JP4486433B2 - Absorption measuring device - Google Patents

Description

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

  As a technique for acquiring the absorption coefficient of a sample to be measured, cavity ring-down spectroscopy (CRDS), which is one of absorption spectroscopy, is known. In this CRDS, first, pulsed light is incident into a cavity into which a sample to be measured is introduced. The pulsed light incident on the cavity is multiple-reflected in the cavity, and at that time, it is attenuated by the component absorbed by the light absorbing material contained in the sample to be measured and the reflection / transmittance of the mirror pair constituting the cavity. Depending on the component, the intensity decreases with each reflection. As a result, the intensity of the transmitted pulsed light obtained by transmitting the pulsed light through the mirror every time it is reflected by the mirror constituting the cavity attenuates exponentially. In CRDS, after measuring the intensity of a plurality of transmitted pulsed light beams from a cavity into which pulsed light is incident, the absorption coefficient of the sample to be measured is determined from its exponential decay curve. Thus, when the absorption coefficient of the sample to be measured is determined, the concentration of the light-absorbing substance contained in the sample to be measured can be determined by using the absorption coefficient.

As a measurement apparatus using the CRDS, Patent Document 1 discloses an apparatus to which a heterodyne method is applied in order to improve detection sensitivity. That is, in the apparatus described in Patent Document 1, two light beams having slightly different frequencies are simultaneously passed through the cavity, and the two light beams are caused to interfere with each other, and a change in the time intensity of the transmitted pulse light is detected from the interference component. is doing.
US Pat. No. 6,094,267

  By the way, when the interference method is used, if the intensity of one of the two lights (reference light) to be interfered is increased, the detected signal is also increased, so that highly sensitive measurement is expected. However, in the apparatus described in Patent Document 1, since two light beams having slightly different frequencies are allowed to pass through the sample to be measured, there is a possibility that optical destruction of the sample to be measured may occur when the intensity of the reference light is increased. Sensitive measurement is difficult. Further, the apparatus described in Patent Document 1 has a problem that the frequency difference between the two lights must be controlled with high accuracy, and the configuration of the apparatus becomes complicated. In addition, as described in Patent Document 1, when the transmitted pulsed light is directly detected by the photodetector and time-resolved measurement is performed without using the interferometry, a detector that follows the temporal change of the transmitted pulsed light, Since a time-resolved measuring device such as an oscilloscope or a streak camera is required, there is a problem that the device becomes large.

  Therefore, an object of the present invention is to provide an absorption measurement apparatus that can measure the absorption characteristics of a sample to be measured with high sensitivity using cavity ring-down spectroscopy and can be miniaturized.

  In order to solve the above problems, an absorption measurement apparatus according to the present invention includes a light supply unit that outputs measurement pulse light and reference pulse light having the same center frequency on different optical paths, and a pair of mirrors facing each other. A sample to be measured is introduced into the configured cavity, and a cavity ring-down portion arranged on the optical path of the measurement pulse light, and a measurement pulse in the cavity in the cavity ring-down portion where the measurement pulse light is incident An optical delay means for adjusting a delay time between the signal light composed of a plurality of transmitted pulse lights output from the cavity ring-down portion according to the multiple reflection and the reference pulse light, and the signal light and the reference pulse light are caused to interfere with each other. Detecting means for detecting the interference light between the signal light and the reference pulse light, and the test sample based on the temporal change in the intensity of the interference light detected by the detection means. Characterized in that it comprises a analyzing means for determining the absorption characteristics of the.

  In this case, the measurement pulse light and the reference pulse light having the same center frequency are generated by the light supply means and are output on different optical paths. And since the cavity ring down part is arrange | positioned on the optical path of the measurement pulse light output from a light supply means, the measurement pulse light output from the light supply means injects into a cavity ring down part. Since the cavity ring-down part has a cavity composed of a pair of mirrors, the measurement pulse light incident on the cavity ring-down part is multiple-reflected in the cavity. In addition, since the sample to be measured is introduced into the cavity, the measurement pulse light is absorbed by the sample to be measured every time it passes through the sample to be measured in the cavity due to multiple reflection. Therefore, the intensity of the signal light consisting of a plurality of transmission pulses obtained by passing the measurement pulse light through the cavity ring-down part attenuates in time according to the absorption characteristics of the sample to be measured and the reflection / transmission characteristics of the mirror pair. . In the absorption measurement device, the detection means causes the signal light having the same center frequency as the measurement pulse light and the reference pulse light having the same center frequency as the measurement pulse light output from the light supply means to interfere with each other. Interfering light is detected. Then, the absorption characteristic of the sample to be measured is determined by analyzing the time change of the intensity of the interference light by the analyzing means. Therefore, it is possible to calculate the concentration of the light-absorbing substance contained in the sample to be measured from the absorption characteristics.

