JP3567234B2 - Spectrometry method and spectrometer - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a spectrometry and a spectrometer, and more particularly to a spectrometry and a spectrometer using a tunable laser as a spectral light source.
[0002]
[Prior art]
As a highly sensitive sample analysis method, the sample is irradiated with light in the infrared, visible, or ultraviolet region to measure light absorption by the sample, or reflected light from the sample, Rayleigh scattered light, Raman scattered light, fluorescence, etc. Spectrometry is widely used. According to this spectroscopic measurement method, qualitative analysis such as sample identification and confirmation, quantitative analysis such as measurement of the concentration of characteristic components contained in the sample and component ratio of the mixture, and analysis of the electronic state and three-dimensional structure of molecules are performed. The reaction process, the molecular structure analysis of the reaction intermediate, and the like can be performed by time-resolved measurement of the absorption spectrum and the like of the sample.
[0003]
In spectrometry, it is necessary to irradiate a sample with monochromatic light of a specific selected wavelength, or to irradiate light while continuously sweeping the wavelength of monochromatic light. Usually, a white light source and a monochromator are used. A spectrophotometer that extracts monochromatic light in combination is used. The wavelength sweep of the monochromatic light emitted from the exit slit of the monochromator is performed by rotating a wavelength dispersion element, for example, a diffraction grating incorporated in the monochromator.
[0004]
FIG. 14 is a schematic diagram of a double beam type spectrophotometer which is an example of a conventional spectrometer. This spectrophotometer measures the absorption spectrum of the sample, and a light beam from a light source such as a tungsten lamp or a deuterium lamp disposed in the light source unit 200 is incident on the entrance slit S of the monochromator 210. ₁ Through the mirror M ₁ , M ₂ And enters the diffraction grating G via. The light wavelength-dispersed by the diffraction grating G is a mirror M ₃ , M ₄ Exit slit S through ₂ A spectral image is formed at the position ₂ , A monochromatic light 211 is extracted. The monochromatic light 211 extracted from the monochromator 210 is incident on the rotating first sector mirror 221. The first sector mirror 221 has a light transmitting portion and a light reflecting portion, and alternately distributes a light beam to an optical path on the sample S side and an optical path on the reference sample R side. The monochromatic light 211 transmitted through the first sector mirror 221 is incident on the sample S, and the sample transmitted light is reflected by the reflection mirror 223 and then rotated by the control unit 220 in synchronization with the sector mirror 221. The light is reflected by the sector mirror 224 and enters the detector 230. The monochromatic light 211 reflected by the first sector mirror 221 is transmitted through the reference sample R after being reflected by the reflection mirror 222, transmitted through the second sector mirror 224, and detected by the detector 230.
[0005]
A wavelength tunable laser is used as a light source for some spectroscopic measurements. As a wavelength tunable laser, Ti: Al is used as a laser medium. ₂ O ₃ A solid laser using a crystal such as (titanium sapphire) and a liquid laser using a dye solution or the like as a laser medium are known. As a wavelength selection method for causing such a wavelength tunable laser to oscillate at a desired wavelength, for example, a diffraction grating or a birefringent plate is disposed in a laser resonator containing a laser medium, and it is mechanically rotated. As a result, a wavelength selection method is employed in which only a specific wavelength can resonate in the laser resonator and a laser beam of a desired wavelength is extracted.
[0006]
[Problems to be solved by the invention]
Spectrophotometry using a spectrophotometer is a technique that has already been established and can perform high-precision measurement. However, a monochromator for irradiating monochromatic light is required, and the apparatus becomes large. In addition, since the light source and detector cannot be separated, the size of the sample that can be loaded into the spectrophotometer and the state of the sample are limited, so that spectrometry can be flexibly performed under various sample conditions or conditions. Can't do it. Further, there is a problem that it is not easy to two-dimensionally measure a spectrum such as an absorption spectrum and a reflection spectrum of the sample as a function of a position on the sample.
[0007]
On the other hand, when performing spectral measurement using a laser as a light source, it is not necessary to use a monochromator because monochromatic light is obtained from the laser. However, dye lasers, which are currently most widely used as wavelength tunable lasers, have a narrow wavelength tunable range that can be obtained with one type of dye.The wavelength is selected by mechanically rotating a diffraction grating or birefringent plate. Therefore, it is difficult to change the wavelength at a high speed, and there is a problem that the wavelength can be swept only in one direction in order to improve the wavelength reproduction accuracy. Therefore, it is not suitable for general spectroscopic measurement such as absorption spectrum measurement of a sample.
[0008]
When an optical parametric oscillator (OPO: Optical Parametric Oscillator) is used as the wide-range wavelength tunable laser, the wavelength tunable range can be widened, but the wavelength sweep speed is low and the wavelength reproducibility is poor. Also, the position and direction of the output beam slightly change depending on the wavelength, and the optical axis is not constant.
[0009]
In a spectroscope using an infrared semiconductor laser, the wavelength variable range of one semiconductor laser is narrow, and semiconductor lasers must be replaced one after another in order to perform measurement in a wide wavelength range.
