JP2006189392A - Absorption measuring apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an absorption measuring apparatus, capable of determining the optical absorption coefficients of samples to be measured, even when the dynamic range of the output light to be measured is large. <P>SOLUTION: The absorption measuring apparatus 1 is provided with a resonator 20, having a first mirror 21 and a second mirror 22 facing each other; a light source 10 for making measuring pulsed light 70, having the angle of incidence to the resonator 20 larger than 0 incident on the first mirror 21; a first detection means 30 for detecting a first output light 71 among output light outputted from a plurality of locations of the resonator 20 and outputting first detection signals; a second detection means 40, having higher sensitivity than that of the first detection means 30 for detecting a second output light 72, having a larger number of reflections in the resonator 20 than that of the first output light 71 and outputting second detection signals; and a determination device 50 for determining the optical absorption coefficient of the sample to be measured, arranged in between the first mirror 21 and the second mirror 22, on the basis of the first detection signals and the second detection signals. <P>COPYRIGHT: (C)2006,JPO&NCIPI

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, two 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 according to the present invention includes a first mirror and a second mirror that each reflect a part of incident light and transmit the remaining part, and the first mirror, The resonator arranged so that the second mirror faces each other, and the measurement light are output to the first mirror so that the incident angle of the measurement light to the resonator has an angle greater than zero. Either a light source to be incident on the first mirror from the outside of the resonator, pass through the first mirror, enter the resonator, repeat multiple reflection, and either the first mirror or the second mirror First detection means for detecting the first output light and outputting the first detection signal out of the output lights respectively transmitted from the plurality of locations through the light, and the first detection means has a higher sensitivity than the first detection means, A second detector for detecting the second output light having a higher number of reflections in the resonator than the first output light and outputting a second detection signal; And a determining means for determining the light absorption coefficient of the sample to be measured placed between the first mirror and the second mirror based on the first detection signal and the second detection signal. And

  Thus, since the first output light is detected by the first detection means and the second output light is detected by the second detection means, detection by the first detection means and the second detection means is possible. The measurement range of the light intensity and the sensitivity of the detection element can be selected according to the intensity of the light to be detected. Further, since the second output light having a higher number of reflections in the resonator than the first output light is detected by the second detector having higher sensitivity than the first detector, the intensity is higher than that of the first output light. The second output light having a low value can be detected by the second detector.

  Moreover, it is desirable that the absorption measuring apparatus according to the present invention includes an angle varying means for changing the incident angle of the measuring light to the resonator. Since the incident angle of the measurement light to the resonator is changed by the angle variable means in this way, the light absorption coefficient at a plurality of incident angles can be measured for a single sample to be measured, and the light absorption can be performed more accurately. A coefficient can be determined.

  In addition, the absorption measurement apparatus according to the present invention preferably includes angle control means for controlling the incident angle of the measurement light to the resonator. Thus, by controlling the incident angle so that the first detection signal and the second detection signal have substantially the same value, the light absorption coefficient is determined depending on the incident angle. When the first detection signal and the second detection signal have different values, the light absorption coefficient is determined depending on the ratio between the first detection signal and the second detection signal in addition to the incident angle. Is done. Therefore, if the angle control means changes the incident angle of the measurement light to the resonator so that the first detection signal and the second detection signal are substantially the same, the first light absorption coefficient is determined when the light absorption coefficient is determined. There is no need to consider the ratio between the first detection signal and the second detection signal. Therefore, the light absorption coefficient can be determined more easily.

  Moreover, it is desirable that the absorption measurement apparatus according to the present invention includes a distance variable unit that changes a distance between the first mirror and the second mirror. Thus, by changing the distance between the first mirror and the second mirror, the light intensity of the first output light and the light intensity of the second output light are respectively changed according to the changed distance. Change. Accordingly, the ratio between the first detection signal and the second detection signal changes. From this, the distance between the first mirror and the second mirror can be changed and adjusted so that the ratio between the first detection signal and the second detection signal becomes a desired value. .