  The above absorption measurement device employs a so-called homodyne method in which the interference light is detected by causing the signal light of the same center frequency to interfere with the reference pulse light, so the configuration of the absorption measurement device is simple and downsized. Is possible. Further, since the reference pulse light does not pass through the sample to be measured, the intensity of the reference pulse light can be increased without damaging the sample to be measured, so that highly sensitive measurement is possible.

  Further, the light supply means in the absorption measurement device according to the present invention includes a pulse light source unit that outputs pulse light, and the pulse light output from the pulse light source unit is branched into measurement pulse light and reference pulse light, thereby measuring pulses. It is preferable to have an optical branching unit that outputs light and reference pulse light on different optical paths. In this configuration, one pulsed light output from the same pulsed light source unit is branched into the measurement pulsed light and the reference pulsed light by the optical branching unit, and is output on different optical paths. In this case, the measurement pulse light and the reference pulse light having the same center frequency can be easily generated.

  Furthermore, the light supply means in the absorption measurement apparatus according to the present invention is preferably a semiconductor laser that outputs measurement pulse light from one of the end faces facing each other and outputs reference pulse light from the other. In this case, since the measurement pulse light and the reference pulse light are simultaneously output from one semiconductor laser, the configuration of the apparatus is further simplified and the size can be easily reduced.

  The optical delay means in the absorption measurement apparatus according to the present invention preferably comprises a delay optical system having a variable optical path length provided on at least one of the optical path of the measurement pulse light and the optical path of the reference pulse light. In this case, the delay time between the signal light and the reference pulse light can be adjusted by changing the optical path length of at least one of the signal light and the reference pulse light by the delay optical system.

  Furthermore, the absorption measurement apparatus according to the present invention further includes a modulation unit that modulates the optical path length difference between the signal light and the reference pulse light, and the modulation unit includes at least one of the measurement pulse light and the reference pulse light. It is preferable to be provided on the optical path. In this case, since the optical path length difference between the signal light and the reference pulse light is modulated by the modulation means, a higher S / N ratio can be realized by detecting the interference light in synchronization with the modulation frequency of the modulation means. There is a tendency.

  Furthermore, in the absorption measurement apparatus according to the present invention, it is preferable that the light supply means, the cavity ring down portion, the optical delay means, and the detection means are provided on the same support plate. In this case, since the light supply unit, the cavity ring-down unit, the optical delay unit, and the detection unit are provided on the same support plate, the optical system used in the absorption measurement apparatus is stabilized.

  According to the absorption measurement apparatus of the present invention, the absorption characteristic of a sample to be measured can be measured with high sensitivity using cavity ring-down spectroscopy, and the size can be reduced.

  Hereinafter, preferred embodiments of an absorption measurement apparatus according to the present invention will be described with reference to the 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 the absorption characteristics of the sample S to be measured using cavity ring-down spectroscopy (CRDS). First, the principle of CRDS will be described.

As shown in FIG. 1, in CRDS, a sample cell 12 for holding a sample S to be measured is arranged in a cavity 11 composed of a pair of mirrors 11a and 11b having high reflectivity (for example, reflectivity is 99% or more). deep. Then, the measurement pulse light L 1 is incident on the cavity 11 with the sample S to be measured introduced into the sample cell 12. The measurement pulse light L1 is multiple-reflected between the pair of mirrors 11a and 11b, but part of the measurement pulse light L1 leaks from the mirror 11b and has a plurality of transmitted pulse lights L1 _n having a pulse interval Δt (n is an integer of 1 or more) The signal light M consisting of the columns is obtained.

  The pulse interval Δt is mainly determined by the distance W between the mirrors 11a and 11b and the refractive index of the sample S to be measured. For example, the refractive index of the sample S to be measured is 1.3, and the distance between the mirrors 11a and 11b is determined. If the distance W is 1 cm, the pulse interval Δt corresponds to (2 × 1 [cm] × 1.3) divided by the speed of light and is about 87 ps.

Here, since the sample S to be measured is introduced into the sample cell 12, the measurement pulse light L1 that is multiply reflected in the cavity 11 is absorbed by the sample S every time it passes through the sample S. Is done. Therefore, the intensity of each transmitted pulsed light L1 _n attenuates according to the absorption of the sample S to be measured. Therefore, the absorption coefficient (absorption characteristic) of the sample S to be measured can be obtained from the time change (attenuation characteristic) of the intensity of the signal light M, and the concentration of the light absorbing substance contained in the sample S to be measured can be determined from this absorption coefficient. It is possible to ask.