[0010]
For a pulsed dye laser, CaMoO is contained in a dye solution as a laser medium. ₄ Arrange the crystals and use CaMoO ₄ There has been proposed an electrical oscillation wavelength sweeping method in which an acoustic wave is input to a crystal and a resonator is constituted by light components interacting with the acoustic wave to variably control the oscillation wavelength of the laser (Applied Physics Letters, vol. 19, No. 8, pp. 269-271). However, this sweeping method requires a narrow range of tunable wavelengths and a complicated structure for integrating the dye and the crystal. ₄ There are problems such as the necessity of a special crystal called a crystal, and difficulty in separation because the difference between the interacting light component and the non-interacting light component is the rotation of the polarization plane.
[0011]
The present invention has been made in view of such problems of the related art, and has as its object to provide a simple spectroscopic measurement method and a spectroscopic measurement device using a novel wavelength tunable laser as a monochromatic light source.
[0012]
[Means for Solving the Problems]
In the present invention, an electronically controlled tunable laser (hereinafter, referred to as an ETT (Electronically Tunable Tunable)) capable of electrically controlling a laser oscillation wavelength without providing a mechanically movable portion such as a rotating mechanism to enable high-speed wavelength sweeping. The above object is achieved by newly developing a "laser" and using this ETT laser as a spectral light source.
[0013]
The ETT laser used in the present invention has a laser medium capable of oscillating laser in a predetermined wavelength region and a birefringent acousto-optical element arranged in a laser resonator, and is diffracted at a predetermined angle by the birefringent acousto-optical element. Is a wavelength tunable laser that configures a laser resonator only for the reflected light component and performs wavelength selection by selecting the frequency of the acoustic wave to be excited in the birefringent acousto-optic element.For example, titanium sapphire is used as a laser medium. In this case, the wavelength can be swept over the wavelength range of 680 nm to 1100 nm in a time within 1 second. Further, since the wavelength is electrically selected using the birefringent acousto-optical element, the wavelength can be switched instantaneously, and, for example, switching between any two wavelengths can be stably performed within 1 ms or less.
[0014]
The fact that the wavelength can be swept in such a wide wavelength range instantaneously and while maintaining the monochromaticity of the laser means that the light source 200 and the spectroscope 210 shown in FIG. Is obtained as a light beam having This ETT laser can, of course, be used as a light source of a conventional absorption spectroscope, and since it is a laser beam, it can be easily introduced into an optical fiber, making it easy to realize remote monitoring type spectroscopy using an optical fiber. it can.
[0015]
Hereinafter, the principle of selecting the laser oscillation wavelength of the ETT laser using the birefringent acousto-optic device will be described.
When an acoustic wave is excited in an acousto-optic crystal exhibiting birefringence, diffracted light of a specific wavelength corresponding to the frequency of the acoustic wave in the light incident on the crystal becomes the acoustic wave, the incident light, and the diffracted light. Strongly diffracted in a direction that satisfies the phase matching condition between the two. FIG. 1 is a conceptual diagram showing the state of this diffraction.
[0016]
Now, TeO ₂ It is assumed that incident light 102 having an angular frequency ωi is incident on a birefringent acousto-optic element 100 in which a piezoelectric element 22 is attached to an acousto-optic crystal having birefringence such as a crystal. Further, when the piezoelectric element 22 excites an acoustic wave 104 having an angular frequency ωa in the birefringent acousto-optic element 100, the interaction between the incident light 102 and the acoustic wave 104 causes an angle represented by the following [Equation 1]. The diffracted light 106 frequency-shifted to the frequency ωo is obtained. The incident light 102 is an extraordinary ray, the diffracted light 106 is an ordinary ray, and the plane of polarization of the diffracted light 106 is orthogonal to the plane of polarization of the incident light 102. Reference numeral 108 denotes undiffracted light.
[0017]
(Equation 1)
ωo = ωi + ωa
[0018]
However, ωa≪ωi, ωo, and ωi ≒ ωo may be considered.
At this time, when the wave vector of the incident light 102 is ki, the wave vector of the acoustic wave 104 is ka, and the wave vector of the diffracted light 106 is ko, a vector equation represented by the following [Equation 2] is established from the phase matching condition. I do.
[0019]
(Equation 2)
ko = ki + ka
[0020]
FIG. 2 shows the relationship between the k-vector of an ordinary ray and the k-vector of an extraordinary ray propagating in the birefringent acousto-optic element 100. The magnitude of the k vector with respect to the ordinary ray is constant irrespective of the traveling direction, and the trajectory of the end point of the k vector is a circle. On the other hand, the magnitude of the k vector for the extraordinary ray changes depending on the propagation angle of the birefringent acousto-optic element 100 with respect to the crystal axis, and the trajectory of the end point of the k vector becomes elliptical. The circle or ellipse formed by the trajectory of the k vector expands or contracts almost similarly when the wavelength is changed. FIG. 2A shows the wavelength λ. ₁ Shows a state where the phase matching condition of [Equation 2] is satisfied. In the figure, Va is the velocity of the acoustic wave 104 propagating in the crystal, and the wave number vector ka of the acoustic wave 104 ₁ Is | ωa / Va |.
