WO2020195674A1

WO2020195674A1 - Spectrometer

Info

Publication number: WO2020195674A1
Application number: PCT/JP2020/009387
Authority: WO
Inventors: 拓郎井手口; 和樹橋本
Original assignee: 国立大学法人東京大学
Priority date: 2019-03-28
Filing date: 2020-03-05
Publication date: 2020-10-01
Also published as: JPWO2020195674A1; JP7456639B2

Abstract

A double pulse generator 110 generates a near-infrared double pulse 2 having a variable delay amount. A nonlinear optical crystal 120 is disposed inside the double pulse generator 110 or in a subsequent stage. A detection system 130 is capable of measuring Raman scattered light 6 obtained by irradiating a sample SMP with the near-infrared double pulse 2 and infrared light obtained by irradiating the sample SMP with an infrared double pulse 4 generated by the nonlinear optical crystal 120.

Description

Spectrometer

The present invention relates to a spectroscope.

Vibration spectroscopy such as infrared spectroscopy and Raman spectroscopy is used to measure the structure and state of molecules. Infrared spectroscopy is to irradiate a substance with infrared rays and measure the spectrum of infrared absorption or emission, and can measure molecular vibration accompanied by a change in dipole moment. Raman spectroscopy measures the wavelength and intensity of Raman rays (Stokes lines and anti-Stokes lines) obtained by the Raman effect by irradiating a substance with strong light, and measures molecular vibrations accompanied by changes in polarizability. be able to. In a molecule with centrosymmetry, infrared and Raman vibration modes cannot be shared with respect to reference oscillation, so infrared absorption and Raman scattering have a complementary relationship, which is called alternating forbiddenness.

If infrared active vibration and Raman active vibration can be measured in a wide band and simultaneously, a spectrum covering all of both molecular vibrations can be obtained, and a complete set of reference vibrations can be obtained.

Non-Patent Document 1 reports that infrared absorption and Raman scattering were detected by the same measurement system by using a near-infrared 10 fs (femtosecond) laser and generating a difference frequency with a 4 f pulse shaper.

However, in the technique of Non-Patent Document 1, infrared absorption and Raman scattering must be measured by switching, so that they cannot be detected at the same time. That is, when the structure and chemical state of a molecule change with time, infrared absorption and Raman scattering are measured for molecules in different states or structures.

Further, the technique of Non-Patent Document 1 has a low wave number (frequency) resolution. In addition, it is difficult to obtain a wide-band infrared spectrum that can cover the fingerprint region (800 to 1800 cm ^-1 ) and the CH vibration region (2800 to 3300 cm ^-1 ), and applicable molecules are limited.

The present invention has been made in such a situation, and one of the exemplary purposes of the embodiment is to provide a spectroscope capable of simultaneously measuring infrared active vibration and Raman active vibration.

One aspect of the present invention relates to a spectroscope. The spectroscope is obtained by irradiating a sample with a double pulse generator that generates a first double pulse with a variable delay amount, a nonlinear optical crystal provided inside or after the double pulse generator, and a first double pulse. A detection system capable of measuring Raman scattered light and infrared rays obtained by irradiating a sample with an infrared second double pulse generated by a nonlinear optical crystal is provided.

It should be noted that any combination of the above components and the conversion of the expression of the present invention between devices, methods, systems, etc. are also effective as aspects of the present invention.

According to the present invention, infrared active vibration and Raman active vibration can be measured at the same time.

It is a figure which shows the basic structure of the spectroscope which concerns on embodiment. It is a figure explaining the Fourier transform coherent anti-Stoke Raman spectroscopy in a spectroscope. It is a figure explaining the Fourier transform infrared spectroscopy in a spectroscope. It is a figure which shows the spectroscope which concerns on Example 1. FIG. It is a figure which shows the spectroscope which concerns on Example 2. FIG. It is a figure which shows the specific structural example of the spectroscope of FIG. It is a figure which shows the spectrum of the near infrared double pulse and the infrared double pulse. It is a figure which shows the measurement result of the fringe decomposition autocorrelation (Fringe-resolved Autocorrelation) of a near infrared pulse. 9 (a) to 9 (c) are diagrams illustrating compensation for spectral distortion. 10 (a) and 10 (b) are diagrams showing the measurement results. 11 (a) and 11 (b) are diagrams showing complementary spectra obtained by Fourier transforming the interferogram of FIG. 10 (b). 12 (a) to 12 (c) are diagrams showing spectra measured for a mixed solution of benzene, chloroform, benzene and DMSO (mixing ratio 4: 1). It is a figure which shows the spectroscope which concerns on the modification 1. It is a figure which shows the spectroscope which concerns on the modification 2. It is a figure which shows the spectroscope which concerns on the modification 9. FIG. 16A is a diagram for explaining the generation of the intra-pulse difference frequency by one nonlinear optical crystal, and FIG. 16B is a diagram for explaining the generation of the cascade-type intra-pulse difference frequency by the two nonlinear optical crystals. It is a figure. It is a figure which shows the specific structural example of the spectroscope of FIG. It is a figure which shows the specific implementation of the spectroscope of FIG. 19 (a) to 19 (c) are diagrams showing the spectra obtained by the spectroscope of FIG.

(Outline of Embodiment)
One embodiment disclosed herein relates to a spectroscope. The spectroscope uses a double pulse generator that generates a first double pulse with a variable delay amount, a nonlinear optical crystal provided inside the double pulse generator or after the double pulse generator, and a first double pulse as a sample. A detection system capable of measuring Raman scattered light obtained by irradiation and infrared rays obtained by irradiating a sample with a second double pulse of infrared rays generated by a nonlinear optical crystal is provided.