  The absorption measurement apparatus 1 according to the present embodiment shown in FIG. 2 is characterized in that the homodyne method is applied to the detection of the signal light M. In the absorption measurement apparatus 1, the measurement pulse light L1 is used in order to apply the homodyne method. A Mach-Zehnder type interferometer that causes the reference pulse light L2 having the same center frequency to interfere with the signal light M described above is employed. Hereinafter, the configuration of the absorption measurement apparatus 1 will be described.

  The absorption measurement apparatus 1 includes a light supply unit 20 that generates the measurement pulse light L1 and the reference pulse light L2. The light supply means 20 includes a laser light source (pulse light source unit) 21 that outputs a pulsed light L having a specific wavelength and a pulse width, and an optical branching unit 22 that divides the pulsed light L output from the laser light source 21 into two. It is comprised including. The light branching unit 22 is, for example, a half mirror or a beam splitter.

  In the light supply means 20, after the pulsed light L output from the laser light source 21 is branched into the measurement pulsed light L1 and the reference pulsed light L2 by the optical branching unit 22, the first and second optical paths R1, R2 which are different from each other. Output to. Since the measurement pulse light L1 and the reference pulse light L2 are generated by being branched from one pulse light L, they have the same center frequency and phase. Here, the same phase means that there is a fixed relationship between the phases.

On the first optical path R1 of the measurement pulsed light L1 generated by the light supply means 20, a cavity ring down (CRD) unit 10 is arranged. The CRD unit 10 includes a cavity 11 including a pair of mirrors 11 a and 11 b illustrated in FIG. 1 and a sample cell 12 disposed in the cavity 11. A sample supply source 13 is connected to the sample cell 12 via a pipe, and a liquid or gas measurement sample S is introduced from the sample supply source 13 by a pump 14. Then, when the measuring pulse light L1 in a state in which the measured sample S is accumulated is incident into the cavity 11 in the sample cell 12, CRD unit 10, the signal light M consisting of a plurality of transmitted pulsed light L1 _n first 1 to the optical path R1. In addition, a waste reservoir 15 is connected to the sample cell 12 via a pipe, and the measured sample S to be measured is discharged to the waste reservoir 15.

  In order for the signal light M output from the CRD unit 10 and the reference pulse light L2 to interfere with each other in the detection unit 50 described later, the absorption measurement apparatus 1 adjusts the delay time between the signal light M and the reference pulse light L2. A measurement side delay unit 31 and a reference side delay unit 32 as optical delay units.

  The measurement-side delay means 31 is disposed on the first optical path R1 and in the subsequent stage of the CRD unit 10, and a delay optical system in which a corner cube prism (hereinafter simply referred to as a prism) 34 is provided on the automatic stage 33. Consists of. The prism 34 inverts the traveling direction of the signal light M incident after being reflected by the mirror M1 and outputs the result. That is, the prism 34 reflects the signal light M incident on the side surface 34a by the side surfaces 34b and 34c orthogonal to each other and outputs the reflected light from the side surface 34a. The automatic stage 33 to which the prism 34 is attached can move back and forth along the incident direction of the signal light M to the prism 34, and the measurement-side delay means 31 moves the signal light M by moving the automatic stage 33. The optical path length can be changed.

  Further, the reference side delay means 32 is disposed on the second optical path R2, and includes a delay optical system in which a prism 36 is provided on the automatic stage 35. The prism 36 inverts the traveling direction of the incident reference pulse light L2 and outputs it. That is, the prism 36 reflects the reference pulsed light L2 incident from the side surface 36a by the side surfaces 36b and 36c orthogonal to each other and outputs the reflected light from the side surface 36a. The automatic stage 35 to which the prism 36 is attached is movable back and forth along the incident direction of the reference pulse light L2 to the prism 36, and the reference side delay means 32 is moved by the movement of the automatic stage 35. The optical path length can be changed.

