JP4522882B2 - Absorption measuring device - Google Patents

Description

  The present invention relates to an absorption measurement apparatus using cavity ring-down spectroscopy.

  As a technique for obtaining the light absorption coefficient of a sample to be measured, cavity ring-down spectroscopy (CRDS), which is one of absorption spectroscopy, is known. CRDS uses a resonator in which a sample to be measured is introduced between a pair of mirrors. The measurement light incident on the resonator repeats multiple reflections and is attenuated by a component that passes through the mirror surface and a component that is absorbed by the sample to be measured. CRDS is a technique for acquiring the light absorption coefficient of a sample to be measured by analyzing the light intensity attenuated by a resonator. There are several types of configurations of apparatuses that perform CRDS.

For example, the following non-patent document 1 describes a walk-off type CRDS. In the walk-off type CRDS, the incident angle of the measurement light to the resonator is larger than zero. The measurement light incident on the resonator is repeatedly reflected at a plurality of locations on the mirror surface, and transmitted light is output from the reflected location to the outside of the resonator. When the light intensity of the output light output from the resonator is analyzed, an attenuation curve of the pulse train is obtained. The light absorption coefficient of the sample to be measured is obtained from the attenuation curve. In the following non-patent document 1, output light is detected by a single one-dimensional or two-dimensional photodetector.
H. a. RYPKEMA, 2 others, MOLECULAR PHYSICS, 2004, VOL. 102, no. 14-15, pp. 1501-1508

  In CRDS, the light intensity that attenuates is analyzed. Similarly, in the walk-off type CRDS, the light intensity attenuated is analyzed. When the dynamic range of the photodetector used in Non-Patent Document 1 is insufficient, the pulse train corresponding to the output light having a higher intensity than the maximum measurable value or the output light having an intensity lower than the measurable minimum value is attenuated. I can't get a curve. The dynamic range is the ratio between the maximum value and the minimum value. In the past, particularly in the case of high intensity output light, the detector element may be optically saturated and a corresponding attenuation curve may not be obtained. If an attenuation curve corresponding to high-intensity output light or low-intensity output light cannot be obtained, a sufficiently accurate light absorption coefficient cannot be determined. Therefore, the measurable dynamic range of the photodetector in Non-Patent Document 1 needs to be larger than the dynamic range of the light intensity of the output light output from the resonator necessary for measurement. On the other hand, a photodetector with a large dynamic range is problematic because it leads to an increase in size and cost.

  The present invention has been made to solve the above problems, and provides an absorption measurement apparatus capable of determining the light absorption coefficient of a sample to be measured even when the dynamic range of output light to be measured is large. For the purpose.

In order to achieve the above object, an absorption measurement apparatus of the present invention includes (1) a light source that outputs measurement light, and (2) a first mirror that reflects a part of the incident measurement light and transmits the remainder. A second mirror, the reflecting surfaces of the first mirror and the second mirror are arranged to face each other with an angle larger than 0, and the measurement light is incident on the first mirror and A resonator that passes through one mirror, repeats multiple reflections in the resonator, passes through one of the first mirror and the second mirror, and outputs output light from a plurality of locations, respectively (3) First detection means for detecting the first output light output from the resonator and outputting a first detection signal; and (4) higher sensitivity than the first detection means, and more resonant than the first output light. a second detecting means for outputting a second detection signal by detecting a second output beam greater number of reflections within the vessel, (5) second detection means Ri sensitive, and third detecting means than the second output light to output a third detection signal by detecting a third output light large number of reflections in the resonator, (6) first Determining means for determining a light absorption coefficient of a sample to be measured placed between the first mirror and the second mirror based on the detection signal, the second detection signal, and the third detection signal; It is characterized by.
Furthermore, the absorption measurement apparatus of the present invention includes: (a) a first attenuation means in which the first detection means attenuates the first output light to be detected and outputs the first attenuation light; First attenuation light detection means for detecting the first attenuated light output by the means, and (b) the second output light detected by the second detection means is attenuated by the first attenuation means. A second attenuating means for outputting the second attenuating light after being attenuated at a lower attenuating rate, a second attenuating light detecting means for detecting the second attenuating light output by the second attenuating means, (C) a distance along the first mirror between the first detection means and the second detection means and a first mirror between the first detection means and the third detection means The ratio with the distance along the line is equivalent to the ratio of the logarithm of the attenuation factor of the second attenuation means and the logarithm of the attenuation factor of the first attenuation means. To do.

  As described above, since the reflecting surfaces of the first mirror and the second mirror are arranged to face each other with an angle larger than 0, the incident angle of the measurement light to the resonator can be arbitrarily set. . That is, it becomes possible to make the measurement light incident perpendicularly to the reflecting surface of the first mirror. In addition, since the first output light is detected by the first detection means and the second output light is detected by the second detection means, the detection range between the first detection means and the second detection means is Each can be selected according to the intensity of light to be detected. Therefore, even if the dynamic range of the output light is large, the first detection means and the second detection means are the first detection signal and the second detection signal corresponding to the light intensity of each output light. Can be output. Therefore, even when the dynamic range of the output light is large, it is possible to determine the light absorption coefficient of the sample to be measured based on the first detection signal and the second detection signal.

In the absorption measurement apparatus of the present invention, the first detection means attenuates the first output light to be detected and outputs the first attenuation light, and the first attenuation means outputs the first attenuation light. a first attenuating light detecting means for detecting a first attenuation optical, Ru comprising a.

  According to this configuration, even when the maximum value of the light intensity measurable by the attenuated light detection means is smaller than the light intensity of the first output light, the first attenuation means attenuates the first output light. Thus, the first attenuated light is output. Therefore, the first attenuated light detection means can detect the first attenuated light having a light intensity smaller than that of the first output light and output the first detection signal.

  In the absorption measurement device of the present invention, it is also preferable that the first attenuated light detection means and the second detection means exhibit the same sensitivity characteristics. With this configuration, when determining the light absorption coefficient based on the first detection signal output from the first attenuated light detection means and the second detection signal output from the second detection means, There is no need to consider the difference in sensitivity characteristics between the first attenuated light detection means and the second detection means. Therefore, the light absorption coefficient can be determined more easily.

The absorption measurement device of the present invention (1) detects third output light that has higher sensitivity than the second detection means and has a higher number of reflections in the resonator than the second output light, and detects the third detection signal. (2) The second detection means attenuates the second output light to be detected with an attenuation rate lower than the attenuation rate of the first attenuation means, and the second attenuation. A second attenuating means for outputting light, and a second attenuating light detecting means for detecting the second attenuating light output by the second attenuating means, and (3) the first detecting means and the second attenuating light. The ratio of the distance along the first mirror between the two detection means and the distance along the first mirror between the first detection means and the third detection means is the second attenuation means Is equal to the ratio of the logarithm of the attenuation rate of the first attenuation unit and the logarithm of the attenuation rate of the first attenuation unit, and (4) the determining unit is configured to output the first detection signal and the second detection signal. When it determines the light absorption coefficient based on the third detection signal.