In a nonlinear optical crystal, a difference frequency (intra-pulse differential frequency: IDFG: Intra-pulse Differential Frequency Generation) between different spectral components contained in the first double pulse is generated, and as a result, a second infrared ray having a wide spectrum is generated. A double pulse is generated. The sample is irradiated with the first double pulse and the second double pulse at the same time, and the delay amount of the two pulses contained in each double pulse is changed, and the infrared region and the near infrared region (or visible or ultraviolet) are respectively. By measuring the light intensity of the above, it is possible to simultaneously generate an infrared interferogram and a Raman-scattered interferogram. As a result, infrared active vibration and Raman active vibration can be measured at the same time. For this reason, the spectroscopy according to the embodiment is referred to as CVS (Complementary Vibrational Spectroscopy).

The double pulse generator may include a pulsed laser light source that generates pulsed light and an interferometer that receives pulsed light and generates a first double pulse.

The nonlinear optical crystal may be arranged after the interferometer. Each of the two pulses included in the first double pulse is converted into an infrared double pulse by generating an intra-pulse difference frequency in the nonlinear optical crystal. In this case, since the interferometer only needs to cover the wavelength band of the first double pulse, it can be configured inexpensively and with high efficiency.

The spectroscope may be further provided with a first dispersion compensator, which is provided after the nonlinear optical crystal and compresses the pulse width of the first double pulse. By propagating the pulsed light constituting the first double pulse in the nonlinear optical crystal, a second-order or higher-order dispersion is introduced, the phase characteristics are disturbed, the pulse width is widened, and the light intensity is lowered. On the other hand, since Coherent Anti-Stokes Raman Scattering (CARS) is a third-order nonlinear optical phenomenon, it is desirable that the light intensity of the first double pulse applied to the sample is high. Therefore, by performing dispersion compensation before irradiating the sample with the first dispersion compensator, the pulse width of the first double pulse can be brought close to the Fourier limit pulse width to increase the light intensity, and the intensity of Raman scattered light can be increased. be able to. This enables measurement with a high S / N ratio.

The spectroscope may further include a signal processing unit that processes the output of the detection system. The signal processing unit may correct the interferogram of infrared transmitted light.

The detection system has a dichroic mirror that separates the transmitted light of the sample into the wavelength region of the first double pulse and the infrared region, the first detector that has sensitivity in the wavelength region of the first double pulse, and the sensitivity in the infrared region. A second detector may be included.

The detection system may include a polarizer inserted in front of the second detector.

The double pulse generator may further include a second dispersion compensator that compresses the pulse width of the pulse included in the first double pulse incident on the nonlinear optical crystal. Since the generation of the difference frequency in the nonlinear optical crystal is a second-order nonlinear optical phenomenon, it is desirable that the light intensity of the first double pulse incident on the nonlinear optical crystal is high. Therefore, by performing dispersion compensation before irradiating the nonlinear optical crystal with the second dispersion compensator, the pulse widths of the two pulses included in the first double pulse can be brought closer to the Fourier limit pulse width to increase the light intensity. It is possible to improve the efficiency of differential frequency generation.

The first dispersion compensator and the second dispersion compensator may include a chirped mirror pair. Alternatively, a prism pair or a grating pair may be used.

The spectroscope may further include a focused optical system that irradiates the sample with a first double pulse that has passed through a nonlinear optical crystal. The focusing optical system may coaxially focus the first double pulse and the second double pulse on the sample. The focusing optical system may include an off-axis parabolic mirror (OAPM). As a result, the near-infrared double pulse and the infrared double pulse can be focused at the same position in the in-plane direction and the depth direction. Alternatively, the focal position of the first double pulse in the sample and the focal position of the second double pulse in the sample may be intentionally shifted. Thereby, the vibration of infrared activity and the vibration of Raman activity can be measured as independent phenomena.

The optical path length of the first double pulse leading to the sample and the optical path length of the second double pulse leading to the sample may be different. As a result, the interaction between the first double pulse and the second double pulse can be suppressed, and Raman scattering and infrared absorption can be separately measured as separate phenomena.

The optical path length from which the first double pulse reaches the sample may be equal to the optical path length from which the second double pulse reaches the sample. This makes it possible to measure the behavior of unknown molecules due to the interaction between the first double pulse and the second double pulse.

The detection system may be configured to be able to detect light obtained by irradiating a sample with a double pulse of a second harmonic or a third harmonic generated in a nonlinear optical crystal.

When the above-mentioned nonlinear optical crystal is used as the first nonlinear optical crystal, the spectroscope may further include a second nonlinear optical crystal. By using a plurality of nonlinear optical crystals, the mid-infrared spectrum can be further widened.

The first nonlinear optical crystal may be LiIO ₃ , and the second nonlinear optical crystal may be GaSe. In this case, it is possible to obtain a wide-band spectrum covering of H 2 _O absorption region and the CO ₂ absorbing region.

(Embodiment)
Hereinafter, the present invention will be described with reference to the drawings based on preferred embodiments. The same or equivalent components, members, and processes shown in the drawings shall be designated by the same reference numerals, and redundant description will be omitted as appropriate. Further, the embodiment is not limited to the invention but is an example, and all the features and combinations thereof described in the embodiment are not necessarily essential to the invention.

FIG. 1 is a diagram showing a basic configuration of the spectroscope 100 according to the embodiment. The spectroscope 100 simultaneously disperses infrared absorption (or reflection) and Raman scattering of the sample SMP by a Fourier transform method.

The spectroscope 100 mainly includes a double pulse generator 110, a nonlinear optical crystal 120, and a detection system 130.

The double pulse generator 110 repeatedly generates a near-infrared double pulse (referred to as a near-infrared double pulse) 2 having a variable delay difference τ. The near-infrared double pulse 2 includes a reference first pulse 2A and a subsequent (or preceding) second pulse 2B. Regarding the measurement of CARS, of the first pulse 2A and the second pulse 2B, the preceding one becomes the pump light and the succeeding one becomes the probe light. The delay difference τ changes with each iteration. The pulse width of the near-infrared double pulse 2 generated by the double pulse generator 110 is on the order of femtoseconds (for example, 10 fs) and contains a very wide spectrum component.