[0021]
Here, when the frequency ωa of the acoustic wave 104 excited in the birefringent acousto-optic element 100, that is, the magnitude of the wave number vector ka is changed, the wavelength λ ₁ Then, the phase matching condition of [Equation 2] is not satisfied. At this time, the phase matching condition is satisfied, as shown in FIG. ₂ become. Thus, the wavelength λ of light that satisfies the phase matching condition and the angular frequency ωa of the acoustic wave have a one-to-one correspondence.
[0022]
As described above, the size of the circle or ellipse connecting the end points of the locus of the k vector changes depending on the wavelength, but its shape hardly changes. Therefore, if the wavelength is λ ₁ To λ ₂ , So that even if the magnitudes of the vectors ki and ko of the incident light 102 and the diffracted light 106 are changed, they become similar, so that the vector (ko ₁ -Ki ₁ ) And vector (ko ₂ -Ki ₂ ) Are parallel. As a result, ka ₁ = Ko ₁ -Ki ₁ , Ka ₂ = Ko ₂ -Ki ₂ The acoustic wave having the vector of can be input simply by changing the acoustic frequency.
[0023]
When the light of the wave vector ko emitted from the birefringent acousto-optical element 100 is reflected by the reflecting mirror 110 and enters the birefringent acousto-optical element 100 from the opposite direction, as shown in FIG. The returned light is also diffracted by the acoustic wave, and travels again in the opposite direction to the incident light ki to become -ki, which follows the optical path of the incident light in reverse.
[0024]
Therefore, when the total reflection mirror 110 and the exit side mirror 112 having a predetermined transmittance are arranged, for example, as shown in FIG. 3 with the laser medium 14 and the birefringent acousto-optic element 100 interposed therebetween, The side mirror 112 constitutes a laser resonator in which only light having a specific wavelength component reciprocates between the two. The wavelength λo of the diffracted light 106 changes when the frequency ωa of the acoustic wave 104 generated in the birefringent acousto-optic element 100 changes, and as a result of selecting ki, the wavelength λi = 2π / | ki | . Accordingly, the laser oscillation wavelength λi can be controlled by driving the piezoelectric element 22 attached to the birefringent acousto-optic element 100 with an RF signal of a predetermined frequency from the RF power supply 20.
[0025]
Further, since the diffraction efficiency of the diffracted light 106 is determined by the intensity of the acoustic wave excited in the birefringent acousto-optic element 100, the amplitude of the RF signal output from the RF power source 20 is controlled to control the diffracted light 106. And thus the laser output can be variably controlled.
[0026]
In the above description, the shape of the circle or ellipse connecting the end points of the locus of the k vector hardly changes depending on the wavelength. However, the shape actually changes slightly. Therefore, the diffraction angle also slightly changes depending on the wavelength, the condition of the resonator constituted by the total reflection mirror 110 and the partial transmission mirror 112 changes, and the direction of the emitted laser light changes slightly. This wavelength dependence of the diffraction angle can be compensated for by disposing a wavelength dispersion correction element such as a prism between the birefringent acousto-optic element 100 and the total reflection mirror 110, and the emission laser light at all wavelengths can be compensated. The direction can be constant.
Ti: Al as the laser medium ₂ O ₃ Any known tunable laser medium such as a laser crystal such as LiSAF, LiCAF, or a dye solution can be used.
[0027]
The ETT laser can be a continuous wave laser by using a continuous wave laser (CW laser) as a pump laser source, or a pulsed laser by using a pulse laser as a pump laser source. For example, Ti: Al as a laser medium ₂ O ₃ When Nd is used, Nd: YAG laser, Nd: YLF laser, Nd: YVO ₄ A second harmonic of an Nd solid-state laser such as a laser and an argon ion laser can be used. When a LiSAF laser crystal, a LiCAF laser crystal, or the like is used as a laser medium, a semiconductor laser or a krypton ion laser can be used.
[0028]
By matching the pumping volume of the pumping laser in the laser medium with the optical mode volume in the laser resonator to increase efficiency and lowering the pumping input, a high repetition pulsed pump laser or continuous Oscillation lasers can also be used as excitation lasers. For example, the laser resonator may be a Z-hold type laser resonator or an X-hold type laser resonator, and the pump laser light may be introduced along the optical path in the laser resonator, so that the pump light is efficiently used and the laser light is reduced. Laser oscillation can be caused by the excitation light of energy.
[0029]
By using this ETT laser as a light source for spectrometry, the light source unit, the sample unit, and the detection unit can be arranged separately, and remote measurement of a sample arranged at a distant position becomes possible. In addition, since the laser light is output as a beam with good directivity, it can be efficiently incident on the optical fiber, and the optical fiber connects between the light source section and the sample section and between the sample section and the detection section, so that remote measurement can be performed. Can be easily achieved.
[0030]
Further, by two-dimensionally scanning the sample with a laser beam while sweeping the wavelength of the ETT laser, spectrum measurement in a two-dimensional region of the sample can be easily performed.
In addition, by utilizing the good condensing property of the laser light, the laser light can be narrowed down to the sample with a lens or the like, and spectroscopic measurement can be performed in a spatially limited place.
[0031]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, an ETT laser used in the present invention will be described with reference to FIGS. In the following drawings, the same components or corresponding components are denoted by the same reference numerals, and detailed description thereof will be omitted.
