JP6720383B2 - Far infrared spectrometer - Google Patents

Description

The present invention relates to a far infrared spectroscopy device.

Electromagnetic waves in the far infrared region with a wavelength of about 25 μm to about 4 mm are also called terahertz waves and have both radio wave transparency and light straightness. Electromagnetic waves in the far infrared region are expected to be effective for identifying substances because the absorption spectrum in this region has a peak peculiar to many substances. However, conventionally, there is no small and easy-to-use light source that emits light in this region, and the detector needs to be cooled with liquid helium or the like, which is difficult to handle. Therefore, in the past, electromagnetic waves in the far infrared region have been used only for limited research purposes.

In the 1990s, a light source and a detector using a femtosecond laser, which is small and does not require cooling, has been put into practical use. At present, general-purpose spectrometers based on time-domain spectroscopy are also on the market, and research and development for applications in various fields such as security, biosensing, medical/pharmaceutical, industry, and agriculture are under way. In such industrial application, it is required to quantitatively analyze the components.

JP, 2003-302666, A

In industrial applications, quantitative analysis of ingredients is one of the keys. Although there are attempts at quantitative analysis using time-domain spectroscopy, this method is difficult to measure at 1 to 3 THz, which is effective for detecting hydrogen bonds or molecular networks, and can be measured through shields such as paper and packing materials. However, it is difficult to measure powder with strong scattering. On the other hand, the method using a variable frequency coherent light source is easy to obtain a high output in the range of 1 to 3 THz, and is effective for analysis through a shield and powder analysis.

However, in the above method, since the direction in which the far infrared light is emitted changes when the frequency is changed, there is a problem that the irradiation position on the sample changes and the accuracy of the quantitative analysis deteriorates.

Therefore, the present invention provides a far-infrared spectroscopic device capable of reducing the deviation of the irradiation position of far-infrared light due to frequency change.

For example, in order to solve the above-mentioned subject, the composition described in a claim is adopted. The present application includes a plurality of means for solving the above problems. To give an example thereof, a wavelength tunable far-infrared light source that generates a first far-infrared light, and the first far-infrared light as a sample An illumination optical system that irradiates the sample upward, a nonlinear optical crystal for detection that converts the second far infrared light from the sample into near infrared light using pump light, and a nonlinear optical crystal for detection that is an image of the sample. A far-infrared light imaging optical system for forming an image on a crystal, and the irradiation position of the first far-infrared light on the sample does not depend on the wavelength of the first far-infrared light. An infrared spectroscopy device is provided.

According to the present invention, it is possible to reduce the deviation of the irradiation position of far infrared light due to the frequency change. Further features related to the present invention will be apparent from the description of the present specification and the accompanying drawings. Further, problems, configurations and effects other than those described above will be clarified by the following description of the embodiments.

It is the figure which looked at the example of composition of the spectroscopic device using the light of the far infrared region in the 1st example of the present invention from the side. It is the figure which looked at the example of composition of the spectroscopic device using the light of the far infrared region in the 1st example of the present invention from the upper surface. FIG. 3 is a plan view showing an irradiation area of a sample in the first embodiment of the present invention. It is a figure which shows the mode of propagation of the far infrared light in 1st Example of this invention. It is a figure explaining the adjustment method of the incident angle at the time of making far infrared light which permeate|transmitted the sample in the 1st Example of this invention inject into the nonlinear optical crystal for a detection. It is a figure explaining the adjustment method of the incident angle at the time of making far infrared light which permeate|transmitted the sample in the 1st Example of this invention inject into the nonlinear optical crystal for a detection. FIG. 5 is a diagram showing how far infrared light is generated in the first embodiment of the present invention. It is a figure which shows each wave number vector of far-infrared light, pump light, and seed light. It is a figure which shows the structural example of the incident angle adjustment optical system in 1st Example of this invention. It is a figure which shows the structural example of the spectroscopic apparatus using the light of the far infrared region in 2nd Example of this invention. It is a figure explaining the irradiation position of the far-infrared light on the sample surface in 2nd Example of this invention. It is a figure explaining the irradiation position of the far-infrared light on the sample surface in the 2nd Example of this invention, and its correction method. It is a figure explaining the irradiation position of the far-infrared light on the sample surface in the 2nd Example of this invention, and its correction method. It is a figure which shows the structural example of the light source for pump light of a wavelength variable far-infrared light source in 2nd Example of this invention. It is the figure which looked at the example of composition of the spectroscopic device using the light of the far infrared region in the 3rd example of the present invention from the side. It is the figure which looked at the example of composition of the spectroscopic device using the light of the far infrared region in the 3rd example of the present invention from the upper surface. It is a top view which shows the irradiation area|region of the sample in 3rd Example of this invention. It is the figure which looked at the example of composition of the spectroscopic device using the light of the far infrared region in the 4th example of the present invention from the side. It is the figure which looked at the example of composition of the spectroscopic device using the light of the far infrared region in the 4th example of the present invention from the upper surface. It is a top view which shows the irradiation area|region of the sample in 4th Example of this invention. It is the figure which looked at the example of composition of the spectroscopic device using the light of the far infrared region in the 5th example of the present invention from the side. It is an enlarged view of the surface of the cylindrical lens of the illumination optical system in the 5th Example of this invention. It is an enlarged view of the surface of the cylindrical lens of the illumination optical system in the 5th Example of this invention. It is a figure explaining the groove|channel structure of the surface of the cylindrical lens of the illumination optical system in 5th Example of this invention. It is a figure explaining the groove|channel structure of the surface of the cylindrical lens of the illumination optical system in 5th Example of this invention. It is a figure explaining the groove|channel structure of the surface of the lens used for the optical system which adjusts the optical path in 5th Example of this invention, and a far-infrared light imaging optical system. It is a figure which shows the structural example of the conventional far-infrared spectroscopy apparatus using the light of a far-infrared region.

Embodiments of the present invention will be described below with reference to the accompanying drawings. It should be noted that although the attached drawings show specific examples according to the principle of the present invention, these are for understanding the present invention, and are used for limiting interpretation of the present invention. is not.

