JP2014002101A - Concentration measurement apparatus and concentration measurement method - Google Patents

Concentration measurement apparatus and concentration measurement method Download PDF

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JP2014002101A
JP2014002101A JP2012138624A JP2012138624A JP2014002101A JP 2014002101 A JP2014002101 A JP 2014002101A JP 2012138624 A JP2012138624 A JP 2012138624A JP 2012138624 A JP2012138624 A JP 2012138624A JP 2014002101 A JP2014002101 A JP 2014002101A
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JP6144881B2 (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 measurement apparatus capable of accurately measuring concentrations of a measurement object.SOLUTION: A concentration measurement apparatus includes: a laser light source 22 for generating a laser beam as excitation light 23; a probe light generation unit 24 for generating, due to wavelength conversion of the excitation light 23, probe light beams 10 and 12 having an ON wavelength and an OFF wavelength for a measurement object S; an optical path branching unit 27 for branching a part of the probe light beams 10 and 12 as intensity reference light 15; a photodetector 26 for receiving the intensity reference light 15 and the probe light beams 10 and 12 which are transmitted by the measurement object S or reflected by the measurement object S on the same light receiving surface; and a concentration calculation unit 28 for specifying the probe light beams 10 and 12 on the basis of a difference between respective times at which the intensity reference light 15 and the probe light beams 10 and 12 arrive at the detector 26, and for calculating a concentration of the measurement object S on the basis of the intensity of the probe light beams 10 and 12.

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）のレーザ光と測定対象物で吸収されない波長（即ち、オフ波長）のレーザ光の各透過率を基に測定対象物の濃度を算出する。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 based on the transmittances of the laser light having a wavelength that is absorbed by the measurement object (that is, the on wavelength) and the laser light having a wavelength that is not absorbed by the measurement object (that is, the off wavelength). Is calculated. Patent Documents 1 to 4 disclose a concentration measuring device using the differential absorption method.

特開平０８−１２２２５４号公報Japanese Patent Laid-Open No. 08-122254 特開２０１１−３３９４１号公報JP 2011-33941 A 特開２０１２−２６９４９号公報JP 2012-26949 A 特開２０１０−１８１１９３号公報JP 2010-181193 A

差分吸収法では、測定対象物を通過したレーザ光の透過率を算出するために、測定対象物に入射する前後でレーザ光の強度を測定する。通常、これらの測定には半導体検出器等の光検出器が個別に使用される。ところが、光検出器の量子効率にばらつきがあるため、得られた強度比に誤差が生じる。   In the differential absorption method, the intensity of the laser light is measured before and after entering the measurement object in order to calculate the transmittance of the laser light that has passed through the measurement object. Usually, a photo detector such as a semiconductor detector is individually used for these measurements. However, since the quantum efficiency of the photodetectors varies, an error occurs in the obtained intensity ratio.

本発明は、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。   An object of the present invention is to provide a concentration measuring apparatus and a concentration measuring method capable of accurately measuring the concentration of a measurement object.

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、前記励起光の波長変換によって、測定対象物に対するオン波長及びオフ波長のプローブ光を発生するプローブ光発生部と、前記プローブ光の一部を強度基準光として分岐させる光路分岐部と、前記強度基準光、並びに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を同一の受光面で受光する光検出器と、前記強度基準光と前記プローブ光の前記光検出器までの各到達時間の違いから前記プローブ光を特定すると共に、前記プローブ光の強度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 generates a probe light having an on wavelength and an off wavelength for a measurement object by converting a laser light source that generates laser light as excitation light and wavelength conversion of the excitation light. A probe light generating unit, an optical path branching unit for branching a part of the probe light as intensity reference light, the intensity reference light, and the probe light transmitted through or reflected from the measurement object A photo detector that receives light on the same light receiving surface, and the probe light is identified from the difference in arrival times of the intensity reference light and the probe light to the photo detector, and the measurement object is determined from the intensity of the probe light. The gist is to include a concentration calculation unit that calculates the concentration of an object.

前記光路分岐部はビームスプリッタであってもよい。   The optical path branching unit may be a beam splitter.

