JP2014038063A - Concentration measuring apparatus and concentration measuring method - Google Patents

Concentration measuring apparatus and concentration measuring method Download PDF

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JP2014038063A
JP2014038063A JP2012181594A JP2012181594A JP2014038063A JP 2014038063 A JP2014038063 A JP 2014038063A JP 2012181594 A JP2012181594 A JP 2012181594A JP 2012181594 A JP2012181594 A JP 2012181594A JP 2014038063 A JP2014038063 A JP 2014038063A
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JP6089493B2 (en
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Atsushi Izawa
淳 伊澤
Soichiro Omi
聡一郎 大海
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IHI Corp
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Abstract

PROBLEM TO BE SOLVED: To provide a concentration measuring apparatus capable of accurately measuring a concentration of a measuring object with a simple structure without being affected by a state change of the measuring object.SOLUTION: The concentration measuring apparatus comprises: a laser light source 22 for generating laser light as excitation light 23; a probe light generation section 24 for simultaneously generating probe light 10 of an ON wavelength and reference light 12 of an OFF wavelength for a measuring object S from the excitation light 23 by an optical parametric oscillation; a light separation section M2 for separating the probe light 10 and the reference light 12, each having transmitted through the measuring object S or reflected from the measuring object S into different optical paths respectively; a photodetector 26 for detecting the probe light 10 separated by the light separation section M2; a photodetector 27 for detecting the reference light 12 separated by the light separation section M2; and a concentration calculation section 29 for calculating a concentration of the measuring object S from each transmittance of the probe light 10 and the reference light 12 that are detected by the photodetectors 26 and 27.

Description

本発明は、レーザ光を用いた差分吸収法により物質の濃度を測定する濃度測定装置及び濃度測定方法に関する。   The present invention relates to a concentration measuring apparatus and a concentration measuring method for measuring a concentration of a substance by a differential absorption method using laser light.

二酸化炭素ガスやメタンガス等の測定対象物の濃度を測定する方法の１つとして、レーザ光を用いた差分吸収法が知られている。この方法では、測定対象物で吸収される波長（即ち、オン波長）と測定対象物で吸収されない波長（即ち、オフ波長）の各透過率を基に測定対象物の濃度を算出する。通常は回折格子やエタロン等で構成された波長切替機構を用いて、オン波長とオフ波長の光を交互に測定対象物に照射している。特許文献１乃至特許文献４は、上記の差分吸収法を用いた濃度測定装置を開示している。   As one of methods for measuring the concentration of a measurement object such as carbon dioxide gas or methane gas, a differential absorption method using laser light is known. In this method, the concentration of the measurement object is calculated based on the transmittances of the wavelength absorbed by the measurement object (that is, the on wavelength) and the wavelength that is not absorbed by the measurement object (that is, the off wavelength). Usually, the object to be measured is alternately irradiated with light having an on wavelength and an off wavelength by using a wavelength switching mechanism composed of a diffraction grating, an etalon, or the like. Patent Documents 1 to 4 disclose a concentration measuring device using the differential absorption method.

特開２０１０−５０８９４号公報JP 2010-50894 A 特開平１０−１８５８０４号公報Japanese Patent Laid-Open No. 10-185804 特開２０１１−２１９９６号公報JP 2011-21996 A 特開２００１−１５９６０４号公報JP 2001-159604 A

上述したように、従来の濃度測定方法では、オン波長の光の照射とオフ波長の光の照射を交互に切り替えており、各光の照射時刻にはズレが生じている。従って、測定対象物の状態の変化が早い場合は、基準となるオフ波長の透過率が各照射時刻で異なっている可能性があり、算出した濃度の信頼性が低下する恐れがある。また、波長切替機構は波長の切り替えを機械的に行っているので構造が複雑であり、各部品に対して高い加工精度や組立精度も要求される。その結果、製造コストが嵩む問題がある。   As described above, in the conventional concentration measurement method, the irradiation of the on-wavelength light and the irradiation of the off-wavelength light are alternately switched, and a deviation occurs in the irradiation time of each light. Therefore, when the state of the measurement object changes quickly, the reference off-wavelength transmittance may be different at each irradiation time, and the reliability of the calculated concentration may be reduced. Further, since the wavelength switching mechanism mechanically switches the wavelength, the structure is complicated, and high processing accuracy and assembly accuracy are required for each component. As a result, there is a problem that the manufacturing cost increases.