The following examples are far-infrared spectroscopic devices for analyzing a sample by using light in the far-infrared region in an inspection process such as an analysis of the content of chemical substance components in a sample, or an inspection of different components or foreign substances. Regarding Here, the light in the far infrared region is light having a wavelength of, for example, 25 μm to 4 mm. Although there are numerical ranges of various wavelengths as the definition of "far infrared region", light in the far infrared region described below is interpreted in the widest range defined in all fields. It should be. Further, the term “terahertz wave” is assumed to be included in the far infrared region described above.

[First embodiment]
1A and 1B show an example of the overall configuration of the far-infrared spectroscopic device according to the first embodiment. As an example, the far-infrared spectroscopic device is a device that measures the absorption spectrum of the sample 200 using the light that has passed through the sample 200.

The far-infrared spectroscopic device includes a wavelength-tunable far-infrared light source 100 that generates far-infrared light, an illumination optical system 150 that irradiates the sample 200 with far-infrared light, a sample stage 202 that mounts the sample 200, and a sample. Far-infrared light imaging optical system 170 that images far-infrared light from 200 on detection nonlinear optical crystal 132, and far-infrared light from sample 200 is converted into near-infrared light using pump light. The detection nonlinear optical crystal 132, a photodetector (sensor) 290, a signal processing unit 400, and a control unit 500 are provided.

The wavelength tunable far infrared light source 100 includes a light source 110 for a pump light 115, a wavelength tunable light source 120 for a seed light 125, an incident angle adjusting optical system 121, and a nonlinear optical crystal (a far infrared light generating nonlinear optical crystal. ) 130 and. As the wavelength tunable far infrared light source 100, a configuration in which two laser lights having different wavelengths (pump light 115 and seed light 125) are put into the nonlinear optical crystal 130 to generate far infrared light by difference frequency generation or parametric generation. To use.

For example, MgO:LiNbO3 may be used as the nonlinear optical crystal 130, and a short-pulse Q-switch YAG laser may be used as the light source 110 of the pump light 115. In this configuration, the light from the variable wavelength light source 120 enters the nonlinear optical crystal 130 as the seed light 125 at a slight angle with respect to the pump light 115 via the incident angle adjusting optical system 121 and the mirror 126. Thereby, far infrared light can be obtained by parametric generation.

The Si prism 140 may be attached to the nonlinear optical crystal 130. According to this configuration, the generated far infrared light can be efficiently extracted. If the wavelength of the seed light 125 is changed between about 1066 nm and 1076 nm, and the incident angle to the nonlinear optical crystal 130 is adjusted by the incident angle adjusting optical system 121, the frequency of the far infrared light generated is 0.5 THz to. It can be changed within the range of about 3 THz.

The far infrared light thus obtained is irradiated onto the irradiation region 205 on the sample 200 using the illumination optical system 150. FIG. 1C is a plan view showing an irradiation region of the sample 200.

The illumination optical system 150 is an anamorphic image forming optical system including at least three cylindrical lenses 152, 154 and 156. Here, “anamorphic” means that the optical characteristics are different from each other in two orthogonal planes including the optical axis. Specifically, in the “imaging optical system”, anamorphic means that magnifications are different from each other in two orthogonal planes including the optical axis.

The illumination optical system 150 will be described more specifically. In the plane of FIG. 1B, the cylindrical lenses 152 and 154 have optical power. A light emitting region of far infrared light is arranged on the front focal plane of the cylindrical lens 152. The light emitting area here is a linear light emitting area along the pump light 115 (for example, a linear area passing through B0 and A0 in FIG. 2). Further, the cylindrical lens 154 is arranged so that the rear focal plane of the cylindrical lens 152 and the front focal plane of the cylindrical lens 154 coincide with each other. Further, the sample 200 is arranged on the rear focal plane of the cylindrical lens 154.

An aperture stop may be installed in the rear focal plane of the cylindrical lens 152 (that is, also in the front focal plane of the cylindrical lens 154). According to this configuration, the optical system is strictly telecentric on both sides in the plane of FIG. 1B, but the aperture stop is not essential here. The use range of far infrared light can be limited by using the aperture stop.

It should be noted that the illumination optical system 150 is an afocal optical system, and may function as a substantially bilateral telecentric optical system due to the spreading characteristics of the far infrared beam emitted from the nonlinear optical crystal 130.

Also, in the plane of FIG. 1A, the cylindrical lens 156 has optical power. The cylindrical lens 156 is arranged so that the emission region of far infrared light is imaged on the sample 200.

The illumination optical system 150 is an imaging optical system that collimates far-infrared light within the first cross section including the optical axis of far-infrared light from the wavelength tunable far-infrared light source 100 and focuses it again on the surface of the sample 200. In addition, in the second cross section orthogonal to the first cross section, it is a condensing optical system that condenses the far infrared light from the wavelength tunable far infrared light source 100 on the surface of the sample 200. Specifically, the far infrared light emitted from the wavelength tunable far infrared light source 100 is a linear light source (FIG. 2) along the beam of the pump light 115. Far-infrared light emitted from the wavelength tunable far-infrared light source 100 spreads in the plane of FIG. 1A, but becomes a parallel light flux in the plane of FIG. 1B. In the plane of FIG. 1A, the far-infrared light is converged by the cylindrical lens 156 on the irradiation area on the sample 200. On the other hand, in the plane of FIG. 1B, the far-infrared light is once condensed by the cylindrical lens 152, made into a parallel light flux again by the cylindrical lens 154, and irradiated onto the sample 200. In this way, the illumination optical system 150 can form an image on the sample 200 of the linear light emitting region formed by the wavelength tunable far infrared light source 100 by reducing the longitudinal direction of the linear region.

The illumination optical system 150 is afocal in the first section including the optical axis of far infrared light from the wavelength tunable far infrared light source 100. By setting the illumination optical system 150 as an afocal system (that is, by arranging the cylindrical lens 154 so that the rear focal surface of the cylindrical lens 152 and the front focal surface of the cylindrical lens 154 are aligned), the inside of the nonlinear optical crystal 130 is obtained. It is possible to irradiate the sample 200 with far-infrared light that is substantially parallel to the plane of FIG. Further, the far infrared light transmitted through the sample 200 can be efficiently taken into the far infrared light imaging optical system 170.