  In addition, the absorption measurement apparatus according to the present invention inputs the modulation means for intensity-modulating the measurement light at a predetermined frequency, and at least one of the first detection signal and the second detection signal, and inputs the signal. It is desirable to provide a lock-in amplifier that outputs a level of a signal component of a predetermined frequency among the signals. The first detection signal and the second detection signal include an output light signal and noise with respect to the measurement light, but since the modulation means intensity-modulates the measurement light at a predetermined frequency, the signal at the predetermined frequency is a signal of the output light. Can be determined. Since the lock-in amplifier outputs the level of the signal component of the predetermined frequency among the detection signals of one of the first detection signal and the second detection signal, noise of frequencies other than the predetermined frequency can be removed. . Therefore, the light absorption coefficient can be determined with higher accuracy.

  In addition, the absorption measurement apparatus according to the present invention preferably includes 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.

  In the absorption measurement apparatus according to the present invention, the first detection means includes an attenuation means for attenuating the first output light to be measured and outputting the attenuated light, and an attenuated light for detecting the attenuated light output from the attenuation means. It is desirable to provide a detection means. According to this configuration, even if the maximum measurable value of the attenuated light detection means is smaller than the light intensity of the first output light, the attenuation means attenuates the first output light. 1 output light can be detected.

  Further, it is desirable that the attenuated light detection means and the second detection means exhibit the same sensitivity characteristics. With this configuration, when the light absorption coefficient is determined based on the first detection signal output from the attenuated light detection means and the second detection signal output from the second detection means, attenuated light detection is performed. There is no need to consider the difference in sensitivity characteristics between the means and the second detection means.

  In the absorption measurement apparatus according to the present invention, the first detection means may be a photodiode, and the second detection means may be an avalanche photodiode. Therefore, the first output light 71 can be detected by the photodiode, and the second output light 72 having a light intensity lower than that of the first output light 71 can be detected by the avalanche photodiode having higher sensitivity than the photodiode.

  In the absorption measurement apparatus according to the present invention, the first detection means may be a phototube and the second detection means may be a photomultiplier tube. Therefore, 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.

  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.

  The absorption measurement apparatus according to the present embodiment acquires a light absorption coefficient of a sample to be measured using a walk-off type CRDS. In addition, the absorption measurement apparatus according to the present embodiment determines the concentration of the sample to be measured using the acquired light absorption coefficient.

  First, the configuration of the absorption measurement apparatus according to the present embodiment will be described. FIG. 1 is a configuration diagram of an absorption measurement apparatus 1 according to the present 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.

  The resonator 20 includes a first mirror 21 and a second mirror 22 that reflect a part of incident light and transmit the remaining part. The first mirror 21 and the second mirror 22 are disposed so as to face each other. Moreover, it is preferable that the 1st mirror 21 and the 2nd mirror 22 are arrange | positioned in parallel. The resonator 20 includes a rectangular parallelepiped-shaped sample cell 23 that is disposed between the first mirror 21 and the second mirror 22 and introduces the sample to be measured. The sample to be measured is liquid or gas. The sample to be measured is introduced into the sample cell 23 by a pump (not shown) from a supply source (not shown).

  The light source 10 outputs the measurement light and makes the measurement light incident on the first mirror 21 so that the incident angle of the measurement light to the resonator 20 has an angle larger than zero. The measurement light may be pulsed light or continuous light. In FIG. 1, the measurement pulse light 70 which is pulse light is shown as measurement light. In the measurement pulse light 70 of FIG. 1, the horizontal axis represents time. As the light source 10, a semiconductor laser, a quantum cascade laser, a titanium sapphire laser, or the like can be used.

  The measurement pulse light 70 enters the first mirror 21 from the outside of the resonator 20, passes through the first mirror 21, enters the resonator 20, passes through the second mirror 22, and passes from the resonator 20. Is output. 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. Further, the measurement pulse light 70 is reflected at a plurality of locations in the resonator 20, and transmitted light is output from the resonator 20 to the outside of the resonator 20.

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、Ｄは、光が共振器２０内で反射してから次に反射するまでに被測定試料中を透過する距離である。その距離Ｄは、試料セル２３の第１の鏡と平行な２面の内壁間の距離をｄ、共振器２０への測定パルス光７０の入射角をθとすると、次のように表される。

Out of the output light output from the second mirror 22, the output light L _n output through 2n reflections in the resonator 20 becomes an attenuation curve 73 of the pulse train. In the pulse train attenuation curve 73 shown in FIG. 1, the vertical axis indicates the spatial distance of the output position of the output light. The light intensity I (n) of the output light L _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 of the measurement sample, D, is the distance that light passes through the sample to be measured from the time it is reflected in the resonator 20 to the next time it is reflected. The distance D is expressed as follows, where d is the distance between the inner walls of two surfaces parallel to the first mirror of the sample cell 23 and θ is the incident angle of the measurement pulsed light 70 to the resonator 20. .