[0032]
FIG. 3 is a diagram showing a schematic configuration of an example of the ETT laser used in the present invention. 3, the same components as those shown in FIG. 1 are denoted by the same reference numerals for easy understanding.
[0033]
In this ETT laser, a laser resonator is configured by an emission-side mirror 112 having a predetermined transmittance (for example, a reflectance of 98% and a transmittance of 2%) and a total reflection mirror 110, and a wavelength tunable is provided in the laser resonator. The laser medium 14 and the birefringent acousto-optic element 100 for wavelength selection are arranged between the emission side mirror 112 and the total reflection mirror 110 in this order. A piezoelectric element 22 driven by an RF power supply 20 is attached to the birefringent acousto-optic element 110 as acoustic wave input means. When the piezoelectric element 22 is driven by the RF power supply 20, an acoustic wave propagates through the birefringent acousto-optic element 100. The total reflection mirror 110 is configured to vertically reflect only the diffracted light 106 diffracted in a predetermined direction by the birefringent acousto-optic element 100.
[0034]
The laser medium 14 is excited by the excitation laser light 24. Further, based on the above-described principle, the frequency of the RF power supply is controlled according to the frequency (wavelength) of the laser light to be oscillated. In this way, the light of the next frequency ωo corresponding to the frequency ωa of the RF power source 20 is diffracted in the light of a wide wavelength band emitted from the laser medium 14 and incident on the birefringent acousto-optic element 100. The light 106 is diffracted from the birefringent acousto-optic device 100 toward the total reflection mirror 110.
ωo = ωi + ωa
[0035]
Thus, only the light having the frequency ωi can reciprocate in the laser medium 14, is amplified by the laser medium, generates laser oscillation, and emits the laser light from the laser resonator.
[0036]
FIG. 4 shows an arrangement in which a beam diameter expanding means for avoiding optical damage to the birefringent acousto-optic element is provided, and laser oscillation is performed in a wide wavelength range by compensating for the frequency dependence of the diffraction angle. An example of a laser in which a prism as a wavelength dispersion correction element is arranged between a refractive acousto-optic element and a total reflection mirror will be described.
[0037]
A telescope 30 for adjusting the beam diameter is arranged between the laser medium 14 and the birefringent acousto-optic device 100, and the parallel light whose diameter has been enlarged by the telescope 30 passes through the birefringent acousto-optic device 100. I do. According to this arrangement, the light reciprocating in the laser resonator passes through the laser medium 14 as a light beam having a high light intensity, and thus does not lower the laser efficiency. On the other hand, at the position of the birefringent acousto-optical element 100, the intensity of light emitted per unit area decreases, so that optical damage to the birefringent acousto-optical element 100 can be suppressed.
[0038]
Further, a prism 28 is arranged between the birefringent acousto-optic element 100 and the total reflection mirror 110 as a wavelength dispersion correction element for the diffraction angle. The prism 28 is designed so that the diffracted light 106 emitted from the birefringent acousto-optic element 100 always enters the total reflection mirror 110 perpendicularly regardless of the wavelength of the diffracted light. In this case, the light beam diffracted by the birefringent acousto-optic element 100 to become the diffracted light 106 is reflected by the total reflection mirror 110 at any wavelength, and can follow the same optical path in reverse. The laser light can be efficiently amplified by the laser medium 14 to perform laser oscillation. If there is wavelength dispersion in the diffraction angle of the diffracted light, the optical path in the laser resonator changes, and the wavelength tunable range is restricted. However, the provision of the dispersion correcting prism 28 solves such a problem. Can be eliminated. Further, by using the prism 28 for correcting the wavelength dispersion of the diffraction angle, the direction of the emitted laser light can be made constant.
[0039]
In the example of FIG. 4, the telescope 30 for adjusting the beam diameter and the chromatic dispersion compensating element 28 of the diffraction angle are arranged together in the laser resonator, but it is not necessary to consider the optical damage of the birefringent acousto-optical element 100. In such a case, the telescope 30 can be omitted, and when it is not necessary to consider the wavelength dependence of the diffraction angle by the birefringent photoacoustic element 100, the chromatic dispersion correction element 28 can be omitted.
[0040]
FIG. 5 shows the wavelength and output power of the laser light emitted when the frequency of the RF power supply 20 is changed using an ETT laser in which the wavelength dispersion correction element 28 of the diffraction angle is incorporated in the laser resonator as shown in FIG. It shows the relationship. The laser oscillation conditions are as follows. Ti: Al for the laser medium 14 ₂ O ₃ , And a pulsed laser beam having a pulse width of 8 ns and a wavelength of 532 nm, which is the second harmonic of the Nd: YAG laser, was used as the excitation laser beam 24. The energy per pulse of the excitation laser light was 155 mJ. The reflectance of the exit side mirror 112 was 60%, and the reflectance of the total reflection mirror 110 was 99.9% at a wavelength of 800 nm. The RF power supply had a frequency variable range of 40 MHz to 150 MHz and was used at an output of 2 W. The diffraction efficiency of the birefringent acousto-optic element 100 is 98%. As is clear from FIG. 5, laser oscillation was possible in the wavelength variable range of about 750 to 850 nm.