The nonlinear optical crystal 120 is provided inside or after the double pulse generator 110. In FIG. 1, the nonlinear optical crystal 120 is provided after the double pulse generator 110 and is irradiated with the near infrared double pulse 2. In the nonlinear optical crystal 120, a difference frequency between different spectral components contained in the near-infrared pulse 2A (2B) is generated, whereby an infrared double pulse 4 having a wide-band spectrum is generated. A part of the near-infrared double pulse 2 is converted into the infrared double pulse 4 in the nonlinear optical crystal 120, and the remaining 2'is transmitted through the nonlinear optical crystal 120 without being converted. The material of the nonlinear optical crystal 120 is not particularly limited, and may be selected in consideration of the wavelength of the near infrared double pulse 2 and the wavelength of the infrared double pulse 4 to be generated. For example, as the nonlinear optical crystal 120, GaSe (gallium selenium) may be used.

The near-infrared double pulse 2'and the infrared double pulse 4 are applied to the sample SMP. The detection system 130 irradiates the sample SMP with the Raman scattered light 6 obtained by irradiating the sample SMP with the near infrared double pulse 2 and the infrared double pulse 4 generated by the nonlinear optical crystal 120. The transmitted light 8 is configured to be measurable. For example, the detection system 130 includes a first detector 132 and a second detector 134. The first detector 132 has sensitivity to the wavelength of the Raman scattered light 6 and generates a detection signal S1 according to the amount of received light. Similarly, the second detector 134 has sensitivity to the wavelength of the infrared transmitted light 8 and generates a detection signal S2 according to the amount of received light. The digitizer 136 converts the detection signals S1 and S2 into digital sampling values D1 and D2. The outputs D1 and D2 of the digitizer 136 are supplied to the signal processing unit 140 in the subsequent stage.

The signal processing unit 140 acquires the waveform DW1 which is the data string of the sampling value D1 and the waveform DW2 which is the data string of the sampling value D2. The signal processing unit 140 generates an interferogram IF_CARS of Raman scattered light 6 based on the waveform DW1 and Fourier transforms it to generate a Raman spectrum. Further, the signal processing unit 140 acquires the interferogram IF_IR of the infrared transmitted light 8 based on the waveform DW2 and Fourier transforms it to generate an infrared absorption spectrum.

The signal processing unit 140 may be a computer, workstation or tablet terminal. Alternatively, the signal processing unit 140 may be mounted by a microcomputer, an FPGA (Field Programmable Gate Array), or an IC (Integrated Circuit) and incorporated into the detection system 130.

The above is the configuration of the spectroscope 100. Next, the operation will be described.

FIG. 2 is a diagram illustrating Fourier transform coherent anti-Stoke Raman spectroscopy (FT-CARS) in the spectroscope 100. The double pulse generator 110 repeatedly generates near-infrared double pulses 2 having different delay amounts (time difference) τ. The i-th infrared double pulse 2 is denoted by 2_I, the time difference between the first pulse 2A and the second pulse 2B in the near-infrared double pulse 2_I expressed as tau _i.

When the preceding near-infrared first pulse 2A is applied to the sample SMP, the light of a certain frequency becomes the excitation light when it is included in the first pulse 2A, and the other frequency becomes the Stokes light in the sample SMP. , Molecular vibrations with the same vibrational frequency as their frequency difference are induced. After that, when the second pulse 2B is applied to the sample SMP in which the molecular vibration is induced, the second pulse 2B and the molecular vibration act to shift the frequency contained in the second pulse 2B, resulting in Raman scattering. Light 6 is emitted.

By repeating the measurement of Raman scattered light 6 while changing the delay amount τ, the interferogram IF_CARS of Raman scattered light 6 is generated. A Raman spectrum is generated by performing a fast Fourier transform on this interferogram IF_CARS.

FIG. 3 is a diagram illustrating Fourier transform infrared spectroscopy (FT-IR) in the spectroscope 100. The double pulse generator 110 repeatedly generates near-infrared double pulses 2 having different delay amounts (time difference) τ, and the nonlinear optical crystal 120 converts them into infrared double pulses 4. The time difference τ _i between the first pulse 4A and the second pulse 4B of the infrared double pulse 4 is equal to the time difference τ _i of the near infrared double pulse 2 before conversion.

The preceding infrared first pulse 4A is applied to the sample SMP to absorb a predetermined spectral component. Subsequently, the second pulse 4B is applied to the sample SMP to absorb a predetermined spectral component. FIG. 3 shows transmitted lights 8A and 8B of the sample SMPs of the first pulse 4A and the second pulse 4B, respectively. The infrared transmitted light 8 is interference light of transmitted lights 8A and 8B. Interferogram IF_IR infrared transmitted light, shows the energy relationship between each pulse of the delay tau _i and the infrared light transmitted through 8. An infrared absorption spectrum is generated by performing a fast Fourier transform on this interferogram IF_IR.

The above is the operation of the spectroscope 100. According to this spectroscope 100, it is possible to generate an infrared double pulse having a wide spectrum in a nonlinear optical crystal. Then, by irradiating the sample with an infrared double pulse and a near-infrared double pulse and measuring the light intensity of each of the infrared region and the near-infrared region while changing the time difference of the double pulse, the infrared interferogram IF_IR and near-infrared CARS interferogram IF_CARS can be generated at the same time. As a result, infrared active vibration and Raman active vibration can be measured at the same time.

The present invention extends to various devices and methods derived from the above description, and is not limited to a specific configuration. Hereinafter, more specific configuration examples and examples will be described not for narrowing the scope of the present invention but for helping to understand the essence and operation of the invention and clarifying them.

