WO2014125775A1 - Infrared spectrum measuring device and method - Google Patents

Infrared spectrum measuring device and method Download PDF

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WO2014125775A1
WO2014125775A1 PCT/JP2014/000368 JP2014000368W WO2014125775A1 WO 2014125775 A1 WO2014125775 A1 WO 2014125775A1 JP 2014000368 W JP2014000368 W JP 2014000368W WO 2014125775 A1 WO2014125775 A1 WO 2014125775A1
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light pulse
infrared light
spectrum
infrared
pulse
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PCT/JP2014/000368
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French (fr)
Japanese (ja)
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貴夫 藤
雄高 野村
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大学共同利用機関法人自然科学研究機構
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Priority to JP2015500127A priority Critical patent/JP6281983B2/en
Publication of WO2014125775A1 publication Critical patent/WO2014125775A1/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
    • G01J3/28—Investigating the spectrum
    • G01J3/42—Absorption spectrometry; Double beam spectrometry; Flicker spectrometry; Reflection spectrometry
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
    • G01J3/02—Details
    • G01J3/0205—Optical elements not provided otherwise, e.g. optical manifolds, diffusers, windows
    • G01J3/0208—Optical elements not provided otherwise, e.g. optical manifolds, diffusers, windows using focussing or collimating elements, e.g. lenses or mirrors; performing aberration correction
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/35—Non-linear optics
    • G02F1/353—Frequency conversion, i.e. wherein a light beam is generated with frequency components different from those of the incident light beams
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/35—Non-linear optics
    • G02F1/353—Frequency conversion, i.e. wherein a light beam is generated with frequency components different from those of the incident light beams
    • G02F1/3536—Four-wave interaction
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/35—Non-linear optics
    • G02F1/355—Non-linear optics characterised by the materials used

Definitions

  • the present invention relates to an infrared spectrum measuring apparatus and method, and more particularly to an apparatus and method for measuring a high band infrared spectrum at high speed and high sensitivity.
  • the absorption wavelength of the molecule is in the infrared range. Infrared range resonance for many molecular vibrations (e.g., resonance wave number of CO stretching vibration of protein 1650 cm -1, resonance wave number of the CH stretching vibration of lipids, 2900 cm -1, resonance wave number of the OH stretching vibration of water, It is 3400 cm -1 ). Therefore, by irradiating infrared light to a substance (gas, liquid, solid) and measuring the spectrum of reflected light or transmitted light, the composition and structure of the substance are revealed nondestructively and unstained.
  • a substance gas, liquid, solid
  • FT-IR Fourier transform infrared
  • Visible light has a large energy, and in the visible range, the SN ratio of a detector (for example, a photomultiplier) is high. Therefore, recently, a visible light conversion measurement technique has been developed that converts infrared light into visible light and measures it with a visible light detector (see, for example, Non-Patent Document 2).
  • a visible light conversion measurement technique has been developed that converts infrared light into visible light and measures it with a visible light detector (see, for example, Non-Patent Document 2).
  • a measured infrared light pulse spectrum is obtained as follows. First, an infrared light pulse to be measured and a reference light pulse are mixed and incident on the nonlinear optical crystal, and the infrared light pulse to be measured is converted into a visible light pulse. The converted visible light pulse is detected by a visible light detector. The detected visible light pulse spectrum data is calculated by a recovery algorithm to obtain a measured infrared light pulse spectrum.
  • the infrared light pulse to be measured is converted into a visible light pulse by using the non-linear optical characteristics of the solid crystal.
  • P NL is nonlinear polarization
  • E is an electric field
  • ⁇ (2) is a second-order nonlinear susceptibility
  • ⁇ (3) is a third-order nonlinear susceptibility.
  • This technology uses the following physical phenomena. That is, when an electromagnetic wave is incident on the dielectric medium, polarization occurs and an electric dipole is formed. Since the electric field of the electromagnetic wave is sinusoidally oscillated, the formed dipole also oscillates to emit the electromagnetic wave.
  • the dielectric medium is a solid crystal
  • infrared light is easily converted to visible light because the nonlinear susceptibility is large, but the solid crystal has a narrow transmission wavelength range, and the bandwidth of the measured spectrum is about 600 cm ⁇ 1 ( The spectrum width in the infrared region is as narrow as 4.6-5.6 ⁇ m). Therefore, in the conventional visible light conversion measurement technology, resonance due to various molecular vibrations could not be widely captured.
  • the present invention has been made in view of the above problems, and an object of the present invention is to provide a measuring apparatus and method capable of measuring a wide-band infrared light spectrum.
  • the gaseous medium has a weak interaction with light because of its low density, and, for example, ⁇ (3) of air is as small as 100,000 times smaller than that of the MgO crystal. Therefore, the inventors considered that it is difficult to perform wavelength conversion with gas, and conducted wavelength conversion experiments using solid crystals.
  • the present invention was created from the fact that the inventors noticed that a signal was output even if they accidentally removed a solid crystal from the experimental system. It should be noted that even when the solid crystal is removed, the signal is produced because the incident light intensity is so high that the experimental conditions of the inventors even cause air to have a nonlinear optical effect. That is, the present invention is created as a coincidence happens twice.
  • the infrared spectrum measuring apparatus which has been made to solve the above-mentioned problems, is characterized in that the measured infrared light pulse and the reference light pulse are mixed and incident, and the measured infrared light pulse is visible by the nonlinear optical effect. It has a gas medium which up-converts to a light pulse, and a spectroscope which disperses the visible light pulse up-converted by the gas medium to acquire visible light pulse spectrum data.
  • the absorption of light by the gaseous medium is less than the absorption of light by the solid medium, and the transmission wavelength band of the gaseous medium is wider than the transmission wavelength band of the solid medium.
  • a wide-band infrared light spectrum can be measured because a gas medium having a wide transmission wavelength band is used as a medium for up-converting an infrared light pulse to a visible light pulse by the nonlinear optical effect.
  • the above infrared light spectrum measuring apparatus has a recovery operation means for obtaining the infrared light pulse spectrum to be measured by calculating the visible light pulse spectrum data acquired by the spectroscopic device according to a predetermined recovery algorithm. It is also good.
  • the infrared spectrum measuring apparatus may further include a multiplexer for multiplexing the measured infrared light pulse and the reference light pulse. This improves the efficiency of up-converting the measured infrared light pulse to the visible light pulse.
  • the infrared spectrum measuring apparatus may include a focusing optical system which focuses the measured infrared light pulse and the reference light pulse on the gas medium. By focusing, the light intensity in the focusing region is increased, and high-order nonlinear optical effects of the gas medium can be easily induced.
  • the to-be-measured infrared light pulse is a coherent light pulse.
  • the gas medium becomes a high-order nonlinear optical medium.
  • the measured infrared light pulse may be an ultra-wide band light pulse having a bandwidth of 500 to 5000 cm -1 .
  • the infrared light spectrum with a wavelength range of 2-20 ⁇ m is measured, resonances due to various molecular vibrations can be widely captured.
  • the reference light pulse may be a chirped light pulse or a picosecond pulse of a single wavelength. This allows spectra to be measured with high frequency resolution. If the reference light pulse is a chirped light pulse, the measured infrared light spectrum can be reproduced with higher resolution by precise measurement of the chirp amount (time change of frequency).
  • the non-linear optical effect may be a third-order non-linear optical effect.
  • the infrared light pulse to be measured can be converted into a visible light pulse.
  • the gas medium may be xenon gas.
  • the xenon gas is a gas with a large non-linear coefficient, and the measured infrared light pulse can be upconverted at high efficiency.
  • the infrared spectrum measuring method of the present invention which has been made to solve the above problems, is characterized in that the measured infrared light pulse and the reference light pulse are mixed and incident in the gas medium, and the nonlinear optical effect of the gas medium is obtained. It has an up-conversion step of converting a measured infrared light pulse into a visible light pulse, and a spectroscopy step of separating the visible light pulse converted in the up-conversion step to acquire visible light pulse spectrum data.
  • the above infrared light spectrum measuring method may have a spectrum recovery step of recovering the spectrum of the measured infrared light pulse by using a predetermined recovery algorithm for the visible light pulse spectrum data acquired in the spectroscopy step. .
  • the measured infrared light pulse may be a coherent light pulse.
  • the measured infrared light pulse may be an ultra-wide band light pulse having a bandwidth of 500 to 5000 cm -1 .
  • the reference light pulse may be a chirped light pulse or a picosecond pulse of a single wavelength. Further, when the reference light pulse is a chirped light pulse, it is preferable to measure the chirp amount (time change of frequency).