[0041]
FIG. 6 shows a change in the output of the laser light emitted when the output of the RF power source is changed to change the input power of the acoustic wave. From FIG. 6, when the power of the acoustic wave input to the birefringent acousto-optic element changes from 0.5 W to 2 W, the output of the emitted laser light also changes accordingly, It can be seen that the output of the emitted laser light can be controlled by changing the power of the input acoustic wave.
[0042]
FIG. 7 is a schematic view showing another example of the ETT laser. In this example, a so-called Z-hold type laser resonator is used in which an optical path of light reciprocating in the laser resonator has a Z-shape of an alphabet. The Z-hold type laser resonator includes an emission side mirror 112 having a predetermined transmittance and a total reflection mirror 110. Further, a first intermediate mirror 37 that receives the excitation laser light A and reflects the light B reciprocating between the emission side mirror 112 and the total reflection mirror 110, and a path between the emission side mirror 112 and the total reflection mirror 110. There is provided a second intermediate mirror 38 for reflecting the reciprocating light B, and the optical path of the reciprocating light B in the laser resonator has a Z-shaped alphabet.
[0043]
Between the first intermediate mirror 37 and the second intermediate mirror 38 on the optical path of the laser resonator, a laser medium 14 having a Brewster-cut incident end face of incident light as a wavelength-variable laser medium, and an incident end face of which is incident light. Are arranged so as to have a Brewster's angle at which the reflection of light becomes zero, and laser oscillation is generated by the excitation laser light A by longitudinal coaxial excitation. A birefringent acousto-optic element 100 is disposed as a wavelength selecting means between the second intermediate mirror 38 and the total reflection mirror 110 on the optical path of the laser resonator.
[0044]
A piezoelectric element 22 driven by an RF power source 20 whose frequency is controlled by a personal computer 26 is attached to the birefringent acousto-optic element 100 as acoustic wave input means. Therefore, the piezoelectric element 22 is driven by the RF power supply 20 set to an arbitrary frequency under the control of the personal computer 26 to excite an acoustic wave corresponding to the frequency to the birefringent acousto-optical element 100, thereby obtaining a birefringent light. The acousto-optic device 100 diffracts the light D having the frequency ωo represented by the above [Equation 1]. The piezoelectric element 22 diffracts only the light corresponding to the light B (frequency ωi ≒ ωo) having the wavelength of the emission laser light C to be emitted from the emission side mirror 112 by the birefringent acousto-optic element 100 in a predetermined direction. The personal computer 26 controls the frequency ωa of the acoustic wave input to the birefringent acousto-optic device 100 so that the light is emitted as light D and laser resonance occurs.
[0045]
Between the birefringent acousto-optic element 100 and the total reflection mirror 110, a prism 28 as a wavelength dispersion correction element for correcting the dispersion of the diffracted light D is provided. By using the wavelength dispersion correcting prism 28 having this diffraction angle, the direction of the emitted laser light C can be made constant. A pulse laser or a continuous wave laser (CW laser) can be used as the excitation laser 32 for injecting the excitation laser light A into the laser resonator.
[0046]
The excitation laser light A generated by the excitation laser 32 is reflected by the total reflection mirror 36 by the total reflection mirror 34, collected by the total reflection collection mirror 36, and condensed by the laser medium 14 through the first intermediate mirror 37. Is input so as to excite the longitudinal coaxial excitation.
[0047]
In the above configuration, to obtain the emission laser light C, the laser medium 14 is excited by using the excitation laser light A incident by the excitation laser 32. Further, the frequency ωa of the RF power supply 20 is controlled by the personal computer 26 in accordance with the wavelength (frequency ωi) of the emission laser light C to be emitted from the emission side mirror 112, and the piezoelectric element 22 is driven. In this way, of the light in a wide wavelength range emitted from the laser medium 14 and incident on the birefringent acousto-optic element 100, light having a wavelength corresponding to the frequency of the RF power supply 20 is converted into a birefringent acoustic wave. The light is diffracted by the optical element 100 as diffracted light D (frequency ωo). The diffracted light D is vertically incident on the total reflection mirror 110 via the wavelength dispersion correcting prism 28 of the diffraction angle, is reflected by the total reflection mirror 110, and reciprocates in the laser resonator along a Z-shaped optical path. (Angular frequency ωi at the position of the laser medium 14). Therefore, only the light of the wavelength corresponding to the frequency of the RF power supply 20 is amplified and laser oscillates, and the emitted laser light C (frequency ωi) of the wavelength is emitted from the laser resonator.
[0048]
As described above, the wavelength selection of the output laser light C can be realized by selecting the frequency ωa of the RF power supply 20 under the control of the personal computer 26. Therefore, the high-speed and random wavelength selection of the output laser light C (frequency ωi) is performed. As a result, the speed of changing the wavelength of the emitted laser light can be increased.
[0049]
In the ETT laser shown in FIG. 7, since the structure of the laser resonator is a Z-hold type, the excitation laser beam A is focused by the total reflection focusing mirror 36 and is incident on the laser medium 14, so that the excitation input intensity is The laser oscillation can be sufficiently generated even by the excitation laser light A using a low-power pulse excitation laser or a low-power CW laser.