前記光路分岐部は前記プローブ光の一部に挿入される散乱体であってもよい。   The optical path branching unit may be a scatterer inserted into a part of the probe 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、前記励起光の波長変換によって、測定対象物に対するオン波長及びオフ波長のプローブ光を発生し、前記プローブ光の一部を強度基準光として分岐させ、前記強度基準光、並びに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を同一の受光面で受光し、前記強度基準光と前記プローブ光の前記受光面までの各到達時間の違いから前記プローブ光を特定すると共に、前記プローブ光の強度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, generates on-wavelength and off-wavelength probe light for a measurement object by wavelength conversion of the excitation light, and A part of the probe light is branched as intensity reference light, and the intensity reference light and the probe light transmitted through or reflected from the measurement object are received by the same light receiving surface, and the intensity reference light is received. The probe light is specified from the difference in the arrival times of the probe light to the light receiving surface, and the concentration of the measurement object is calculated from the intensity of the probe light.

本発明によれば、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。   ADVANTAGE OF THE INVENTION According to this invention, the density | concentration measuring apparatus and density | concentration measuring method which can measure the density | concentration of a measuring object with a sufficient precision can be provided.

本発明の一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 one 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発生部の構成図であり、図２の変形例である。It is a block diagram of the probe light generation part which concerns on one Embodiment of this invention, and is a modification of FIG. 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光路分岐部および光路合流部の構成図である。It is a block diagram of the optical path branching part and optical path confluence | merging part which concern on one Embodiment of this invention. 本発明の一実施形態に係る光路分岐部の構成図である。It is a block diagram of the optical path branching part which concerns on one Embodiment of this invention. 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.

以下、本発明の一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。   Hereinafter, an embodiment of the present invention will be described 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.

図１は、本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、図２に示すプローブ光発生部の変形例である。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、光路分岐部２７と、光路合流部２９と、光検出器２６と、濃度算出部２８とを備える。   FIG. 1 is a configuration diagram of a concentration measuring apparatus according to the present embodiment. FIG. 2 is a configuration diagram of the probe light generator according to the present embodiment. FIG. 3 is a modification of the probe light generator shown in FIG. 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, an optical path branching unit 27, an optical path merging unit 29, a photodetector 26, and a concentration calculating unit 28. With.

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、測定対象物に対するオン波長のプローブ光１０及びオフ波長のプローブ光１２（図４参照）を発生する。以下、説明の便宜上、オフ波長のプローブ光１２を単に参照光１２と称する。吸収の感度を高める観点からは、図４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 probe light 12 (see FIG. 4) for the measurement object by wavelength conversion of the excitation light 23. Hereinafter, for convenience of explanation, the off-wavelength probe light 12 is simply referred to as reference light 12. 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、反射面が対向するように光軸（光路）２０に沿って配置された終端鏡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 along the optical axis (optical path) 20 so that the reflecting surfaces thereof face each other. 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 reflectances of the terminal mirror 32 and the output mirror 34 with respect to the probe light 10 and the reference light 12 are 50 to 99.5%.

非線形光学結晶３６は例えばＫＴＰ結晶やＢＢＯ結晶であり、励起光２３による光パラメトリック発振によって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。プローブ光１０の中心波長λｏｎは例えば２００４ｎｍ、参照光１２の中心波長λｏｆｆは例えば１９９８ｎｍである。非線形光学結晶３６によって発生する光の波長は、励起光２３の光軸に対する結晶の光学軸３６ａの角度θを調整することで適宜変更可能である。そこで、本実施形態の非線形光学結晶３６は、この角度θを調整できるように回転ステージ３８に搭載されている。即ち、回転ステージ３８の回転・逆回転を例えば所定の周期で繰り返すことで、プローブ光１０及び参照光１２が出力鏡３４から交互に出射され、測定対象物Ｓに照射される。なお、回転ステージ３８の回転は制御部（図示せず）によって制御される。   The nonlinear optical crystal 36 is, for example, a KTP crystal or a BBO crystal, and generates on-wavelength probe light 10 and off-wavelength reference light 12 by optical parametric oscillation by the excitation light 23. The center wavelength λon of the probe light 10 is, for example, 2004 nm, and the center wavelength λoff of the reference light 12 is, for example, 1998 nm. The wavelength of light generated by the nonlinear optical crystal 36 can be changed as appropriate by adjusting the angle θ of the optical axis 36a of the crystal with respect to the optical axis of the excitation light 23. Therefore, the nonlinear optical crystal 36 of the present embodiment is mounted on the rotary stage 38 so that the angle θ can be adjusted. In other words, the probe beam 10 and the reference beam 12 are alternately emitted from the output mirror 34 and irradiated onto the measurement object S by repeating the rotation and reverse rotation of the rotation stage 38 at a predetermined cycle, for example. The rotation of the rotary stage 38 is controlled by a control unit (not shown).