(Example 1)
FIG. 4 is a diagram showing the spectroscope 100A according to the first embodiment. In the spectroscope 100A, the double pulse generator 110A includes a pulsed laser light source 112, a Michelson interferometer 114, and a long pass filter 116. The pulsed laser light source 112 is a femtosecond-titanium sapphire laser that produces a near-infrared ultrashort pulse 10 having a broadband spectrum with a wavelength of 690 to 920 nm. The Michelson interferometer 114 has a beam splitter BS, a fixed mirror M1 and a movable mirror M2. The interferometer 114 splits the near-infrared ultrashort pulse 10 into two arms. In the Michelson interferometer 114, the optical path length difference L of the two arms is variably configured, and the optical path length difference L is the delay time τ of the two

pulses

2A and 2B included in the near infrared double pulse 2. give. The pulse 2A propagating in the reference arm and the pulse 2B propagating in the scan arm are recombined by the beam splitter BS and transmitted through the long path filter 116 to generate a near-infrared double pulse 2.

The detection system 130A includes a dichroic mirror DM1, a first detector 132, a second detector 134, a digitizer 136, and a short pass filter SPF. The dichroic mirror DM1 has a high reflectance in the near infrared region and a high transmittance in the infrared region.

The reflected light of the dichroic mirror DM1 includes a spectrum component of the original double pulse in the near infrared and a Raman spectrum component in the near infrared. The short pass filter SPF removes the spectral component of the double pulse and transmits only the Raman spectral component. The first detector 132 measures the intensity of the Raman scattered light 6.

The infrared transmitted light 8 transmits through the dichroic mirror DM1. The second detector 134 is, for example, an MCT (HgCdTe: Mercury Cadmium Telluride) infrared photodetector, which detects the intensity of the infrared transmitted light 8 transmitted through the dichroic mirror DM1. The digitizer 136 converts the outputs of the first detector 132 and the second detector 134 into digital signals.

(Example 2)
FIG. 5 is a diagram showing the spectroscope 100B according to the second embodiment. The spectroscope 100B includes a first dispersion compensator 150 and a condensing optical system 160 in addition to the double pulse generator 110, the nonlinear optical crystal 120, and the detection system 130 shown in FIG.

The first dispersion compensator 150 is provided after the nonlinear optical crystal 120 and compresses the pulse width of the pulse included in the near-infrared double pulse 2'transmitted through the nonlinear optical crystal 120. By propagating the near-infrared double pulse 2 in the nonlinear optical crystal 120, a second-order and higher-order dispersion is introduced, the pulse width of the two pulses of the near-infrared double pulse 2'is extended, and the light is emitted. The strength decreases. On the other hand, since coherent anti-Stoke Raman scattering is a third-order nonlinear optical phenomenon, it is desirable that the light intensity of the near-infrared double pulse irradiating the sample SMP is high. Therefore, by performing dispersion compensation before irradiating the sample SMP with the first dispersion compensator 150, the pulse width of the near-infrared double pulse 2 "can be brought closer to the Fourier limit pulse width to increase the light intensity, and Raman The intensity of the scattered light 6 can be increased, which enables measurement with a high S / N ratio.

The type of the first dispersion compensator 150 is not particularly limited, and various known or future available dispersion compensators can be used. For example, the first dispersion compensator 150 may be composed of a chirped mirror pair (CMP: Chirped Mirror Pair), or may use a prism pair or a grating pair. In the first dispersion compensator 150, it is desirable to compensate at least the second-order, preferably the third-order dispersion.

The condensing optical system 160 receives a near-infrared double pulse 2 ”that has passed through the first dispersion compensator 150 and an infrared double pulse 4, and irradiates the sample SMP coaxially. , Off-Axis Parabolic Mirror (OAPM) may be included, which causes the near-infrared double pulse and the infrared double pulse to be placed at the same position in the in-plane direction and the depth direction. Can be focused.

FIG. 6 is a diagram showing a specific configuration example of the spectroscope 100B of FIG. The double pulse generator 110B includes a pulsed laser light source 112, a Michelson interferometer 114B, a long pass filter 116, and a second dispersion compensator 118. The Michelson interferometer 114B includes a polarizing beam splitter PBS, a fixed mirror M1, a movable mirror M2, 1/2 wave plates HWP1 and HWP2, and 1/4 wave plates QWP1 and QWP2. In this Michelson interferometer 114B, the polarization directions of the

optical pulses

2A and 2B propagating in the two arms are orthogonal to each other, and they are combined to generate a near-infrared double pulse 2. In the Michelson interferometer 114 of FIG. 4, 1/2 of the light energy of the pulsed laser light source 112 is discarded, but by adopting the Michelson interferometer 114B of FIG. 6, the light utilization efficiency is theoretically 100%. Can be enhanced to.

The second dispersion compensator 118 is provided to compensate for the dispersion introduced while the ultrashort pulse 10 propagates through the Michelson interferometer 114B. Compared to the Michelson interferometer 114 of FIG. 4, the Michelson interferometer 114B has a larger number of optical elements through which light transmits, so that it is more susceptible to dispersion, the pulse waveform is deteriorated, and the intensity is lowered. Since the generation of the difference frequency in the nonlinear optical crystal 120 in the subsequent stage is a second-order nonlinear optical phenomenon, it is desirable that the light intensity of the near-infrared double pulse incident on the nonlinear optical crystal 120 is high. Therefore, by performing dispersion compensation before irradiating the nonlinear optical crystal 120 with the second dispersion compensator 118, the pulse width of the near-infrared

double pulses

2A and 2B can be brought close to the Fourier limit pulse width to increase the light intensity. It is possible to improve the efficiency of differential frequency generation. Similar to the first dispersion compensator 150, the configuration of the second dispersion compensator 118 is not limited, but FIG. 5 includes a chirped mirror pair CMP2.