  • the non-linear optical effect may be a third-order non-linear optical effect.
  • the gas medium may be xenon gas.
  • a wide-band infrared light spectrum can be measured because a gas medium with a wide transmission wavelength range is used as the medium for up-converting the measured infrared light pulse into a visible light pulse by the nonlinear optical effect.
  • FIG. 1 is a block diagram of an infrared spectrum measuring apparatus according to an embodiment of the present invention.
  • the infrared spectrum measuring apparatus 1 includes a multiplexer 11, a condensing optical system 12, a gas medium 13, a visible spectroscope 14, and a recovery operation means 15. Of these components, the coupler 11 and the focusing optical system 12 can be omitted.
  • a multiplexer 11 for multiplexing the reference optical pulse L r and the measured infrared light pulse L IR is perforated mirror, two-color mirror, a polarizing beam splitter or the like can be used.
  • a lens, a parabolic mirror or the like may be used for the condensing optical system 12.
  • the gas medium 13 is preferably a gas that is transparent in the visible to infrared region.
  • the gas medium 13 may be air, but since air has strong absorption by CO 2 molecules in the vicinity of 4 ⁇ m and 8 ⁇ m, inert gas (argon, xenon, neon, etc.) that absorbs less than air is preferable.
  • inert gas argon, xenon, neon, etc.
  • xenon gas is particularly preferred.
  • the gaseous medium may be jetted out from a cylinder (not shown) to the condensing area S by the condensing optical system 12, the gaseous medium is diffused into the air, so the concentration of the gaseous medium 13 is kept high. I can not do it.
  • the gas medium from the cylinder is injected into a cylinder having a hole through which light collected by the light collection optical system 12 passes.
  • a band pass filter 16 transmits only the visible light pulse Lv up-converted from the measured infrared light pulse L IR by the nonlinear optical effect of the gas medium 13.
  • a lens 17 collimates the visible light pulse Lv.
  • the spectroscope 14 is a spectroscope in the visible region, and includes a prism or a diffraction grating and a CCD (or a photodiode array) for photoelectrically converting a spatial distribution of diffracted light.
  • the recovery operation means 15 is a computer and performs the operation shown in FIG. That is, in step S 11, the visible light pulse Lv up-converted by the gas medium 13 is converted into data by the spectroscope 14, and the spectrum data is acquired by the recovery calculation unit 15. In the subsequent step S12, the spectrum (wavelength) data acquired in step S11 is converted into spectrum (frequency) data.
  • step S13 spectral (frequency) data is inverse Fourier transformed.
  • step S14 assuming that the phase of the reference light pulse L r in the time domain is ⁇ (t), the phase ⁇ (t) from the portion of t> 0 in the time domain in the inverse Fourier transformed spectral data, From the portion of t ⁇ 0, phase correction is performed by subtracting the phase - ⁇ (-t).
  • the phase-corrected spectrum data is Fourier-transformed in step S15 to form a measured infrared light pulse spectrum.
  • the infrared absorption spectrum of the sample 100 can be measured at high speed by the spectroscope in the visible range by irradiating the sample 100 indicated by the dotted line with the measured infrared light pulse L IR generated from the infrared light pulse generating means 10. .
  • the non-linear optical effect of the gas medium 13 depends on the intensity (power per unit area, ie, W / cm 2 ) of light injected into the gas medium, and higher order non-linear optics are provided to the gas medium 13 as the intensity increases. An effect is induced.
  • the pulse width of L r and L IR should be short.
  • the pulse width is preferably femtosecond to picosecond.
  • the intensity of light injected into the gas medium 13 becomes higher as L r and L IR are smaller and condensed by the condensing optical system 12.
  • the condensing spot diameter of L r and L IR by the condensing optical system 12 depends on the focal length of the condensing optical system 12 and the coherency of Lr and L IR . Therefore, the focal length of the focusing optical system 12 may be 50 mm, and more preferably 25 mm.
  • the power required for wavelength conversion by the nonlinear optical effect of the gas medium depends on the type of gas and the measurement time, but according to the experiments of the inventors, it is as follows.
  • a third-order nonlinear optical effect is induced. That is, in this case, assuming that the angular frequency of the reference light pulse L r is ⁇ 1 , the third-order nonlinear optical effect (four-wave difference frequency generation: ⁇ 1 + ⁇ 1 - ⁇ 0 ⁇ ⁇ 2 ) occurs and the angular frequency is ⁇ 1 of the measured infrared light pulse L IR ( ⁇ 1), the angular frequency is up-converted to omega 2 of the visible light pulse L V ( ⁇ 2).
  • I r 2 ⁇ I IR 4.4 ⁇ 10 36 W 3 / cm 6
  • the power required for wavelength conversion by the nonlinear optical effect of the gas medium is I r 2 ⁇
  • the power is such that the I IR is 4.4 ⁇ 10 36 W 3 / cm 6 or more.
  • the measured infrared light pulse L IR may be an ultra-wide band (500 to 5000 cm ⁇ 1 ) light pulse. If the measured infrared light pulse L IR is in the ultra-wide band (500 to 5000 cm -1 ), the infrared light spectrum in the wavelength range of 2 to 20 ⁇ m can be measured, so resonances due to various molecular vibrations are widely caught. Can be
  • An off-axis parabolic mirror 22 focuses the combined light pulse L 1 ( ⁇ 1 ) + L 2 ( ⁇ 2 ) into the gas medium 23.
  • a collimator 24 is an off-axis parabolic mirror.
  • 25 is a filter.
  • Ultra-short light pulses (wavelength: 800 nm, pulse width: 25 fs, pulse energy: 0.7 mJ, repetition frequency: 1 KHz) from mode-locked Ti: sapphire laser, BBO ( ⁇ -BaB 2 O 4 with a thickness of 0.1 mm) 2.)
  • the crystal was made incident and a second harmonic light pulse was generated.
  • the second harmonic light pulse is L 2 ( ⁇ 2 ), and the fundamental wave light pulse is L 1 ( ⁇ 1 ).
  • the pulse width of the fundamental wave light pulse L 1 ( ⁇ 1 ) is 25 fs
  • the pulse energy is 675 ⁇ J
  • the wavelength of the second harmonic light pulse L 2 ( ⁇ 2 ) is 400 nm
  • the pulse width is 25 fs
  • the pulse energy is 25 ⁇ J.
  • the fundamental wave light pulse L 1 ( ⁇ 1 ) and the second harmonic light pulse L 2 ( ⁇ 2 ) are combined by the two-color mirror 21 and collected in the argon gas 23 by the off-axis parabolic mirror 22 having a focal length of 150 mm. It is lighted. Then, four-wave mixing ( ⁇ 1 + ⁇ 1 - ⁇ 2 ⁇ ⁇ 0 ) occurs due to filamentation of argon gas, and from the filter 25 transmitting only light of ⁇ 0 , four-wave mixed light pulse L 0 ( ⁇ 0 ) Is obtained.
  • the band of the four-wave mixed light pulse L 0 ( ⁇ 0 ) is, as shown in FIG. 4, 200-6000 cm -1 (1.7-50 ⁇ m in wavelength) in wavenumber, and is an ultra-wide band.
  • the pulse width of the light pulse L 0 ( ⁇ 0 ) was 6.9 fs.
  • the reference light pulse Lr may be a chirped light pulse.
  • the reference light pulse is a chirped light pulse or a single wavelength picosecond pulse
  • the spectrum can be measured with high frequency resolution.
  • the delay time for sweeping is increased, the frequency resolution is improved. Therefore, according to the same logic, the longer the pulse width of the reference light pulse, the more the frequency resolution is improved.
  • the pulse time width of the reference light pulse may be extended by, for example, a diffraction grating stretcher.
  • the reference light pulse is a chirped light pulse
  • the above-described four-wave-mixed ultra-wideband light pulse L 0 ( ⁇ 0 ) is defined as a measured infrared light pulse L IR ( ⁇ 0 ).
  • the pulse energy of this measured infrared light pulse L IR ( ⁇ 0 ) is 0.5 ⁇ J.
  • a portion (pulse energy: 0.1 mJ) of a fundamental pulse (wavelength: 800 nm) of a mode-locked Ti: sapphire laser for generating ultra-broadband light pulse L 0 ( ⁇ 0 ) is stretched by a stretcher to obtain a reference light Pulse L r ( ⁇ 1 ) was used.
  • the pulse width of the reference light pulse L r ( ⁇ 1 ) is 10.3 ps.
  • the measured infrared light pulse L IR ( ⁇ 0 ) and the reference light pulse L r ( ⁇ 1 ) are combined by the perforated mirror 11 and condensed onto the xenon gas 13 by the parabolic mirror 12 having a focal distance of 50 mm.
