light delay, resulting in a change in the pulse acquisition delay T2, which may require a corresponding change in the delay time T4. In this case, adjustments can be made by slightly cutting the TrADC cable 73 or adding a short cable, but in some cases, the problem can be addressed by changing the temperature. In such cases, adjustments can be made by changing the set temperature of the temperature adjustment mechanism 75. Although the example of the thermostatic bath described above is an example of indirectly adjusting the temperature of the surplus portion 731, it may also be adjusted directly. That is, a temperature monitor (for example, a temperature monitor that measures the temperature of the surplus portion 731 with a non-contact thermometer by exposing a part of the wire) may be provided to monitor the temperature of the surplus portion 731, and feedback control may be performed using the output of this monitor.

[0053] Next, a pulse spectroscopy device according to a third embodiment will be described below. Fig. 6 is a schematic diagram of the pulse spectroscopy device according to the third embodiment. The pulse spectrometer of the third embodiment is configured to acquire reference spectrum data in real time. Specifically, a splitting element 31 such as a beam splitter is provided on the output side of the stretching element 2. One of the optical paths split by the splitting element 31 extends toward the receiver 30, as in the above-described embodiments, and the broadband stretched pulsed light traveling along this optical path is irradiated onto the target S. The other split optical path serves as a reference optical path. A reference photodetector 91 is provided on the reference optical path, as shown in FIG. 6.

[0054] The reference photoreceiver 91 is connected to the calculation means 5 via a reference AD ​​converter 92, and similarly, the analog signal is digitized and input to the calculation means 5. The reference AD ​​converter 92 is the same as the measurement AD converter 6 (a product with the same specifications). In this embodiment, a trigger signal generating unit 7 and a trigger delay unit 74 are also provided. A TrADC cable 73 including a surplus portion 731 serving as the trigger delay unit 74 branches midway and is connected in parallel to two AD converters 6 and 92, as shown in FIG. 6. Therefore, a similarly delayed trigger signal is input to the measurement AD converter 6 and the reference AD ​​converter 92. Note that the TrADC cable 73 to the measurement AD converter 6 and the TrADC cable 73 to the reference AD ​​converter 92 have the same length from the branch point (or the difference in length is sufficiently small) so that there is no significant difference in the timing of the arrival of the trigger signal.

[0055] 6, a synchronizing means 93 is provided so that sampling is performed synchronously in the two AD converters 6, 92. In this example, the synchronizing means 93 is a means for supplying a clock signal of the measurement AD converter 6 to the reference AD ​​converter 92. In other words, the clock signal output section and clock signal transmission line of the measurement AD converter 6 constitute the synchronizing means 93. The output of the reference photodetector 91 is digitized by a reference AD ​​converter 92 and input to the calculation means 5, thereby acquiring reference spectrum data in real time in the calculation means 5. The processing in the calculation means 5 (processing by the measurement program 53) is basically the same as in the first and second embodiments.

[0056] According to the third pulse spectrometer, reference spectrum data is acquired in real time, enabling consistently high-precision spectroscopic measurements to be performed without being affected by disturbances such as changes in the characteristics of the pulsed light source 1. Furthermore, periodic measurements (calibration measurements) to obtain reference spectrum data are not required. A similarly delayed trigger signal is also supplied to the reference AD ​​converter 92, so the effect of reducing pulse dropouts is not lost. Furthermore, the provision of synchronization means 93 prevents deviations in the sampling times of the two AD converters 6 and 92. Deviations in sampling result in calculations of absorption rates and the like based on reference values ​​at different times (i.e., different wavelengths), which can reduce the reliability of measurement results. However, this embodiment does not have such problems, providing a highly reliable pulse spectrometer.

[0057] The effect of improving the reliability of the measurement results by the synchronization means 93 can be obtained even without providing the trigger delay unit 74. That is, if the pulse acquisition delay T2 is originally small, the trigger delay unit 74 may not be provided, but even in that case, providing the synchronization means 93 will provide the effect of improving the reliability of the measurement results.