  In the absorption measurement device of the present invention, the second or third detection is performed as the number of reflections of the output light detected by the second or third detection means in the resonator is larger than that of the first output light. The distance along the first mirror between the means and the first detection means is increased. In addition, the light intensity of the output light decreases exponentially as the number of reflections in the resonator increases. Therefore, the distance along the first mirror between the first detection means and the second detection means, and the distance along the first mirror between the first detection means and the third detection means, Is equal to the ratio of the logarithm of the attenuation factor of the second attenuation means and the logarithm of the attenuation factor of the first attenuation means, so that the light intensity of the output light is an exponent. The larger the function, the more exponentially attenuated it will be detected. Therefore, even when the detection ranges of the first to third detection units are approximately the same, the first to third output lights can be detected by the first to third detection units, respectively. Moreover, since the determination means determines the light absorption coefficient based on the first to third detection signals, the light absorption coefficient can be determined with higher accuracy.

  In the absorption measurement apparatus of the present invention, it is also preferable that the first detection means is a photodiode and the second detection means is an avalanche photodiode. According to this configuration, the first output light can be detected by the photodiode, and the second output light having a light intensity lower than that of the first output light can be detected by the avalanche photodiode having higher sensitivity than the photodiode. .

  In the absorption measurement apparatus of the present invention, it is also preferable that the first detection means is a phototube and the second detection means is a photomultiplier tube. According to this configuration, the first output light can be detected by the phototube, and the second output light having a light intensity lower than that of the first output light can be detected by the photomultiplier tube having higher sensitivity than the phototube.

  In the absorption measuring apparatus of the present invention, it is also preferable to include angle varying means for changing the angle formed by the reflecting surfaces of the first mirror and the second mirror.

  Thus, it becomes possible to measure at a plurality of angles by changing the angle. Therefore, the light absorption coefficient can be determined with higher accuracy. Furthermore, by changing the angle, the number of times the output light from the resonator is reflected in the resonator can be changed, and the intensity of the light detected by the detection means can be adjusted. It is also possible to adjust so that the values of the detection signals to be output are approximately the same.

  In the absorption measuring apparatus of the present invention, it is also preferable to include a position changing unit that changes the position of at least one of the plurality of detecting units.

  In this way, by changing the position of at least one detection means, it is possible to perform measurement under a plurality of conditions, so that the light absorption coefficient can be determined with higher accuracy. Furthermore, by changing the position, the number of reflections of the output light from the resonator in the resonator can be changed, and the intensity of the light detected by the plurality of detection means can be adjusted. It is also possible to adjust so that the values of the detection signals to be output are approximately the same.

  In the absorption measuring apparatus of the present invention, it is also preferable to include a distance changing means for changing the distance between the first mirror and the second mirror.

  In this way, by changing the distance between the first mirror and the second mirror, it becomes possible to perform measurement under a plurality of conditions, so that the light absorption coefficient can be determined more accurately. . Furthermore, by changing the position, the number of reflections of the output light from the resonator in the resonator can be changed, and the intensity of the light detected by the plurality of detection means can be adjusted. It is also possible to adjust so that the values of the detection signals to be output are approximately the same.

  In the absorption measurement apparatus of the present invention, the determination means includes a differential measurement apparatus that differentially measures the detection signals output from the plurality of detection means, and determines the light absorption coefficient using the differential measurement result. Is also preferable. Thus, since differential measurement is performed and the light absorption coefficient is determined using the result, the light absorption coefficient can be determined more accurately.

  In the absorption measuring apparatus of the present invention, it is also preferable to include a control unit that controls the number of times the output light is reflected in the resonator so that the detection signals output by the plurality of detection units are substantially the same.

  By performing such control, when the light absorption coefficient is determined, the ratio between the detection signals output by the plurality of detection means can be used as 1. Therefore, the light absorption coefficient can be determined more easily.

  In the absorption measurement apparatus of the present invention, it is also preferable to include a lens that condenses the output light on each detection means. As described above, since the output light is condensed on the respective detection means, it is possible to prevent the adjacent output lights from overlapping at the detection position and to detect the intensity of the output light more accurately.

  In the absorption measurement device of the present invention, it is also preferable that the area of the light receiving surface of the detecting means is equal to the cross-sectional area at the position of the light receiving surface of the output light. By adopting such a configuration, it is possible to prevent the detection means from receiving up to the output light next to the output light to be detected, and to detect the intensity of the output light more accurately.

  In the absorption measurement device of the present invention, a lock-in amplifier that inputs a modulation means for intensity-modulating measurement light at a predetermined frequency and at least one detection signal and outputs a level of a signal component of the predetermined frequency among the input signals It is also preferable to comprise.

  The detection signal includes the detection signal of the output light with respect to the measurement light and noise. Since the modulation means intensity-modulates the measurement light at a predetermined frequency, it can be determined that the signal of the predetermined frequency is the detection signal of the output light. Since the lock-in amplifier outputs a level of a signal component having a predetermined frequency in at least one detection signal, noise having a frequency other than the predetermined frequency can be removed. Therefore, the light absorption coefficient can be determined with higher accuracy.

  In the absorption measuring device of the present invention, it is also preferable to include an angle measuring means for measuring the angle. Since the angle is measured, the light absorption coefficient depending on the angle can be determined with higher accuracy.

  In the absorption measurement apparatus of the present invention, the determining means calculates the number of reflections of the output light detected by the plurality of detecting means within the resonator based on the angle, and determines the light absorption coefficient using the calculation result. It is also preferable.

  Thus, since the number of reflections is calculated according to the angle, the light absorption coefficient depending on the number of reflections can be determined more easily at a plurality of angles.

  In the absorption measuring apparatus of the present invention, it is also preferable to include a display means for displaying the light absorption coefficient determined by the determining means. With this configuration, the light absorption coefficient can be displayed.

  In the absorption measurement apparatus of the present invention, it is also preferable to include a sample cell for introducing the sample to be measured between the first mirror and the second mirror.

  By providing the sample cell in this way, the sample to be measured can be easily introduced between the first mirror and the second mirror.

  The absorption measurement apparatus of the present invention includes a main surface parallel to the optical path of measurement light that is multiple-reflected in the resonator, a first side surface that forms an angle greater than 0 degrees and less than 90 degrees, and a first side surface. A dove prism disposed in the resonator, and having a second side surface that is opposite to the main surface and forms an angle similar to the angle between the main surface and the first side surface. Incident measurement light is incident on the Dove prism from one of the first side surface and the second side surface, totally reflected on the main surface, emitted from the side surface opposite to the incident side surface, and multiple reflected in the resonator. It is also preferable that the sample to be measured is placed at a position including a range where the measurement light on the main surface is totally reflected.

  Thus, by installing the sample to be measured at a position where the measurement light is totally reflected on the main surface of the Dove prism, the absorption of the evanescent light of the measurement light by the sample to be measured can be measured. The light absorption coefficient can be determined based on the measurement result. Since the evanescent light oozes out from the totally reflected surface into a region of about the wavelength, it is possible to determine the light absorption coefficient of the sample to be measured whose size is, for example, about a polymer.

  ADVANTAGE OF THE INVENTION According to this invention, even if it is a case where the dynamic range of the output light to measure is large, the absorption measuring device which can determine the light absorption coefficient of a to-be-measured sample can be provided.

  The best mode for carrying out the invention will be described below in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

  First, the configuration of the absorption measurement apparatus according to the first embodiment will be described. FIG. 1 is a configuration diagram of an absorption measurement apparatus 1 according to the first embodiment. The absorption measurement device 1 includes a light source 10, a resonator 20, a first detection unit 30, a second detection unit 40, a determination device 50 (determination unit), and a display device 60 (display unit). .