In this way, by using the illumination optical system 150 as the imaging optical system, it is possible to ensure the stability of the illumination when the wavelength of the far infrared light emitted from the wavelength tunable far infrared light source 100 is changed. Becomes That is, by using the illumination optical system 150 as the imaging optical system, the irradiation position of the far infrared light on the sample 200 does not depend on the wavelength of the far infrared light from the wavelength tunable far infrared light source 100.

In order to change the wavelength of the far infrared light, the wavelength of the seed light 125 is changed and the incident angle on the nonlinear optical crystal 130 is adjusted. At that time, the emission direction of the generated far infrared light changes in the in-plane direction of FIG. 1B (for example, θ1 to θ2 in FIG. 1B). Even in this case, the illumination optical system 150 is an imaging optical system, and the far infrared light emission region and the sample 200 surface are in a conjugate relationship (imaging relationship), so that the far infrared light spot is also formed on the sample 200 surface. Can be prevented from moving. Even if the wavelength of far infrared light is changed, the irradiation position of the sample 200 does not shift, so that the amount of illumination light does not change and stable illumination can be secured. On the other hand, when the illumination optical system 150 is not the imaging optical system, the illumination position of the illumination light may be completely different, which makes stable imaging difficult. However, this is not the case when imaging is performed with a fixed wavelength, or when the wavelength change range is small and the change in the azimuth of the far infrared light is sufficiently small.

Further, by using the illuminating optical system 150 as an anamorphic optical system, the linear emission area of the wavelength tunable far infrared light source 100 is reduced in the longitudinal direction of the linear area, and the sample 200 is illuminated as a spot. can do. According to this configuration, as described below, two-dimensional data can be obtained by scanning the spot on the sample 200.

The sample 200 to be imaged is mounted on the stage 202. The stage 202 includes a mechanism that can move in at least one direction. For example, the stage 202 can move in the x direction in FIG. According to this configuration, the irradiation region 205 can be scanned on the surface of the sample 200 by moving the sample 200 in the x direction, and the data of the linear region of the sample 200 can be acquired. Further, the stage 202 may be an xy stage that can move in the x and y directions. By combining scanning in the x direction and scanning in the y direction, it is possible to obtain two-dimensional data (image) of a wider area of the sample 200.

The far infrared light transmitted through the sample 200 is wavelength-converted by the non-linear optical crystal 132 for detection into near infrared light having a wavelength of around 1066 nm to 1076 nm. The converted near-infrared light is photoelectrically converted by the photodetector 290 having sensitivity to the near-infrared light and detected as a detection signal. The photodetector (sensor) 290 for near infrared light may be a light receiving element (1D array detector) in which a plurality of light receiving elements are arranged in a one-dimensional array, or a plurality of light receiving elements are arranged in a two-dimensional array. Alternatively, a light receiving element (2D array detector) may be used. Near-infrared 1D array detectors and 2D array detectors are relatively easily available, have a fast response speed, and can be used at room temperature. Therefore, these detectors are suitable for industrial applications.

As in the above example, when the wavelength of far-infrared light is converted into near-infrared light by using the detection nonlinear optical crystal 132, a part of the pump light 115 is branched and, after adjustment, the detection nonlinear optical crystal 132 is adjusted. Incident on. For example, the pump light 115 is split into transmitted light and reflected light by a polarization beam splitter (hereinafter referred to as PBS) 127. The transmitted light that has passed through the PBS 127 enters the nonlinear optical crystal 130. Reflected light (pump light for wavelength conversion) 235 reflected by the PBS 127 is incident on the detection nonlinear optical crystal 132.

The wavelength conversion pump light 235 is incident on the detection nonlinear optical crystal 132 at the same timing as the incidence of the far infrared light pulse that has passed through the sample 200. For this reason, although not shown, on the optical path of the pump light 235 for wavelength conversion, a delay optical system (for example, an optical path length correction stage) for adjusting the timing of the optical pulse, and a polarization direction A half-wave plate or the like for adjusting is provided as necessary. With this configuration, a beam with a clean profile can be used for wavelength conversion when detecting far infrared light. This makes it possible to improve the efficiency of wavelength conversion and the detection sensitivity.

The far infrared light transmitted through the sample 200 is guided to the detection nonlinear optical crystal 132 by using the far infrared light imaging optical system 170. For example, the far infrared light image forming optical system 170 is an afocal image forming optical system including at least two lenses 177 and 179. The lens 177 is arranged on the stage 178a. The lens 179 is arranged on the stage 178b. The stages 178a and 178b are movable in at least one direction (here, the y direction). A mechanism for moving at least one of the two lenses 177 and 179 on the sample 200 side in at least one direction may be provided. An image of the surface of the sample 200 is formed in the detection nonlinear optical crystal 132 through the Si prism 142. LiNbO3 or MgO:LiNbO3 may be used as the detection nonlinear optical crystal 132. Each light that has passed through the detecting nonlinear optical crystal 132 and the nonlinear optical crystal 130 is received and processed by the termination processing unit 240 (see FIG. 1B).

When the output of the light source 110 for the pump light 115 has no margin, the pump light passing through the non-linear optical crystal 130 may be guided to the non-linear optical crystal for detection 132 and reused (for example, see FIG. 6). .. Since the quality of the pump light beam used for wavelength conversion deteriorates, the detection efficiency decreases, but the pump light can be used efficiently for far infrared light generation and wavelength conversion to near infrared light.

The signal processing unit 400 takes in the signal photoelectrically converted by the photodetector 290. The signal processing unit 400 generates a signal proportional to the light transmitted through the sample 200 and its distribution image based on the position information of the stage 202 at the time of signal acquisition. The signal processing unit 400 calculates the absorption spectrum by comparing the acquired image data with the spectral image data (reference data) when there is no sample accumulated in the storage area of the signal processing unit 400. It is also possible to obtain a two-dimensional distribution of spectrum (absorption spectrum image).