  • the intensity I IR in the focusing region was estimated to be 4 ⁇ 10 16 W / m 2 .
  • the intensity I r in the focusing region of the reference light pulse L r ( ⁇ 1 ) was 2.2 ⁇ 10 12 W / cm 2 .
  • the index of the equation (2) is estimated to be 2 ⁇ 10 37 W 3 / cm 6, and it is expected that the xenon gas 13 induces the third-order nonlinear optical effect.
  • Band pass filter 16 for cutting the measured infrared light pulse L IR ( ⁇ 0 ) at 200-6000 cm -1 (wavelength 1.7 to 50 ⁇ m) in wave number and the reference light pulse L r ( ⁇ 1 ) at wavelength 800 nm
  • the light path that has passed through is measured by the visible region spectrometer 14 equipped with a camera EMCCD (ProEM + 1600, Princeton Instrument). The camera was synchronized to the repetition rate (1 kHz) of a mode-locked Ti: sapphire laser and spectra were measured on a single shot ( ⁇ 1 ms).
  • the measured spectrum is shown in FIG.
  • the non-linear optical effect induced in the xenon gas 13 is up-conversion by the third-order non-linear optical effect (four-wave difference frequency generation: ⁇ 1 + ⁇ 1 - ⁇ 0 ⁇ ⁇ 2 ).
  • the spectrum waveform obtained by processing the spectrum data of the waveform i of FIG. 5 by the recovery operation means 15 is the waveform b of FIG. From the waveform, CO 2 absorption (wave number: ⁇ 2300 cm -1 , wavelength: ⁇ 4.3 ⁇ m) and water vapor absorption (wave number: ⁇ 1600 cm -1 , wavelength: ⁇ 6.3 ⁇ m and wave number: ⁇ 3700 cm -1 , wavelength : ⁇ 2.7 ⁇ m) is clearly observed.
  • the amount of chirp of the reference light pulse (time change in frequency, ((t)) may be measured in advance. Measure the spectrum of the four-wave difference frequency mixing by sweeping the delay time of the reference light pulse and the infrared light pulse, and measure ⁇ (t) directly from the delay time dependency of the spectrum it can.

Abstract

This infrared spectrum measuring device (1) is characterized by being able to measure a wide band of the infrared spectrum by being provided with a gaseous medium (13) where an infrared pulse being measured LIR and a reference light pulse Lr are incident and mix and which up-converts the infrared pulse being measured LIR to a visible light pulse Lv by a non-linear optical effect, and a spectral device (14) which acquires visible light pulse spectrum data by analyzing the visible light pulse Lv up-converted in the gaseous medium (13).

Description

赤外光スペクトル計測装置及び方法Infrared light spectrum measuring apparatus and method
　本発明は、赤外光スペクトル計測装置と方法に関し、詳しくは、高帯域の赤外光スペクトルを高速、高感度に計測する装置と方法に関する。 The present invention relates to an infrared spectrum measuring apparatus and method, and more particularly to an apparatus and method for measuring a high band infrared spectrum at high speed and high sensitivity.
　分子の吸収波長は赤外領域にある。赤外領域は多くの分子振動に共鳴（例えば、タンパク質のＣＯ伸縮振動の共鳴波数は１６５０ｃｍ－１、脂質のＣＨ伸縮振動の共鳴波数は、２９００ｃｍ－１、水のＯＨ伸縮振動の共鳴波数は、３４００ｃｍ－１である）する。したがって、赤外光を物質（気体、液体、固体）に照射して反射光或いは透過光のスペクトルを測定することにより、その物質の組成や構造が非破壊、無染色で明らかにされる。 The absorption wavelength of the molecule is in the infrared range. Infrared range resonance for many molecular vibrations (e.g., resonance wave number of CO stretching vibration of protein 1650 cm -1, resonance wave number of the CH stretching vibration of lipids, 2900 cm -1, resonance wave number of the OH stretching vibration of water, It is 3400 cm -1 ). Therefore, by irradiating infrared light to a substance (gas, liquid, solid) and measuring the spectrum of reflected light or transmitted light, the composition and structure of the substance are revealed nondestructively and unstained.
これまで、赤外光スペクトルの計測はフーリエ変換型赤外分光（FT-IR）測定装置（例えば、非特許文献１参照）で行われていた。しかし、赤外光は光子エネルギが小さく、検出器（例えば、HgCdTe半導体検出器）が熱雑音の影響を大きく受けるため、FT-IR測定装置の検出感度や測定精度が低かった。また、FT-IR測定装置では、ミラーを精密に掃引する必要があり、赤外光スペクトルを高速に計測することが難しかった。 Heretofore, the measurement of infrared light spectrum has been performed with a Fourier transform infrared (FT-IR) measuring apparatus (see, for example, Non-Patent Document 1). However, since infrared light has small photon energy and a detector (for example, an HgCdTe semiconductor detector) is greatly affected by thermal noise, the detection sensitivity and the measurement accuracy of the FT-IR measurement apparatus are low. In addition, in the FT-IR measurement apparatus, it is necessary to precisely sweep the mirror, which makes it difficult to measure the infrared light spectrum at high speed.
　可視光はエネルギが大きく、可視域では検出器（例えば、光電子増倍管）のＳＮ比が高い。そこで、最近、赤外光を可視光に変換して可視光検出器で計測する可視光変換計測技術が開発された（例えば、非特許文献２参照）。 Visible light has a large energy, and in the visible range, the SN ratio of a detector (for example, a photomultiplier) is high. Therefore, recently, a visible light conversion measurement technique has been developed that converts infrared light into visible light and measures it with a visible light detector (see, for example, Non-Patent Document 2).
　この可視光変換計測技術では、次のようにして被測定赤外光パルススペクトルが得られる。先ず、被測定赤外光パルスと参照光パルスが非線形光学結晶に混合入射され、被測定赤外光パルスが可視光パルスに変換される。変換された可視光パルスが可視光検出器で検出される。検出された可視光パルススペクトルデータが回復アルゴリズムで演算され、被測定赤外光パルススペクトルが得られる。 In this visible light conversion measurement technique, a measured infrared light pulse spectrum is obtained as follows. First, an infrared light pulse to be measured and a reference light pulse are mixed and incident on the nonlinear optical crystal, and the infrared light pulse to be measured is converted into a visible light pulse. The converted visible light pulse is detected by a visible light detector. The detected visible light pulse spectrum data is calculated by a recovery algorithm to obtain a measured infrared light pulse spectrum.
　上記した従来の可視光変換計測技術では、被測定赤外光パルスが固体結晶の非線形光学特性を使って可視光パルスに変換される。この技術は巨視的には媒質の電場に対する非線形応答、すなわち
　ＰNL＝χ（２）;ＥＥ＋χ（３）;ＥＥＥ＋・・・　　　　　　　　　　（１）
に基づく（稲場文男、編集、「レーザーハンドブック」、朝倉書店、１９８２年５月１日刊行、４０５～４２６頁参照）。ここで、ＰNLは非線形分極、Ｅは電場、χ（２）は２次の非線形感受率、χ（３）は３次の非線形感受率である。 In the above-described conventional visible light conversion measurement technology, the infrared light pulse to be measured is converted into a visible light pulse by using the non-linear optical characteristics of the solid crystal. This technique is macroscopically non-linear response to the electric field of the medium, ie, P NL = χ (2) ; EE + χ (3) ; EEE + (1)
(Refer to Fumio Inaba, edited by "Laser Handbook", Asakura Shoten, published May 1, 1982, pages 405-426). Here, P NL is nonlinear polarization, E is an electric field, χ (2) is a second-order nonlinear susceptibility, and χ (3) is a third-order nonlinear susceptibility.
この技術は次のような物理現象を利用している。すなわち、誘電体媒質に電磁波が入射されると、分極が起こり電気双極子が形成される。電磁波の電場は正弦波振動しているので、形成された双極子も振動して電磁波を放出する。 This technology uses the following physical phenomena. That is, when an electromagnetic wave is incident on the dielectric medium, polarization occurs and an electric dipole is formed. Since the electric field of the electromagnetic wave is sinusoidally oscillated, the formed dipole also oscillates to emit the electromagnetic wave.