The condensing optical system 170 condenses the near-infrared double pulse 2 on the nonlinear optical crystal 120, and collimates the near-infrared double pulse 2 and the infrared double pulse 4 that have passed through the nonlinear optical crystal 120. Although the condensing optical system 170 can be composed of a transmission optical system, it is preferable to use a reflective optical system because the spectra of the near infrared double pulse 2 and the infrared double pulse 4 are very wide. For example, the condensing optical system 170 can be configured by an off-axis parabolic mirror (OAPM).

The first dispersion compensator 150 includes a dichroic mirror DM2, DM3 and a chirp mirror pair CMP1. The dichroic mirrors DM2 and DM3 have a high reflectance in the near infrared and a high transmittance in the infrared. The dichroic mirror DM2 reflects the near-infrared double pulse 2. The chirped mirror pair CMP1 compresses the pulse width of the near-infrared double pulse 2. The compressed near-infrared double pulse 2 is recombined with the infrared double pulse 4 by the dichroic mirror DM3 and guided to the focusing optical system 160.

The detection system 130B includes a first detector 132, a second detector 134, a dichroic mirror DM1, a short pass filter SPF, a digitizer 136, a polarizer 138, and low-pass filters LPF1 and LPF2 for noise removal.

A polarizer 138 is inserted in front of the second detector 134. The polarizer 138 is provided to remove extra orthogonal components when they remain.

The above is the configuration of the spectroscope 100B. Subsequently, the result of actually mounting the spectroscope 100B and evaluating its characteristics will be described.

As the pulsed laser light source 112, a titanium sapphire laser Synergy Pro-WG-KE (repetition frequency 75 MHz, center wavelength 800 nm, bandwidth 230 nm) manufactured by Spectra Physics was used. As the long pass filter 116, FELH0700 manufactured by Thorlabs is used.

The energy of the first pulse 2A of the reference arm is 2.5 nJ, and the energy of the second pulse 2B of the scan arm is 5.5 nJ. They are focused on a 30-micron GaSe crystal (GaSe-30H1 by EKSMA OPTICS) by an off-axis radial mirror with a focal length of 25.4 mm on the input side of the focusing optical system 170, and have the same focal length of 25.4 mm. It is collimated by an off-axis radial mirror on the output side.

In the first dispersion compensator 150, the optical path length of the near-infrared double pulse to the sample SMP is about 30 cm longer than the optical path length of the infrared double pulse to the sample SMP, whereby near red. Raman scattering and infrared absorption can be separated and measured as separate phenomena by suppressing the interaction between external pulses and infrared pulses.

The total energy of the near-infrared double pulse 2 incident on the sample SMP is 3.5 nJ, and the breakdown is 1.1 nJ for the first pulse 2A and 2.4 nJ for the second pulse 2B.

As a sample holder, a KBr (potassium bromide) window having a thickness of 3 mm was used. KBr is transparent to both near infrared (10870-14490cm ^-1 ) and mid-infrared (790-1800cm ^-1 ). A 50 μm Teflon® spacer is provided between the two KBr windows and a liquid sample is filled between them. ZnSe (zinc selenide) is used as the dichroic mirror DM1. The first detector 132 is an avalanche photodetector (Thorlabs APD410A2 / M), and the second detector 134 is a nitrogen-cooled HgCdTe detector (Kolmar Technologies KDL-0.5-J1-3 /). 11). For anti-Stokes detection, the original incident pulse and second harmonic signal are removed by a short pass filter SPF (Thorlabs FESH0700) and a long pass filter (Thorlabs FESH0550). The digitizer 136 uses ATS9440 manufactured by AlazarTech.

FIG. 7 is a diagram showing spectra of a near-infrared double pulse 2 and an infrared double pulse 4. A near-infrared ultrashort pulse titanium sapphire laser having a spectrum of 700 to 920 nm with a spectrum of 700 to 920 nm is used as the pulsed laser light source 112, and GaSe is used as the nonlinear optical crystal 120. It can be seen that an infrared (mid-infrared) spectrum of 790 to 1800 cm ^-1 can be obtained by generating a difference frequency in the pulse. The spectrum on the long wavelength side of mid-infrared drops sharply near 900 nm, but this is due to the limitation of the wavelength sensitivity of the detector used to measure the spectrum, and in reality, it is mid-red. The outer spectrum extends to the longer wavelength side.

FIG. 8 is a diagram showing the measurement results of Fringe-resolved Autocorrelation of the near-infrared pulse. From this measurement result, it can be seen that the minimum compensation is about 12 fs.

In CVS, when the delay amount of the first pulse 2A and the second pulse 2B is small, the influence of the non-linear interaction between the first pulse 2A and the second pulse 2B appears in the generation of the difference frequency in the nonlinear optical crystal 120. It is preferable to compensate for this interaction because it causes distortion of the spectrum after the Fourier transform.

9 (a) to 9 (c) are diagrams illustrating compensation for spectral distortion. FIG. 9A shows the uncorrected time waveform DW2 obtained by the photodetector. The time waveform obtained by CVS contains several components in addition to the linear MIR interferogram. The unwanted component is due to the mid-infrared light generated when the two near-infrared pulses overlap in time in the nonlinear optical crystal. This is understood by the analogy with differential frequency generation type interferometric autocorrelation. FIG. 9A shows the AC component of the waveform obtained by the CVS measurement. It contains several components such as intensity autocorrelation, high frequency fringes added to the MIR interferogram. Therefore, the spectrum obtained by Fourier transforming this waveform contains some parts as shown by the broken line. The lowest frequency side (long wavelength side) near the zero frequency is due to the slowly changing intensity autocorrelation waveform (shown in FIG. 9A), which is around 12,500 cm ^-1 and 25, The spectral component near 000 cm ^-1 is the high frequency fringe corresponding to the fundamental wave and the second harmonic of the near infrared pulse. The mid-infrared spectrum of interest appears over 790-1800 cm ^-1 . Since the mid-infrared spectrum is sufficiently separated from other frequency components in the frequency domain, the mid-infrared spectrum can be extracted from the spectrum obtained by simply Fourier transforming the waveform of FIG. 9A.