  The light source 10 outputs measurement light. The measurement light may be pulsed light or continuous light. In FIG. 1, the waveform of the measurement pulsed light 70 which is pulsed light as measurement light is shown. In the waveform of the measurement pulse light 70 in FIG. 1, the horizontal axis represents time. The light source 10 is, for example, a semiconductor laser. In addition, the light source 10 may be a quantum cascade laser, a YAG laser, a titanium sapphire laser, or the like.

  The resonator 20 includes a first mirror 21 and a second mirror 22 that reflect a part of the incident measurement light and transmit the remaining part. The reflecting surfaces of the first mirror 21 and the second mirror 22 are arranged to face each other with an angle θ larger than zero. The resonator 20 is incident on the first mirror 21, passes through the first mirror 21, repeats multiple reflections in the resonator 20, and repeats any of the first mirror 21 and the second mirror 22. One of them is transmitted and output as output light from a plurality of locations.

  The resonator 20 includes a rectangular parallelepiped sample cell 23 that introduces a sample to be measured, which is disposed between a first mirror 21 and a second mirror 22. The sample to be measured is liquid or gas. The sample to be measured is, for example, a biological sample or an environmental substance. The sample to be measured is introduced into the sample cell 23 by a pump (not shown) from a supply source (not shown).

  The measurement pulse light 70 enters the first mirror 21 from the outside of the resonator 20 at an arbitrary incident angle, passes through the first mirror 21, enters the resonator 20, and passes through the second mirror 22. And output from the resonator 20. The incident angle of the measurement pulse light 70 on the first mirror 21 is, for example, 90 degrees. Since the measurement pulse light 70 repeats multiple reflections in the resonator 20 and passes through the sample to be measured, the light intensity of the measurement pulse light 70 is attenuated according to the light absorption characteristics of the sample to be measured. With respect to the measurement pulse light 70 that is repeatedly reflected at a plurality of locations in the resonator 20, transmitted light is output from the reflected plurality of locations to the outside of the resonator 20 as output light.

ここで、Ｉ_０は測定パルス光７０が共振器２０への入射するときの光強度、Ｒ_１は第１の鏡２１の反射率、Ｒ_２は第２の鏡２２の反射率、ａは被測定試料の光吸収係数、Ｌｔは、測定パルス光７０の被測定試料中の透過距離である。 The output light P _n obtained from the second mirror 22 after obtaining 2n reflections in the resonator 20 becomes an attenuation curve 73 of the pulse train. In the pulse train decay curve 73 shown in FIG. 1, the vertical axis indicates the position. The light intensity I (n) of the output light P _n is expressed as in Equation 1. However, for the sake of explanation, in Equation 1, coefficients related to reflection, refraction, and absorption of the measurement pulse light 70 in the sample cell 23 are omitted.

Here, I ₀ is the light intensity when the measurement pulse light 70 is incident on the resonator 20, R ₁ is the reflectivity of the first mirror 21, R ₂ is the reflectivity of the second mirror 22, and a is the target. The light absorption coefficient, Lt, of the measurement sample is the transmission distance of the measurement pulse light 70 through the sample to be measured.

  The first detection means 30 and the second detection means 40 are respectively output from predetermined two positions of the second mirror 22 among the output lights that are transmitted from the second mirror 22 and output from the resonator 20. The first output light 71 and the second output light 72 are detected. In the waveforms of the first output light 71 and the second output light 72 shown in FIG. 1, the vertical axis indicates the spatial position. The first detection means 30 is disposed on the optical path of the first output light 71. The second detection means 40 is disposed on the optical path of the second output light 72.

  The first detection means 30 detects the first output light 71 and outputs a first detection signal. The first output light 71 is output light having a stronger intensity than the second output light 72 out of the output light output from the resonator 20. The first detection signal is a signal output from the first detection unit 30 to the determination device 50 according to the light intensity of the first output light 71. The first detection means 30 includes a first attenuator 31 (attenuation means) and a first detector 32 (first attenuation light detection means). A first aperture 33 is disposed between the first attenuator 31 and the first detector 32.

  The first attenuator 31 attenuates the first output light 71 with the attenuation factor Nd and outputs the first output light 71 to the first detector 32 as the first attenuated light. The first aperture 33 is disposed on the optical path of the first output light 71 between the first attenuator 31 and the first detector 32, and passes only the first output light 71. The first aperture 33 blocks output light other than the first output light 71 output from around the output position of the first output light 71 in the second mirror 22.

  The first detector 32 detects the first attenuated light that has been attenuated by the first attenuator 31 and passed through the first aperture 33, and outputs a first detection signal corresponding to the intensity of the detected light. The data is output to the determination device 50. The first detector 32 is, for example, a phototube.

  The second detection means 40 detects the second output light 72 having a higher number of reflections in the resonator 20 than the first output light 71 and outputs a second detection signal. The second detection signal is a signal output from the second detection unit 40 to the determination device 50 in accordance with the light intensity of the second output light 72. The second output light 72 has a light intensity weaker than that of the first output light 71 because the second output light 72 has a larger number of reflections in the resonator 20 than the first output light 71. The second output light 72 is weaker than the first output light 71, but the second detection means 40 can be detected because it is more sensitive than the first detection means 30. The second detection means 40 includes a second detector 42 and a second aperture 43.

  The second aperture 43 is disposed on the optical path of the second output light 72 between the second detector 42 and the resonator 20, and allows only the second output light 72 to pass through. The second aperture 43 blocks output light other than the second output light 72 output from the vicinity of the output position of the second output light 72 in the second mirror 22.

  The second detector 42 detects the second output light 72 that has passed through the second aperture 43, and outputs a second detection signal corresponding to the detected light intensity to the determination device 50. The sensitivity characteristic of the second detector 42 is the same as that of the first detector 32. The second detector 42 is, for example, a photoelectric tube having the same sensitivity characteristics as the first detector 32.

  The determination device 50 determines the light absorption coefficient a of the sample to be measured based on the first detection signal and the second detection signal. The determination device 50 includes a differential amplifier 51, an analysis device 52, and a concentration determination device 54.

The differential amplifier 51 differentially measures the input first detection signal and the second detection signal, and calculates the light intensity of the first attenuated light and the light intensity I _{2 of} the second output light 72. A light intensity ratio signal indicating the light intensity ratio ΔI is output to the analyzer 52. With the light intensity ratio [Delta] it, the ratio between the light intensity I ₂ of the light intensity I ₁ and the second output light 72 of the first output light 71 can be expressed as follows.

  The analysis device 52 determines the light absorption coefficient a of the sample to be measured based on the result of differential measurement by the differential amplifier 51. The analysis device 52 includes a difference ΔL in the transmission distance between the first output light 71 and the second output light 72 calculated by the arithmetic circuit in the sample to be measured, and a difference 2Δn in the number of reflections in the resonator 20. Based on the intensity ratio ΔI, the light absorption coefficient a is determined by referring to the stored coefficient lookup table 53.

  The arithmetic circuit included in the analysis device 52 includes an angle θ formed by the first mirror 21 and the second mirror 22, the first mirror 21, the second mirror 22, the first detection means 30, and the second detection. Based on the arrangement position with the means 40, the number of reflections of the first output light 71 and the second output light 72 in the resonator 20 is calculated. Further, a difference 2Δn in the number of reflections in the resonator 20 between the first output light 71 and the second output light 72 and a transmission distance difference ΔL are calculated. The angle θ is a value that can be acquired by measuring in advance. The transmission distance difference ΔL is obtained by calculating the respective transmission distances Lt of the first output light 71 and the second output light 72 as described later.