誘電体媒質が固体結晶の場合、非線形感受率が大きいので、赤外光が可視光に変換されやすいが、固体結晶は透過波長範囲が狭く、計測されるスペクトルのバンド幅が約６００ｃｍ－１（赤外域のスペクトル幅は４．６－５．６μｍ）と狭い。そのため、従来の可視光変換計測技術では、様々な分子振動による共鳴を広く捕えることができなかった。
　本発明は、上記の問題点に鑑みてなされたものであり、広帯域の赤外光スペクトルを計測できる計測装置及び方法を提供することを課題としている。 When the dielectric medium is a solid crystal, infrared light is easily converted to visible light because the nonlinear susceptibility is large, but the solid crystal has a narrow transmission wavelength range, and the bandwidth of the measured spectrum is about 600 cm −1 ( The spectrum width in the infrared region is as narrow as 4.6-5.6 μm). Therefore, in the conventional visible light conversion measurement technology, resonance due to various molecular vibrations could not be widely captured.
The present invention has been made in view of the above problems, and an object of the present invention is to provide a measuring apparatus and method capable of measuring a wide-band infrared light spectrum.
　はじめに、本発明がなされた経緯を説明する。気体媒質は、密度が低いために光との相互作用が弱く、例えば、空気のχ（３）はＭｇＯ結晶の１０万分の１と小さい。そのため、発明者等は、気体で波長変換を行うことは難しいと考え、固体結晶を使って波長変換実験を行った。しかし、発明者等が偶然にも実験系から固体結晶を外しても信号が出ていることに気が付いたことから、本発明が創出された。なお、この固体結晶を外しても信号が出ることは、発明者らの実験条件が偶々空気でも非線形光学効果を起こすほど入射光強度が高かったことによる。すなわち、偶然が２回重なって、本発明は創出されたことになる。 First, the process of making the present invention will be described. The gaseous medium has a weak interaction with light because of its low density, and, for example, χ (3) of air is as small as 100,000 times smaller than that of the MgO crystal. Therefore, the inventors considered that it is difficult to perform wavelength conversion with gas, and conducted wavelength conversion experiments using solid crystals. However, the present invention was created from the fact that the inventors noticed that a signal was output even if they accidentally removed a solid crystal from the experimental system. It should be noted that even when the solid crystal is removed, the signal is produced because the incident light intensity is so high that the experimental conditions of the inventors even cause air to have a nonlinear optical effect. That is, the present invention is created as a coincidence happens twice.
　上記の課題を解決するためになされた本発明の赤外光スペクトル計測装置は、被測定赤外光パルスと参照光パルスとが混合入射されて該被測定赤外光パルスを非線形光学効果で可視光パルスにアップコンバージョンする気体媒質と、前記気体媒質でアップコンバージョンされた前記可視光パルスを分光して可視光パルススペクトルデータを取得する分光装置と、を有する。 The infrared spectrum measuring apparatus according to the present invention, which has been made to solve the above-mentioned problems, is characterized in that the measured infrared light pulse and the reference light pulse are mixed and incident, and the measured infrared light pulse is visible by the nonlinear optical effect. It has a gas medium which up-converts to a light pulse, and a spectroscope which disperses the visible light pulse up-converted by the gas medium to acquire visible light pulse spectrum data.
　気体媒質による光の吸収は、固体媒質による光の吸収より少なく、気体媒質の透過波長帯域は固体媒質の透過波長帯域より広い。非線形光学効果で赤外光パルスから可視光パルスにアップコンバージョンする媒質に、透過波長帯域の広い気体媒質が用いられるので、広帯域の赤外光スペクトルが計測され得る。 The absorption of light by the gaseous medium is less than the absorption of light by the solid medium, and the transmission wavelength band of the gaseous medium is wider than the transmission wavelength band of the solid medium. A wide-band infrared light spectrum can be measured because a gas medium having a wide transmission wavelength band is used as a medium for up-converting an infrared light pulse to a visible light pulse by the nonlinear optical effect.
上記の赤外光スペクトル計測装置は、前記分光装置で取得された前記可視光パルススペクトルデータを所定の回復アルゴルリズムで演算して前記被測定赤外光パルススペクトルを得る回復演算手段を有してもよい。 The above infrared light spectrum measuring apparatus has a recovery operation means for obtaining the infrared light pulse spectrum to be measured by calculating the visible light pulse spectrum data acquired by the spectroscopic device according to a predetermined recovery algorithm. It is also good.
　また、前記赤外光スペクトル計測装置は、前記被測定赤外光パルスと前記参照光パルスとを合波する合波器を備えてもよい。これにより、被測定赤外光パルスから可視光パルスにアップコンバージョンする効率が向上する。 The infrared spectrum measuring apparatus may further include a multiplexer for multiplexing the measured infrared light pulse and the reference light pulse. This improves the efficiency of up-converting the measured infrared light pulse to the visible light pulse.
　また、前記赤外光スペクトル計測装置は、前記被測定赤外光パルスと前記参照光パルスとを前記気体媒質に集光する集光光学系を備えるとよい。集光することにより集光領域の光強度が高くなり、気体媒質の高次の非線形光学効果が容易に誘起され得る。 The infrared spectrum measuring apparatus may include a focusing optical system which focuses the measured infrared light pulse and the reference light pulse on the gas medium. By focusing, the light intensity in the focusing region is increased, and high-order nonlinear optical effects of the gas medium can be easily induced.
また、前記被測定赤外光パルスがコヒーレント光パルスであるとよい。これにより、被測定赤外光パルスが小さいスポット径に集光されるので、気体媒質が高次非線形光学媒質になる。 Preferably, the to-be-measured infrared light pulse is a coherent light pulse. As a result, since the measured infrared light pulse is condensed to a small spot diameter, the gas medium becomes a high-order nonlinear optical medium.
また、前記被測定赤外光パルスは、帯域幅が５００～５０００ｃｍ－１の超広帯域光パルスであるとよい。波長範囲が２－２０μｍの赤外光スペクトルが計測されるので、様々な分子振動による共鳴が広く捕えられ得る。 The measured infrared light pulse may be an ultra-wide band light pulse having a bandwidth of 500 to 5000 cm -1 . As the infrared light spectrum with a wavelength range of 2-20 μm is measured, resonances due to various molecular vibrations can be widely captured.
　また、前記参照光パルスはチャープ光パルスであるか、或いは単一波長のピコ秒パルスであるとよい。これにより、高い周波数分解能でスペクトルが測定され得る。前記参照光パルスがチャープ光パルスである場合、チャープ量（周波数の時間変化）の精密な測定により被測定赤外光スペクトルが一層高い分解能で再現され得る。 Also, the reference light pulse may be a chirped light pulse or a picosecond pulse of a single wavelength. This allows spectra to be measured with high frequency resolution. If the reference light pulse is a chirped light pulse, the measured infrared light spectrum can be reproduced with higher resolution by precise measurement of the chirp amount (time change of frequency).
　また、前記非線形光学効果は、３次非線形光学効果であるとよい。これにより、反転対称性のある気体を波長変換媒質として使用しても、被測定赤外光パルスが可視光パルスに変換され得る。 The non-linear optical effect may be a third-order non-linear optical effect. Thus, even if a gas having inversion symmetry is used as the wavelength conversion medium, the infrared light pulse to be measured can be converted into a visible light pulse.
　また、前記気体媒質はキセノンガスであるとよい。キセノンガスは非線形係数の大きい気体であり、被測定赤外光パルスが高い効率でアップコンバージョンされ得る。 The gas medium may be xenon gas. The xenon gas is a gas with a large non-linear coefficient, and the measured infrared light pulse can be upconverted at high efficiency.
　上記の課題を解決するためになされた本発明の赤外光スペクトル計測方法は、被測定赤外光パルスと参照光パルスとを気体媒質中に混合入射させて該気体媒質の非線形光学効果で該被測定赤外光パルスを可視光パルスに変換するアップコンバージョンステップと、前記アップコンバージョンステップで変換された可視光パルスを分光して可視光パルススペクトルデータを取得する分光ステップと、を有する。 The infrared spectrum measuring method of the present invention, which has been made to solve the above problems, is characterized in that the measured infrared light pulse and the reference light pulse are mixed and incident in the gas medium, and the nonlinear optical effect of the gas medium is obtained. It has an up-conversion step of converting a measured infrared light pulse into a visible light pulse, and a spectroscopy step of separating the visible light pulse converted in the up-conversion step to acquire visible light pulse spectrum data.