このような事情を鑑み、本発明は、測定対象物の状態変化に影響されず、且つ、簡便な構成で当該測定対象物の濃度を精度良く測定できる濃度測定装置及び濃度測定方法の提供を目的とする。   In view of such circumstances, it is an object of the present invention to provide a concentration measuring apparatus and a concentration measuring method that are not affected by a change in the state of the measuring object and that can accurately measure the concentration of the measuring object with a simple configuration. And

本発明の第１の態様は濃度測定装置であって、励起光としてのレーザ光を発生するレーザ光源と、光パラメトリック発振によって前記励起光から、測定対象物に対するオン波長のプローブ光及びオフ波長の参照光を同時に発生するプローブ光発生部と、前記測定対象物を透過した又は前記測定対象物から反射した前記プローブ光及び前記参照光をそれぞれ別の光路に分離する光分離部と、前記光分離部によって分離された前記プローブ光を検出する第１の光検出器と、前記光分離部によって分離された前記参照光を検出する第２の光検出器と、前記第１及び第２の光検出器によって検出された前記プローブ光及び前記参照光の各透過率から前記測定対象物の濃度を算出する濃度算出部とを備えることを要旨とする。   A first aspect of the present invention is a concentration measurement apparatus, which includes a laser light source that generates laser light as excitation light, and an on-wavelength probe light and an off-wavelength of an object to be measured from the excitation light by optical parametric oscillation. A probe light generation unit that simultaneously generates reference light, a light separation unit that separates the probe light and the reference light transmitted through the measurement object or reflected from the measurement object into separate optical paths, and the light separation A first photodetector for detecting the probe light separated by the optical detector, a second photodetector for detecting the reference light separated by the optical separator, and the first and second optical detectors. And a concentration calculation unit that calculates the concentration of the measurement object from the transmittances of the probe light and the reference light detected by a detector.

前記プローブ光発生部は、前記波長変換を行う光学素子として、第２種の位相整合をとる非線形光学結晶を有してもよく、前記光分離部は偏光ビームスプリッタであってもよい。   The probe light generation unit may include a nonlinear optical crystal that performs the second type of phase matching as the optical element that performs the wavelength conversion, and the light separation unit may be a polarization beam splitter.

前記光分離部は、前記プローブ光及び前記参照光の各波長間にカットオフ波長をもつダイクロイックミラーであってもよい。   The light separation unit may be a dichroic mirror having a cutoff wavelength between the wavelengths of the probe light and the reference light.

本発明の第２の態様は濃度測定方法であって、励起光としてのレーザ光を発生し、光パラメトリック発振によって前記励起光から、測定対象物に対するオン波長のプローブ光及びオフ波長の参照光を同時に発生し、前記測定対象物を透過した又は前記測定対象物から反射した前記プローブ光及び前記参照光をそれぞれ別の光路に分離し、前記光分離部によって分離された前記プローブ光及び前記参照光を検出し、検出された前記プローブ光及び前記参照光の各透過率から前記測定対象物の濃度を算出することを要旨とする。   A second aspect of the present invention is a concentration measurement method, which generates laser light as excitation light, and generates on-wavelength probe light and off-wavelength reference light for the measurement object from the excitation light by optical parametric oscillation. The probe light and the reference light, which are generated at the same time, are separated from the probe light and the reference light transmitted through the measurement object or reflected from the measurement object into separate optical paths, and are separated by the light separation unit. And the concentration of the measurement object is calculated from the detected transmittances of the probe light and the reference light.

本発明によれば、測定対象物の状態変化に影響されず、且つ、簡便な構成で当該測定対象物の濃度を精度良く測定できる濃度測定装置及び濃度測定方法を提供できる。   According to the present invention, it is possible to provide a concentration measuring apparatus and a concentration measuring method that can accurately measure the concentration of an object to be measured with a simple configuration without being affected by the state change of the object to be measured.

本発明の第１実施形態に係る濃度測定装置の構成図である。It is a block diagram of the density | concentration measuring apparatus which concerns on 1st Embodiment of this invention. 本発明の一実施形態に係るプローブ光発生部の構成図である。It is a block diagram of the probe light generation part which concerns on one Embodiment of this invention. 本発明の一実施形態に係るプローブ光及び参照光の各波長と、測定対象物の吸収線の波長との関係を示す模式図である。It is a schematic diagram which shows the relationship between each wavelength of the probe light and reference light which concern on one Embodiment of this invention, and the wavelength of the absorption line of a measuring object. 本発明の一実施形態に係る濃度測定方法によって得られる測定結果の一例である。It is an example of the measurement result obtained by the density | concentration measuring method which concerns on one Embodiment of this invention. 本発明の第２実施形態に係る濃度測定装置の構成図である。It is a block diagram of the density | concentration measuring apparatus which concerns on 2nd Embodiment of this invention.

以下、本発明の実施形態を添付図面に基づいて詳細に説明する。なお、各図において共通する部分には同一の符号を付し、重複した説明を省略する。   Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, the same code | symbol is attached | subjected to the common part in each figure, and the overlapping description is abbreviate | omitted.

（第１実施形態）
図１は、本発明の第１実施形態に係る濃度測定装置の構成図である。図２は、本実施形態に係るプローブ光発生部の構成図である。図３は、本実施形態に係るプローブ光及び参照光の各波長と、測定対象物の吸収線の波長との関係を示す模式図である。図４は、本実施形態に係る濃度測定方法によって得られる測定結果の一例である。 (First embodiment)
FIG. 1 is a configuration diagram of a concentration measuring apparatus according to the first embodiment of the present invention. FIG. 2 is a configuration diagram of the probe light generator according to the present embodiment. FIG. 3 is a schematic diagram showing the relationship between the wavelengths of the probe light and the reference light according to this embodiment and the wavelength of the absorption line of the measurement object. FIG. 4 is an example of a measurement result obtained by the concentration measurement method according to the present embodiment.