Unwanted components may be removed from the mid-infrared interferrogram. The high frequency spectrum is far enough away from the mid-infrared spectrum and can be removed by a low pal filter. Further, the intensity autocorrelation component can be obtained by fitting from the raw waveform of FIG. 9A, and it may be subtracted from the raw waveform. FIG. 9B shows the interferogram restored by removing unwanted components. In FIG. 9 (c), the spectrum obtained by Fourier transforming the interferogram of FIG. 9 (b) is shown by a solid line. This waveform restoration is useful in situations where it is necessary to measure the mid-infrared spectrum at low frequencies (frequency lower than 850 cm ^{-1 in} this example).

A sample (toluene) was measured using the mounted spectroscope 100B. 10 (a) and 10 (b) are diagrams showing the measurement results. FIG. 10A shows digital waveforms CVS-IR (corresponding to the above-mentioned DW2) and CVS-Raman (corresponding to the above-mentioned DW1) generated by the detection system 130. As is clear from FIG. 10A, it can be seen that the peaks of the two waveforms occur at the same timing, and therefore infrared spectroscopy and Raman spectroscopy are performed at the same time. Since the movable mirror M2 is reciprocated in the Michelson interferometer 114B, the digital waveforms CVS-IR and CVS-Raman can obtain waveforms inverted in the time axis direction on the outward path and the return path.

The upper part of FIG. 10B shows an interferogram (corresponding to the above-mentioned IF_IR) obtained from the waveform CVS-IR of FIG. 10A. Specifically, an interferogram can be obtained by cutting out only the waveform of the outward path (or the return path) from the waveform CVS-IR for a plurality of cycles (15 cycles in this case) and averaging them. When generating the interferogram, the horizontal axis is converted to the optical path length difference L.

Further, in the lower part of FIG. 10B, the interferogram obtained from the waveform CVS-Raman of FIG. 10A is shown. The interferogram can be obtained by performing the same processing as CVS-IR for the waveform CVS-Raman.

11 (a) and 11 (b) are diagrams showing complementary spectra obtained by Fourier transforming the interferogram of FIG. 10 (b). In FIG. 11A, what is shown as Reference is the result obtained by general FT-IR. Further, in FIG. 11B, what is shown as a reference is a result obtained by a spontaneous Raman scattering spectroscope.

12 (a) to 12 (c) show the spectra measured for a mixed solution of benzene, chloroform, benzene and DMSO (mixing ratio 4: 1). The infrared, an area of 800 ~ 1700 cm ^-1, CARS is measured region of 3100 cm ^-1 from 600 cm ^-1, C-H vibrations of benzene from 667 cm ^-1 is a C-Cl vibration of chloroform It covers 3063 cm ^-1 . It can be seen that the characteristic Raman / IR peak can be measured in each spectrum.

Although the present invention has been described using specific terms and phrases based on the embodiments, the embodiments show only one aspect of the principles and applications of the present invention, and the embodiments are claimed. Many modifications and arrangement changes are permitted within the range not departing from the idea of the present invention defined in the scope.

(Modification example 1)
FIG. 13 is a diagram showing the spectroscope 100C according to the first modification. In the spectroscope 100C, the nonlinear optical crystal 120 is incorporated in the double pulse generator 110C. Specifically, the nonlinear optical crystal 120 is provided between the pulsed laser light source 112 and the Michelson interferometer 114, and an infrared pulse 11 is generated in front of the Michelson interferometer 114. The Michelson interferometer 114 branches the near-infrared ultrashort pulse 10 and the infrared pulse 11 into two arms to generate the near-infrared double pulse 2 and the infrared double pulse 4.

In this modification 1, it is necessary to configure the Michelson interferometer 114 so that the transmittance is high in a wide wavelength range from the near infrared to the infrared region, which is not easy with today's technology, but future technological progress. It can be said that the technology can be adopted by. The first modification has the advantage that the correction of the interferogram IF_IR described with reference to FIG. 9 is unnecessary. Further, the second dispersion compensator 118 shown in FIG. 6 is also unnecessary.

In the first modification, the Michelson interferometer 114 may adopt the configuration shown in FIG. 6 or the configuration shown in FIG. 4.

(Modification 2)
FIG. 14 is a diagram showing the spectroscope 100D according to the second modification. The double pulse generator 110D is constructed based on the dual comb spectroscopic architecture. Specifically, the double pulse generator 110D includes two

pulse light sources

112A and 112B, and the phase difference of the near

infrared pulses

2A and 2B generated by the two

pulse light sources

112A and 112B can be controlled. There is. The two near-

infrared pulses

2A and 2B are combined to generate a near-infrared double pulse 2. The nonlinear optical crystal 120 is irradiated with the near-infrared double pulse 2 to generate the infrared double pulse 4.

(Modification 3)
The configuration of the interferometer 114 is not limited to those described in the embodiment, and the architecture of high-speed scan FTS (Fourier transform spectroscopy) and phase control FTS is introduced to increase the speed and improve the acquisition speed of the continuous spectrum. You may let me. Specifically, it may be combined with the description described in Patent Document 1. Alternatively, the interferometer 114 may be configured by using an optical fiber or a waveguide.

(Modification example 4)
The second detector 134 may be implemented by introducing an EO-sampling architecture. In this case, the spectral region of the measurable infrared transmitted light 8 can be further expanded. Further, when EO sampling is introduced, the first detector 132 and the second detector 134 may be integrally configured.