上記の赤外光スペクトル計測方法は、前記分光ステップで取得した可視光パルススペクトルデータを所定の回復アルゴリズムを使って前記被測定赤外光パルスのスペクトルを回復させるスペクトル回復ステップを有してもよい。
　また、前記赤外光スペクトル計測方法において、前記被測定赤外光パルスはコヒーレント光パルスであるとよい。
　また、前記被測定赤外光パルスは、帯域幅が５００～５０００ｃｍ－１の超広帯域光パルスであるとよい。
　また、前記参照光パルスはチャープ光パルスであるか、或いは単一波長のピコ秒パルスであるとよい。
　また、前記参照光パルスがチャープ光パルスである場合、そのチャープ量（周波数の時間変化）を測定しておくとよい。
　また、前記非線形光学効果は、３次非線形光学効果であるとよい。
　また、前記気体媒質はキセノンガスであるとよい。 The above infrared light spectrum measuring method may have a spectrum recovery step of recovering the spectrum of the measured infrared light pulse by using a predetermined recovery algorithm for the visible light pulse spectrum data acquired in the spectroscopy step. .
Further, in the infrared light spectrum measuring method, the measured infrared light pulse may be a coherent light pulse.
The measured infrared light pulse may be an ultra-wide band light pulse having a bandwidth of 500 to 5000 cm -1 .
Also, the reference light pulse may be a chirped light pulse or a picosecond pulse of a single wavelength.
Further, when the reference light pulse is a chirped light pulse, it is preferable to measure the chirp amount (time change of frequency).
The non-linear optical effect may be a third-order non-linear optical effect.
The gas medium may be xenon gas.
　非線形光学効果で被測定赤外光パルスを可視光パルスにアップコンバージョンする媒質に透過波長範囲の広い気体媒質を用いているので、広帯域の赤外光スペクトルが計測され得る。 A wide-band infrared light spectrum can be measured because a gas medium with a wide transmission wavelength range is used as the medium for up-converting the measured infrared light pulse into a visible light pulse by the nonlinear optical effect.
本発明の実施形態に係る赤外光スペクトル計測装置の構成図である。It is a block diagram of the infrared-light spectrum measuring device which concerns on embodiment of this invention. 本発明の実施形態に係る赤外光スペクトル計測装置の回復演算手段における演算動作を説明するフローチャートである。It is a flowchart explaining the calculation operation | movement in the recovery calculating means of the infrared-light spectrum measuring apparatus based on embodiment of this invention. 超広帯域コヒーレント光発生装置の構成図である。It is a block diagram of an ultra-wide band coherent light generator. 図３の超広帯域コヒーレント光発生装置で発生させた赤外光パルスのスペクトルである。It is a spectrum of the infrared-light pulse generated with the ultra-wide band coherent light generator of FIG. 実施例で計測したスペクトルである。It is the spectrum measured in the Example.
発明を実施する形態MODES FOR CARRYING OUT THE INVENTION
　以下、添付図面を参照して、本発明を実施する形態を詳細に説明する。図１は、本発明の実施形態に係る赤外光スペクトル計測装置の構成図である。赤外光スペクトル計測装置１は、合波器１１、集光光学系１２、気体媒質１３、可視分光装置１４及び回復演算手段１５を備えている。なお、これら構成要素のうち、合波器１１と集光光学系１２とは省かれ得る。 Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings. FIG. 1 is a block diagram of an infrared spectrum measuring apparatus according to an embodiment of the present invention. The infrared spectrum measuring apparatus 1 includes a multiplexer 11, a condensing optical system 12, a gas medium 13, a visible spectroscope 14, and a recovery operation means 15. Of these components, the coupler 11 and the focusing optical system 12 can be omitted.
　被測定赤外光パルスＬIRと参照光パルスＬrを合波する合波器１１には、穴あきミラー、２色ミラー、偏光ビームスプリッタ等が用いられ得る。集光光学系１２には、レンズ、放物面鏡等が用いられ得る。 A multiplexer 11 for multiplexing the reference optical pulse L r and the measured infrared light pulse L IR is perforated mirror, two-color mirror, a polarizing beam splitter or the like can be used. A lens, a parabolic mirror or the like may be used for the condensing optical system 12.
　気体媒質１３は、可視～赤外域で透明な気体が好ましい。気体媒質１３は空気でもよいが、空気には４μｍと８μｍ付近にＣＯ２分子による強い吸収があるので、空気よりは吸収の少ない不活性ガス（アルゴン、キセノン、ネオン等）が好ましい。不活性ガスの中でもキセノンガスが特に好ましい。 The gas medium 13 is preferably a gas that is transparent in the visible to infrared region. The gas medium 13 may be air, but since air has strong absorption by CO 2 molecules in the vicinity of 4 μm and 8 μm, inert gas (argon, xenon, neon, etc.) that absorbs less than air is preferable. Among the inert gases, xenon gas is particularly preferred.
　ボンベ（不図示）から集光光学系１２による集光領域Ｓに、気体媒質を噴き出すようにしてもよいが、それでは、気体媒質が空気中に拡散してしまうので気体媒質１３の濃度を高く保つことができない。本実施形態では、集光光学系１２で集光される光が通過する孔のあいた筒にボンベからの気体媒質が注入される。 Although the gaseous medium may be jetted out from a cylinder (not shown) to the condensing area S by the condensing optical system 12, the gaseous medium is diffused into the air, so the concentration of the gaseous medium 13 is kept high. I can not do it. In the present embodiment, the gas medium from the cylinder is injected into a cylinder having a hole through which light collected by the light collection optical system 12 passes.
　１６は、バンドパスフィルターであり、気体媒質１３の非線形光学効果で被測定赤外光パルスＬIRからアップコンバージョンされた可視光パルスＬvのみを透過する。
　１７は、可視光パルスＬvをコリメートするレンズである。
　分光装置１４は、可視域の分光装置で、プリズム或いは回折格子と回折光の空間分布を光電変換するＣＣＤ（或いはフォトダイオードアレイ）を備えている。 A band pass filter 16 transmits only the visible light pulse Lv up-converted from the measured infrared light pulse L IR by the nonlinear optical effect of the gas medium 13.
A lens 17 collimates the visible light pulse Lv.
The spectroscope 14 is a spectroscope in the visible region, and includes a prism or a diffraction grating and a CCD (or a photodiode array) for photoelectrically converting a spatial distribution of diffracted light.
　回復演算手段１５は、コンピュータであり、図２に示す演算動作を行う。すなわち、ステップＳ１１では、気体媒質１３でアップコンバージョンされた可視光パルスＬvが分光装置１４でデータ化され、この分光スペクトルデータが回復演算手段１５により取得される。続くステップＳ１２では、ステップＳ１１で取得された分光スペクトル（波長）データが分光スペクトル（周波数）データに変換される。 The recovery operation means 15 is a computer and performs the operation shown in FIG. That is, in step S 11, the visible light pulse Lv up-converted by the gas medium 13 is converted into data by the spectroscope 14, and the spectrum data is acquired by the recovery calculation unit 15. In the subsequent step S12, the spectrum (wavelength) data acquired in step S11 is converted into spectrum (frequency) data.
　ステップＳ１３で、分光スペクトル（周波数）データが逆フーリエ変換される。ステップＳ１４では、参照光パルスＬｒの時間領域での位相をΦ（ｔ）としたとき、逆フーリエ変換されたスペクトルデータにおいて、時間領域でｔ＞０の部分からは位相Φ（ｔ）を、ｔ＜０の部分からは位相－Φ（－ｔ）を差し引く位相補正が行われる。位相補正されたスペクトルデータは、ステップＳ１５でフーリエ変換され、被測定赤外光パルススペクトルとなる。 In step S13, spectral (frequency) data is inverse Fourier transformed. In step S14, assuming that the phase of the reference light pulse L r in the time domain is Φ (t), the phase Φ (t) from the portion of t> 0 in the time domain in the inverse Fourier transformed spectral data, From the portion of t <0, phase correction is performed by subtracting the phase -Φ (-t). The phase-corrected spectrum data is Fourier-transformed in step S15 to form a measured infrared light pulse spectrum.
　赤外光パルス発生手段１０から発生された被測定赤外光パルスＬIRを点線で示す試料１００に照射することで、試料１００の赤外吸収スペクトルが可視域の分光装置で高速に測定され得る。 The infrared absorption spectrum of the sample 100 can be measured at high speed by the spectroscope in the visible range by irradiating the sample 100 indicated by the dotted line with the measured infrared light pulse L IR generated from the infrared light pulse generating means 10. .
　気体媒質１３の非線形光学効果は、気体媒質に注入される光の強度（単位面積当たりのパワー、すなわちＷ／ｃｍ２）に依存し、強度が大きくなるにつれて気体媒質１３には高次の非線形光学効果が誘起される。 The non-linear optical effect of the gas medium 13 depends on the intensity (power per unit area, ie, W / cm 2 ) of light injected into the gas medium, and higher order non-linear optics are provided to the gas medium 13 as the intensity increases. An effect is induced.