図１に示すように、本実施形態の濃度測定装置は、レーザ光源２２と、プローブ光発生部２４と、ビームスプリッタＭ１と、光分離部Ｍ２と、４台の光検出器２５、２６、２７、２８と、濃度算出部２９とを備える。   As shown in FIG. 1, the concentration measuring apparatus according to the present embodiment includes a laser light source 22, a probe light generator 24, a beam splitter M1, a light separator M2, and four photodetectors 25, 26, and 27. , 28 and a density calculation unit 29.

レーザ光源２２は、後段のプローブ光発生部２４に入力される励起光（ポンプ光）２３としてのレーザ光を発生する。レーザ光の波長や発振モード（パルス発振又は連続発振）は、プローブ光発生部２４における波長変換の仕様（変換方法、出力波長など）に応じて選定する。本実施形態では、パルスレーザ光源であるＮｄ：ＹＡＧレーザを使用する。Ｎｄ：ＹＡＧレーザは、基本波である１０６４ｎｍのパルスレーザ光を、数ｎｓ〜数十ｎｓのパルス幅、且つ、１０Ｈｚ〜数ｋＨｚの繰り返し周波数で出力する。   The laser light source 22 generates laser light as excitation light (pump light) 23 input to the probe light generation unit 24 at the subsequent stage. The wavelength and oscillation mode (pulse oscillation or continuous oscillation) of the laser light are selected according to the wavelength conversion specifications (conversion method, output wavelength, etc.) in the probe light generator 24. In this embodiment, an Nd: YAG laser that is a pulse laser light source is used. The Nd: YAG laser outputs a fundamental laser beam of 1064 nm with a pulse width of several ns to several tens of ns and a repetition frequency of 10 Hz to several kHz.

プローブ光発生部２４は、励起光２３の波長変換によって、測定対象物Ｓに対するオン波長のプローブ光１０及びオフ波長の参照光１２を発生する。吸収の感度を高める観点からは、図３に示すように、プローブ光１０の波長λｏｎが測定対象物Ｓの吸収線１４の波長に一致していることが好ましい。しかしながら、少なくとも吸収線１４の波長が、プローブ光１０の線幅内に含まれていれば吸収を確認することは可能である。   The probe light generator 24 generates the on-wavelength probe light 10 and the off-wavelength reference light 12 for the measurement object S by wavelength conversion of the excitation light 23. From the viewpoint of increasing the sensitivity of absorption, it is preferable that the wavelength λon of the probe light 10 coincides with the wavelength of the absorption line 14 of the measurement object S, as shown in FIG. However, absorption can be confirmed if at least the wavelength of the absorption line 14 is included in the line width of the probe light 10.

図２に示すように、プローブ光発生部２４は、光軸（光路）２０に沿って、反射面を対向させるように配置された終端鏡３２と出力鏡３４とを有する。出力鏡３４と終端鏡３２との間隔Ｄは例えば２０ｍｍである。更に、終端鏡３２と出力鏡３４の間の光軸２０上には、波長変換を行う光学素子として、非線形光学結晶３６が設けられている。後述するように、非線形光学結晶３６は、励起光２３の光パラメトリック発振によってプローブ光１０及び参照光１２を発生する。   As shown in FIG. 2, the probe light generator 24 includes a terminal mirror 32 and an output mirror 34 that are arranged so that the reflecting surfaces thereof face each other along the optical axis (optical path) 20. The distance D between the output mirror 34 and the terminal mirror 32 is, for example, 20 mm. Further, on the optical axis 20 between the terminal mirror 32 and the output mirror 34, a nonlinear optical crystal 36 is provided as an optical element for performing wavelength conversion. As will be described later, the nonlinear optical crystal 36 generates the probe light 10 and the reference light 12 by optical parametric oscillation of the excitation light 23.

終端鏡３２は、励起光２３を透過させ、且つ、非線形光学結晶３６によって発生したプローブ光１０及び参照光１２を反射する波長特性を有する。通常、励起光２３の波長はプローブ光１０及び参照光１２の各波長よりも短いので、終端鏡３２は所謂ロングパスフィルター（ＬＰＦ）である。一方、出力鏡３４も、終端鏡３２と同じく、プローブ光１０及び参照光１２を反射する波長特性を有する。従って、終端鏡３２及び出力鏡３４は所謂光共振器を構成する。終端鏡３２及び出力鏡３４のプローブ光１０及び参照光１２に対する反射率は５０〜９９．５％であり、プローブ光１０及び参照光１２の一部は最終的に出力鏡３４から出射する。   The terminal mirror 32 has a wavelength characteristic that transmits the excitation light 23 and reflects the probe light 10 and the reference light 12 generated by the nonlinear optical crystal 36. Since the wavelength of the excitation light 23 is usually shorter than the wavelengths of the probe light 10 and the reference light 12, the terminal mirror 32 is a so-called long pass filter (LPF). On the other hand, the output mirror 34 also has a wavelength characteristic that reflects the probe light 10 and the reference light 12, similarly to the terminal mirror 32. Accordingly, the terminal mirror 32 and the output mirror 34 constitute a so-called optical resonator. The reflectance of the terminal mirror 32 and the output mirror 34 with respect to the probe light 10 and the reference light 12 is 50 to 99.5%, and part of the probe light 10 and the reference light 12 is finally emitted from the output mirror 34.