なお、本実施形態のプローブ光発生部については、次のように変形できる。図３に示すプローブ光発生部２５は、図２に示すプローブ光発生部２４の変形例である。図２のプローブ光発生部２４では、波長変換を行う光学素子として非線形光学結晶３６を用いていた。一方、図３のプローブ光発生部２５は、波長変換を行う光学素子としてレーザ結晶４６を用いる。レーザ結晶４６は、例えば、Ｔｍ：ＹＡＧ、Ｔｍ：ＹＬＦ、Ｔｍ：ＹＶＯ４、Ｔｍ，Ｈｏ：ＹＡＧ、Ｔｍ，Ｈｏ：ＹＬＦ、Ｔｍ，Ｈｏ：ＹＶＯ４などある。これらのうちの何れかをレーザ結晶４６に用いる場合、励起光２３を発生するレーザ光源には半導体レーザ（ＬＤ）を使用する。半導体レーザは、励起光２３として中心波長が例えば７８５ｎｍの光を発生する。半導体レーザから出射した光は、レーザ結晶４６内での変換効率を上げるため、レンズ等の光学系４８によってレーザ結晶４６に集光される。 Note that the probe light generator of this embodiment can be modified as follows. A probe light generator 25 shown in FIG. 3 is a modification of the probe light generator 24 shown in FIG. In the probe light generator 24 of FIG. 2, a nonlinear optical crystal 36 is used as an optical element for performing wavelength conversion. On the other hand, the probe light generator 25 in FIG. 3 uses a laser crystal 46 as an optical element for wavelength conversion. Examples of the laser crystal 46 include Tm: YAG, Tm: YLF, Tm: YVO 4 , Tm, Ho: YAG, Tm, Ho: YLF, Tm, Ho: YVO 4 and the like. When any of these is used for the laser crystal 46, a semiconductor laser (LD) is used as a laser light source for generating the excitation light 23. The semiconductor laser generates light having a central wavelength of, for example, 785 nm as the excitation light 23. The light emitted from the semiconductor laser is condensed on the laser crystal 46 by an optical system 48 such as a lens in order to increase the conversion efficiency in the laser crystal 46.

図３に示すように、レーザ結晶４６の出射側と出力鏡３４との間には、レーザ結晶４６から出射した光の波長を選別する波長調整機構４２が設置される。波長調整機構４２は、例えばエタロンやプリズムであり、波長調整機構４２を搭載した回転ステージ４４の回転によって、出力鏡３４へ進行する光の波長を選別できる。つまり、回転ステージ４４の回転・逆回転を例えば所定の周期で繰り返すことで、プローブ光１０及び参照光１２を交互に出射させることができる。   As shown in FIG. 3, a wavelength adjusting mechanism 42 that selects the wavelength of light emitted from the laser crystal 46 is installed between the emission side of the laser crystal 46 and the output mirror 34. The wavelength adjustment mechanism 42 is, for example, an etalon or a prism, and can select the wavelength of light traveling to the output mirror 34 by the rotation of the rotary stage 44 on which the wavelength adjustment mechanism 42 is mounted. That is, the probe light 10 and the reference light 12 can be alternately emitted by repeating the rotation / reverse rotation of the rotary stage 44 at a predetermined cycle, for example.