  The coefficient lookup table 53 is a table in which the light intensity ratio ΔI and the light absorption coefficient a are associated with each other and stored in the analysis device 52 with respect to the transmission distance difference ΔL and the reflection frequency difference 2Δn.

式２と式３より光吸収係数ａは次のように表すことができる。

The principle of uniquely determining the light absorption coefficient a as described above will be described. The ratio between the light intensity I ₂ of the light intensity I ₁ and the second output light 72 of the first output light 71 can be expressed as follows from equation 1.

From equations 2 and 3, the light absorption coefficient a can be expressed as follows.

In the above formula 4, the reflectance R ₁ of the first mirror 21, the reflection factor R ₂ of the second mirror 22, that the attenuation factor Nd of the first attenuator 31 to know the value by previously measuring it can.

  The difference ΔL in transmission distance and the difference 2Δn in the number of reflections are the angle θ formed by the first mirror 21 and the second mirror, the first mirror 21, the second mirror 22, and the first detection means 30. Based on the arrangement position with the second detection means 40, it can be calculated geometrically as described later. The angle θ and the arrangement positions of the first mirror 21, the second mirror 22, the first detection means 30, and the second detection means 40 can be measured in advance.

  Therefore, by measuring the light intensity ratio ΔI, the light absorption coefficient a can be uniquely determined using Equation 4. Specifically, the light absorption coefficient a is unambiguous by obtaining one attenuation curve as a result of measurement with measurement pulsed light 70 having a wavelength of about 9 μm using carbon monoxide as a sample to be measured. It can be proved that it can be determined.

  Therefore, in the absorption measuring apparatus 1, the above-described coefficient lookup table 53 is created in advance by calculating the light absorption coefficient a with respect to the transmission distance difference ΔL, the reflection frequency difference 2Δn, and the light intensity ratio ΔI. be able to.

  Therefore, the light absorption coefficient a is uniquely determined by referring to the coefficient look-up table 53 using the calculated transmission distance difference ΔL, the number of reflection differences 2Δn, and the measured light intensity ratio ΔI. Can be determined.

  In this way, by using the coefficient look-up table 53, the light absorption coefficient a can be calculated in real time by measuring about two points by the first detection means and the second detection means without performing the calculation process of Expression 4. Can be determined. The analysis device 52 outputs a signal indicating the determined light absorption coefficient a to the concentration determination device 54.

  The concentration determination device 54 determines the concentration of the sample to be measured based on the signal indicating the light absorption coefficient a output from the analysis device 52. The concentration determination device 54 determines the concentration of the sample to be measured using the stored concentration lookup table 55. The concentration lookup table 55 is a table in which the light absorption coefficient a and the concentration of the sample to be measured are associated with the wavelength of the measurement pulse light 70. By referring to the concentration lookup table 55, the concentration of the sample to be measured corresponding to the obtained light absorption coefficient a can be determined. The density determination device 54 outputs a signal indicating the determined density to the display device 60.

  The display device 60 displays the concentration of the sample to be measured based on the signal indicating the concentration output from the concentration determining device 54.

  Next, the operation of the absorption measurement apparatus 1 will be described. First, with the sample to be measured introduced into the sample cell 23 of the resonator 20, the measurement pulse light 70 is incident on the resonator 20 by the light source 10. The measurement pulse light 70 that has passed through the first mirror 21 is subjected to multiple reflections between the first mirror 21 and the second mirror 22 while the intensity is attenuated by the sample to be measured. Of the measurement pulse light 70 incident on the resonator 20, the first output light 71 transmitted from the second mirror 22 and output from the resonator 20 is attenuated by the first attenuator 31 to be the first attenuated light. Is output as The light that has passed through the first aperture 33 in the first attenuated light is detected by the first detector 32, and a first detection signal indicating the light intensity of the first attenuated light is output to the differential amplifier 51. Is done. In addition, light that has passed through the second aperture 43 out of the second output light 72 that has been transmitted through the second mirror 22 and output from the resonator 20 is detected by the second detector 42, and is output as the second output light. A second detection signal indicating the light intensity of the light 72 is output to the differential amplifier 51.

  The differential amplifier 51 outputs a light intensity ratio signal indicating a light intensity ratio ΔI between the light intensity of the first attenuated light and the light intensity of the second output light 72 to the analyzer 52. The analysis device 52 determines the light absorption coefficient a of the sample to be measured using the light intensity ratio signal and the coefficient lookup table 53, and outputs a signal indicating the light absorption coefficient a to the concentration determination device 54. The concentration determination device 54 determines the concentration of the sample to be measured using the signal indicating the light absorption coefficient a and the concentration lookup table 55, and outputs a signal indicating the concentration to the display device 60. The display device 60 displays the concentration of the sample to be measured based on the signal indicating the concentration.

  Subsequently, a geometric calculation method of the transmission distance Lt of the output light in the sample to be measured will be described.

For example, when the width d of the inner wall of the sample cell 23 which transmits the measurement pulse light 70 is constant, transmission distance Lt can be calculated by using the width d and the respective reflection angle theta _n of the sample cell 23. The reflection angle θ _n is the reflection angle at the first mirror 21 or the second mirror 22 of the measurement pulsed light 70 with the nth reflection in the resonator 20. Since the angle formed by the first mirror 21 and the second mirror 22 is θ, the reflection angle θ _n increases by θ when the number of reflections in the resonator 20 increases once.

For example, when the sample to be measured is filled between the first mirror 21 and the second mirror 22 included in the resonator 20, the transmission distance Lt can be obtained as follows. FIG. 2 is a diagram for explaining a method of calculating the transmission distance Lt. For the sake of explanation, an XYZ orthogonal coordinate system is set. A plane including the optical path of the measurement pulse light 70 in the resonator 20 is a plane parallel to the XY plane. Further, when the reflecting surface of the first mirror 21 is a YZ plane, the second mirror 22 is represented by a surface y = Bx + C inclined at an angle θ counterclockwise from the YZ plane in the XY plane. In order to simplify the explanation, considering the XY plane, the first mirror 21 can be represented by a straight line M ₁ parallel to the Y axis, and the second mirror 22 can be represented by a straight line M ₂ : y = Bx + C.

The optical path of the measurement pulse light 70 incident vertically to the first mirror 21 can be represented by a straight line k ₀ parallel to the X axis. Therefore, the transmission distance L ₀ of the measurement pulsed light 70 from the first mirror 21 until it reaches the second mirror 22 is a straight line M ₂ from the intersection of the straight line k _{0 with} the straight line M ₁ in the XY plane. Is the distance to the intersection.

The measurement pulse light 70 that has undergone the first reflection in the resonator 20 passes through the intersection of the straight line k ₀ and the straight line M _2, and is represented by a straight line k ₁ inclined at an angle 2θ counterclockwise from the straight line k ₀ . Transmission distance L ₁ measured pulse light 70 from via the first reflection in the resonator 20 until it reaches again the first mirror 21, the intersection of the straight line M ₂ straight lines k ₁ between the straight line M ₁ This is the distance to the intersection.