非線形光学結晶３６は、上述したように、励起光２３よる光パラメトリック発振によってプローブ光１０及び参照光１２を発生する。非線形光学結晶３６として、例えばＫＴＰ結晶が使用される。プローブ光１０の波長（オン波長）をλｏｎ、参照光１２の波長（オフ波長）をλｏｆｆ、励起光２３の波長をλｅｘとすると、非線形光学結晶３６は、一般的な特性である（１／λｅｘ）＝（１／λｏｎ）＋（１／λｏｆｆ）の条件を満たす波長変換を行う。本実施形態では、測定対象物が二酸化炭素ガスであるため、オン波長λｏｎ及びオフ波長λｏｆｆを、例えば２０１５ｎｍ及び２２５４ｎｍに設定する。なお、これらオン波長λｏｎ及びオフ波長λｏｆｆは、励起光２３の光軸に対する結晶の光学軸の角度を調整することで適宜変更できる。この角度調整は、例えば、非線形光学結晶３６を支持する回転ステージ３８によって実行可能である。   As described above, the nonlinear optical crystal 36 generates the probe light 10 and the reference light 12 by optical parametric oscillation by the excitation light 23. As the nonlinear optical crystal 36, for example, a KTP crystal is used. When the wavelength of the probe light 10 (on wavelength) is λon, the wavelength of the reference light 12 (off wavelength) is λoff, and the wavelength of the excitation light 23 is λex, the nonlinear optical crystal 36 has general characteristics (1 / λex ) = (1 / λon) + (1 / λoff) The wavelength conversion that satisfies the condition is performed. In this embodiment, since the measurement object is carbon dioxide gas, the on wavelength λon and the off wavelength λoff are set to, for example, 2015 nm and 2254 nm. The on wavelength λon and the off wavelength λoff can be appropriately changed by adjusting the angle of the optical axis of the crystal with respect to the optical axis of the excitation light 23. This angle adjustment can be performed by, for example, the rotary stage 38 that supports the nonlinear optical crystal 36.

本実施形態の非線形光学結晶３６には、第２種の位相整合が得られる結晶（所謂タイプＩＩの結晶）を用いる。上述のＫＴＰ結晶は、この位相整合が得られる結晶である。即ち、非線形光学結晶３６から出射したプローブ光１０及び参照光１２は何れも直線偏光であり、しかも、その偏光方向が互いに直交している。また、非線形光学結晶３６におけるプローブ光１０及び参照光１２の強度比も既知である。   As the nonlinear optical crystal 36 of the present embodiment, a crystal (so-called type II crystal) capable of obtaining the second type of phase matching is used. The above KTP crystal is a crystal that can achieve this phase matching. That is, the probe light 10 and the reference light 12 emitted from the nonlinear optical crystal 36 are both linearly polarized light, and the polarization directions thereof are orthogonal to each other. The intensity ratio of the probe light 10 and the reference light 12 in the nonlinear optical crystal 36 is also known.

ビームスプリッタＭ１は、出力鏡３４から出射したプローブ光１０及び参照光１２の一部をそれぞれのサンプル光１０ｐ、１２ｐとして、後段の光分離部Ｍ３に反射すると共に、その残りを透過させる。ビームスプリッタＭ１の反射率は予め規定されており、後述するように、反射した光の強度を測定することで、ビームスプリッタＭ１に入射した光の強度を逆算できる。   The beam splitter M1 reflects a part of the probe light 10 and the reference light 12 emitted from the output mirror 34 as the respective sample light 10p and 12p to the subsequent light separation unit M3 and transmits the remainder. The reflectance of the beam splitter M1 is defined in advance, and the intensity of the light incident on the beam splitter M1 can be calculated backward by measuring the intensity of the reflected light, as will be described later.

光分離部Ｍ３は、ビームスプリッタＭ１から反射したプローブ光１０のサンプル光１０ｐ及び参照光１２のサンプル光１２ｐをそれぞれ別の光路に分離する。このような機能をもつ光分離部Ｍ３は、例えば、偏光ビームスプリッタである。偏光ビームスプリッタは、誘電多層膜を入射面にもち、入射光の偏光方向に応じて当該入射光の透過または反射を行う。本実施形態では、ＫＴＰ結晶における第２種の位相整合によって、プローブ光１０及び参照光１２の偏光方向が互いに直交している。偏光方向は、ビームスプリッタＭ１の反射によって影響されないので、サンプル光１０ｐ、１２ｐの各偏光方向も互いに直交している。従って、サンプル光１０ｐ、１２ｐが光分離部Ｍ３に入射すると、一方は反射し、他方は透過する。図１の光分離部Ｍ３はプローブ光１０のサンプル光１０ｐを反射し、参照光１２のサンプル光１２ｐを透過させているが、この反対に、プローブ光１０を透過させ、参照光１２を反射してもよい。   The light separation unit M3 separates the sample light 10p of the probe light 10 and the sample light 12p of the reference light 12 reflected from the beam splitter M1 into separate optical paths. The light separation unit M3 having such a function is, for example, a polarization beam splitter. The polarization beam splitter has a dielectric multilayer film on the incident surface, and transmits or reflects the incident light according to the polarization direction of the incident light. In the present embodiment, the polarization directions of the probe light 10 and the reference light 12 are orthogonal to each other by the second type phase matching in the KTP crystal. Since the polarization direction is not affected by the reflection of the beam splitter M1, the polarization directions of the sample lights 10p and 12p are also orthogonal to each other. Accordingly, when the sample lights 10p and 12p are incident on the light separating portion M3, one of them is reflected and the other is transmitted. The light separation unit M3 in FIG. 1 reflects the sample light 10p of the probe light 10 and transmits the sample light 12p of the reference light 12, but conversely transmits the probe light 10 and reflects the reference light 12. May be.