  Returning to FIG. 1, the first detection means 30 and the second detection means 40 are on the surface of the second mirror 22 out of the output light transmitted through the second mirror 22 and output from the resonator 20. The first output light 71 and the second output light 72 output from two predetermined positions are detected. In the first output light 71 and the second output light 72 shown in FIG. 1, the vertical axis indicates the spatial distance. 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 an optical attenuator 31 (attenuation means) and a first detector 32 (attenuation light detection means). A first aperture 33 is arranged between the optical attenuator 31 and the first detector 32.

  The optical attenuator 31 attenuates the first output light 71 with the attenuation factor Nd and outputs the attenuated light to the first detector 32. The optical attenuator 31 is preferably configured so that the attenuation factor Nd can be varied. The optical attenuator 31 includes, for example, a filter having a different transmittance depending on a location where light is transmitted. By using such an optical attenuator 31, the attenuation factor can be optimized by moving the optical attenuator 31 in accordance with the light intensity of the first output light 71 and the dynamic range of the first detector 32. it can.

  The first aperture 33 is disposed on the optical path of the first output light 71 between the optical attenuator 31 and the first detector 32, and allows only the first output light 71 to pass through. 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 attenuated light that has been attenuated by the optical attenuator 31 and has passed through the first aperture 33, and outputs a first detection signal corresponding to the intensity of the detected light to the determination device 50. To do. The first detector 32 is, for example, a phototube.

  The second detection means 40 detects the second output light 72 having a greater number of reflections in the resonator 20 than the first output light 71 and outputs a second detection signal. 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 above-described second detection signal is a signal output from the second detection means 40 to the determination device 50 according to the light intensity of the second output light 72. The second detection means 40 includes a second detector 41 and a second aperture 42.

  The second aperture 42 is disposed on the optical path of the second output light 72 between the second detector 41 and the resonator 20, and allows only the second output light 72 to pass through. The second aperture 42 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 41 detects the second output light 72 that has passed through the second aperture 42 and outputs a second detection signal corresponding to the detected light intensity to the determination device 50. The sensitivity characteristic of the second detector 41 is the same as that of the first detector 32. The second detector 41 is, for example, a phototube 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 analysis device 52 stores a coefficient lookup table 53. The density determination device 54 stores a density lookup table 55.

The differential amplifier 51 receives the light intensity I ₁ of the attenuated light and the light of the second output light 72 that attenuates the first output light 71 based on the input first detection signal and second detection signal. A light intensity ratio signal indicating the light intensity ratio ΔI with the intensity I ₂ 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 using the light intensity ratio signal and the coefficient lookup table 53 stored in advance. The coefficient lookup table 53 is a table in which the incident angle θ of the measurement pulse light 70 to the resonator 20, the light intensity ratio ΔI, and the light absorption coefficient a are associated with each other and stored in the analysis device 52. That is, when the incident angle θ is known, the light absorption coefficient a can be determined by measuring the value of ΔI and referring to the coefficient lookup table 53. The analysis device 52 outputs a signal indicating the determined light absorption coefficient a to the concentration determination device 54.

式３と式４より光吸収係数ａは次のように表すことができる。

上記式５において、第１の鏡２１の反射率Ｒ_１と、第２の鏡２２の反射率Ｒ_２と、光減衰器３１の減衰率Ｎｄは予め測定することにより値を知ることができる。第１の出力光７１と第２の出力光７２との被測定試料中の透過距離の差ΔＬ＝２ＤΔｎは、光路長Ｄと、第１の出力光７１と第２の出力光７２との共振器２０内における反射回数の差２Δｎとを知ることにより算出できる。第２の鏡２２上における第１の出力光７１の出力位置と第２の出力光７２の出力位置との間の距離をｘ、第１の鏡２１と第２の鏡２２との間の距離をＸとすると、反射回数の差２Δｎは幾何学的に次のように表すことができる。

上記式６において、出力位置の距離ｘと鏡間の距離Ｘは、予め測定することによって値を得ることができる。以上より、光強度比ΔＩと共振器２０への測定パルス光７０の入射角θとを得ることによって、式５を用いて光吸収係数ａは一義的に決定することができる。よって、予め係数ルックアップテーブル５３を作成することができる。 The principle of determining the light absorption coefficient a by the analysis device 52 will be described. The difference in the number of reflections in the resonator 20 between the first output light 71 and the second output light 72 is 2Δn (> 0). The difference ΔL in the transmission distance between the first output light 71 and the second output light 72 in the sample to be measured is 2DΔn. Then, 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 Equation 3 and Equation 4, the light absorption coefficient a can be expressed as follows.