The measurement pulse light 70 that has undergone the second reflection in the resonator 20 passes through the intersection of the straight line k ₁ and the straight line M ₁ and is represented by a straight line k ₂ that is inclined 4θ clockwise from the straight line k ₁ . The transmission distance L ₂ of the measurement pulse light 70 from the second reflection in the resonator 20 until reaching the second mirror 21 again is from the intersection of the straight line k _{2 with} the straight line M ₁ and the straight line M ₂ . This is the distance to the intersection.

In this way, when the transmission distance L _n from the n-th reflection to the mirror facing the n-th reflection surface is obtained one after another, the transmission distance Lt of the output light P _n is obtained from the transmission distances L ₀ to L. It can be obtained as a sum up to _2n .

  Then, the effect in the absorption measuring apparatus 1 is demonstrated. In the absorption measuring apparatus 1, the reflecting surfaces of the first mirror 21 and the second mirror 22 are arranged so as to face each other with an angle larger than 0, so that the measurement pulse light 70 is applied to the resonator 20. The incident angle can be set arbitrarily. That is, it becomes possible to make the measurement pulse light 70 enter perpendicularly to the reflecting surface of the first mirror.

  Further, in the absorption measuring apparatus 1, the first detector 30 detects the first output light 71 having a high light intensity after the first attenuator 31 attenuates the first output light 71 with the first detector 32. Therefore, even if the maximum measurable value of the first detector 32 is smaller than the light intensity of the first output light 71, the attenuation rate of the first attenuator 31 according to the light intensity of the first output light 71. By selecting, the first output light 71 having a high light intensity can be detected. Further, in the absorption measurement apparatus 1, the second output light 72 having a low light intensity is detected by the second detector 42 that does not depend on the measurement range of the first detector 32. Therefore, the second detector 42 can be selected according to the light intensity of the second output light 72. Therefore, in the absorption measuring apparatus 1, the light absorption coefficient a of the sample to be measured can be determined even if the dynamic range of the output light to be measured is large.

More specifically, the effect of the configuration of the first detection means 30 and the second detection means 40 included in the absorption measurement apparatus 1 will be described. In the conventional walk-off type CRDS, one CCD camera is used to detect output light. This CCD camera has a measurable dynamic range of about 3 digits in one image. In the above embodiment, for example, the first detection means 30 includes the first attenuator 31 having an attenuation rate Nd of 10 ⁻³ and the first detector 32 having a dynamic range of about 3 digits, and the second A case where the measurement range of the first detector 42 is the same as that of the first detector 32 will be described. Since attenuation factor Nd is 10 ^-3 of the first attenuator 31, the measurement range of the first detection means 30 is shifted to 10 ³ times the measurement range of the first detector 32, the maximum value of the measuring range Is 10 ³ times. Therefore, the ratio between the maximum value detected by the first detection means 30 and the minimum value detected by the second detection means 40 is about 6 digits.

Furthermore, in the above embodiment, for example, the first detection means 30 includes the first attenuator 31 having an attenuation factor Nd of 10 ⁻⁶ and the first detector 32 having a dynamic range of about three digits, A case where the measurement range of the second detector 42 is the same as that of the first detector 32 will be described. Attenuation factor Nd is because ^10-6 of the first attenuator 31, the measurement range of the first detection means 30 is shifted to 10 ⁶ times the measurement range of the first detector 32, the maximum value of the measuring range Is 10 ⁶ times. Therefore, the ratio between the maximum value detected by the first detection means 30 and the minimum value detected by the second detection means 40 is about nine digits. As described above, the maximum value and the minimum value that can be detected by the absorption measuring apparatus 1 are determined by the combination of the attenuation rate Nd of the first attenuator 31 and the dynamic range of the first detector 32 and the second detector 42. The ratio of values can be set to a desired value.

  In the first embodiment, it is also preferable to make the following devices.

  In the first embodiment, when continuous light is used as measurement light, interference fringes are generated spatially due to temporal coherence. Therefore, it is also preferable to give a minute vibration to the absorption measuring device 1 so as not to generate interference fringes.

  In the first embodiment, the first detector 32 and the second detector 42 are, for example, phototubes, but may be photodiodes.

  In the first embodiment, the difference 2Δn in the number of reflections is geometrically calculated by the arithmetic circuit, but the pulsed light is incident on the resonator 20, and the first detection signal and the second detection signal are differential amplifiers. The difference 2Δn in the number of reflections may be obtained based on the time difference to reach 51.

  In the first embodiment, it is also preferable that the absorption measurement apparatus 1 includes a condenser lens between the resonator 20 and the first and second detection means 30 and 40. FIG. 3 is a diagram for explaining a condensing lens included in the absorption measurement apparatus according to the first embodiment. The condensing lens 81 is a lens that condenses the first output light 71 and the second output light 72 on the first detection means 30 and the second detection means 40, respectively.

  The measurement pulse light 70 is parallel light. Accordingly, the output lights output from the resonator 20 are each parallel light. On the other hand, since the plurality of output lights are not parallel to each other, the output light can be condensed on separate detection means by the condenser lens 81. As described above, since the output light is condensed on the respective detection means, it is possible to prevent the adjacent output lights from overlapping at the detection position and to detect the intensity of the output light more accurately.

  In the first embodiment, the areas of the light receiving surfaces of the first detecting means 30 and the second detecting means 40 are preferably equal to the cross-sectional area of the light to be detected at the position of the light receiving surface. By adopting such a configuration, it is possible to prevent the detection means from receiving up to the output light next to the output light to be detected, and to detect the intensity of the output light more accurately.

  In the first embodiment, the absorption measurement device 1 preferably includes an angle measurement device (angle measurement means) that measures an angle θ formed by the first mirror 21 and the second mirror 22. FIG. 4 is a diagram for explaining a configuration of an angle measurement device included in the absorption measurement device according to the first embodiment.

  The angle measurement device 82 includes an angle measurement light source 83, a lens 84, and a position detector 85. The angle measurement light source 83 is a semiconductor laser that outputs angle measurement light to the reflection surface of the second mirror 22. The lens 84 converts the angle measurement light output from the angle measurement light source 83 into parallel light. The position detector 85 receives the angle measurement light that has been transmitted through the lens 84 and reflected by the second mirror 22, and measures the incident position. When the angle of the second mirror 22 changes, the incident position in the position detector 85 changes, so that the angle θ formed by the first mirror 21 and the second mirror 22 can be obtained from the change in the incident position. .

  By measuring the angle θ as described above, the light absorption coefficient depending on the angle can be determined more accurately. In the angle measuring device 82, a mirror may be further installed between the second mirror 22 and the position detector 85. As the number of reflections of the angle measurement light is increased, the change in the incident position in the position detector 85 with respect to the change in the angle θ is increased, so that the angle θ can be measured more accurately.

  In the first embodiment, the absorption measurement apparatus 1 inputs a modulator (modulation means) that modulates the intensity of the measurement pulse light 70 at a predetermined frequency, and a first detection signal, a second detection signal, and a detection signal, respectively. It is also preferable to include a first lock-in amplifier and a second lock-in amplifier that output a level of a signal component having a predetermined frequency in the input detection signal.

  The modulator modulates the intensity of the measurement pulse light 70 at a predetermined frequency. The modulator outputs a synchronization signal whose intensity changes with time at a predetermined frequency to the light source 10, the first lock-in amplifier, and the second lock-in amplifier. The light source 10 outputs the measurement pulse light 70 that is intensity-modulated at a predetermined frequency based on the synchronization signal output from the modulator.