気体媒質１３に入射するＬｒ、ＬIRがパルス光の場合、Ｌｒ、ＬIRのパワーはパルス幅が短い程高くなるので、Ｌｒ、ＬIRのパルス幅は短い方がよい。パルス幅はフェムト秒～ピコ秒が望ましい。 When L r and L IR incident on the gas medium 13 are pulsed light, the power of L r and L IR increases as the pulse width decreases , so the pulse width of L r and L IR should be short. The pulse width is preferably femtosecond to picosecond.
気体媒質１３に注入される光の強度は、Ｌｒ、ＬIRが集光光学系１２で小さく集光される程高くなる。集光光学系１２によるＬｒ、ＬIRの集光スポット径は、集光光学系１２の焦点距離とＬｒ、ＬIRのコヒレンシーに依存する。したがって、集光光学系１２の焦点距離は５０ｍｍであるとよく、２５ｍｍであるとさらによい。また、Ｌｒ、ＬIRのコヒレンシーは、Ｍ２＝１のコヒーレント光が望ましい。
気体媒質の非線形光学効果で波長変換するのに必要なパワーは、気体の種類や計測時間に依存するが、発明者らの実験によれば次のようになる。 The intensity of light injected into the gas medium 13 becomes higher as L r and L IR are smaller and condensed by the condensing optical system 12. The condensing spot diameter of L r and L IR by the condensing optical system 12 depends on the focal length of the condensing optical system 12 and the coherency of Lr and L IR . Therefore, the focal length of the focusing optical system 12 may be 50 mm, and more preferably 25 mm. In addition, the coherency of L r and L IR is preferably coherent light of M 2 = 1.
The power required for wavelength conversion by the nonlinear optical effect of the gas medium depends on the type of gas and the measurement time, but according to the experiments of the inventors, it is as follows.
発明者らの実験によれば、角周波数がω０の被測定赤外光パルスＬIR（ω０）のパルス幅が７ｆｓ、エネルギが５００ｎＪ、ピークパワーが７０ＭＷの場合、直径１００μｍの集光スポットの強度ＩIRは、０．９×１０１２Ｗ／ｍ２になる。角周波数がω１の参照光パルスＬｒのパルス幅が１０ｐｓ、エネルギが０．１ｍＪ、パワーが１０ＭＷの場合、直径２４μｍの集光スポットの強度Ｉrは、２．２×１０１２Ｗ／ｍ２になる。 According to the experiments of the inventors, when the pulse width of the measured infrared light pulse L IR (ω 0 ) whose angular frequency is ω 0 is 7 fs, the energy is 500 nJ, and the peak power is 70 MW, a focused spot with a diameter of 100 μm The intensity I IR of this is 0.9 × 10 12 W / m 2 . When the pulse width of the reference light pulse L r with angular frequency ω 1 is 10 ps, the energy is 0.1 mJ, and the power is 10 MW, the intensity I r of the focused spot with a diameter of 24 μm is 2.2 × 10 12 W / m Become two .
気体媒質１３がアルゴン又はキセノンの場合、３次の非線形光学効果が誘起された。すなわち、この場合、参照光パルスＬｒの角周波数をω１とすると、３次の非線形光学効果（４光波差周波発生：ω１＋ω１－ω０→ω２）が起こり、角周波数がω１の被測定赤外光パルスＬIR（ω１）が、角周波数がω２の可視光パルスＬV（ω２）にアップコンバージョンされた。
なお、角周波数ωは、波長をλ、光速をｃとすると、
ω＝２πｃ／λ　　　　　　　　　　　　　　　　　　　（２）
と表される。
３次の非線形光学効果の場合、（１）式から、下記の指標
参照光の強度の２乗×被測定光の強度＝Ｉr ２×ＩIR 　　　（３）
が重要となる。 When the gas medium 13 is argon or xenon, a third-order nonlinear optical effect is induced. That is, in this case, assuming that the angular frequency of the reference light pulse L r is ω 1 , the third-order nonlinear optical effect (four-wave difference frequency generation: ω 1 + ω 1 -ω 0 → ω 2 ) occurs and the angular frequency is ω 1 of the measured infrared light pulse L IR (ω 1), the angular frequency is up-converted to omega 2 of the visible light pulse L V (ω 2).
Note that the angular frequency ω has a wavelength of λ and a light velocity of c:
ω = 2πc / λ (2)
It is expressed as
In the case of the third-order non-linear optical effect, from the equation (1), the intensity of the index reference light below the square of the intensity of the light to be measured = I r 2 × I IR (3)
Is important.
　発明者らの上記実験では、Ｉr ２×ＩIR＝４．４×１０３６Ｗ３／ｃｍ６であり、気体媒質の非線形光学効果で波長変換するのに必要なパワーは、Ｉr ２×ＩIRが４．４×１０３６Ｗ３／ｃｍ６以上になるパワーである。 In the above experiment by the inventors, I r 2 × I IR = 4.4 × 10 36 W 3 / cm 6 , and the power required for wavelength conversion by the nonlinear optical effect of the gas medium is I r 2 × The power is such that the I IR is 4.4 × 10 36 W 3 / cm 6 or more.
　被測定赤外光パルスＬIRは、超広帯域（５００～５０００ｃｍ－１）光パルスであるとよい。被測定赤外光パルスＬIRが超広帯域（５００～５０００ｃｍ－１）であると、波長範囲が２－２０μｍの赤外光スペクトルを計測することができるので、様々な分子振動による共鳴を広くとらえられ得る。 The measured infrared light pulse L IR may be an ultra-wide band (500 to 5000 cm −1 ) light pulse. If the measured infrared light pulse L IR is in the ultra-wide band (500 to 5000 cm -1 ), the infrared light spectrum in the wavelength range of 2 to 20 μm can be measured, so resonances due to various molecular vibrations are widely caught. Can be
　超広帯域（５００～５０００ｃｍ－１）コヒーレント光パルスは、例えば、図３に示す超広帯域コヒーレント光発生装置２で発生され得る。図３において、２１は２色ミラーで、波数ω１のコヒーレント光パルスＬ１（ω１）と波数ω２（＝２ω１）の光パルスＬ２（ω２）を合波する。２２は、軸外し放物面鏡で、合波された光パルスＬ１（ω１）＋Ｌ２（ω２）を気体媒質２３の中に集光する。２４は、コリメータであり、軸外し放物面鏡である。２５は、フィルタである。 The ultra-wide band (500 to 5000 cm -1 ) coherent light pulse can be generated, for example, by the ultra-wide band coherent light generator 2 shown in FIG. 3, 21 is a two-color mirror, for multiplexing the optical pulses L 2 of the coherent light pulse L 1 wavenumber ω 1 (ω 1) and wavenumber ω 2 (= 2ω 1) ( ω 2). An off-axis parabolic mirror 22 focuses the combined light pulse L 1 (ω 1 ) + L 2 (ω 2 ) into the gas medium 23. A collimator 24 is an off-axis parabolic mirror. 25 is a filter.
　モードロックＴｉ：サファイアレーザからの超短光パルス（波長：８００ｎｍ、パルス幅：２５ｆｓ、パルスエネルギ：０．７ｍＪ、繰り返し周波数：１ＫＨｚ）を、厚さ０．１ｍｍのＢＢＯ（β－ＢａＢ２Ｏ４）結晶に入射させて第２高調波光パルスを発生させた。その第２高調波光パルスがＬ２（ω２）であり、基本波光パルスがＬ１（ω１）である。基本波光パルスＬ１（ω１）のパルス幅は２５ｆｓ、パルスエネルギは６７５μＪ、第２高調波光パルスＬ２（ω２）の波長は４００ｎｍ、パルス幅は２５ｆｓ、パルスエネルギは２５μＪである。 Ultra-short light pulses (wavelength: 800 nm, pulse width: 25 fs, pulse energy: 0.7 mJ, repetition frequency: 1 KHz) from mode-locked Ti: sapphire laser, BBO (β-BaB 2 O 4 with a thickness of 0.1 mm) 2.) The crystal was made incident and a second harmonic light pulse was generated. The second harmonic light pulse is L 2 (ω 2 ), and the fundamental wave light pulse is L 1 (ω 1 ). The pulse width of the fundamental wave light pulse L 1 (ω 1 ) is 25 fs, the pulse energy is 675 μJ, the wavelength of the second harmonic light pulse L 2 (ω 2 ) is 400 nm, the pulse width is 25 fs, and the pulse energy is 25 μJ.