[0050]
FIG. 8 shows an experimental result on the input / output characteristics of the ETT laser shown in FIG. Here, Ti: Al is used as the laser medium 14. ₂ O ₃ A crystal was used, a CW-Q switch pulse Nd: YLF laser was used as the excitation laser 32, and its second harmonic was used as the excitation laser light A. The wavelength of the pump laser light A is 523 nm, the pulse repetition frequency is 1 kHz, and the maximum output per pulse is 200 μJ. The diameter of the total reflection mirror 36 was 200 mm, the radius of the first intermediate mirror 37 and the radius of the second intermediate mirror 38 was 100 mm, and the reflectance of the output side mirror 112 was 97% (transmittance 3%). In the laser medium 14, the excitation region and the cavity mode diameter are reduced to several tens of μm, and the excitation laser beam A is focused on this region by the total reflection focusing mirror 36, thereby improving the excitation efficiency. FIG. 8 shows input / output characteristics of the energy of the excitation laser light A (input) and the energy of the output laser light C (output) when the wavelength of the output laser light C is fixed to 800 nm. As apparent from FIG. 8, the laser oscillation threshold was reached when the energy of the excitation laser beam A became about 40 mJ per pulse.
[0051]
FIG. 9 shows a wavelength tunable characteristic when the energy of the excitation laser beam A is 100 μJ. As is clear from FIG. 9, the wavelength variable range is from about 740 nm to about 870 nm. With the provision of the prism 28 for correcting the wavelength dispersion of the diffraction angle, the beam deflection observed at the time of tuning the wavelength of the laser was below the observation limit.
[0052]
Next, the spectroscopic measurement method of the present invention using the ETT laser will be described.
FIG. 10 is a schematic diagram illustrating an example of spectrometry according to the present invention. The above-mentioned ETT laser 40 is used as a spectral light source. As described above, the ETT laser 40 has a laser medium capable of oscillating laser in a predetermined wavelength region and a birefringent acousto-optic element arranged in a laser resonator, and a light component diffracted by the birefringent acousto-optic element. A wavelength tunable laser that forms a laser resonator and selects a wavelength by selecting a frequency of an acoustic wave to be excited in a birefringent acousto-optic element.For example, titanium sapphire is selected as a laser medium. Thereby, monochromatic light can be extracted in a wavelength range of about 680 nm to about 1100 nm. The ETT laser 40 can generate pulsed laser light or can generate continuous laser light.
[0053]
The monochromatic laser light 41 of wavelength λ extracted from the ETT laser 40 is split into two by a half mirror 42, one of which is incident on the sample S, and the other is incident on the reference sample R. The light beam transmitted through the sample S is detected by a photodetector 43 such as a photomultiplier tube, and the light beam transmitted through the reference sample R is similarly detected by a photodetector 44. The absorbance of the sample S at the wavelength λ is obtained by calculating the ratio of the outputs of the two photodetectors 43 and 44 in the calculation unit 45 and performing logarithmic calculation, and the result is displayed on a display device 46 such as a CRT. Now, let the oscillation wavelength of the ETT laser 40 be λ. ₁ ~ Λ ₂ Sweeping up to the wavelength λ ₁ ~ Λ ₂ Can be obtained. Although the measurement of the absorption spectrum of the sample S has been described here, the reflection spectrum of the sample S can be measured by arranging the photodetectors 43 and 44 at positions where the reflected light from the sample S and the reference sample R is measured.
[0054]
When the ETT laser 40 is used as the spectral light source and the laser light is used as the sample incident light, the diameter of the sample incident light can be reduced and the light intensity can be increased. It can be carried out.
[0055]
FIG. 11 is an explanatory diagram of an example of spectrometry in which remote measurement is enabled by connecting the ETT laser 50 as a spectral light source and the sample S and the sample S and the photodetectors 54 and 58 by optical fibers 52a, 52b and 52c. It is.
[0056]
The light emitted from the ETT laser 50 enters the light transmitting optical fiber 52a from the optical coupler 51a, passes through the light transmitting optical fiber 52a, exits from the irradiation optical coupler 51b at the other end, and irradiates the sample S. . The light transmitted through the sample S enters the light receiving optical fiber 52b from the light receiving optical coupler 51c, exits from the light coupler 51d provided at the other end of the light receiving optical fiber 52b, and is detected by a photomultiplier tube or the like. Is detected by the detector 54. The detection output of the photodetector 54 is input to a signal processing device 55.
[0057]
The control unit 57 sends a control signal to the ETT laser 50 and the signal processing device 55 to control the frequency of the acoustic wave to be excited in the birefringent acousto-optic element of the ETT laser 50, thereby causing the ETT laser 50 to have a desired wavelength. Oscillate. The signal processing device 55 knows the sample irradiation wavelength based on the control signal sent from the control unit 57, and calculates the absorbance of the sample S at that wavelength. Here, when the wavelength of the ETT laser 50 is swept, the transmission absorption spectrum of the sample S can be measured.