  The first lock-in amplifier receives the first detection signal and outputs a level of a signal component having a predetermined frequency based on the synchronization signal among the input signals. The second lock-in amplifier receives the second detection signal and outputs a level of a signal component having a predetermined frequency based on the synchronization signal among the input signals.

  The detection signal includes an output light detection signal for the measurement pulse light 70 and noise. Since the modulator modulates the intensity of the measurement pulse light 70 at a predetermined frequency, the signal at the predetermined frequency is a detection signal for the output light. Can be judged. Therefore, noise of frequencies other than the predetermined frequency can be removed by the first and second lock-in amplifiers. Therefore, the light absorption coefficient a can be determined with higher accuracy.

  In the said 1st Embodiment, it is preferable that the 1st attenuator 31 becomes a structure which can vary the attenuation factor Nd. The first attenuator 31 includes, for example, a filter having a different transmittance depending on a location where light is transmitted. By using such a first attenuator 31, the attenuation factor is optimized by moving the first attenuator 31 in accordance with the light intensity of the first output light 71 and the dynamic range of the first detector 32. Can be

  Subsequently, second to sixth embodiments according to the present invention will be described.

  First, an absorption measurement apparatus according to the second embodiment will be described. FIG. 5 is a configuration diagram of the absorption measurement apparatus 2 according to the second embodiment. The absorption measurement device 2 includes an angle variable device 24 (angle variable means) and an angle control device 25 in addition to the configuration of the absorption measurement device 1.

  The angle varying device 24 changes the angle θ formed by the first mirror 21 and the second mirror 22. The angle variable device 24 changes the angle θ based on a signal indicating the change angle output from the angle control device 25. The angle control device 25 controls the change of the angle θ by the angle variable device 24. The angle control device 25 outputs a signal instructing the angle change device 24 and the analysis device 52 to change the angle θ. The analysis device 52 calculates the angle θ based on the signal instructing the change of the incident angle θ output from the angle control device 25, and determines the light absorption coefficient a based on the changed angle θ.

  By changing the angle θ, the spatial position of the measurement pulse light 70 passing through the sample to be measured can be changed, and measurement can be performed at multiple points. Therefore, a more accurate absorbed coefficient a can be determined by analyzing the relationship between the angle θ and the light intensity ratio ΔI.

  In the second embodiment, it is also preferable to perform measurement by the following method. First, the blank sample is measured without introducing the sample to be measured into the sample cell 23 of the absorption measuring apparatus 1. During the blank measurement, the angle θ is adjusted so that the light intensity ratio ΔI is 1. That is, the angle θ is adjusted so that the light intensity of the first attenuated light and the second output light 72 is approximately the same. Subsequently, the sample to be measured is introduced into the sample cell 23 and measured. The light absorption coefficient a is calculated based on the amount of change in the light intensity ratio ΔI.

By performing such measurement, it is not necessary to previously measured reflectivity of the first mirror 21 R ₁ and the reflectivity R ₂ of the second mirror 22. Further, in the above-described blank measurement, the case where the light absorption coefficient a is 0 is measured and used as a reference, so that it can be measured more accurately.

  In the second embodiment, it is also preferable to perform measurement as follows. The angle θ is adjusted so that the value of the light intensity ratio ΔI becomes 1 with the sample to be measured introduced into the sample cell 23. That is, the angle θ is adjusted so that the light intensity of the first attenuated light and the second output light 72 is approximately the same. The light absorption coefficient a can be obtained by using the angle θ when the value of the light intensity ratio ΔI becomes 1.

  Furthermore, it is preferable that the absorption measurement apparatus 2 further includes a position moving unit that moves the position of the first mirror 21. The first mirror 21 is placed on a movable base so as to be easily moved. By moving the position of the first mirror 21, the transmission distance Lt of each output light in the sample to be measured can be changed. By changing the transmission distance Lt by the position moving means, the light intensity of the first attenuated light and the second output light 72 can be finely adjusted.

  An absorption measurement apparatus according to the third embodiment will be described. FIG. 6 is a configuration diagram of the absorption measurement apparatus 3 according to the third embodiment. In addition to the configuration of the absorption measurement device 1, the absorption measurement device 3 includes a position variable device 44 (position variable means) and a position control device 45.

  The position variable device 44 is a device that changes the distance between the first detection means 30 and the second detection means 40. The position variable device 44 moves the second detection means 40 based on a signal instructing movement output from the position control device 45. The second detection means 40 is placed on a movable base so as to be easily moved.

  The position control device 45 controls the movement of the second detection means 40 by the position variable device 44. The position control device 45 outputs a signal instructing the movement of the second detection means 40 to the position variable device 44 and the analysis device 52.

  The analysis device 52 calculates the distance between the output position of the first output light 71 and the output position of the second output light 72 based on the signal instructing the movement output by the position control device 45, and A difference ΔL in the transmission distance of the output light and a difference 2Δn in the number of reflections are calculated.

  By changing the position of the second detection means 40, the distance through which the second output light 72 is transmitted through the sample to be measured can be changed, and measurement can be performed at multiple points. Therefore, a more accurate absorbed coefficient a can be determined. Furthermore, the spatial distribution of the sample to be measured can be measured by analyzing the relationship between the output position of the output light detected by the detecting means and the light intensity ratio ΔI.

An absorption measurement apparatus according to the fourth embodiment will be described. FIG. 7 is a configuration diagram of the absorption measurement apparatus 4 according to the fourth embodiment. In addition to the configuration of the absorption measurement device 2, the absorption measurement device 4 includes a third detection unit 90 and a second differential amplifier 56. Further, in the absorbent measurement device 4, which replaces the second detection means 40 in the absorption measuring device 2 to the second detection means 40 _4.

  The third detection means 90 has a higher sensitivity than the second detection means 40 and detects the third output light 74 having a higher number of reflections in the resonator 20 than the second output light 72, thereby detecting the third detection. Output a signal. The third detection signal is a signal output from the third detection unit 90 to the determination device 50 according to the light intensity of the third output light 74. The third output light 74 has a smaller number of reflections in the resonator 20 than the second output light 72, and therefore has a light intensity lower than that of the second output light 72. Although the intensity of the third output light 74 is weaker than that of the second output light 72, the third detection means 90 can be detected because it is more sensitive than the second detection means 40. The third detection means 90 includes a third detector 92 and a third aperture 93.

  The third aperture 93 is disposed on the optical path of the third output light 74 between the third detector 92 and the resonator 20, and allows only the third output light 74 to pass therethrough. The third aperture 93 blocks output light other than the third output light 74 output from the vicinity of the output position of the third output light 74 in the second mirror 22.

  The third detector 92 detects the third output light 74 that has passed through the third aperture 93 and outputs a third detection signal corresponding to the detected light intensity to the determination device 50. The sensitivity characteristic of the third detector 92 is the same as that of the first detector 32. The third detector 92 is, for example, a photoelectric tube having the same sensitivity characteristics as the first detector 32.

Second detecting means 40 _4, the second detector 42 (second attenuating light detecting means) in addition to the second aperture 43, a second attenuator 41. The second attenuator 41 attenuates the second output light 72 to be detected with an attenuation rate lower than that of the first attenuator 31 and outputs the second attenuated light. The second detector 42 detects the second attenuated light and outputs a second detection signal.