The control unit 500 controls the entire device. For example, the control unit 500 controls the wavelength tunable far infrared light source 100, the stages 202, 178a and 178b, and the signal processing unit 400. The control unit 500 also functions as a user interface. For example, the control unit 500 may include a display unit that displays signals and data (spectral information) acquired by the signal processing unit 400. In the case of fixing the wavelength and acquiring the data of the sample 200, the control unit 500 controls the wavelength tunable far infrared light source 100 to generate the designated far infrared light, and the movement of the stage 202 and the photodetector. Controls the synchronization of data acquisition on the 290. Further, when acquiring the data of the sample 200 by changing the wavelength, the control unit 500 sets the wavelength of the wavelength tunable far-infrared light source 100, moves the stage 202, and acquires data by the photodetector 290. Control the synchronization of.

In the present embodiment, an example in which a short pulse Q-switch YAG laser is used as the light source 110 for the pump light of the wavelength tunable far infrared light source 100 is shown, but the present invention is not limited to this. A mode-locked laser may be used as the light source 110 for the pump light, as long as the line width of the basic spectrum is narrow. Since the mode-locked laser repeats quickly, higher speed measurement is possible.

Here, how far infrared light is generated will be described with reference to FIG. 4A. FIG. 4A shows an example in which MgO:LiNbO3 is used as the nonlinear optical crystal 130 and far infrared light is generated by parametric generation.

The pump light 115 is made incident on the nonlinear optical crystal 130, and the seed light 125 is made incident on this at an angle θ. The far infrared light 145 can be generated with high efficiency by setting the wavelength of the seed light and the angle θ with respect to the pump light so as to satisfy the following conditions. The frequency (ω _T ) of the far infrared light 145 generated in the nonlinear optical crystal 130 is calculated from the following equation using the respective frequencies (ω _p and ω _s ) of the pump light 115 and the seed light 125 according to the law of conservation of energy. Required (however, ω is the angular frequency).

On the other hand, the generation efficiency of the far infrared light 145 becomes high when the law of conservation of momentum is satisfied. That is, high efficiency is obtained when the following relational expression and the condition (phase matching condition) of FIG. 4B are satisfied between the emission direction of the far infrared light 145 and the directions of the pump light 115 and the seed light 125. Here, the wave number vectors of the far infrared light 145, the pump light 115, and the seed light 125 are k _T , k _p , and k _s , respectively.

Therefore, by setting the wavelength and incident direction (θ) of the seed light 125 so as to satisfy these conditions, it is possible to generate far infrared light (terahertz light) with high efficiency.

In this embodiment, the incident angle adjusting optical system 121 adjusts the incident angle of the seed light 125 to the nonlinear optical crystal 130. FIG. 5 shows a configuration example of the incident angle adjusting optical system 121.

The incident angle adjusting optical system 121 includes a lens 122, an optical deflector 123, and an image forming optical element 124. The light from the variable wavelength light source 120 is guided by the fiber 128. The light from the fiber 128 passes through the lens 122 and the light deflector 123 to form a beam waist near the front focal plane of the imaging optical element 124. According to this configuration, the beam that has passed through the imaging optical element 124 becomes a beam having a long Rayleigh length (that is, close to a collimated state) and enters the nonlinear optical crystal 130.

On the other hand, the image forming optical element 124 is configured to form an image on the surface of the optical deflector 123 on the incident surface of the nonlinear optical crystal 130. This makes it possible to realize the condition that the beam position does not change and only the incident angle changes on the incident surface of the nonlinear optical crystal 130 when the beam is deflected by the optical deflector 123.

As the optical deflector 123, a reflection type deflector such as a galvanometer mirror or a mirror using the MEMS technique may be used, or a transmission type optical deflector may be used. That is, any optical deflector 123 may be used as long as the angle can be controlled.

Further, in this example, a concave mirror is used as the imaging optical element 124. However, a lens may be used as the imaging optical element 124 as long as the optical deflector 123 and the incident surface of the non-linear optical crystal 130 can be in an imaging relationship. When a reflection type optical deflector such as a galvanometer mirror is used as the optical deflector 123 and a concave mirror is used as the image forming optical element 124, the optical path can be bent and folded, so that the incident angle adjusting optical system 121 is compact. It becomes possible to form it.

When the incident angle adjusting optical system 121 is linearly mounted, a transmissive optical deflector may be used as the optical deflector 123 and a lens may be used as the imaging optical element 124. Further, depending on mounting restrictions, one of the optical deflector 123 and the imaging optical element 124 may be configured with a reflective optical element and the other may be configured with a transmissive optical element.

In this embodiment, as the imaging optical element 124, a single imaging optical element such as a single lens or a single concave mirror can be used. Therefore, the optical system can be formed compactly.

Further, according to the incident angle adjusting optical system 121 of this example, when the wavelength of the variable wavelength light source 120 is changed, the incident angle θ of the seed light 125 to the nonlinear optical crystal 130 is controlled and set by the optical deflector 123. By doing so, it is possible to set the incident angle θ to the nonlinear optical crystal 130 with high accuracy. Therefore, it is possible to improve the stability of the far infrared light output and the stability of the absorption spectrum measurement when the wavelength of the seed light 125 is changed. As a result, highly accurate quantitative measurement becomes possible.

Next, how the far infrared light propagates will be described with reference to FIG. The far infrared light emitted from the wavelength tunable far infrared light source 100 is a linear light source along the beam of the pump light 115. Since this linear light source is tilted with respect to the optical axis (z axis in FIG. 2), care must be taken when guiding the beam to the detection nonlinear optical crystal 132.

In FIG. 2, far infrared light generated by the nonlinear optical crystal 130 passes through the illumination optical system 150, the sample 200, and the far infrared light imaging optical system 170, and then enters the detection nonlinear optical crystal 132. The light path is shown.

Here, two points (A ₀ and B ₀ ) on the linear light source of far infrared light along the beam of the pump light 115 will be described as an example. The points A ₀ and B ₀ are imaged in the vicinity of the sample 200 by the illumination optical system 150, but since the point B ₀ is farther from the illumination optical system 150 than the point A ₀ , the image of the point B is , Is formed at a position near the illumination optical system 150 near the sample 200. These points A and B are again guided to the detection nonlinear optical crystal 132 by the far infrared light imaging optical system 170. Here, since point B is farther from the far-infrared light imaging optical system 170 than point A, point B′ in the image is far-infrared light coupling from point A′ in the nonlinear optical crystal for detection 132. It is formed at a position close to the image optical system 170. Therefore, the nonlinear optical crystal 130 and the detecting nonlinear optical crystal 132 are arranged so that the incident direction of the pump light 115 on the nonlinear optical crystal 130 and the incident direction of the pump light 235 on the detecting nonlinear optical crystal 132 are substantially parallel. To be done. Since the incident direction of the pump light 115 on the nonlinear optical crystal 130 and the incident direction of the pump light 235 on the detecting nonlinear optical crystal 132 are substantially parallel to each other, the points A′ and B′ are both pump light for wavelength conversion. It becomes possible to superimpose it on the beam of 235, and it becomes possible to efficiently convert far infrared light into near infrared light.