(Modification 5)
Nonlinear optical crystal 120 is not limited to GaSe, LBO (lithium Torihou acid), KDP (potassium dihydrogen phosphate), BBO (barium borate), KD * P (potassium phosphate), LiNbO ₃ (lithium niobate ), CLBO (CsLiB ₆ O ₁₀ ) and the like can be used. The type of crystal may be selected in consideration of the required band and strength. Further, the spectral width of the infrared double pulse 4 may be further widened by using a combination of a plurality of different nonlinear optical crystals.

(Modification 6)
A laser other than titanium sapphire may be used as the pulsed laser light source 112, and the wavelength of the near-infrared double pulse 2 may be different from that of titanium sapphire.

(Modification 7)
In the embodiment, the optical path length of the near-infrared double pulse 2 to the sample SMP and the optical path length of the infrared double pulse 4 to the sample SMP are different, but they are not limited to the same. May be good. In this case, it may be possible to measure the behavior of unknown molecules or non-linear effects due to the interaction between near-infrared pulses and infrared pulses.

(Modification 8)
In the nonlinear optical crystal 120, a double pulse of a near-infrared second harmonic (wavelength around 400 nm) is also generated. Therefore, the detection system 130 may be configured to be able to detect the light obtained by irradiating the sample SMP with a double pulse of the second harmonic. For example, in this modification, it is also possible to measure two-photon absorption and the like.

Further, the near-infrared spectroscopy (that is, the absorption spectrum in the near-infrared region) may be measured by the spectroscope 100.

(Modification 9)
In the above-mentioned spectroscope, the band of the infrared spectrum obtained by generating the differential frequency within the pulse is limited by the phase matching condition of the nonlinear optical crystal. Therefore, the band as a complementary vibration spectrum is limited to the fingerprint region of 800 to 1800 cm ^-1 . Therefore, there is a possibility that the band of the infrared spectrum can be expanded by reducing the thickness of the nonlinear optical crystal 120, but there is a problem that the output of the mid-infrared light generated as a compensation is reduced. Modification 9 describes the extension of the infrared spectrum.

FIG. 15 is a diagram showing the spectroscope 100E according to the modified example 9. The spectroscope 100E includes a plurality of different nonlinear optical crystals 120 (two in this example). The plurality of nonlinear crystals 120_1 and 120_2 are provided after the double pulse generator 110, but may be provided inside the double pulse generator 110 as described above.

Near infrared double pulse 2 is applied to a plurality of nonlinear optical crystals 120_1 and 120_2. In each of the nonlinear optical crystals 120_1 and 120_2, a difference frequency between different spectral components contained in the near-infrared pulse 2A (2B) is generated, whereby an infrared double pulse 4 having a wide-band spectrum is generated.

The mid-infrared spectrum band of this double pulse 4 is significantly expanded as compared with the case where only one type of nonlinear optical crystal 120 is used. A method using a plurality of nonlinear optical crystals as in the modified example 9 is called a cascade method.

FIG. 16A is a diagram illustrating the generation of the intra-pulse difference frequency by one nonlinear optical crystal 120, and FIG. 16B is a diagram showing the generation of the cascade-type intra-pulse difference frequency by the two nonlinear optical crystals 120. It is a figure explaining. In FIG. 16A, GaSe is used as the nonlinear optical crystal 120, and in FIG. 16B, lithium iodate crystals (LiIO ₃ ) and GaSe are used as the nonlinear optical crystals 120_1 and 120_2. The cascaded pulse in difference frequency generation, it is possible to obtain a wide-band spectrum covering of H 2 _O absorption region and the CO ₂ absorbing region.

FIG. 17 is a diagram showing a specific configuration example of the spectroscope 100E. The configurations of the double pulse generator 110 and the detection system 130 are the same as those in FIG. The near-infrared double pulse generated by the double pulse generator 110 is incident on the nonlinear optical crystal 120_1 which is LiIO ₃ and is wavelength-converted. The mid-infrared light (MIR) generated from the nonlinear optical crystal 120_1 is once separated from the near-infrared light, and only the near-infrared light NIR is incident on the nonlinear optical crystal 120_2 which is the subsequent GaSe. It is preferable that the near-infrared light NIR after separation is dispersed and compensated as necessary before being incident on the nonlinear optical crystal 120_2.

The mid-infrared light generated from the nonlinear optical crystals 120_1 and 120_2 are wavelengthally and spatially coupled by the reflection and transmission characteristics of the long-pass filter, respectively, and are applied to the sample SMP.

Considering from the transmission wavelength range of the crystal, it is possible in principle to generate a cascade type intra-pulse difference frequency without spatially separating the mid-infrared light in the order of LiIO ₃ and Gase. For example, it is possible to take a structure in which two crystals are joined. In this case, the mid-infrared light generated by LiIO3 in the previous stage passes through the Gase crystal as it is.

FIG. 18 is a diagram showing a specific implementation of the spectroscope 100E of FIG. The configuration of the double pulse generator 110 and the detection system 130 is similar to that of FIG.

The focusing optical system 170 focuses the near-infrared double pulse 2 generated by the double pulse generator 110 on the nonlinear optical crystal 120_1, and also passes through the nonlinear optical crystal 120_1 to the near-infrared double pulse 2 and the infrared double pulse. Collimate 4 As described above, the condensing optical system 170 can be configured by an off-axis parabolic mirror (OAPM).

The near-infrared double pulse 2 and the infrared double pulse 4 collimated by the condensing optical system 170 are separated by the dichroic mirror DM2. The pulse width of the near-infrared double pulse 2 expanded by passing through the nonlinear optical crystal 120_1 is compressed by the chirped mirror pair CMP3. The condensing optical system 172 condenses the near-infrared double pulse 2 whose pulse width is compensated on the nonlinear optical crystal 120_2, and passes through the nonlinear optical crystal 120_2 to the near-infrared double pulse 2 and the mid-infrared double pulse 3. Collimate.