プローブ光発生部２４（２５）から出射したプローブ光１０及び参照光１２は、光路分岐部２７に入射する。光路分岐部２７は、プローブ光１０及び参照光１２の一部をそれぞれ強度基準光１５として分岐させる。残りのプローブ光１０及び参照光１２は、測定対象物Ｓに照射される。光路分岐部２７の分岐比は予め設定されている。従って、強度基準光１５を後述の光検出器２６で測定することで、出力鏡３４を出射した直後のプローブ光１０及び参照光１２の強度を逆算できる。さらに、逆算したプローブ光１０及び参照光１２の各強度は、プローブ光１０及び参照光１２の各透過率を算出する際の基準値として使用される。   The probe light 10 and the reference light 12 emitted from the probe light generation unit 24 (25) enter the optical path branching unit 27. The optical path branching unit 27 branches a part of the probe light 10 and the reference light 12 as the intensity reference light 15. The remaining probe light 10 and reference light 12 are applied to the measuring object S. The branching ratio of the optical path branching unit 27 is set in advance. Therefore, the intensity of the probe light 10 and the reference light 12 immediately after exiting the output mirror 34 can be calculated backward by measuring the intensity reference light 15 with a photodetector 26 described later. Furthermore, the calculated intensities of the probe light 10 and the reference light 12 are used as reference values when calculating the transmittances of the probe light 10 and the reference light 12.

図５に示すように、本実施形態の光路分岐部２７は、例えば、反射率（透過率）が規定されたビームスプリッタである。この場合、ビームスプリッタによって取り出された強度基準光１５は、光検出器２６の前段に配置された光路合流部２９に入射する。   As shown in FIG. 5, the optical path branching unit 27 of the present embodiment is, for example, a beam splitter with a defined reflectance (transmittance). In this case, the intensity reference light 15 extracted by the beam splitter is incident on the optical path merging portion 29 disposed in the front stage of the photodetector 26.

光路合流部２９は、光路分岐部２７によって取り出された強度基準光１５の光路と、測定対象物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、これらの光を光検出器２６に導くものである。光路合流部２９は例えばハーフミラーであり、合流したプローブ光１０、参照光１２、強度基準光１５の全てを光検出器２６の受光面（図示せず）に導く。   The optical path merging unit 29 merges the optical path of the intensity reference light 15 extracted by the optical path branching unit 27 with the optical paths of the probe light 10 and the reference light 12 that have arrived from the measurement object, and these lights are passed to the photodetector 26. It is a guide. The optical path merging unit 29 is, for example, a half mirror, and guides all of the merged probe light 10, reference light 12, and intensity reference light 15 to the light receiving surface (not shown) of the photodetector 26.

また、図６に示すように、本実施形態の光路分岐部２７は、プローブ光１０及び参照光１２を散乱させる散乱体でもよい。散乱体は反射面を有する線状、棒状、板状などの部材であり、プローブ光１０及び参照光１２の散乱光が光検出器２６の受光面に届く位置で、プローブ光１０及び参照光１２の一部に挿入される。   Further, as shown in FIG. 6, the optical path branching unit 27 of the present embodiment may be a scatterer that scatters the probe light 10 and the reference light 12. The scatterer is a member having a reflecting surface, such as a line, a rod, or a plate. The scattered light of the probe light 10 and the reference light 12 reaches the light receiving surface of the photodetector 26, and the probe light 10 and the reference light 12 are scattered. Is inserted into a part of

光検出器２６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を検出する。さらに、光検出器２６は、光路分岐部２７によって取り出されたプローブ光１０及び参照光１２の各強度基準光１５も検出する。つまり、光検出器２６は、これらの光を同一の受光面で受光する。本実施形態では、光検出器２６として、周知の半導体検出器を使用する。半導体検出器は、光の強度に比例した電圧を検出信号として出力する。なお、光検出器２６の前段にはプローブ光１０及び参照光１２を集光するためのレンズ等の光学系３０が設けられており、集光率を向上させている。   The light detector 26 detects the probe light 10 and the reference light 12 transmitted through the measurement object S or reflected from the measurement object S. Further, the photodetector 26 also detects the intensity reference light 15 of the probe light 10 and the reference light 12 extracted by the optical path branching unit 27. That is, the photodetector 26 receives these lights on the same light receiving surface. In the present embodiment, a known semiconductor detector is used as the photodetector 26. The semiconductor detector outputs a voltage proportional to the light intensity as a detection signal. In addition, an optical system 30 such as a lens for condensing the probe light 10 and the reference light 12 is provided in the previous stage of the photodetector 26, and the light condensing rate is improved.