光分離部Ｍ３から分岐した各光路には、光検出器２５、２６がそれぞれ設けられている。光検出器２５は、光分離部Ｍ３によって反射したプローブ光１０のサンプル光１０ｐを検出し、その強度に比例した電圧の電気信号を検出信号として出力する。一方、光検出器２６は、光分離部Ｍ３を透過した参照光１２のサンプル光１２ｐを検出し、その強度に比例した電圧の電気信号を検出信号として出力する。上述したように、ビームスプリッタＭ１の反射率は予め規定されている。従って、光検出部２５、２６で検出したサンプル光１０ｐ、１２ｐの各強度から、出力鏡３４から出射した直後のプローブ光１０及び参照光１２の各強度を逆算できる。なお、光検出部２５、２６は周知の半導体検出器である。   Photodetectors 25 and 26 are provided in the respective optical paths branched from the light separation unit M3. The photodetector 25 detects the sample light 10p of the probe light 10 reflected by the light separation unit M3, and outputs an electrical signal having a voltage proportional to the intensity as a detection signal. On the other hand, the photodetector 26 detects the sample light 12p of the reference light 12 that has passed through the light separation unit M3, and outputs an electric signal having a voltage proportional to the intensity as a detection signal. As described above, the reflectance of the beam splitter M1 is defined in advance. Therefore, the intensities of the probe light 10 and the reference light 12 immediately after being emitted from the output mirror 34 can be calculated backward from the intensities of the sample lights 10p and 12p detected by the light detection units 25 and 26. The light detection units 25 and 26 are well-known semiconductor detectors.

光分離部Ｍ２は、測定対象物Ｓを透過した又は測定対象物Ｓから反射したプローブ光１０及び参照光１２をそれぞれ別の光路に分離する。このような機能をもつ光分離部Ｍ２は、例えば、偏光ビームスプリッタである。上述したように、入射したプローブ項１０及び参照光１２のうちの一方を反射し、他方を透過させる。図１の光分離部Ｍ２はプローブ光１０を反射し、参照光１２を透過させているが、この反対に、プローブ光１０を透過させ、参照光１２を反射してもよい。なお、光分離部Ｍ２の前段にはプローブ光１０を光検出器２７に集光すると共に、参照光１２を光検出器２８に集光するためのレンズ等の光学系（図示せず）が設けられている。   The light separation unit M2 separates the probe light 10 and the reference light 12 that have passed through the measurement object S or reflected from the measurement object S into separate optical paths. The light separation unit M2 having such a function is, for example, a polarization beam splitter. As described above, one of the incident probe term 10 and the reference light 12 is reflected and the other is transmitted. The light separation unit M2 in FIG. 1 reflects the probe light 10 and transmits the reference light 12. However, on the contrary, the probe light 10 may be transmitted and the reference light 12 may be reflected. An optical system (not shown) such as a lens for condensing the probe light 10 on the light detector 27 and condensing the reference light 12 on the light detector 28 is provided in the front stage of the light separation unit M2. It has been.

光検出器（第１の光検出器）２７は、光分離部Ｍ２によって反射したプローブ光１０を検出し、光検出器（第２の光検出器）２８は、光分離部Ｍ２を透過した参照光１２を検出する。光検出器２７及び光検出器２８は、光検出器２５、２６と同じく、周知の半導体検出器であり、検出した光の強度に比例した電圧の電気信号を検出信号として出力する。   The light detector (first light detector) 27 detects the probe light 10 reflected by the light separation unit M2, and the light detector (second light detector) 28 passes through the light separation unit M2. The light 12 is detected. The photodetector 27 and the photodetector 28 are well-known semiconductor detectors like the photodetectors 25 and 26, and output an electric signal having a voltage proportional to the detected light intensity as a detection signal.