　基本波光パルスＬ１（ω１）と第２高調波光パルスＬ２（ω２）が２色ミラー２１で合波され、焦点距離１５０ｍｍの軸外し放物面鏡２２でアルゴンガス２３の中に集光される。すると、アルゴンガスのフィラメンテーションにより４光波混合（ω１＋ω１－ω２→ω０）が起こり、ω０の光のみ透過するフィルタ２５からは４光波混合された光パルスＬ０（ω０）が得られる。 The fundamental wave light pulse L 1 (ω 1 ) and the second harmonic light pulse L 2 (ω 2 ) are combined by the two-color mirror 21 and collected in the argon gas 23 by the off-axis parabolic mirror 22 having a focal length of 150 mm. It is lighted. Then, four-wave mixing (ω 1 + ω 1 -ω 2 → ω 0 ) occurs due to filamentation of argon gas, and from the filter 25 transmitting only light of ω 0 , four-wave mixed light pulse L 0 (ω 0 ) Is obtained.
　４光波混合された光パルスＬ０（ω０）の帯域は、図４に示すように、波数で２００－６０００ｃｍ－１（波長で１．７－５０μｍ）であり、超広帯域である。また、光パルスＬ０（ω０）のパルス幅は、６．９ｆｓであった。 The band of the four-wave mixed light pulse L 0 (ω 0 ) is, as shown in FIG. 4, 200-6000 cm -1 (1.7-50 μm in wavelength) in wavenumber, and is an ultra-wide band. The pulse width of the light pulse L 0 (ω 0 ) was 6.9 fs.
　参照光パルスＬｒは、チャープ光パルスであるとよい。フーリエ分光法では、掃引する遅延時間が長くなると周波数分解能が向上するので、参照光パルスのパルス幅が長いほど周波数分解能が向上する。 The reference light pulse Lr may be a chirped light pulse. In Fourier spectroscopy, the longer the delay time for sweeping, the better the frequency resolution, so the longer the pulse width of the reference light pulse, the better the frequency resolution.
　参照光パルスがチャープ光パルス或いは単一波長のピコ秒パルスの場合、高い周波数分解能でスペクトルが測定され得る。何故なら、フーリエ分光法では掃引する遅延時間を長くすれば周波数分解能が向上するので、同様の論理で参照光パルスのパルス幅が長ければ長いほど周波数分解能が向上するからである。
　参照光パルスをチャープ光パルスにするには、参照光パルスのパルス時間幅を、例えば、回折格子型伸張器で伸張させればよい。 If the reference light pulse is a chirped light pulse or a single wavelength picosecond pulse, the spectrum can be measured with high frequency resolution. The reason is that, in the Fourier spectroscopy, if the delay time for sweeping is increased, the frequency resolution is improved. Therefore, according to the same logic, the longer the pulse width of the reference light pulse, the more the frequency resolution is improved.
In order to make the reference light pulse into a chirped light pulse, the pulse time width of the reference light pulse may be extended by, for example, a diffraction grating stretcher.
　参照光パルスがチャープ光パルスである場合、そのチャープ量（周波数の時間変化）を実測しておき、計測された可視光スペクトルから赤外スペクトルへの変換を精密に行えるようにしておくとよい。 When the reference light pulse is a chirped light pulse, it is preferable to measure the amount of chirp (time change of frequency) in advance so that conversion of the measured visible light spectrum to an infrared spectrum can be accurately performed.
　前述の４光波混合された超広帯域光パルスＬ０（ω０）を、被測定赤外光パルスＬIR（ω０）とした。この被測定赤外光パルスＬIR（ω０）のパルスエネルギは、０．５μＪである。 The above-described four-wave-mixed ultra-wideband light pulse L 0 (ω 0 ) is defined as a measured infrared light pulse L IR (ω 0 ). The pulse energy of this measured infrared light pulse L IR (ω 0 ) is 0.5 μJ.
超広帯域光パルスＬ０（ω０）を生成するためのモードロックＴｉ：サファイアレーザの基本波パルス（波長：８００ｎｍ）の一部（パルスエネルギ：０．１ｍＪ）を伸張器で伸張して参照光パルスＬｒ（ω１）とした。参照光パルスＬｒ（ω１）のパルス幅は、１０．３ｐｓである。 A portion (pulse energy: 0.1 mJ) of a fundamental pulse (wavelength: 800 nm) of a mode-locked Ti: sapphire laser for generating ultra-broadband light pulse L 0 (ω 0 ) is stretched by a stretcher to obtain a reference light Pulse L r (ω 1 ) was used. The pulse width of the reference light pulse L r (ω 1 ) is 10.3 ps.
　被測定赤外光パルスＬIR（ω０）と参照光パルスＬｒ（ω１）とが穴あきミラー１１で合波され、焦点距離５０ｍｍの放物面鏡１２でキセノンガス１３に集光された。被測定赤外光パルスＬIR（ω０）が超短光パルス（パルス時間幅：７ｆｓ）であるため、集光領域での強度ＩIR～４×１０１６Ｗ／ｍ２と見積もられた。また、参照光パルスＬｒ（ω１）の集光領域での強度Ｉｒ～２．２×１０１２Ｗ／ｃｍ２と見積もられた。
　したがって、（２）式の指標は２×１０３７Ｗ３／ｃｍ６と見積もられ、キセノンガス１３に３次の非線形光学効果が誘起されることが期待さる。 The measured infrared light pulse L IR (ω 0 ) and the reference light pulse L r (ω 1 ) are combined by the perforated mirror 11 and condensed onto the xenon gas 13 by the parabolic mirror 12 having a focal distance of 50 mm. The Since the measured infrared light pulse L IR (ω 0 ) is an ultrashort light pulse (pulse time width: 7 fs), the intensity I IR in the focusing region was estimated to be 4 × 10 16 W / m 2 . Further, it was estimated that the intensity I r in the focusing region of the reference light pulse L r (ω 1 ) was 2.2 × 10 12 W / cm 2 .
Accordingly, the index of the equation (2) is estimated to be 2 × 10 37 W 3 / cm 6, and it is expected that the xenon gas 13 induces the third-order nonlinear optical effect.
　波数で２００－６０００ｃｍ－１（波長で１．７－５０μｍ）の被測定赤外光パルスＬIR（ω０）と、波長８００ｎｍの参照光パルスＬｒ（ω１）をカットするバンドパスフィルタ１６を透過した光パスがカメラEMCCD（ProEM＋1600,Princeton Instrument）を備える可視域分光装置１４で測定された。カメラはモードロックＴｉ：サファイアレーザの繰り返し周波数（１ｋＨｚ）に同期され、シングルショット（＜１ｍｓ）でスペクトルが測定された。 Band pass filter 16 for cutting the measured infrared light pulse L IR (ω 0 ) at 200-6000 cm -1 (wavelength 1.7 to 50 μm) in wave number and the reference light pulse L r (ω 1 ) at wavelength 800 nm The light path that has passed through is measured by the visible region spectrometer 14 equipped with a camera EMCCD (ProEM + 1600, Princeton Instrument). The camera was synchronized to the repetition rate (1 kHz) of a mode-locked Ti: sapphire laser and spectra were measured on a single shot (<1 ms).
　測定されたスペクトルを図５に示す。図５の波形イ（横軸：波長）が測定されたスペクトルで、４００－５２０ｎｍの可視光スペクトルが得られた。したがって、バンドパスフィルタ１６を通過した可視光パルスは、角周波数がω２（＝ω１＋ω１－ω０）の可視光パルスＬｖ（ω２）であることがわかる。 The measured spectrum is shown in FIG. A visible light spectrum of 400 to 520 nm was obtained from the spectrum obtained by measuring the waveform a (horizontal axis: wavelength) in FIG. Therefore, it can be seen that the visible light pulse that has passed through the band pass filter 16 is a visible light pulse L v (ω 2 ) whose angular frequency is ω 2 (= ω 1 + ω 1 -ω 0 ).
　よって、キセノンガス１３に誘起された非線形光学効果は、３次の非線形光学効果（４光波差周波発生：ω１＋ω１－ω０→ω２）によるアップコンバージョンであることが検証された。 Therefore, it was verified that the non-linear optical effect induced in the xenon gas 13 is up-conversion by the third-order non-linear optical effect (four-wave difference frequency generation: ω 1 + ω 1 -ω 0 → ω 2 ).