Next, a method of adjusting the incident angle when the far infrared light transmitted through the sample 200 is incident on the detection nonlinear optical crystal 132 will be described with reference to FIG.

In order to convert the far infrared light transmitted through the sample 200 into near infrared light with high efficiency in the near infrared light, the nonlinear optical crystal 132 for detection of the far infrared light transmitted through the sample 200 is used. It is necessary to optimize the angle of incidence on. In this embodiment, the incident angle is adjusted by adjusting the positions of the lenses 177 and 179 that form the far-infrared light imaging optical system 170.

3A and 3B show a far infrared light imaging optical system 170. Points A and B are two points on the sample 200, and these points A and B are imaged by the far-infrared light imaging optical system 170 at points A′ and B′ in the nonlinear optical crystal for detection 132. ing.

3A shows a reference state, and FIG. 3B shows a state in which the incident angle of the far infrared light transmitted through the sample 200 to the nonlinear optical crystal for detection 132 is changed with respect to the state of FIG. 3A. First, the lens 177 is moved by the distance S in the -y direction by driving the stage 178a. If the lens 179 is not moved in this state, the image points A′ and B′ of the points A and B will move in the −y direction in the detection nonlinear optical crystal 132. Therefore, in order to correct this shift, the stage 178b is driven to move the lens 179 in the +y direction by the distance S'. By performing such control, it is possible to change (adjust) the incident angle θ of the far-infrared light incident on the points A′ and B′ with the positions of the points A′ and B′ being the same as in FIG. 3A. It will be possible. The distances S and S′ are not always the same value, and may not be the same value due to the focal length.

The effects of this embodiment will be described below. Conventionally, when the frequency of the light source for generating far-infrared light is changed, the direction in which far-infrared light is emitted changes, so the irradiation position on the sample changes, and uneven distribution of components and changes in signal detection efficiency are quantitatively analyzed. However, there is a problem that the accuracy of is reduced. On the other hand, according to the present embodiment, the illuminating light from the light source is irradiated onto the analyte (sample 200) by the anamorphic imaging optical system, and the transmitted light (or reflected light) from the sample 200 is emitted. Is subjected to wavelength conversion using the non-linear optical crystal for detection 132 and detected using the photodetector 290. With this configuration, it is possible to reduce the deviation of the irradiation position of the far infrared light due to the frequency change. Therefore, the uneven distribution of components and the change in signal detection efficiency do not occur, and the accuracy of quantitative analysis can be improved.

Further, if the optical system is complicated in order to reduce the deviation of the irradiation position of the sample, there is a problem that far infrared light is significantly attenuated by the optical system and measurement through a shield becomes difficult. On the other hand, in the present embodiment, the structure for reducing the deviation of the irradiation position of the sample is simple, the attenuation of far infrared light is small, and the analysis through the shield is also possible. According to this embodiment, it is possible to realize quantitative analysis of various types of samples including powder regardless of the presence or absence of a shield.

[Second Embodiment]
FIG. 6 shows the configuration of the spectroscopic device according to the second embodiment. The constituent elements described in the above-described embodiments are designated by the same reference numerals, and the description thereof will be omitted. The difference from the first embodiment of FIG. 1 is mainly (i) the configuration of the illumination optical system 150 and the far-infrared light imaging optical system 170, (ii) the arrangement of the detection nonlinear optical crystal 132, and (iii) ) The point is that the pump light used for generating far infrared light passing through the nonlinear optical crystal 130 is guided to the detecting nonlinear optical crystal 132 and is reused.

The light source 110 of the pump light 115 has a short pulse Q-switched YAG laser 111, a polarization separation system including a polarization beam splitter (PBS) 114 and a quarter-wave plate 116, and a laser as main components. An amplifier unit (here, solid-state amplifier 118) for amplifying the output is provided. For example, the output beam of the YAG laser 111 is collimated by the lens 112, passes through the polarization separation system including the PBS 114 and the quarter-wave plate 116, and is amplified by the solid-state amplifier 118.

More specifically, the output beam of the YAG laser 111 is reflected by the mirror 181, collimated by the lens 112, reflected by the mirror 182, and incident on the PBS 114. The beam that has passed through the PBS 114 is reflected by the mirror 183 via the quarter-wave plate 116 and the solid-state amplifier 118. The reflected beam enters the PBS 114 via the solid-state amplifier 118 and the quarter-wave plate 116. After that, the beam is emitted from the PBS 114 via the mirror 184 as the pump light 115. By using the solid-state amplifier 118, the output of the YAG laser 111 is amplified, and it becomes possible to extract strong far-infrared light of kW level with peak power from the nonlinear optical crystal 130.

In this embodiment, the illumination optical system 150 is composed of a cylindrical lens 151 and a condenser lens 155. Far infrared light emitted from the wavelength tunable far infrared light source 100 having a linear light emitting region along the beam of the pump light 115 becomes a parallel light flux by the cylindrical lens 151, and a spot on the sample 200 by the condenser lens 155. Is focused on.

The far-infrared light that has passed through the sample 200 is guided to the detection nonlinear optical crystal 132 by the far-infrared light imaging optical system 170. The far-infrared light imaging optical system 170 is an imaging optical system that forms an image on the surface of the sample 200 in the detection nonlinear optical crystal 132. The far infrared light imaging optical system 170 includes a lens 176, a mirror 172, and a condenser lens 174. Specifically, the far-infrared light transmitted through the sample 200 is collimated by the lens 176, reflected by the mirror 172, and condensed by the condenser lens 174 on the detection nonlinear optical crystal 132.