[0058] It is also possible to use a multi-channel (multiple inputs possible) AD converter 6, and use one AD converter for both measurement and reference. In this case, the same effect as above can be obtained by using a configuration in which the clock is synchronized internally. A separate clock generating unit may also be provided to supply a common clock signal to the two AD converters 6 and 92.

[0059] In the above-described embodiments, a single fiber (group delay fiber) is used as the stretching element 2. However, multiple fibers may be used to split and delay the light while transmitting it, and then combine the split light and irradiate the target S. One advantage of using multiple fibers is that by splitting the light into multiple beams and transmitting them for pulse stretching, unintended nonlinear optical effects can be avoided during stretching. Research by the inventors has revealed that if high-energy light is transmitted through a single fiber to achieve high output and pulse stretched, additional nonlinear optical effects occur in the stretching fiber, destroying the uniqueness of the time-to-wavelength relationship. To avoid this problem, it is effective to use a configuration in which the light from the pulse light source 1 is split and transmitted through separate fibers, and the pulses are stretched by delaying them.

[0060] When splitting light and transmitting it through multiple fibers, a simple configuration using a beam splitter or the like is acceptable, but a more effective configuration is to split the light according to wavelength and transmit each wavelength through a separate fiber. One reason for this is that by optimizing the fiber length or fiber material according to wavelength, it is possible to achieve a delay amount according to wavelength. This makes it possible to optimize the overall amount of pulse elongation and to achieve uniform wavelength resolution by making Δλ / Δt uniform across wavelengths. When splitting light according to wavelength, an arrayed waveguide grating (AWG) can be used as a splitting element. Figure 7 shows this embodiment, and is a schematic diagram of a pulse spectroscopic device of the fourth embodiment using an arrayed waveguide grating.

[0061] 7, an arrayed waveguide grating 8 serving as a dividing element is provided on the output side of a pulse light source 1. On the output side of the arrayed waveguide grating 8, a plurality of elongated fibers 21 serving as an elongating element 2 are provided in parallel. The output ends of the elongated fibers 21 are bundled together, and an output element 22 is provided. The light emitted from the output element 22 is superimposed at the object S and irradiated onto the object S. The output element 22 is an element that causes the light emitted from each elongated fiber 21 to be superimposed and irradiated onto the same irradiation area, and may include a lens that collimates the light (makes it into a beam that does not diverge) or expands the beam for irradiating.

[0062] FIG. 8 is a schematic plan view of an arrayed-waveguide grating used as a dividing element. Arrayed-waveguide gratings were developed for optical communications, and their use in spectroscopic measurement is unknown. As shown in FIG. 8, arrayed-waveguide grating 8 is configured by forming functional waveguides 82 to 86 on a substrate 81. Each functional waveguide includes a number of grating waveguides 82 with slightly different optical path lengths, slab waveguides 83 and 84 connected to both ends (the entrance side and the exit side) of grating waveguide 82, an entrance-side waveguide 85 that inputs light to entrance-side slab waveguide 83, and exit-side waveguides 86 that extract light of each wavelength from exit-side slab waveguide 84.

[0063] The slab waveguides 83 and 84 are free space, and light incident through the input waveguide 85 spreads in the input slab waveguide 83 and enters each grating waveguide 82. Because each grating waveguide 82 has a slightly different length, the light reaching the end of each grating waveguide 82 is shifted in phase by this difference. Light is diffracted and emitted from each grating waveguide 82, and the diffracted light interferes with each other while passing through the output slab waveguide 84 and reaching the input end of the output waveguide 86. Due to the phase shift, the intensity of the interference light is maximized at a position corresponding to the wavelength. In other words, light of successively different wavelengths enters each output waveguide 86, and the light is spatially dispersed. Strictly speaking, each output waveguide 86 is formed so that its input end is positioned at the position where the light is dispersed. Incidentally, each elongated fiber 21 is connected to each output waveguide 86. The pulsed light divided into wavelengths is transmitted by each elongated fiber 21, and at this time, a group delay occurs, causing the overall pulse width to be extended.