光検出器２６は、上述した三種類の光を検出する。従って、そこから得られる検出信号は同一の量子効率の下で生成されることにある。つまり、光検出器の個体差による検出信号上の誤差を排除できるため、測定対象物Ｓの濃度の算出における精度が向上する。また、従来の濃度測定装置と比べて、使用する検出器の個数を削減できる。従って、構成が簡略になると共に製造コストを削減することができる。   The photodetector 26 detects the three types of light described above. Therefore, the detection signal obtained therefrom is generated under the same quantum efficiency. That is, the error in the detection signal due to the individual difference of the photodetectors can be eliminated, so that the accuracy in calculating the concentration of the measuring object S is improved. In addition, the number of detectors used can be reduced as compared with the conventional concentration measuring apparatus. Therefore, the configuration is simplified and the manufacturing cost can be reduced.

濃度算出部２８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、光検出器２６によって検出されたプローブ光１０及び参照光１２の各透過率（吸光度）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２８は、参照光１２の強度基準光１５と、測定対象物を経由した参照光１２の各強度から、参照光１２の透過率（第１の透過率）を算出する。濃度算出部２８は、更に、プローブ光１０の強度基準光１５と、測定対象物を経由したプローブ光１０の各強度から、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ことを考慮して、濃度算出部２８は、第１の透過率を用いて、第２の透過率から第３の透過率を逆算する。その結果、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 28 is configured as a part of a control unit (not shown) that controls the entire concentration measurement apparatus, and transmits (absorbance) each of the probe light 10 and the reference light 12 detected by the photodetector 26. The concentration of the measuring object S is calculated from Specifically, the concentration calculation unit 28 calculates the transmittance (first transmittance) of the reference light 12 from the intensity standard light 15 of the reference light 12 and each intensity of the reference light 12 that has passed through the measurement object. To do. The concentration calculation unit 28 further calculates the transmittance (second transmittance) of the probe light 10 from the intensity reference light 15 of the probe light 10 and each intensity of the probe light 10 that has passed through the measurement object. Considering that the second transmittance is obtained by multiplying the first transmittance by the transmittance due to the absorption of the measurement object S (third transmittance), the concentration calculating unit 28 Using the transmittance of 1, the third transmittance is calculated backward from the second transmittance. As a result, the concentration of the measuring object S is calculated from the third transmittance.

なお、上述の濃度算出において、濃度算出部２８は時間分解しながら光検出器２６の検出信号を受信することで、当該検出信号を発生した光が、プローブ光１０、参照光１２、及びこれらの強度基準光１５の何れかであるかを特定している。上述したように、プローブ光１０、参照光１２、及びこれらの強度基準光１５は、何れも同一の光検出器２６によって検出される。ただし、測定対象物Ｓに一度に照射されるのはプローブ光１０及び参照光１２の何れかである。また、測定対象物Ｓを経由して光検出器２６に到達するプローブ光１０及び参照光１２の光路長は、強度基準光１５として光検出器２６に到達するプローブ光１０及び参照光１２の光路長よりも圧倒的に長い。従って、濃度算出部２８は、時間分解しながら光検出器２６の検出信号を受信することで、図７に示すような測定結果を得る。この図において、時刻ｔ１で現れたピークＰ１は、強度基準光１５の検出信号である。また、時刻ｔ２（＞ｔ１）で現れたＰ２は、Ｐ１の強度基準光１５として一部が取り出されたプローブ光１０（又は参照光１２）であって、測定対象物Ｓを経由したものの検出信号である。このような時間差があるため、光検出器までの各到達時間の違いから前記プローブ光を特定でき、濃度の算出が可能になる。   In the above-described concentration calculation, the concentration calculation unit 28 receives the detection signal of the photodetector 26 while time-resolving, so that the light that has generated the detection signal is the probe light 10, the reference light 12, and these The intensity reference light 15 is specified. As described above, the probe light 10, the reference light 12, and the intensity reference light 15 are all detected by the same photodetector 26. However, either the probe light 10 or the reference light 12 is irradiated onto the measuring object S at a time. Further, the optical path lengths of the probe light 10 and the reference light 12 that reach the light detector 26 via the measurement object S are the optical paths of the probe light 10 and the reference light 12 that reach the light detector 26 as the intensity reference light 15. Overwhelmingly longer than the length. Therefore, the concentration calculation unit 28 receives the detection signal of the photodetector 26 while performing time resolution, thereby obtaining a measurement result as shown in FIG. In this figure, a peak P 1 that appears at time t 1 is a detection signal of the intensity reference light 15. Further, P2 that appears at time t2 (> t1) is a probe signal 10 (or reference beam 12) that is partially extracted as the intensity reference beam 15 of P1, and is a detection signal that has passed through the measuring object S. It is. Since there is such a time difference, the probe light can be identified from the difference in arrival time to the photodetector, and the concentration can be calculated.