FIG. 7A shows spots 205a, 205b, 205c of far infrared light on the surface of the sample 200. As described above, the far infrared light emitted from the wavelength tunable far infrared light source 100 changes its emission direction within the plane of FIG. 6 when wavelength scanning is performed (for example, θ1 in FIG. 6). ~ Θ2). Therefore, for example, when the wavelength of the seed light 125 is changed and the frequency of the generated far infrared light is changed from 1 THz to 3 THz, the far infrared light spot on the surface of the sample 200 is 1 THz at the low frequency side. The position is 205c, the position is 205b at the intermediate frequency of 2THz, and the position is 205a at the high frequency side of 3THz. When the frequency is changed in this way, the irradiation position on the sample 200 is different. Therefore, the absorption spectrum is affected by the position dependence of the concentration distribution, and an accurate spectrum cannot be obtained. Therefore, in this embodiment, the stage 202 of the sample 200 is controlled according to the frequency of the far infrared light so that the irradiation position does not change even if the frequency of the far infrared light changes.

The control unit 500 moves the stage 202 according to the change in the irradiation position of the far infrared light that can be generated on the surface of the sample 200 when the wavelength of the seed light 125 is changed. With this configuration, when the wavelength of the far infrared light from the variable wavelength far infrared light source 100 changes, the far infrared light can be applied to the same position of the sample 200. That is, the irradiation position of the far infrared light on the sample 200 does not depend on the wavelength of the far infrared light from the wavelength tunable far infrared light source 100.

For example, when the wavelength of the far infrared light from the wavelength tunable far infrared light source 100 is 1 THz on the low frequency side, the spot of the far infrared light is located at 205c, so the control unit 500 sets the stage 202 to -y. Direction (see FIG. 7C). Further, when the wavelength of the far infrared light from the wavelength tunable far infrared light source 100 is 3 THz on the high frequency side, the spot of the far infrared light is located at 205a, so the control unit 500 controls the stage 202 to move in the +y direction. Drive (see FIG. 7B). When the wavelength of the seed light 125 is changed, the control unit 500 moves the stage 202 according to the change of the irradiation position of far infrared light that can be generated on the surface of the sample 200, and the same position (FIGS. It is configured to irradiate a spot of far infrared light on the center) in FIG. 7C. According to this configuration, the influence of the position dependence of the concentration distribution on the absorption spectrum can be avoided, and accurate and stable spectrum measurement can be performed.

In addition, in this embodiment, the pump light that has passed through the nonlinear optical crystal 130 is used as the pump light for wavelength conversion. Specifically, the pump light that has passed through the nonlinear optical crystal 130 is reflected by the mirror 210 and guided to the detecting nonlinear optical crystal 132 as pump light 235 for wavelength conversion. This configuration allows the pump light 115 to be used efficiently and is suitable when the power of the pump light 115 has no margin. However, due to reuse, the pump light 235 for wavelength conversion may have a distorted time waveform. Therefore, the conversion efficiency to the near infrared light and the beam quality of the converted near infrared light may deteriorate. When the pump light 115 has sufficient power, it is desirable to split the pump light into two beams for generating far infrared light and for converting into near infrared light, as shown in FIG.

FIG. 8 shows another configuration example of the light source 110 for the pump light 115 used in the wavelength tunable far infrared light source 100. The configuration of the light source 110 shown in FIG. 8 can be applied to other embodiments. 8, the same components as those in FIG. 6 are designated by the same reference numerals.

The wavelength tunable far infrared light source 100 in this example includes lenses 119a and 119b that correct the thermal lens effect generated in the solid-state amplifier 118. That is, the difference from the example shown in FIG. 6 is that two lenses 119a and 119b for correcting the thermal lens effect are arranged between the solid-state amplifier 118 and the mirror 183. When the output of the YAG laser 111 is amplified using the solid-state amplifier 118, the amplified beam may be narrowed by the thermal lens effect, and the PBS 114 and the quarter-wave plate 116 may be damaged. Therefore, an optical system for correcting the thermal lens generated in the solid-state amplifier 118 is provided between the solid-state amplifier 118 and the folding mirror 183. The amplified light emitted from the solid-state amplifier 118 enters the correction lenses 119a and 119b, and the light that has passed through the lenses 119a and 119b enters the PBS 114 and the quarter-wave plate 116.

Specifically, the combination of the concave lens 119a and the convex lens 119b is arranged between the solid-state amplifier 118 and the mirror 183 so that the combined focal length becomes negative. Further, the synthesized main surface is arranged near the solid-state amplifier 118. With this configuration, it is possible to return the beam that has become a convergent beam by the thermal lens to a parallel beam and hit the mirror 183, and the beam reflected by the mirror 183 follows the reverse optical path and enters the solid-state amplifier 118 again. However, a configuration is possible in which the thermal lens returns to a parallel light beam and is emitted. Since the beam output from the solid-state amplifier 118 is a parallel light beam, the energy density on the polarization beam splitter 114 and the quarter-wave plate 116 can be suppressed, and damage can be avoided.

Further, by configuring the optical system for correcting the thermal lens effect with the two lenses 119a and 119b, it becomes possible to adjust the focal length of the correction system. Even if the gain of the solid-state amplifier 118 is changed and the thermal lens effect is changed, it is possible to deal with it by adjusting the surface spacing of the lenses 119a and 119b, and a system with a high degree of freedom can be configured. Further, in the present embodiment, the optical system for correcting the thermal lens is provided between the solid-state amplifier 118 and the folding mirror 183, but this can be expected to be effective in avoiding damage to the optical system. This is because the beam has passed through the solid-state amplifier 118 only once at this position, and the power of the beam has not increased so much yet.

Conventionally, a variable frequency coherent light source requires a high-power laser, so that there is a problem that the optical system is damaged by the thermal lens effect and stable measurement is difficult. On the other hand, in this embodiment, by providing the two lenses 119a and 119b as the optical system for correcting the thermal lens effect, damage to the optical system is avoided and stable measurement is possible. The configuration of the light source 110 for the pump light 115 shown in FIG. 8 can be applied to other embodiments.

[Third Embodiment]
9A and 9B show an example of the overall configuration of the far-infrared spectroscopic device according to the third embodiment. FIG. 9C is a plan view showing an irradiation area of a sample in the third embodiment. The constituent elements described in the above-described embodiments are designated by the same reference numerals, and the description thereof will be omitted.