[0058]
When the light receiving optical coupler 51e of the light receiving optical fiber 52c is arranged at an angle with respect to the optical axis of the irradiation optical coupler 51b, the scattered light or light emission from the sample S can be measured. The light incident on the light receiving optical coupler 51e passes through the light receiving optical fiber 52c, is received by the light detector 58 having the filter 59, and the detection output of the light detector 58 is supplied to the signal processing device 55. The output of the signal processing device 55 is output to a display device 56 such as a CRT. At this time, when the oscillation wavelength of the ETT laser 50 is swept, the emission excitation spectrum can be measured.
[0059]
As described above, the method of connecting the ETT laser 50 and the sample S and the sample S and the photodetectors 54 and 58 with the optical fibers 52a, 52b, and 52c separates the sample S from the measuring devices 50, 54, 58, 55, and 56. It is effective when it is necessary to set up. An example of a case where such a measurement is required is a case where the concentration of a liquid flowing in a pipeline, the sugar content of fruits transported by a belt conveyor, and the like are centrally controlled from a measurement room. According to this method, sample measurement at measurement positions set at a plurality of locations can be performed intensively in a measurement room several tens meters or several hundred meters away from the measurement positions. In addition, blood analysis and the like of a patient in an operating room or a hospital room in a hospital or the like can be intensively performed in a similar remote monitor room.
[0060]
FIG. 12 is a diagram illustrating measurement of a two-dimensional distribution of a specific component in a sample according to the present invention.
The sample S is held by the sample table 61 and can be moved in the X and Y directions by driving means such as a motor incorporated in the sample table 61. The monochromatic laser light 68 emitted from the ETT laser 60 is narrowed down by the converging lens 62 and spot-irradiated to a minute area on the sample S. The laser light transmitted through the minute area of the sample is condensed by the condenser lens 63 and is incident on the photodetector 64 and detected. The output signal of the photodetector 64 is processed by a signal processing device 65 and then supplied to a monitor 67 such as a CRT. The irradiation position of the monochromatic laser light 68 on the sample S is controlled by moving the sample table 61 in the X and Y directions by the control unit 66, and the control information of the sample table 61 is also supplied from the control unit 66 to the signal processing device 65. You.
[0061]
For example, the sample stage 61 is moved stepwise or continuously by the control unit 66. At this time, the monochromatic laser light 68 emitted from the ETT laser 60 at each position on the sample S is rapidly switched to two wavelengths of the measurement wavelength λs and the reference wavelength λr, and the intensity of the sample transmitted light at each wavelength λs, λr is measured. . The measurement wavelength λs is a wavelength that is strongly absorbed by the target component in the sample, and the reference wavelength λr is a wavelength that is not absorbed by the target component. By calculating the transmitted light intensity of the sample at two wavelengths, the concentration of the target component contained in the minute region of the sample S can be obtained. As described above, by two-dimensionally scanning the laser beam irradiation position on the sample S, the two-dimensional distribution of the target component on the sample S can be displayed on the monitor 67.
[0062]
FIG. 13 is a diagram illustrating another example of two-dimensional measurement of a sample according to the present invention. In this example, monochromatic light from an ETT laser is introduced into a microscope, and the two-dimensional distribution of transmitted light or emission of a cell specimen or the like is measured using a two-dimensional detector.
[0063]
The monochromatic laser light 71 from the ETT laser 70 is enlarged in beam diameter by the lens systems 72a and 72b, reflected by the reflecting mirror 73, and then galvanomirror 74X for oscillating the beam in the X-axis direction and galvano mirror for oscillating in the Y-axis direction. After the beam axis is adjusted by 74Y, the beam is reflected by the reflection mirror 75 and introduced into the microscope 80.
[0064]
The monochromatic laser light introduced into the microscope 80 is reflected by the dichroic mirror 81 and irradiates the sample S through the objective lens 82. The laser beam transmitted through the sample S is converged by the condenser lens 83 and reflected by the reflection mirror 84, and then guided by the imaging lens 85 to a detector 86 such as a photomultiplier tube. Light emitted from the sample S, for example, fluorescence, passes through the dichroic mirror 81 and the excitation light cut filter 87, and then enters the detector 89 such as a photomultiplier tube by the imaging lens 88.
[0065]
The output signal of the detector 86 or 89 is input to the image processing device 91, and is converted into a two-dimensional image by combining the position information obtained by scanning the galvanometer mirrors 74X and 74Y and the output information of the detector 86 or 89. The image signal from the image processing device 91 is stored in the VTR 92 and displayed on the monitor 93. The sample image displayed on the monitor 93 can also be output to the printer 94. If a two-dimensional detector such as a CCD camera is used instead of a photomultiplier by sweeping a laser beam at high speed, it can be directly captured as a two-dimensional image.
[0066]
Since the ETT laser 70 can obtain a monochromatic laser beam of a desired wavelength and can switch wavelengths at high speed, it is effective for detecting a difference or a differential spectrum for measuring a minute absorption and a change in a light emission amount. I do.
[0067]
The laser measurement of the present invention is a general absorption / emission measurement method in which the measurement target is not limited. Examples of the measurement target specific to the oscillation wavelength of the present laser include hemoglobin and silicon in blood. In the former, it is possible to analyze the amount of oxygen binding from the spectrum analysis around 740 nm. In the latter, the position and depth of a defect in a silicon wafer can be measured by utilizing the fact that the absorption at 700 to 1100 nm changes significantly.