The first mirror 21 between the first distance along the mirror 21 of the first detection means 30 and the third detection means 90 between the first detecting means 30 and the second detecting means 40 ₄ The distance to the distance along the line is equivalent to the ratio of the logarithm of the attenuation factor of the second attenuator 41 and the logarithm of the attenuation factor of the first attenuator 31.

The second differential amplifier 56 receives the second detection signal and the third detection signal, attenuates the second output light 72, and attenuates the light intensity I ₂ and the third output light 74. A light intensity ratio signal indicating the second light intensity ratio ΔI ₂ with I ₃ is output to the analyzer 52. Determining device 53 determines the light absorption coefficient a based on the light intensity ratio [Delta] I and a second light intensity ratio [Delta] I _2.

In the absorption measurement device 4, the greater the number of reflections of the output light detected by the detection means in the resonator 20 compared to the first output light 71, the greater the difference between the detection means and the first detection means 30. The distance along the first mirror 21 increases. Further, the output light intensity decreases exponentially as the number of reflections in the resonator 20 increases. Accordingly, the first between the first distance along the mirror 21 of the first detection means 30 and the third detection means 90 between the first detecting means 30 and the second detecting means 40 ₄ The ratio of the distance along the mirror 21 is equivalent to the ratio of the logarithm of the attenuation factor of the second attenuation unit 31 and the logarithm of the attenuation factor of the first attenuation unit 41. Thus, as the light intensity of the output light increases exponentially, it is detected after being attenuated exponentially. Therefore, even when the detection ranges of the first to third detection units 30, 40 ₄ , and 90 are approximately the same, the first to third output lights 71, 72, and 74 are converted to the first to third detection units 30. , 40 ₄ , 90 can be detected respectively. In addition, since the determining unit 53 determines the light absorption coefficient a based on the third detection signal in addition to the first and second detection signals, the light absorption coefficient a can be determined with higher accuracy.

In the fourth embodiment, it is also preferable to perform measurement as follows. The angle θ is adjusted so that the value of the light intensity ratio ΔI and the second light intensity ratio ΔI ₂ is 1. That is, the angle θ is adjusted so that the light intensity of the first attenuated light, the second attenuated light, and the third output light are approximately the same. The light absorption coefficient a can be obtained based on the angle θ at which the value of the light intensity ratio ΔI and the second light intensity ratio ΔI ₂ is 1.

An absorption measurement apparatus according to the fifth embodiment will be described. FIG. 8 is a configuration diagram of the absorption measurement apparatus 5 according to the fifth embodiment. Absorption measurement apparatus 5 is a first detection means 30 of the absorption measuring device 2 a device is replaced with a first detecting means 30 _5. Further, the absorption measuring device 5 includes an attenuator 31 ₅ (attenuating means).

First detecting means 30 ₅ is provided with a first detector 32 described above (the first attenuation optical detecting means) and a first aperture 33. Similar to the absorption measurement apparatus 2, the second detection means 40 includes a second detector 40 (second attenuated light detection means) and a second aperture 43.

Attenuator 31 _5, the attenuation and outputs as a damping light in response to incident incident output light positions. The first output light 71 is output as the first attenuation light, and the second output light 72 is output as the second attenuation light. Attenuator 31 ₅ has an attenuation factor distribution attenuation rate decreases exponentially toward the side of incident reflected Most Viewed output light from the incident side of the low output light number of reflections within the resonator.

Light intensity of the first output light 71 is exponentially greater than the light intensity of the second output light 72, according to the above configuration, the first output light 71 is first by attenuator 31 ₅ The second output light 72 is attenuated at an attenuation rate that is exponentially larger than the attenuation rate. Therefore, also the detection range of the first detector 30 ₅ and the second light detection device 40 is of the same order of magnitude, and detects the first attenuating light by the first detector 30 _5, a second damping Light can be detected by the second optical detector 40.

  In the fifth embodiment, it is also preferable to perform measurement as follows. The angle θ is adjusted so that the light intensity ratio ΔI becomes 1. That is, the angle θ is adjusted so that the light intensity of the first attenuated light and the second attenuated light are approximately the same. The light absorption coefficient a is determined by using the attenuation rate and the angle θ of the attenuation of the first output light 71 and the second output light 72 when the light intensity ratio ΔI becomes 1. Can do.

An absorption measurement apparatus according to the sixth embodiment will be described. FIG. 9 is a configuration diagram of the absorption measurement apparatus 6 according to the sixth embodiment. Absorption measuring device 6 is a device obtained by replacing the first detection means 30 and the second detecting means 40 to the first detection means 30 _6, respectively and the second detecting means 40 ₆ in the absorbent measuring apparatus 1. First detecting means 30 ₆ includes a first detector 32 ₆ and the first aperture 33. Second detecting means 40 ₆ includes a second detector 42 ₆ and a second aperture 43. First detector 32 ₆ a photodiode, and a second detector 42 ₆ is an avalanche photodiode.

  In the sixth embodiment, the first output light 71 is detected by a photodiode, and the second output light 72 having a light intensity lower than that of the first output light 71 is detected by an avalanche photodiode having higher sensitivity than the photodiode. can do.

In the sixth embodiment, the first detector 32 ₆ is phototube, and a second detector 42 ₆ may be a photomultiplier tube. In this case, the first output light 71 can be detected by the phototube, and the second output light 72 having a light intensity lower than that of the first output light 71 can be detected by the photomultiplier tube having higher sensitivity than the phototube.

In the first to sixth embodiments, the sample to be measured is arranged in the resonator 20 using the sample cell 23. However, the sample to be measured may be arranged in the resonator 20 using a dove prism. FIG. 10 is a diagram for explaining a modification using a dove prism in the embodiment according to the present invention. An XYZ rectangular coordinate system is set for explanation. A plane including a plurality of output lights is defined as a plane parallel to the XY plane, and a direction in which the measurement pulse light 70 is output from the light source 10 is defined as a + X axis direction. FIG. 10 is a diagram of the resonator 20 viewed from the −Y direction.

  The dove prism 26 includes a main surface 26a parallel to the optical path of the measurement pulse light 70 that is multiple-reflected in the resonator 20, a first side surface 26b that forms an angle with the main surface 26a that is greater than 0 degree and less than 90 degrees, And a second side surface 26c that is opposite to the first side surface 26b and forms an angle similar to the angle between the main surface 26a and the first side surface 26b. The main surface 26a is a surface parallel to the XY plane.

  The measurement pulse light 70 incident on the resonator 20 enters the Dove prism 26 from one of the first side surface 26b and the second side surface 26c, is totally reflected on the main surface 26a, and faces the incident side surface. The light is emitted from the side surface, and multiple reflection is repeated in the resonator 20, and total reflection is repeated on the main surface.

  The sample to be measured is placed at a position including a range in which the measurement pulse light 70 on the main surface 26a is totally reflected.

  When the measurement pulse light 70 is totally reflected by the main surface 26a of the Dove prism 26, evanescent light oozes out to the side of the main surface 26a where the sample to be measured is installed. The leaked evanescent light is attenuated because the light is absorbed by the sample to be measured. Therefore, the output light output from the resonator 20 is also attenuated by the absorption of the evanescent light of the sample to be measured.