In the above formula 5, the reflectance R ₁ of the first mirror 21, the reflection factor R ₂ of the second mirror 22, the attenuation factor Nd of the optical attenuator 31 can determine the value by previously measured. The difference ΔL = 2DΔn in the measured distance between the first output light 71 and the second output light 72 in the sample to be measured is the optical path length D and the resonance between the first output light 71 and the second output light 72. It can be calculated by knowing the difference 2Δn in the number of reflections in the vessel 20. The distance between the output position of the first output light 71 and the output position of the second output light 72 on the second mirror 22 is x, and the distance between the first mirror 21 and the second mirror 22 If X is X, the difference 2Δn in the number of reflections can be geometrically expressed as follows.

In the above equation 6, the distance x between the output positions and the distance X between the mirrors can be obtained by measuring in advance. From the above, by obtaining the light intensity ratio ΔI and the incident angle θ of the measurement pulsed light 70 to the resonator 20, the light absorption coefficient a can be uniquely determined using Equation 5. Therefore, the coefficient lookup table 53 can be created in advance.

  The light intensity ratio ΔI is the value of the light intensity ratio signal output from the differential amplifier 51. The incident angle θ is a value that can be acquired by measuring in advance. Therefore, the light absorption coefficient a can be determined by measuring the incident angle θ and the light intensity ratio ΔI and referring to the coefficient lookup table 53. As described above, by using the coefficient lookup table 53, the light absorption coefficient a with respect to the acquired light intensity ratio ΔI and the incident angle θ can be determined in real time without performing the calculation process of Expression 5.

  Returning to FIG. 1, 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 and the 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 each other and stored in the concentration determination device. 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.

  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 at an incident angle θ. 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 optical attenuator 31 and output as attenuated light. The light that has passed through the first aperture 33 in the attenuated light is detected by the first detector 32, and a first output signal indicating the light intensity of the attenuated light is output to the differential amplifier 51. In addition, light that has passed through the second aperture 42 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 41, and is output as the second output light. A second output signal indicating the light intensity of the light 72 is output to the differential amplifier 51.

  The differential amplifier 51 generates a light intensity ratio signal indicating a light intensity ratio ΔI between the light intensity of the attenuated light and the light intensity of the second output light 72 based on the first output signal and the second output signal. The data is output to the analysis device 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.

  Next, effects of the above embodiment will be described. In the absorption measuring apparatus 1, the first detector 30 attenuates the first output light 71 having a high light intensity by the optical attenuator 31, and then detects it by the first detector 32. Therefore, even when 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 optical attenuator 31 is selected in accordance with the light intensity of the first output light 71. Therefore, it is possible to detect the first output light 71 having a high light intensity. Further, in the absorption measurement apparatus 1, the second output light 72 having a low light intensity is detected by the second detector 41 that does not depend on the measurement range of the first detector 32. Therefore, the second detector 41 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.

Specifically, in the above embodiment, the effect of the configuration of the first detection unit 30 and the second detection unit 40 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 optical 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 detection. A case where the measurement range of the detector 41 is the same as that of the first detector 32 will be described. Since attenuation factor Nd is ^{10 -3} optical 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 measurement range 10 ³ times to become. 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 optical attenuator 31 having an attenuation factor Nd of 10 ⁻⁶ and the first detector 32 having a dynamic range of about three digits, and the second A case where the measurement range of the detector 41 is the same as that of the first detector 32 will be described. Since attenuation factor Nd is ^10-6 of the optical 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 measurement range 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. Therefore, the ratio between the maximum value and the minimum value that can be detected by the absorption measuring device 1 is determined by the combination of the attenuation factor Nd of the optical attenuator 31 and the dynamic range of the first detector 32 and the second detector 41. It can be set to a desired value.