　図５の波形イのスペクトルデータを回復演算手段１５で処理することで得られたスペクトル波形が図５の波形ロである。波形ロから、ＣＯ２の吸収（波数：～２３００ｃｍ－１、波長：～４．３μｍ）と水蒸気の吸収（波数：～１６００ｃｍ－１、波長：～６．３μｍ及び波数：～３７００ｃｍ－１、波長：～２．７μｍ）が鮮明に観測される。 The spectrum waveform obtained by processing the spectrum data of the waveform i of FIG. 5 by the recovery operation means 15 is the waveform b of FIG. From the waveform, CO 2 absorption (wave number: ~ 2300 cm -1 , wavelength: ~ 4.3 μm) and water vapor absorption (wave number: ~ 1600 cm -1 , wavelength: ~ 6.3 μm and wave number: ~ 3700 cm -1 , wavelength : ̃2.7 μm) is clearly observed.
　前記参照光パルスのチャープ量（周波数の時間変化、Φ（ｔ））を、前もって計測しておくとよい。参照光パルスと赤外光パルスの遅延時間を掃引して、４光波差周波混合のスペクトルを計測しておき、そのスペクトルの遅延時間依存性から、Φ（ｔ）を直接的に計測することができる。 The amount of chirp of the reference light pulse (time change in frequency, ((t)) may be measured in advance. Measure the spectrum of the four-wave difference frequency mixing by sweeping the delay time of the reference light pulse and the infrared light pulse, and measure Φ (t) directly from the delay time dependency of the spectrum it can.
１・・・・・・・・赤外光スペクトル計測装置
１１・・・・・・合波器
１２・・・・・・集光光学系
１３・・・・・・気体媒質
１４・・・・・・分光装置
１５・・・・・・回復演算手段
ＬIR・・・・・・・被測定赤外光パルス
Ｌｒ・・・・・・・参照光パルス
Ｌｖ・・・・・・・可視光パルス 1 · · · · · · · · · · · · · · · · · · · · · · · · · · · infrared light spectrum measurement device 11 · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · Gas medium · spectrometer 15 ...... restoration calculation means L IR · · · · · · · measured infrared light pulse L r · · · · · · · reference optical pulse L v · · · · · · · Visible light pulse

Claims (17)

  1. 　被測定赤外光パルスと参照光パルスとが混合入射されて該被測定赤外光パルスを非線形光学効果で可視光パルスにアップコンバージョンする気体媒質と、
    　前記気体媒質でアップコンバージョンされた前記可視光パルスを分光して可視光パルススペクトルデータを取得する分光装置と、
    　を有し、広帯域の赤外光スペクトルを計測することを特徴とする赤外光スペクトル計測装置。     A gaseous medium in which a measured infrared light pulse and a reference light pulse are mixed and incident, and the measured infrared light pulse is upconverted to a visible light pulse by a nonlinear optical effect;
    A spectroscope configured to disperse the visible light pulse up-converted by the gaseous medium to obtain visible light pulse spectrum data;
    An infrared light spectrum measuring apparatus characterized by measuring a wide band infrared light spectrum.
  2. 　前記分光装置で取得された前記可視光パルススペクトルデータを所定の回復アルゴルリズムで演算して前記被測定赤外光パルススペクトルを得る回復演算手段を有する請求項１に記載の赤外光スペクトル計測装置。 The infrared light spectrum measuring apparatus according to claim 1, further comprising: recovery operation means for obtaining the infrared light pulse spectrum to be measured by calculating the visible light pulse spectrum data acquired by the spectroscopic device according to a predetermined recovery algorithm. .
  3. 　前記被測定赤外光パルスと前記参照光パルスとを合波する合波器を備える請求項１又は２に記載の赤外光スペクトル計測装置。 The infrared light spectrum measuring apparatus according to claim 1 or 2, further comprising a multiplexer for multiplexing the measured infrared light pulse and the reference light pulse.
  4. 　前記被測定赤外光パルスと前記参照光パルスとを前記気体媒質に集光する集光光学系を備える請求項１～３のいずれか１項に記載の赤外光スペクトル計測装置。 The infrared spectrum measuring apparatus according to any one of claims 1 to 3, further comprising a condensing optical system which condenses the measured infrared light pulse and the reference light pulse on the gas medium.
  5. 　前記被測定赤外光パルスはコヒーレント光パルスである請求項１～４のいずれか１項に記載の赤外光スペクトル計測装置。 The infrared spectrum measuring apparatus according to any one of claims 1 to 4, wherein the measured infrared light pulse is a coherent light pulse.
  6. 　前記被測定赤外光パルスは、帯域幅が５００～５０００ｃｍ－１の超広帯域光パルスである請求項１～５のいずれか１項に記載の赤外光スペクトル計測装置。 The infrared spectrum measuring apparatus according to any one of claims 1 to 5, wherein the measured infrared light pulse is an ultra-wide band light pulse having a bandwidth of 500 to 5000 cm -1 .
  7. 　前記参照光パルスはチャープ光パルス或いは単一波長のピコ秒パルスである請求項１～６のいずれか１項に記載の赤外光スペクトル計測装置。 The infrared light spectrum measuring apparatus according to any one of claims 1 to 6, wherein the reference light pulse is a chirped light pulse or a picosecond pulse of a single wavelength.
  8. 　前記非線形光学効果は、３次非線形光学効果である請求項１～７のいずれか１項に記載の赤外光スペクトル計測装置。 The infrared spectrum measuring apparatus according to any one of claims 1 to 7, wherein the nonlinear optical effect is a third-order nonlinear optical effect.
  9. 　前記気体媒質はキセノンガスである請求項１～８のいずれか１項に記載の赤外光スペクトル計測装置。 The infrared spectrum measuring apparatus according to any one of claims 1 to 8, wherein the gas medium is xenon gas.
  10. 　被測定赤外光パルスと参照光パルスとを気体媒質中に混合入射させて該気体媒質の非線形光学効果で該被測定赤外光パルスを可視光パルスに変換するアップコンバージョンステップと、
    　前記アップコンバージョンステップで変換された可視光パルスを分光して可視光パルススペクトルデータを取得する分光ステップと、
    　を有し、広帯域の赤外光スペクトルを計測することを特徴とする赤外光スペクトル計測方法。     An up-conversion step of mixing a measured infrared light pulse and a reference light pulse into a gas medium and converting the measured infrared light pulse into a visible light pulse by the nonlinear optical effect of the gas medium;
    A spectroscopy step of splitting visible light pulses converted in the upconversion step to obtain visible light pulse spectrum data;
    And measuring a wide-band infrared light spectrum.
  11. 　前記分光ステップで取得した可視光パルススペクトルデータを所定の回復アルゴリズムを使って前記被測定赤外光パルスのスペクトルを回復させるスペクトル回復ステップを有する請求項１０に記載の赤外光スペクトル計測方法。 The infrared light spectrum measuring method according to claim 10, further comprising a spectrum recovery step of recovering the spectrum of the measured infrared light pulse by using a predetermined recovery algorithm for the visible light pulse spectrum data acquired in the spectroscopy step.
  12. 　前記被測定赤外光パルスはコヒーレント光パルスである請求項１０又は１１に記載の赤外光スペクトル計測方法。 The infrared light spectrum measurement method according to claim 10, wherein the measured infrared light pulse is a coherent light pulse.
  13. 　前記被測定赤外光パルスは、帯域幅が５００～５０００ｃｍ－１の超広帯域光パルスである請求項１０～１２のいずれか１項に記載の赤外光スペクトル計測方法。 The infrared spectrum measuring method according to any one of claims 10 to 12, wherein the measured infrared light pulse is an ultra-wide band light pulse having a bandwidth of 500 to 5000 cm -1 .
  14. 　前記参照光パルスはチャープ光パルス或いは単一波長のピコ秒パルスである請求項１０～１３のいずれか１項に記載の赤外光スペクトル計測方法。 The infrared light spectrum measuring method according to any one of claims 10 to 13, wherein the reference light pulse is a chirped light pulse or a picosecond pulse of a single wavelength.
  15. 　前記参照光パルスがチャープ光パルスである場合、そのチャープ量（周波数の時間変化）を測定しておく、請求項１４に記載の赤外光スペクトル計測方法。 The infrared light spectrum measuring method according to claim 14, wherein when the reference light pulse is a chirped light pulse, the chirp amount (time change of frequency) is measured in advance.
  16. 　前記非線形光学効果は、３次非線形光学効果である請求項１０～１５のいずれか１項に記載の赤外光スペクトル計測方法。 The infrared light spectrum measuring method according to any one of claims 10 to 15, wherein the nonlinear optical effect is a third order nonlinear optical effect.
  17. 　前記気体媒質はキセノンガスである請求項１０～１６のいずれか１項に記載の赤外光スペクトル計測方法。 The infrared light spectrum measuring method according to any one of claims 10 to 16, wherein the gas medium is xenon gas.
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