濃度算出部２９は、濃度測定装置の全体を制御する制御部（図示せず）の一部として構成され、各光検出器２５〜２８から出力されたプローブ光１０、参照光１２、及びこれらのサンプル光１０ｐ、１２ｐの各検出信号を時間分解しながら受信する。プローブ光１０及び参照光１２の照射は、通常、複数回行われる。濃度算出部２９は、照射タイミングに同期して光検出器２５、２６、２７、２８からの検出信号を受信し、これらの信号を検出信号毎に積算する。図４はその測定結果の一例であり、光検出器２５又は光検出器２６によって検出されたプローブ光１０のサンプル光１０ｐ又は参照光１２のサンプル光１２ｐの検出信号のピークをＰ１、光検出器２７によって検出されたプローブ光１０の検出信号のピークをＰ２、光検出器２８によって検出された参照光１２の検出信号のピークをＰ３で示す。この図に示すように、時刻ｔ１に光検出器２５または光検出器２６からの検出信号が得られるとすると、光検出器２７、２８からの各信号は測定対象物Ｓを経由した光路差によって、時刻ｔ１よりも遅い時刻ｔ２に受信される。時刻ｔ１と時刻ｔ２の時間差は、濃度測定装置と測定対象物Ｓ間の往復距離に比例する。従って、測定対象物Ｓが濃度測定装置から非常に遠方にあるほど、サンプル光１０ｐ、１２ｐからプローブ光１０及び参照光１２を分離することが容易になる。   The concentration calculation unit 29 is configured as a part of a control unit (not shown) that controls the entire concentration measuring device, and the probe light 10 and the reference light 12 output from the respective light detectors 25 to 28, and these The detection signals of the sample lights 10p and 12p are received while being time-resolved. Irradiation of the probe light 10 and the reference light 12 is usually performed a plurality of times. The concentration calculation unit 29 receives detection signals from the photodetectors 25, 26, 27, and 28 in synchronization with the irradiation timing, and integrates these signals for each detection signal. FIG. 4 shows an example of the measurement result. The peak of the detection signal of the sample light 10p of the probe light 10 or the sample light 12p of the reference light 12 detected by the light detector 25 or the light detector 26 is P1, and the light detector The peak of the detection signal of the probe light 10 detected by 27 is indicated by P2, and the peak of the detection signal of the reference light 12 detected by the photodetector 28 is indicated by P3. As shown in this figure, if a detection signal from the light detector 25 or the light detector 26 is obtained at time t1, each signal from the light detectors 27 and 28 is caused by an optical path difference passing through the measurement object S. , Received at time t2 later than time t1. The time difference between time t1 and time t2 is proportional to the reciprocating distance between the concentration measuring device and the measuring object S. Therefore, the farther the measuring object S is from the concentration measuring device, the easier it is to separate the probe light 10 and the reference light 12 from the sample light 10p, 12p.

濃度算出部２９は、これらの信号からプローブ光１０及び参照光１２の各透過率を算出し、これらの透過率から測定対象物Ｓの濃度を算出する。具体的には、濃度算出部２９は、光検出器２６と光検出器２８によって得られた参照光１２とそのサンプル光１２ｐの強度比から、測定対象物Ｓにおける参照光１２の透過率（第１の透過率）を算出する。さらに、光検出器２５と光検出器２７によって得られたプローブ光１０とそのサンプル光１０ｐの強度比から、測定対象物Ｓにおけるプローブ光１０の透過率（第２の透過率）を算出する。第２の透過率は第１の透過率に、測定対象物Ｓへの吸収による透過率（第３の透過率）を乗じたものであるので、濃度算出部２９は、第１の透過率を用いて、第２の透過率から第３の透過率を逆算し、第３の透過率から測定対象物Ｓの濃度を算出する。   The concentration calculation unit 29 calculates the transmittances of the probe light 10 and the reference light 12 from these signals, and calculates the concentration of the measurement object S from these transmittances. Specifically, the concentration calculator 29 calculates the transmittance of the reference light 12 in the measuring object S (the first transmittance) based on the intensity ratio between the reference light 12 obtained by the light detector 26 and the light detector 28 and the sample light 12p. 1). Further, the transmittance (second transmittance) of the probe light 10 in the measuring object S is calculated from the intensity ratio between the probe light 10 obtained by the light detector 25 and the light detector 27 and the sample light 10p. Since the second transmittance is obtained by multiplying the first transmittance by the transmittance (third transmittance) due to the absorption to the measuring object S, the density calculating unit 29 calculates the first transmittance. The third transmittance is calculated backward from the second transmittance, and the concentration of the measuring object S is calculated from the third transmittance.

このように本実施形態の濃度測定では、測定対象物Ｓにオン波長のプローブ光と、オフ波長の参照光とを同時に照射する。従って、従来のようにプローブ光の照射と参照光の照射を切り替える機構が不要になる。従って、装置の構成が簡便なものになる。また、上記２種類の光を同時に照射しているので、測定対象物の状態変化に伴った濃度の誤差が発生しない。すなわち、測定対象物の濃度を精度良く測定できる。   Thus, in the concentration measurement of the present embodiment, the measurement object S is irradiated with the on-wavelength probe light and the off-wavelength reference light simultaneously. Therefore, a mechanism for switching between irradiation of the probe light and irradiation of the reference light as in the prior art becomes unnecessary. Therefore, the configuration of the apparatus becomes simple. In addition, since the two types of light are simultaneously irradiated, a density error accompanying a change in the state of the measurement object does not occur. That is, the concentration of the measurement object can be measured with high accuracy.