[0068]
【The invention's effect】
According to the present invention, the use of a newly developed ETT laser makes it possible to perform spectroscopic measurement of a sample without using a spectrophotometer. Therefore, spectrometry can be performed without being limited by the shape of the sample or the state of the sample, and the applicable range of the spectrometry can be greatly expanded.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram illustrating a wavelength selection action by a birefringent acousto-optic element.
FIG. 2 is a diagram showing a k-vector of an ordinary ray and a k-vector of an extraordinary ray that propagate in a birefringent acousto-optic element.
FIG. 3 is a diagram illustrating an example of an ETT laser.
FIG. 4 is an explanatory diagram of another example of the ETT laser.
FIG. 5 is a diagram illustrating a relationship between a wavelength and an output of an ETT laser.
FIG. 6 is a diagram showing the relationship between the acoustic wave input power input to the birefringent acousto-optic element and the output of the emitted laser light.
FIG. 7 is an explanatory diagram of another example of the ETT laser.
FIG. 8 is a diagram showing input / output characteristics of the energy of the excitation laser light and the energy of the emission laser light when the ETT laser is excited by the pulse laser.
FIG. 9 is a view showing a wavelength tunable characteristic of the ETT laser shown in FIG. 7;
FIG. 10 is a schematic diagram illustrating an example of spectrometry according to the present invention.
FIG. 11 is an explanatory diagram of an example of spectrometry in which remote measurement is enabled by connecting an ETT laser, a sample, and a photodetector with an optical fiber.
FIG. 12 is a diagram illustrating measurement of a two-dimensional distribution of a specific component in a sample.
FIG. 13 is a view for explaining another example of two-dimensional measurement of a sample.
FIG. 14 is a schematic diagram of a conventional spectrophotometer.
[Explanation of symbols]
14 laser medium, 20 RF power supply, 22 piezoelectric element, 24 excitation laser light, 26 personal computer, 28 prism, 30 telescope, 32 excitation laser, 40 ETT laser, 41 monochromatic laser Light, 42 half mirror, 43, 44 photodetector, 45 arithmetic unit, 46 display device, 50 ETT laser, 51a-51d optical coupler, 52a-52c optical fiber, 54 optical detector, 55 ... signal processing device, 56 ... display device, 57 ... control unit, 58 ... photodetector, 59 ... filter, 60 ... ETT laser, 61 ... sample stand, 64 ... photodetector, 65 ... signal processing device, 66 ... Control unit, 67 monitor, 68 monochromatic laser beam, 70 ETT laser, 74X, 74Y galvanometer mirror, 80 microscope, 81 dichroic mirror, 82 pair Lens 83: condenser lens 86, 89: two-dimensional detector 91: image processing device 92: VTR, 93: monitor, 94: printer, 100: birefringent acousto-optic element, 102: incident light, 104: Acoustic wave, 106: diffracted light, 110: total reflection mirror, 112: emission side mirror, 200: light source unit, 210: monochromator, 211: monochromatic light, 221, 224: sector mirror, 222, 223: reflection mirror, 230 …Detector

Claims (4)

In a spectroscopic measurement method for performing spectroscopic measurement of a sample by irradiating the sample with monochromatic laser light from a tunable laser,
As the tunable laser, a laser medium capable of oscillating laser in a predetermined wavelength region, a birefringent acousto-optic element, and an element for correcting wavelength dispersion of a diffraction angle by the birefringent acousto-optic element are arranged in a laser resonator. A laser resonator is formed on a predetermined optical axis of a light component diffracted by the birefringent acousto-optic element, and a wavelength of the acoustic wave to be excited in the birefringent acousto-optic element is selected. A spectrometry method characterized by using a wavelength tunable laser for selection,
As an element for correcting the wavelength dispersion of the diffraction angle due to the birefringent acousto-optic element, a diffracted light satisfying a phase matching condition between an acoustic wave, incident light, and diffracted light by selecting an acoustic frequency is deflected from a predetermined optical axis. Using a prism designed to correct the wavelength dispersion of the diffraction angle. The method according to claim 1, wherein the sample is irradiated with the laser light via an optical fiber. The method according to claim 1, wherein the laser beam is scanned with respect to the sample, and spectral measurement is performed in a two-dimensional area of the sample. A laser medium capable of laser oscillation in a predetermined wavelength region, a birefringent acousto-optic element, and an element for correcting wavelength dispersion of a diffraction angle by the birefringent acousto-optic element are arranged in the laser resonator, A wavelength tunable laser that forms a laser resonator on a predetermined optical axis of a light component diffracted by an acousto-optic element and controls a frequency of an acoustic wave to be excited in the birefringent acousto-optic element to perform wavelength selection. And a irradiating means for irradiating the sample with monochromatic laser light emitted from the wavelength tunable laser, and a photodetector for detecting the monochromatic laser light after interacting with the sample. And
The element that corrects the wavelength dispersion of the diffraction angle due to the birefringent acousto-optic element, the diffraction light that satisfies the phase matching condition between the acoustic wave, the incident light, and the diffracted light by selecting the acoustic frequency is deflected from a predetermined optical axis. spectrometer, characterized in that the prisms designed to correct the chromatic dispersion of the diffraction angle that.

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