The far-infrared spectroscopic device of the present embodiment measures the absorption spectrum using the reflected light of the sample 200. The components from the wavelength tunable far-infrared light source 100 to the illumination optical system 150 and the components after the far-infrared light imaging optical system 170 are tilted with respect to the surface of the sample 200 with the surface of the sample 200 as the center. In the far-infrared spectroscopic device of this embodiment, far-infrared light is obliquely incident on the sample 200, and reflected light from the sample 200 is detected.

According to this configuration, by arranging the illumination optical system 150 and the far-infrared light imaging optical system 170 so as to be inclined with respect to the surface of the sample 200, the reflected light from the sample 200 can be detected. As a result, it becomes possible to measure the sample 200 having low transmittance or the spectral characteristics of the surface of the sample 200. A mechanism that can change the incident angle from the illumination optical system 150 and the angle to the far infrared light imaging optical system 170 may be provided. As a result, it becomes possible to measure the incident angle dependence of the spectral characteristics.

[Fourth Embodiment]
10A and 10B show an example of the overall configuration of the far-infrared spectroscopic device according to the fourth embodiment. FIG. 10C is a plan view showing the irradiation area of the sample in the fourth embodiment. The constituent elements described in the above-described embodiments are designated by the same reference numerals, and the description thereof will be omitted.

In the present embodiment, each of the illumination optical system 150 and the far infrared light imaging optical system 170 further includes an optical system that bends the optical path of the far infrared light and corrects the optical path length of the far infrared light. More specifically, an optical system 158a for adjusting the optical path length and a mirror 159a are arranged between the illumination optical system 150 and the sample 200b. Further, a mirror 159b and an optical system 158b for adjusting the optical path length are arranged between the sample 200b and the far infrared light imaging optical system 170. Further, in this embodiment, the sample 200b is arranged on the yz plane of the stage 202b. According to this configuration, it is possible to measure the absorption spectrum using the reflected light of the sample 200b.

Note that if the layout is such that the optical path of the far infrared light is simply bent by the mirrors 159a and 159b and the reflected light of the sample is detected, the optical path length of the far infrared light is extended and the sample surface is out of focus. Therefore, as a feature of this embodiment, the optical system 158a for correcting the optical path length is arranged in the front stage of the mirror 159a, and the optical system 158b for correcting the optical path length is arranged in the rear stage of the mirror 159b. Since the optical system is symmetrically arranged around the sample 200b, the optical systems 158a and 158b may be the same. The optical systems 158a and 158b need to have a function of extending the optical path length, and thus can be composed of, for example, one concave lens. According to this configuration, the number of additional components is minimized, which is effective when the mounting restrictions are severe.

On the other hand, the optical systems 158a and 158b may be composed of a combination of a convex lens and a concave lens. According to this configuration, by adjusting the distance between these lenses, it is possible to adjust the focal length of the concave lens obtained by combining them. Therefore, it becomes possible to use an off-the-shelf lens. Further, the focal position can be adjusted by adjusting the distance between the lenses.

Note that the differences from the configurations of FIGS. 1A and 1B are only that the mirrors 159a and 159b and optical systems 158a and 158b for adjusting the optical path length are added, and that the sample 200b is held on the yz plane. Therefore, a mechanism for moving the mirrors 159a, 159b and the optical systems 158a, 158b in and out and a mechanism for replacing the sample 200b and the stage 202b with the sample 200a and the stage 202a may be provided (see FIG. 10B). By removing the mirrors 159a, 159b and the optical systems 158a, 158b from the optical path of far infrared light and replacing the stage 202b with the stage 202a, it becomes possible to easily switch the measurement by the reflected light to the measurement by the transmitted light. ..

[Fifth Embodiment]
FIG. 11A shows an example of the overall configuration of the far-infrared spectroscopic device according to the fifth embodiment. The constituent elements described in the above-described embodiments are designated by the same reference numerals, and the description thereof will be omitted.

The difference from the above-described embodiment is that an optical element (for example, a lens) used for the far infrared light illumination optical system 150, an optical element (for example, a lens) used for the optical systems 158a and 158b for adjusting the optical path length, and An optical element (for example, a lens) used in the far infrared light imaging optical system 170 has a structure for antireflection as shown in FIGS. 11A to 11C. At least one optical element used in the illumination optical system 150 and the far-infrared light imaging optical system 170 has groove-shaped processing for reducing the reflection of far-infrared light.

In FIG. 11A, the far-infrared light generated from the far-infrared generating nonlinear optical crystal 130 has a polarization component that vibrates in the vertical direction (x-axis direction in the drawing) in the plane of the paper as the main component. To prevent reflection, the surface of the above-described optical element is provided with a plurality of V-shaped grooves whose longitudinal direction is the direction (y-axis direction) orthogonal to the polarization direction. The plurality of grooves are formed substantially parallel to each other. 11B and 11C are enlarged views of the surface 152a of the cylindrical lens 152 of the illumination optical system 150, as an example. The plurality of grooves have a depth d and are formed with a period p.

In the above configuration, it is known that if the groove period p is made sufficiently small with respect to the wavelength of far infrared light, it becomes equivalent to the case where the refractive index of the interface gradually changes for the incident far infrared light. There is. Therefore, as an example, it is preferable that the surface of the optical element described above is provided with a groove having a period of ⅓ or less of the wavelength of the far infrared light (that is, the plurality of groove-shaped intervals are the wavelength tunable far infrared light source 100. 1/3 or less of the wavelength of the first far infrared light from the sample or the second far infrared light from the sample 200). More preferably, the surface of the above-mentioned optical element is provided with grooves having a period of 1/5 or less of the wavelength of far infrared light. More preferably, the surface of the above-mentioned optical element is provided with a groove having a period of about 1/10 of the wavelength of far infrared light. For example, since far infrared light of 1 to 3 THz has a wavelength of 100 to 300 μm, it is preferable to form a groove having a period of about 10 μm, which is 1/10 of the wavelength. For the purpose of reducing reflection, it is desirable that the groove period be small, but if it is less than 10 μm, which is 1/10 of the wavelength, it becomes difficult to secure the processing accuracy, or the processing cost becomes high, making it practical. descend. Therefore, it is desirable to set the wavelength to about 1/10. The depth d of the groove is preferably about the same as the period p to about 10 times the period p. This is because it is desirable that the change in the refractive index on the surface of the optical element is gentle on the wavelength scale for the purpose of reducing reflection. That is, if the groove is shallow, the change in refractive index is not moderated and the effect of reducing surface reflection cannot be obtained. On the other hand, if the depth exceeds 10 times the period p, the processing becomes difficult and the shape accuracy cannot be maintained. When the groove shape is disturbed, scattered light is generated and the reflection reducing effect is deteriorated.