なお、本実施形態の光分離部Ｍ２はダイクロイックミラーでもよい。このダイクロイックミラーは、プローブ光１０及び参照光１２の各波長λｏｎ、λｏｆｆ間にカットオフ波長をもつ。ダイクロイックミラーはプローブ光１０及び参照光１２のうちの一方を反射し、他方を透過させる。光検出器２７はこれらの光の何れか一方を検出し、光検出器２８はその他方を検出する。従って、偏光ビームスプリッタを使用した場合と同じく、図４に示すような測定結果が得られる。さらに、プローブ光１０及び参照光１２の分離にダイクロイックミラーを用いる場合、非線形光学結晶３６で発生するプローブ光１０及び参照光１２の各偏光状態はこれらの分離に無関係になる。従って、非線形光学結晶３６は、第２種の位相整合が得られる結晶に限られず、ＢＢＯなどの第１種の位相整合が得られる結晶を用いることができる。   Note that the light separation unit M2 of the present embodiment may be a dichroic mirror. This dichroic mirror has a cutoff wavelength between the wavelengths λon and λoff of the probe light 10 and the reference light 12. The dichroic mirror reflects one of the probe light 10 and the reference light 12 and transmits the other. The photodetector 27 detects one of these lights, and the photodetector 28 detects the other. Accordingly, the measurement result as shown in FIG. 4 is obtained as in the case of using the polarization beam splitter. Further, when a dichroic mirror is used to separate the probe light 10 and the reference light 12, the polarization states of the probe light 10 and the reference light 12 generated in the nonlinear optical crystal 36 are irrelevant to the separation. Therefore, the nonlinear optical crystal 36 is not limited to a crystal that can obtain the second type of phase matching, and a crystal that can obtain the first type of phase matching such as BBO can be used.

（第２実施形態）
以下、本発明の第２実施形態を図５に基づいて詳細に説明する。なお、図５において、図１乃至図４と共通する部分には同一の符号を付し、重複した説明を省略する。図５は、第２実施形態に係る濃度測定装置の構成図である。 (Second Embodiment)
Hereinafter, the second embodiment of the present invention will be described in detail with reference to FIG. In FIG. 5, the same reference numerals are given to portions common to those in FIGS. 1 to 4, and redundant description is omitted. FIG. 5 is a configuration diagram of the concentration measuring apparatus according to the second embodiment.

本実施形態の濃度測定装置では、ビームスプリッタＭ１によって取り出されたサンプル光１０ｐ、１２ｐを、測定対象物Ｓを通過したプローブ光１０及び参照光１２の光路に戻している。つまり、本実施形態では、第１実施形態の光検出器２５、２６が省略され、光検出器２７がプローブ光１０の検出だけでなく、そのサンプル光１０ｐの検出も行う。同様に、光検出器２８は、参照光１２とそのサンプル光１２ｐを検出する。   In the concentration measurement apparatus of the present embodiment, the sample lights 10p and 12p extracted by the beam splitter M1 are returned to the optical paths of the probe light 10 and the reference light 12 that have passed through the measurement object S. That is, in the present embodiment, the photodetectors 25 and 26 of the first embodiment are omitted, and the photodetector 27 not only detects the probe light 10 but also detects the sample light 10p. Similarly, the photodetector 28 detects the reference light 12 and its sample light 12p.

従って、測定対象物Ｓからのプローブ光１０及び参照光１２を集光する光学系（図示せず）と、光分離部Ｍ２との間には、光路合流部Ｍ４が設けられる。光路合流部Ｍ４は、例えばハーフミラーであり、ビームスプリッタＭ１によって取り出されたサンプル光１０ｐ、１２ｐの光路と、測定対象物Ｓから到達したプローブ光１０及び参照光１２の光路を合流させ、これらの光を光分離部Ｍ２に導くものである。   Therefore, an optical path merging portion M4 is provided between the optical system (not shown) that collects the probe light 10 and the reference light 12 from the measurement object S and the light separation portion M2. The optical path merging unit M4 is, for example, a half mirror, and combines the optical paths of the sample lights 10p and 12p extracted by the beam splitter M1 with the optical paths of the probe light 10 and the reference light 12 that have arrived from the measurement object S. The light is guided to the light separation unit M2.

上記以外の構成については、第１実施形態と同様であるため、詳細な説明は割愛する。   Since the configuration other than the above is the same as that of the first embodiment, a detailed description thereof is omitted.

第２実施形態の濃度測定装置は、同一の光から派生した２つの光を同一の検出器が検出する。従って、使用する光検出器の個数が削減できると共に、濃度算出における検出器の個体差（検出効率の差など）による影響を低減できる。また、本実施形態でも、第１実施形態と同じ効果が得られる。例えば、本実施形態においても、測定対象物Ｓにオン波長のプローブ光と、オフ波長の参照光とが同時に照射され、従来のようにプローブ光の照射と参照光の照射を切り替える機構が不要になる。従って、装置の構成が簡便なものになる。また、上記２種類の光を同時に照射しているので、測定対象物の状態変化に伴った濃度の誤差が発生しない。すなわち、測定対象物の濃度を精度良く測定できる。   In the concentration measurement apparatus of the second embodiment, the same detector detects two lights derived from the same light. Therefore, the number of photodetectors to be used can be reduced, and the influence of individual detector differences (detection efficiency differences, etc.) in concentration calculation can be reduced. Also in this embodiment, the same effect as in the first embodiment can be obtained. For example, also in the present embodiment, the measuring object S is simultaneously irradiated with the on-wavelength probe light and the off-wavelength reference light, and a conventional mechanism for switching between the probe light irradiation and the reference light irradiation is unnecessary. Become. Therefore, the configuration of the apparatus becomes simple. In addition, since the two types of light are simultaneously irradiated, a density error accompanying a change in the state of the measurement object does not occur. That is, the concentration of the measurement object can be measured with high accuracy.