[0064] In this configuration using the arrayed-waveguide grating 8 as a splitting element, pulses are transmitted through the elongated fibers 21 optimized for each wavelength and then stretched. This has the advantage of making Δλ / Δt uniform across wavelengths, thereby achieving uniform wavelength resolution, as described above. However, the amount of delay of light passing through the elongated fibers 21 tends to increase, which tends to lengthen the pulse acquisition delay T2. This means that problems such as missing pulses and wasted data acquisition periods tend to become more pronounced. Therefore, a configuration that can reduce the effect of T2 by delaying the trigger signal using the trigger delay unit 74 is particularly useful in a configuration in which light is split using the arrayed-waveguide grating 8 and transmitted through each elongated fiber 21.

[0065] In each of the above-described embodiments, the trigger delay unit 74 may be a separately provided delay unit rather than the surplus portion 731 of the TrADC cable 73. For example, the trigger delay unit may be provided by appropriately selecting from various delay elements using semiconductor elements. For example, a DS1100L series delay element manufactured by Maxim Integrated, San Jose, California, USA, may be used. However, delay elements using such semiconductor elements generally have unstable delay characteristics and often do not allow for flexible adjustment of the delay amount. In comparison, a configuration in which the surplus portion 731 is provided in the TrADC cable 73 to cause a delay is preferable because it provides a stable delay amount and allows for flexible adjustment of the delay amount.

[0066] Although the trigger signal is delayed as an electrical signal, it does not necessarily have to be an electrical signal and may be delayed as another type of signal, such as an optical signal. For example, a portion of the output of the seed laser 110 is extracted and transmitted through a transmission fiber. The output of the transmission fiber is detected by a separately provided detector, and this output is input to an AD converter. The length of the transmission fiber is selected so that the delay of the trigger signal in the transmission fiber is the aforementioned pulse capture delay T2 or slightly shorter. Similar results can be obtained with this configuration.

[0067] However, in the case of fiber transmission, changing the length of the line is more troublesome than with an electrical cable. That is, changing the length requires cutting or fusing the fiber to extend it, which requires processing the end face and readjusting the position relative to the photodetector, which is troublesome. Therefore, taking this into consideration, a configuration in which the trigger signal is delayed as an electrical signal is preferable. Note that, as a configuration in which the trigger signal is obtained as an electrical signal, it is also possible to obtain the output from the driver circuit of the seed laser 110 as the trigger signal. Also, if a pulsed excitation laser is used instead of the seed laser 110, it is also possible to obtain the trigger signal from its driver circuit.

[0068] In the above explanation, the spectroscopic measurement of the light transmitted through the object S is taken as an example, but it is also possible to provide a light receiver 4 at a position where the light reflected from the object S is received, and to perform the spectroscopic measurement of the light reflected from the object S. Furthermore, it is also possible to capture and perform the spectroscopic measurement of the scattered light or fluorescence from the object S irradiated with pulsed light. In other words, the light from the object S can be the transmitted light, reflected light, fluorescence, scattered light, etc. from the object S irradiated with light. As the pulse light source 1, in addition to one that emits SC light, an ASE (Amplified Spontaneous Emission) light source, an SLD (Superluminescent diode) light source, or the like may also be adopted. [Explanation of symbols]

[0069] 1. Pulsed light source 11 Ultrashort pulse laser 110 Seed Laser 111 Excitation laser 12 Nonlinear elements 2. Extension element 21 Extension fiber 3 Irradiation optical system 30 Receiving plate 4 Receiver 5 Calculation means 6 AD converter 7 Trigger signal generator 71 Beam Splitter 72 Detector 73 Cable 731 Surplus 74 Trigger delay section 8 Arrayed Waveguide Grating 91 Reference receiver 92 Reference AD ​​converter