  In the above-described embodiment, the above-described effects can be obtained even if the following measures are taken.

  In the above embodiment, when continuous light is used as measurement light, interference fringes are generated spatially due to temporal coherence. Therefore, minute vibrations may be given to the absorption measuring device 1 so as not to generate interference fringes.

  In the above embodiment, the first detector 32 and the second detector 41 are, for example, phototubes, but may be photodiodes.

  In the above embodiment, Δn is calculated geometrically, but pulse light is incident on the resonator 20, and Δn is obtained by the time difference between the first detection signal and the second detection signal reaching the differential amplifier 51. Also good.

  In the above embodiment, the light absorption coefficient a is determined by the analysis device 52 using the coefficient lookup table in addition to the light intensity ratio ΔI and the incident angle θ. The light absorption coefficient a may be calculated by performing the calculation shown in Equation 5 using an arithmetic circuit without using the coefficient lookup table.

よって、式７の右辺の値を取得することができるので、第１の鏡２１の反射率Ｒ_１と第２の鏡２２の反射率Ｒ_２を予め測定することなく、式７を式５に代入して光吸収係数ａを算出することができる。また、式７より（Ｒ_１・Ｒ_２）^Δｎの値を算出することができるので、第１の鏡２１の反射率Ｒ_１と第２の鏡２２の反射率Ｒ_２を予め測定することなく、係数ルックアップデータも作成することもできる。 In the above embodiment, the reflectivity of the first mirror 21 R ₁ and reflectivity R ₂ of the second mirror 22 were obtained value by previously measured. By measuring the blank sample without introducing the sample to be measured into the measurement cell 23 of the absorption measuring device 1, it is possible to perform the measurement when the light absorption coefficient a = 0. The light intensity ratio ΔI ₀ when the light absorption coefficient a = 0 is as follows from Equation 5.

Therefore, it is possible to obtain the value of the right side of Equation 7, without previously measuring the reflectance of the first mirror 21 R ₁ and the reflectivity R ₂ of the second mirror 22, Equation 7 into Equation 5 The light absorption coefficient a can be calculated by substituting. Further, from equation 7 _(R 1 · _R 2) it is possible to calculate the value of ^{[Delta] n,} without previously measuring the reflectance of the first mirror 21 _{R 1} and the reflectivity _{R 2} of the second mirror 22 Coefficient lookup data can also be created.

よって、１の鏡２１の反射率Ｒ_１と第２の鏡２２の反射率Ｒ_２とを予め測定することなく、吸収係数ａを算出することができる。 Further, as described above, when the blank sample is measured, the light intensity ratio ΔI ₀ becomes 1, so that the incident angle θ is between the output position of the first output light 71 and the output position of the second output light 72. The distance x may be adjusted. When the light intensity ratio ΔI ₀ is 1, the light absorption coefficient a is expressed as follows from Equation 5.

Therefore, it is possible without prior measuring the reflectance R ₁ of the first mirror 21 and a reflection factor R ₂ of the second mirror 22, and calculates the absorption coefficient a.

  Next, the second to sixth embodiments, which are modifications of the above embodiment, will be described.

  An absorption measurement apparatus 2 according to the second embodiment will be described. FIG. 2 is a configuration diagram of the absorption measurement apparatus 2 according to the second embodiment. In addition to the configuration of the absorption measurement device 1, the absorption measurement device 2 includes a modulator 12, a first lock-in amplifier 34, and a second lock-in amplifier 43. In addition, the light source 10 outputs the intensity-modulated measurement pulse light 70.

  The modulator 12 intensity-modulates the measurement pulse light 70 at a predetermined frequency. The modulator 12 outputs, to the light source 10, the first lock-in amplifier 34, and the second lock-in amplifier 43, a synchronization signal whose intensity changes with time at a predetermined frequency. The light source 10 outputs measurement pulse light 70 that is intensity-modulated at a predetermined frequency based on the synchronization signal output from the modulator 12.

  The first lock-in amplifier 34 receives the first detection signal and outputs the level of a signal component having a predetermined frequency among the input signals. The second lock-in amplifier 43 receives the second detection signal and outputs the level of a signal component having a predetermined frequency among the input signals. The first lock-in amplifier 34 and the second lock-in amplifier 43 output the level of a signal component having a predetermined frequency based on the synchronization signal output from the modulator 12. By using the first lock-in amplifier 34 and the second lock-in amplifier 43, noise can be eliminated and the light intensity ratio ΔI can be measured with high accuracy.