The dichroic mirror DM3 separates the near-infrared double pulse 2 and the mid-infrared double pulse 3. The pulse width of the near-infrared double pulse 2 is compressed by the chirped mirror pair CMP1. The mid-infrared

double pulses

3 and 4 are combined with the original near-infrared double pulse 2 via a 6 μm long-pass filter LPF and a dichroic mirror DM4.

The above is an example of mounting the spectroscope 100E. Next, the results of an experiment of complementary vibration spectroscopy using cascaded intra-pulse differential frequency generation will be described.

19 (a) to 19 (c) are diagrams showing the spectra obtained by the spectroscope 100E of FIG. 19 (a) to 19 (c) are measurement results using toluene, chloroform, and phenylacetylene as samples, respectively. Each spectrum is an average of the results of 25 measurements. The peaks appearing at 765 cm ^-1 and 819 cm ^-1 are Raman spectra derived from LiIO ₃ crystals, not samples.

As can be seen from this result, in a single nonlinear optical crystal, the mid-infrared spectrum limited to 800 to 1800 cm ^-1 is adopted by cascade type intra-pulse differential frequency generation using two nonlinear optical crystals. As a result, it can be seen that it can be expanded to 800 to 2900 cm ^-1 . As a result, CVS-IR can obtain an ultra-wideband spectrum of a fingerprint region, a silent region, and a CH expansion / contraction vibration region in the same manner as CVS-Raman.

In the modified example 9, two types of nonlinear optical crystals were used, but three or more types of nonlinear optical crystals may be used.

Further, the plurality of nonlinear optical crystals may be made of the same material. In this case, by optimizing the thickness, incident angle, etc. of each nonlinear optical crystal, the band satisfying the phase matching condition can be widened as compared with the case of using one nonlinear optical crystal, thereby expanding the spectrum. Can be widened.

Although the present invention has been described using specific terms based on the embodiments, the embodiments merely indicate the principles and applications of the present invention, and the embodiments are defined in the claims. Many modifications and arrangement changes are permitted without departing from the ideas of the present invention.

The present invention relates to a spectroscope.

100 Spectrometer SMP sample 110 Double pulse generator 112 Pulse laser light source 114 Michaelson interferometer 116 Long path filter 118 Second dispersion compensator 120 Non-linear optical crystal 130 Detection system 132 First detector 134 Second detector 136 Digitizer 138 Polarizer SPF Short Path Filter DM1 Dycroic Mirror 140 Signal Processing Unit 150

1st Dispersion Compensator

160, 170 Condensing Optical System 2 Near Infrared Double Pulse 2A 1st Pulse 2B 2nd Pulse 4 Infrared Double Pulse 4A 1st Pulse 4B 2nd Pulse 6 Raman scattered light 8 Infrared transmitted light 10 Ultra-short pulse

Claims

A double pulse generator that generates a first double pulse with a variable delay amount,
Non-linear optical crystals provided inside or after the double pulse generator,
Raman scattered light obtained by irradiating a sample with the first double pulse and infrared rays obtained by irradiating the sample with an infrared second double pulse generated by the nonlinear optical crystal can be measured. System and
A spectroscope characterized by comprising.
The double pulse generator
With a pulsed laser light source that produces pulsed light,
An interferometer that receives the pulsed light and generates the first double pulse,
The spectroscope according to claim 1, wherein the spectroscope comprises.
The spectroscope according to claim 2, wherein the nonlinear optical crystal is arranged after the interferometer.
The spectroscope according to claim 3, further comprising a first dispersion compensator which is provided after the nonlinear optical crystal and compresses the pulse width of the pulse included in the first double pulse.
A signal processing unit that processes the output of the detection system is further provided.
The spectroscope according to claim 3 or 4, wherein the signal processing unit corrects an infrared interferogram.
The detection system is
A dichroic mirror that separates the transmitted light of the sample into the wavelength region and infrared region of the first double pulse.
The first detector having sensitivity in the wavelength range of the first double pulse, and
The second detector having sensitivity in the infrared region and
The spectroscope according to any one of claims 1 to 5, wherein the spectroscope comprises.
The spectroscope according to claim 6, wherein the detection system includes a polarizer inserted in front of the second detector.
Any of claims 3 to 5, wherein the double pulse generator further includes a second dispersion compensator that compresses the pulse width of the pulse included in the first double pulse incident on the nonlinear optical crystal. The spectroscope described in.
The spectroscope according to any one of claims 1 to 8, further comprising a condensing optical system that irradiates a sample with the first double pulse that has passed through the nonlinear optical crystal.
The spectroscope according to claim 9, wherein the condensing optical system coaxially condenses the first double pulse and the second double pulse on the sample.
The spectroscope according to any one of claims 1 to 10, wherein the optical path length of the first double pulse to reach the sample and the optical path length of the second double pulse to reach the sample are different.
The spectroscope according to any one of claims 1 to 10, wherein the optical path length of the first double pulse to reach the sample is equal to the optical path length of the second double pulse to reach the sample.
The detection system is characterized in that the light obtained by irradiating the sample with a double pulse of a second harmonic and / or a third harmonic generated in the nonlinear optical crystal can be detected. Item 4. The spectroscope according to any one of Items 1 to 12.
The spectroscope according to any one of claims 1 to 13, wherein when the nonlinear optical crystal is a first nonlinear optical crystal, a second nonlinear optical crystal is further provided.
The spectroscope according to claim 14, wherein the first nonlinear optical crystal is LiIO 3 , and the second nonlinear optical crystal is GaSe.