Claims

1. a pulsed light source; an expansion element that expands the pulse width of light from a pulsed light source so that the elapsed time within the pulse corresponds one-to-one to the wavelength of the light; a light receiver that receives light from an object illuminated with light from the elongation element; a computing means for processing the output from the photoreceiver to obtain a measurement result; an AD converter that converts an analog signal output from the photodetector into a digital signal and supplies the digital signal to a computing means; A pulse spectroscopy device comprising: a trigger signal generating unit that generates a trigger signal in response to a rise of pulsed light from the pulsed light source; a trigger supply unit that supplies the trigger signal generated by the trigger signal generation unit to the AD converter, The AD converter is a converter that starts to capture an analog signal from the optical receiver when a trigger signal is supplied. the trigger supply unit includes a trigger delay unit that delays the trigger signal; A pulse spectroscopy device characterized in that the delay amount in the trigger delay unit is a delay amount that causes the trigger signal to be input to the AD converter before the rising edge of the pulse signal that is output from the photodetector and input to the AD converter when pulsed light is irradiated onto an object when the trigger signal is generated.

2. the pulse light source includes an ultrashort pulse laser and a nonlinear element that generates a nonlinear optical effect in the laser light emitted from the ultrashort pulse laser to broaden the bandwidth; 2. The pulse spectroscopy device according to claim 1, wherein the trigger signal generating unit generates a trigger signal by extracting and detecting a portion of the laser light emitted from the ultrashort pulse laser before it enters the nonlinear element.

3. the trigger signal is an electrical signal, the trigger supply unit is a cable connecting the trigger signal generation unit and the AD converter, and the cable has a surplus portion that is longer than a length required for connection at a spatial distance between the trigger signal generation unit and the AD converter, 3. The pulse spectrometer according to claim 1, wherein the trigger delay section is a surplus section of the cable.

4. 4. A pulse spectroscopic device according to claim 3, further comprising a temperature adjusting mechanism for adjusting the temperature of said excess portion.

5. a splitting element that splits the light from the elongating element so that one of the split light beams is irradiated onto the object; a reference light receiver provided at a position where the other light split by the splitting element is incident without passing through the object; a reference AD ​​converter that converts an analog signal output from the reference photoreceiver into a digital signal; 5. A pulse spectroscopy device as described in any one of claims 1 to 4, characterized in that the trigger supply unit also supplies the trigger signal to a reference AD ​​converter, and the trigger delay unit delays the trigger signal supplied to the reference AD ​​converter in the same manner as the trigger signal supplied to the AD converter.

6. 6. A pulse spectrometer according to claim 5, further comprising a synchronizing means for synchronizing the sampling in said AD converter with the sampling in said reference AD ​​converter.

7. 7. The pulse spectroscopy device according to claim 1, further comprising: an arrayed-waveguide grating that divides light from the pulse light source into light of each wavelength; and fibers as the extension elements that transmit the light divided into each wavelength by the arrayed-waveguide grating.

8. the AD converter has a dead time, which is a period during which the next analog signal can be acquired after the analog signal has been acquired; 8. The pulse spectroscopy device according to claim 1, wherein the pulse repetition period of the pulse light source is such that the interval between pulses after being stretched by the stretching element is longer than a dead time.

9. a pulsed light source; an expansion element that expands the pulse width of light from a pulsed light source so that the elapsed time within the pulse corresponds one-to-one to the wavelength of the light; a light receiver that receives light from an object illuminated with light from the elongation element; a computing means for processing the output from the photoreceiver to obtain a measurement result; an AD converter that converts an analog signal output from the photodetector into a digital signal and supplies the digital signal to a computing means; A pulse spectroscopy device comprising: a trigger signal generating unit that generates a trigger signal in response to a rising edge of pulsed light from a pulsed light source (excluding a rising edge of the pulsed light when the target is pulsed light); a trigger supply unit that supplies the trigger signal generated by the trigger signal generation unit to the AD converter, the AD converter starts to capture an analog signal from the optical receiver when a trigger signal is supplied, and has a dead time T3 which is a period from when the capture of the analog signal ends until when the next analog signal can be captured; a pulse repetition period of the pulse light source such that, when an acquisition delay, which is a difference between the rise timing of pulsed light from the pulse light source and the timing at which the pulsed light is received by a photodetector, is T2, the interval between each pulse after being stretched by a stretching element is longer than the sum of T2 and T3;

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