  An absorption measurement apparatus 3 according to the third embodiment will be described. FIG. 3 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 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 x 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.

  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 distance x between the output positions and the light intensity ratio ΔI.

  An absorption measurement apparatus 4 according to the fourth embodiment will be described. FIG. 4 is a configuration diagram of the absorption measurement apparatus 4 according to the fourth embodiment. The absorption measurement device 4 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 25 changes the incident angle θ of the measurement pulse light 70 to the resonator 20. The angle varying device 24 changes the incident angle θ of the measurement pulse light 70 to the resonator 20 by changing the angle of the resonator 20 based on the signal indicating the change angle output from the angle control device 25. . The angle control device 25 controls the change of the incident angle θ by the angle variable device 24. The angle control device 25 outputs a signal that instructs the angle changing device 24 and the analyzing device 52 to change the incident angle θ. The analysis device 52 calculates the incident angle θ based on the signal that instructs the change of the incident angle θ output from the angle control device 25.

  By changing the incident 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 absorption coefficient a can be determined by analyzing the relationship between the incident angle θ and the light intensity ratio ΔI.

  An absorption measurement apparatus 5 according to the fifth embodiment will be described. FIG. 5 is a configuration diagram of the absorption measurement apparatus 5 according to the fifth embodiment. In addition to the configuration of the absorption measurement device 4, the absorption measurement device 5 includes a wavelength variable device 11 (wavelength variable means). The differential amplifier 51 also outputs the light intensity ratio signal to the angle control device 25. Further, the angle control device 25 (angle control means) controls the angle variable device 24 so that the light intensity ratio ΔI becomes 1.

よって係数ルックアップテーブルは、入射角θとａとを関連付けたデータのみで良い。ΔＩを用いることなく、係数ルックアップテーブルにおいて入射角θを参照することによって光吸収係数ａを決定することができる。 The angle control device 25 outputs a signal for controlling the angle varying device 24 so that the light intensity ratio ΔI becomes 1 based on the light intensity ratio signal output from the differential amplifier 51. Therefore, it is possible to perform balance measurement in which measurement is performed by changing the angle of the resonator 20 so that the light intensity ratio ΔI becomes 1. When the light intensity ratio ΔI is 1, Equation 5 is as follows:

Therefore, the coefficient look-up table may be only data relating the incident angle θ and a. The light absorption coefficient a can be determined by referring to the incident angle θ in the coefficient lookup table without using ΔI.

  In addition, the wavelength tunable device 11 changes the wavelength of the measurement pulse light 70. The wavelength tunable device 11 outputs a signal indicating the changed wavelength to the light source 10 and the concentration determining device 54. The above-described balance measurement can be performed at multiple points by changing the wavelength of the measurement pulse light 70 by the wavelength tunable device 11. Therefore, a more accurate light absorption coefficient a can be determined. In this case, in the concentration lookup table 55, the wavelength of the measurement pulse light 70, the light absorption coefficient a, and the concentration are stored in association with each other, and the concentration determination device 54 indicates the change wavelength output from the wavelength variable device 11. The concentration is determined based on the signal to be transmitted and the light absorption coefficient a.

  An absorption measurement apparatus 6 according to the sixth embodiment will be described. FIG. 6 is a configuration diagram of the absorption measurement apparatus 6 according to the sixth embodiment. The absorption measurement device 6 includes a distance variable device 26 (distance variable means) and a distance control device 27 (distance control device) in addition to the configuration of the absorption measurement device 1. Further, in the absorption measurement device 6, the first detector 32 is a photodiode, and the second detector 41 is an avalanche photodiode. Alternatively, the first detector 32 is a phototube, and the second detector 41 is a photomultiplier tube. Further, the differential amplifier 51 outputs the light intensity ratio signal to the distance control device 27 as well.

  The distance variable device 26 changes the distance between the first mirror 21 and the second mirror 22. The distance variable device 26 is an operating table on which the second mirror 22 can be placed, for example. The distance variable device 26 changes the position of the second mirror 22 based on the signal instructing the movement output from the distance control device 27.