なお、本実施形態では測定対象物として二酸化炭素ガスを挙げたが、本発明が適用される測定対象物はこれに限られず、他の種のガスにも適用可能である。また、気体以外の相（即ち、液体や固体）にも適用可能である。   In the present embodiment, carbon dioxide gas is used as the measurement object. However, the measurement object to which the present invention is applied is not limited to this, and can be applied to other types of gases. Moreover, it is applicable also to phases (namely, liquid and solid) other than gas.

また、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。   Further, the present invention is not limited to the above-described embodiment, 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、１２…参照光（プローブ光）、１４…吸収線、１５…強度基準光、２０…光軸、２２…レーザ光源、２３…励起光、２４，２５…プローブ光発生部、２６…光検出器、２７…光路分岐部、２８…濃度算出部、２９…光路合流部、３０…光学系、３２…終端鏡、３４…出力鏡、３６…非線形光学結晶、３６ａ…光学軸、３８…回転ステージ、４２…波長調整機構、４４…回転ステージ、４６…レーザ結晶、４８…光学系 DESCRIPTION OF SYMBOLS 10 ... Probe light, 12 ... Reference light (probe light), 14 ... Absorption line, 15 ... Intensity reference light, 20 ... Optical axis, 22 ... Laser light source, 23 ... Excitation light, 24, 25 ... Probe light generation part, 26 DESCRIPTION OF SYMBOLS ... Photodetector, 27 ... Optical path branching part, 28 ... Concentration calculation part, 29 ... Optical path confluence part, 30 ... Optical system, 32 ... Termination mirror, 34 ... Output mirror, 36 ... Nonlinear optical crystal, 36a ... Optical axis, 38 Rotating stage 42 Wavelength adjusting mechanism 44 Rotating stage 46 Laser crystal 48 Optical system

Claims (4)

励起光としてのレーザ光を発生するレーザ光源と、
前記励起光の波長変換によって、測定対象物に対するオン波長及びオフ波長のプローブ光を発生するプローブ光発生部と、
前記プローブ光の一部を強度基準光として分岐させる光路分岐部と、
前記強度基準光、並びに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を同一の受光面で受光する光検出器と、
前記強度基準光と前記プローブ光の前記検出器までの各到達時間の違いから前記プローブ光を特定すると共に、前記プローブ光の強度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 generating on-wavelength and off-wavelength probe light for the measurement object by wavelength conversion of the excitation light;
An optical path branching part for branching a part of the probe light as intensity reference light;
A photodetector that receives the intensity reference light and the probe light transmitted through the measurement object or reflected from the measurement object on the same light-receiving surface;
A probe that identifies the probe light from the difference in arrival time of the intensity reference light and the probe light to the detector, and a concentration calculator that calculates the concentration of the measurement object from the intensity of the probe light. Concentration measuring device characterized by. 前記光路分岐部は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 concentration measuring apparatus according to claim 1, wherein the optical path branching unit is a beam splitter. 前記光路分岐部は前記プローブ光の一部に挿入される散乱体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 optical path branching unit is a scatterer inserted into a part of the probe light. 励起光としてのレーザ光を発生し、
前記励起光の波長変換によって、測定対象物に対するオン波長及びオフ波長のプローブ光を発生し、
前記プローブ光の一部を強度基準光として分岐させ、
前記強度基準光、並びに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を同一の受光面で受光し、
前記強度基準光と前記プローブ光の前記受光面までの各到達時間の差から前記プローブ光を特定すると共に、前記プローブ光の強度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,
By generating a probe light having an on-wavelength and an off-wavelength with respect to the measurement object by wavelength conversion of the excitation light,
Branching part of the probe light as intensity reference light,
Receiving the intensity reference light and the probe light that has passed through the measurement object or reflected from the measurement object on the same light receiving surface,
The concentration measurement is characterized in that the probe light is specified from the difference in arrival times of the intensity reference light and the probe light to the light receiving surface, and the concentration of the measurement object is calculated from the intensity of the probe light. Method.
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