The reflection on the surface of the optical element increases as the difference in the refractive index on the surface increases, so that it is possible to reduce the surface reflection by forming a structure in which the refractive index gradually changes. When forming the V-shaped groove, a portion that maintains the original surface shape may be formed between the adjacent grooves. As shown in FIG. 11C, the plurality of groove shapes are orthogonal to the optical axis of the first far infrared light from the wavelength tunable far infrared light source 100 or the second far infrared light from the sample 200. A flat surface (w portion) parallel to the surface is formed. The width of the flat surface is larger than the wavelength of visible light. According to this configuration, the effect of reducing the surface reflection is weakened, but it is possible to perform alignment of the optical system using visible light, and the adjustment of the optical system becomes easy. If the V-shaped groove is completely connected (the w portion in FIG. 11C does not remain), the beam of visible light for alignment is refracted by the groove structure, so that the same optical path as that of the far infrared light is obtained. It will not be traced. However, if the width of the w portion is made larger than the wavelength of visible light for alignment (for example, 1 μm or more), the beam of visible light for alignment passing through the w portion follows the same optical path as that of far infrared light. Therefore, it is possible to perform alignment using a visible light beam while reducing the surface reflection of far infrared light.

FIG. 12A is an example in which the groove structure described above is formed on the surfaces of the cylindrical lenses 152 and 154 of the illumination optical system 150. Further, FIG. 12B is an example in which the groove structure described above is formed on the surface of the cylindrical lens 156 of the illumination optical system 150. FIG. 12C is an example in which the groove structure described above is formed on the surfaces of the lenses 177 and 179 used in the optical systems 158a and 158b for adjusting the optical path length and the far-infrared light imaging optical system 170. In the example of FIG. 12A, grooves that are orthogonal to the generatrices of the cylindrical lenses 152 and 154 are formed. Further, in the example of FIG. 12B, a groove parallel to the generatrix of the cylindrical lens 156 is formed. In the example of FIG. 12C, the spherical lens has a groove structure. These lenses for far infrared light are often made of resin. Since a resin lens can be manufactured by molding using a mold, mass production can be relatively easily performed even with such a grooved surface.

The present invention is not limited to the above-mentioned embodiments, but includes various modifications. The above embodiments have been described in detail for the purpose of explaining the present invention in an easy-to-understand manner, and are not necessarily limited to those having all the configurations described. Further, part of the configuration of one embodiment can be replaced with the configuration of another embodiment. Further, the configuration of another embodiment can be added to the configuration of one embodiment. Further, with respect to a part of the configuration of each embodiment, another configuration can be added/deleted/replaced.

The processing of the signal processing unit 400 and the control unit 500 described above can also be realized by a program code of software that realizes those functions. In this case, a storage medium storing the program code is provided to the system or device, and the computer (or CPU or MPU) of the system or device reads the program code stored in the storage medium. In this case, the program code itself read from the storage medium realizes the function of the above-described embodiment, and the program code itself and the storage medium storing the program code constitute the present invention. As a storage medium for supplying such a program code, for example, a flexible disk, a CD-ROM, a DVD-ROM, a hard disk, an optical disk, a magneto-optical disk, a CD-R, a magnetic tape, a non-volatile memory card, a ROM Are used.

The processes and techniques described herein are not inherently related to any particular apparatus and can be implemented with any suitable combination of components. In addition, various types of general purpose devices can be used. In some cases, it may be beneficial to build a dedicated device to perform the processes described here. That is, a part of the signal processing unit 400 and the control unit 500 described above may be realized by hardware using an electronic component such as an integrated circuit.

Further, in the above-mentioned embodiments, the control lines and information lines are shown as being considered necessary for explanation, and not all the control lines and information lines are shown in the product. All configurations may be connected to each other.

100…Tunable wavelength far infrared light source
110… Light source
111… Q switch YAG laser
112… Lens
114 …Polarizing beam splitter
115… Pump light
116… Quarter wave plate
118…Solid-state amplifier (amplifier unit)
119a …Concave lens (thermal lens correction lens)
119b…Convex lens (thermal lens correction lens)
120…Tunable light source
121… Incident angle adjustment optics
122… Lens
123… Optical deflector
124… Imaging optics
125… Seed light
126…Mirror
130… Nonlinear optical crystal
132… Nonlinear optical crystal for detection
140, 142… Si prism
150… Illumination optics
170…Far infrared light imaging optical system
178a, 178b… Stage
200, 200a, 200b …Sample
202,202a,202b...stage

Claims (1)

A tunable far infrared light source for generating a first far infrared light;
An illumination optical system for irradiating the first far infrared light onto the sample;
A non-linear crystal for detection that converts the second far-infrared light from the sample into near-infrared light using pump light for wavelength conversion;
A far-infrared light imaging optical system for forming an image of the sample on the detecting non-linear optical crystal,
The wavelength tunable far infrared light source,
A first light source and a second light source having different wavelengths, a far-infrared light generating nonlinear optical crystal for making light emitted from the first and second light sources incident, and an incident angle adjusting optical system,
Far infrared light is generated by irradiating the nonlinear optical crystal for generating far infrared light with light from the first and second light sources to generate far infrared light by difference frequency generation or parametric generation.
The incident angle adjusting optical system,
From the second light source side on an optical path between the second light source and the far-infrared light generating nonlinear optical crystal, fiber, lens, optical deflector, the imaging optical elements are arranged in this order,
There is one lens, one optical deflector and one imaging optic,
Wherein the beam waist is formed in the vicinity of the front focal plane of the front Kiyui image optical element, a far infrared spectrometer.

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