  The distance control device 27 sends a signal for instructing movement of the distance variable device 26 and the analysis device 52 so that the value of the light intensity ratio ΔI indicated by the light intensity ratio signal output from the differential amplifier 51 becomes 1. Output to. The analysis device 52 calculates the distance X between the first mirror 21 and the second mirror 22 based on the signal indicating the movement distance output by the distance control device 27. Then, using this distance X, the analysis device 52 calculates the light absorption coefficient a as described above. As described above, the light intensity ratio ΔI can be set to 1 more accurately by changing the distance between the first mirror 21 and the second mirror 22 so that the light intensity ratio ΔI becomes 1. .

It is a lineblock diagram of absorption measuring device 1 concerning this embodiment. It is a block diagram of the absorption measuring device 2 which concerns on 2nd Embodiment. It is a block diagram of the absorption measuring device 3 which concerns on 3rd Embodiment. It is a block diagram of the absorption measuring device 4 which concerns on 4th Embodiment. It is a block diagram of the absorption measuring device 5 which concerns on 5th Embodiment. It is a block diagram of the absorption measuring device 6 which concerns on 6th Embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Light source, 11 ... Wavelength variable device, 12 ... Modulator, 20 ... Resonator, 21 ... 1st mirror, 22 ... 2nd mirror, 23 ... Sample cell 24... Angle variable device 25. Angle control device 26. Distance variable device 27. Distance control device 30. First detection means 31 Light Attenuator, 32 ... first detector, 33 ... first aperture, 34 ... first lock-in amplifier, 40 ... second detection means, 41 ... second Detector 42... Second aperture 43. Second lock-in amplifier 44. Position variable device 45. Position control device 50. Determination device 51. Differential amplifier, 52... Analysis device, 53... Coefficient lookup table, 54... Density determination device, 55. Pputeburu, 60 ... display, 70 ... measurement pulse light, 71 ... first output light, 72 ... second output light, 73 ... decay curve

Claims (11)

Resonance having a first mirror and a second mirror that reflect a part of the incident light and transmit the remaining part, and the first mirror and the second mirror are arranged to face each other And
A light source that outputs measurement light and makes the measurement light incident on the first mirror so that an incident angle of the measurement light to the resonator has an angle greater than 0;
Either the first mirror or the second mirror is incident on the first mirror from outside the resonator, passes through the first mirror, enters the resonator, and repeats multiple reflections. First detection means for detecting the first output light among the output lights that are transmitted through one side and output from a plurality of locations, and output 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,
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 first detection signal and the second detection signal; Absorption measuring device characterized by that. The absorption measurement apparatus according to claim 1, further comprising an angle varying unit that changes an incident angle of the measurement light to the resonator. Angle control means for outputting a signal for controlling the incident angle of the measurement light to the resonator to the angle variable means so that the first detection signal and the second detection signal are substantially the same. The absorption measurement apparatus according to claim 1 or 2, wherein The absorption measuring apparatus according to any one of claims 1 to 3, further comprising a distance varying unit that changes a distance between the first mirror and the second mirror. The absorption measurement apparatus according to any one of claims 1 to 4, wherein the light source includes wavelength variable means for changing a wavelength of the measurement light. Modulation means for intensity-modulating the measurement light at a predetermined frequency;
A lock-in amplifier that inputs at least one of the first detection signal and the second detection signal and outputs the level of the signal component of the predetermined frequency in the input signal. The absorption measurement apparatus according to any one of claims 1 to 5, wherein the absorption measurement apparatus is characterized. The absorption measurement apparatus according to any one of claims 1 to 6, further comprising a sample cell for introducing the sample to be measured between the first mirror and the second mirror. The first detection means attenuates the first output light to be measured and outputs attenuation light;
The absorption measurement apparatus according to claim 1, further comprising: attenuated light detection means that detects the attenuated light output from the attenuation means. 9. The absorption measurement apparatus according to claim 8, wherein the second detection unit and the attenuated light detection unit exhibit the same sensitivity characteristic. The absorption measurement apparatus according to claim 1, wherein the first detection unit is a photodiode, and the second detection unit is an avalanche photodiode. The absorption measuring apparatus according to any one of claims 1 to 7, wherein the first detection means is a phototube and the second detection means is a photomultiplier tube.

Images