本発明は上述した実施形態に限定されず、特許請求の範囲の記載によって示され、さらに特許請求の範囲の記載と均等の意味および範囲内でのすべての変更を含むものである。   The present invention is not limited to the above-described embodiment, but is shown by the description of the scope of claims, and further includes all modifications within the meaning and scope equivalent to the description of the scope of claims.

１０…プローブ光、１０ｐ…プローブ光のサンプル光、１２…参照光、１２ｐ…参照光のサンプル光、１４…吸収線、２０…光軸、２２…レーザ光源、２３…励起光、２４…プローブ光発生部、２５，２６，２７，２８…光検出器、２９…濃度算出部、３２…終端鏡、３４…出力鏡、３６…非線形光学結晶、３８…回転ステージ DESCRIPTION OF SYMBOLS 10 ... Probe light, 10p ... Sample light of probe light, 12 ... Reference light, 12p ... Sample light of reference light, 14 ... Absorption line, 20 ... Optical axis, 22 ... Laser light source, 23 ... Excitation light, 24 ... Probe light Generation unit, 25, 26, 27, 28 ... photodetector, 29 ... concentration calculation unit, 32 ... terminal mirror, 34 ... output mirror, 36 ... nonlinear optical crystal, 38 ... rotation stage

Claims (4)

励起光としてのレーザ光を発生するレーザ光源と、
光パラメトリック発振によって前記励起光から、測定対象物に対するオン波長のプローブ光及びオフ波長の参照光を同時に発生するプローブ光発生部と、
前記測定対象物を透過した又は前記測定対象物から反射した前記プローブ光及び前記参照光をそれぞれ別の光路に分離する光分離部と、
前記光分離部によって分離された前記プローブ光を検出する第１の光検出器と、
前記光分離部によって分離された前記参照光を検出する第２の光検出器と、
前記第１及び第２の光検出器によって検出された前記プローブ光及び前記参照光の各透過率から前記測定対象物の濃度を算出する濃度算出部と
を備えることを特徴とする濃度測定装置。 A laser light source that generates laser light as excitation light;
A probe light generator for simultaneously generating on-wavelength probe light and off-wavelength reference light for the measurement object from the excitation light by optical parametric oscillation;
A light separating unit that separates the probe light and the reference light that have passed through the measurement object or reflected from the measurement object into separate optical paths;
A first photodetector for detecting the probe light separated by the light separation unit;
A second photodetector for detecting the reference light separated by the light separation unit;
A concentration measurement apparatus comprising: a concentration calculation unit that calculates a concentration of the measurement object from each transmittance of the probe light and the reference light detected by the first and second photodetectors. 前記プローブ光発生部は、前記波長変換を行う光学素子として、第２種の位相整合が得られる非線形光学結晶を有し、
前記光分離部は偏光ビームスプリッタであることを特徴とする請求項１に記載の濃度測定装置。 The probe light generation unit has a nonlinear optical crystal capable of obtaining the second type of phase matching as an optical element for performing the wavelength conversion,
The concentration measuring apparatus according to claim 1, wherein the light separation unit is a polarization beam splitter. 前記光分離部は、前記プローブ光及び前記参照光の各波長間にカットオフ波長をもつダイクロイックミラーであることを特徴とする請求項１に記載の濃度測定装置。   The concentration measuring apparatus according to claim 1, wherein the light separation unit is a dichroic mirror having a cutoff wavelength between wavelengths of the probe light and the reference light. 励起光としてのレーザ光を発生し、
光パラメトリック発振によって前記励起光から、測定対象物に対するオン波長のプローブ光及びオフ波長の参照光を同時に発生し、
前記測定対象物を透過した又は前記測定対象物から反射した前記プローブ光及び前記参照光をそれぞれ別の光路に分離し、
前記光分離部によって分離された前記プローブ光及び前記参照光を検出し、
検出された前記プローブ光及び前記参照光の各透過率から前記測定対象物の濃度を算出する
ことを特徴とする濃度測定方法。 Generates laser light as excitation light,
An on-wavelength probe light and an off-wavelength reference light for the measurement object are simultaneously generated from the excitation light by optical parametric oscillation,
Separating the probe light and the reference light transmitted through the measurement object or reflected from the measurement object into separate optical paths;
Detecting the probe light and the reference light separated by the light separation unit;
A concentration measurement method, wherein the concentration of the measurement object is calculated from each detected transmittance of the probe light and the reference light.
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