  Therefore, by measuring the light intensity of the output light as described above for the first to sixth embodiments, the absorption of the evanescent light of the measurement light by the sample to be measured can be measured and the light absorption coefficient can be determined. . Since the evanescent light oozes out from the totally reflected surface into a region of about the wavelength, it is possible to determine the light absorption coefficient of the sample to be measured whose size is, for example, about a polymer.

It is a lineblock diagram of the absorption measuring device concerning a 1st embodiment. It is a figure for demonstrating the calculation method of the transmission distance Lt. It is a figure for demonstrating the condensing lens contained in the absorption measuring device which concerns on 1st Embodiment. It is a figure for demonstrating the structure of the angle measuring device contained in the absorption measuring device which concerns on 1st Embodiment. It is a block diagram of the absorption measuring device which concerns on 2nd Embodiment. It is a block diagram of the absorption measuring device which concerns on 3rd Embodiment. It is a block diagram of the absorption measuring device which concerns on 4th Embodiment. It is a block diagram of the absorption measuring device which concerns on 5th Embodiment. It is a block diagram of the absorption measuring device which concerns on 6th Embodiment. It is a figure for demonstrating the modification using the dove prism in embodiment which concerns on this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Light source, 20 ... Resonator, 21 ... 1st mirror, 22 ... 2nd mirror, 23 ... Sample cell, 24 ... Angle variable device, 25 ... Angle control device, 26 ... Dove prism, 27 ... Sample to be measured , 30 ... first detection means, 31 ... first attenuator, 32 ... first detector, 33 ... first aperture, 40 ... second detection means, 41 ... wide attenuator, 42 ... second Detector, 43 ... second aperture, 44 ... position variable device, 45 ... position control device, 50 ... decision device, 51 ... differential amplifier, 52 ... analyzer, 53 ... coefficient lookup table, 54 ... concentration determination Device: 55 ... Concentration lookup table, 60 ... Display device, 70 ... Measurement pulse light, 71 ... First output light, 72 ... Second output light, 73 ... Attenuation curve, 74 ... Second output light, 75 ... third output light, 81 ... condensing lens, 82 ... angle measuring device, DESCRIPTION OF SYMBOLS 3 ... Light source for angle measurement, 84 ... Lens for angle measurement, 85 ... Position detector, 90 ... 2nd detection means, 91 ... 2nd attenuator, 92 ... 2nd detector, 93 ... 2nd aperture 95 ... third detection means, 97 ... third detector, 98 ... third aperture.

Claims (17)

A light source that outputs measurement light;
Each of the first mirror and the second mirror has a first mirror and a second mirror that reflect a part of the incident measurement light and transmit the remaining part, and an angle greater than 0 between the reflection surfaces of the first mirror and the second mirror The measurement light is incident on the first mirror, transmitted through the first mirror, and repeatedly subjected to multiple reflection in the resonator, and the first mirror and the A resonator that passes through one of the second mirrors and outputs as output light from a plurality of locations;
First detection means for detecting a first output light output from the resonator and outputting a first detection signal;
Second detection means for detecting second output light having higher sensitivity than the first detection means and having a higher number of reflections in the resonator than the first output light, and outputting a second detection signal. When,
Third detection means for detecting a third output light having a higher sensitivity than the second detection means and having a higher number of reflections in the resonator than the second output light, and outputting a third detection signal. When,
Based on the first detection signal, the second detection signal, and the third detection signal, the light absorption coefficient of the sample to be measured placed between the first mirror and the second mirror is calculated. Bei example and determination means for determining,
The first detection means attenuates the first output light detected and outputs first attenuation light, and the first attenuation light output by the first attenuation means. First attenuating light detecting means for detecting
A second attenuating means for attenuating the second output light detected by the second detecting means with an attenuation factor lower than the attenuation factor of the first attenuating means and outputting a second attenuating light; Second attenuating light detection means for detecting the second attenuating light output by the second attenuating means,
A distance along the first mirror between the first detection means and the second detection means and the first mirror between the first detection means and the third detection means; The ratio of the distance along the line is equal to the ratio of the logarithm of the attenuation factor of the second attenuation means and the logarithm of the attenuation factor of the first attenuation means;
Absorption measuring device characterized by that. The absorption measurement apparatus according to claim 1 , wherein the first attenuation light detection unit and the second detection unit exhibit the same sensitivity characteristic.   The absorption measurement apparatus according to claim 1, wherein the first detection means is a photodiode, and the second detection means is an avalanche photodiode.   2. The absorption measurement apparatus according to claim 1, wherein the first detection means is a phototube and the second detection means is a photomultiplier tube. Absorption measuring apparatus according to any one of claims 1-4, characterized in that it comprises a tilting means for changing the angle at which the reflecting surface is formed between said first mirror and said second mirror. Absorption measuring apparatus according to any one of claims 1 to 5, characterized in that it comprises position changing means for changing the position of at least one detector of the plurality of said detecting means. Absorption measuring apparatus according to any one of claims 1 to 6, characterized in that it comprises a distance changing means for changing the distance between the first mirror and the second mirror. The determination unit includes a differential measurement device that differentially measures the detection signals output from each of the plurality of detection units, and determines a light absorption coefficient using a result of the differential measurement. Item 8. The absorption measurement device according to any one of Items 1 to 7 . As detection signals outputted by the plurality of the detection means is the same, more of claims 8-8, characterized in that it comprises a control means for controlling the number of reflections by the resonator of the output light The absorption measuring device according to claim 1. Absorption measuring apparatus according to any one of claims 1 to 9, further comprising a lens for focusing the output light in each of said detection means. The area of the light-receiving surface of the detecting means, the absorption measuring apparatus according to any one of claims 1 to 10, characterized in that is equal to the cross-sectional area at the position of the light receiving surface of the output light. Modulation means for intensity-modulating the measurement light at a predetermined frequency;
Enter at least one signal of the detection signal, any one of claims 1 to 11, characterized in that it comprises a lock-in amplifier which outputs a level of the signal component of the predetermined frequency among the input the signal The absorption measuring device according to 1. Absorption measuring apparatus according to any one of claims 1 to 12, characterized in that it comprises angle measuring means for measuring the angle. The determining means calculates the number of reflections of the output light detected by the plurality of detecting means in the resonator based on the angle, and determines the light absorption coefficient using the calculation result. The absorption measurement device according to any one of claims 1 to 13 . Absorption measuring apparatus according to any one of claims 1 to 14, further comprising a display means for displaying the light absorption coefficient the determination unit has determined. Absorption measuring apparatus according the any one of claim 1 to 15, characterized in that it comprises a sample cell for introducing a sample to be measured between the first mirror and the second mirror. A main surface parallel to the optical path of the measurement light that is multiple-reflected in the resonator, a first side surface that forms an angle larger than 0 degrees and smaller than 90 degrees, and opposite to the first side surface. A dove prism disposed in the resonator, and having a second side surface having an angle similar to the angle between the main surface and the first side surface,
The measurement light incident on the resonator enters the Dove prism from one of the first side surface and the second side surface, is totally reflected on the main surface, and is opposed to the side surface that is incident. And repeating multiple reflections in the resonator and repeating total reflection on the main surface,
The sample to be measured, the absorption measuring apparatus according to any one of claims 1 to 15, characterized in that the measuring beam on the main surface is disposed at a position including a range of total reflection.

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