In the absorption measurement apparatus 1, the delay between the signal light M and the reference pulse light L2 is obtained by changing the optical path lengths of the signal light M and the reference pulse light L2 by linking the measurement side delay means 31 and the reference side delay means 32 to each other. Adjust the time. More specifically, for example, when carrying out measurements on 10 transmitted pulse light _L1 1 _{~L1 10,} a pulse interval Δt of the transmitted pulsed light _L1 1 _{~L1 10,} if, if less than 87ps, whole As a result, a delay time of 870 ps is required, so that one of the prisms 34 and 36 is moved by about 13 cm. Here, in order to simplify the description, the prisms 34 and 36 have the same shape. Note that this moving distance depends on the pulse interval Δt mainly determined by the distance W between the mirrors 11a and 11b (see FIG. 1) and the refractive index of the sample S to be measured, and therefore the refractive index of the sample S to be measured. Accordingly, by changing the distance W between the mirrors 11a and 11b, the moving distance can be optimized so as to improve the stability of the interferometer and to reduce the size of the absorption measuring apparatus 1.

  Further, the absorption measurement apparatus 1 includes a modulation unit 40 that modulates the optical path length difference between the signal light M and the reference pulse light L2 in order to reduce noise caused by instability of the interferometer. The modulation means 40 includes a mirror M2 to which a piezo element 41 is attached, and a modulation signal generator 42 that drives the piezo element 41.

The mirror M2 is disposed on the second optical path R2 and in the subsequent stage of the prism 36, reflects the reference pulse light L2 output from the prism 36, and makes it incident on the detection means 50 described later. The piezo element 41 attached to the mirror M2 is driven by the modulation signal input from the modulation signal generator 42, and vibrates at a predetermined frequency (for example, 1 kHz) having an amplitude several times the wavelength of the reference pulse light L2. To do. The predetermined frequency may be different from the frequency (≈1 / Δt) corresponding to the pulse interval Δt of the transmitted pulsed light L1 _n , and is usually a frequency lower than that frequency. As a result, the optical path length of the reference pulse light L2 changes with time according to the vibration of the piezo element 41. As a result, the interference component of the interference signal corresponding to the interference light between the reference pulse light L2 and the signal light M is modulated. The AC signal component changes according to the frequency.

  In addition, the absorption measurement apparatus 1 includes a detection unit 50 that detects the interference light by causing the signal light M output from the measurement-side delay unit 31 to interfere with the reference pulse light L2 modulated by the modulation unit 40. The detection means 50 includes an optical multiplexer 51, a pair of detectors 52 and 53, and a differential amplifier 54, and constitutes a balanced homodyne detection system. The optical multiplexer 51 is, for example, a half mirror or a beam splitter, and multiplexes the signal light M output from the prism 34 and the reference pulse light L2 reflected by the mirror M2, and each detector 52, To 53.

  Each of the detectors 52 and 53 is, for example, a photomultiplier tube, detects interference light between the signal light M and the reference pulse light L2 obtained as a result of multiplexing by the optical multiplexer 51, and corresponds to the interference light. The interference signal to be input is input to the differential amplifier 54. The differential amplifier 54 differentially amplifies a signal component corresponding to the interference component of the interference light among the interference signals, and inputs the amplified signal component to the data analysis circuit (analysis means) 60. In this embodiment, since the optical path length difference between the signal light M and the reference pulse light L2 is modulated by the modulation means 40, an AC signal component is extracted using a Lockin amplifier, a high-sensitivity AC current / voltmeter, and the like. Thus, the S / N ratio can be improved.

  The digital processing circuit 60 has a computer, analyzes the data signal input from the differential amplifier 54, and acquires the absorption characteristic of the sample S to be measured. That is, the absorption coefficient (absorption characteristic) of the sample S to be measured is calculated from the rate of change of each peak intensity of the data signal input from the differential amplifier 54 with respect to the delay time. Based on the absorption coefficient, the concentration of the light-absorbing substance contained in the sample S to be measured is obtained.

  Since the absorption measuring apparatus 1 uses the homodyne method, it is required that the interferometer has good mechanical stability in order to perform measurement with high accuracy. Therefore, in the absorption measurement device 1, each component of the absorption measurement device 1 such as the light supply unit 20, the CRD unit 10, the measurement side delay unit 31, the reference side delay unit 32, the modulation unit 40, and the detection unit 50 is provided. They are provided on the same support plate 70. The support plate 70 is manufactured by cutting out a metal block such as aluminum, invar, or stainless steel, or a plastic material block such as acrylic. In this case, since the light supply means 20, the CRD unit 10, the measurement side delay means 31, the reference side delay means 32, the modulation means 40, and the detection means 50 are provided on one support plate 70, more stable measurement. Can be implemented. In addition, it is more preferable from the viewpoint of the stability of the apparatus that the support plate 70 described above is a part of the container and each component of the absorption measurement apparatus 1 described above is built in the container.

The operation of the absorption measuring apparatus 1 will be described. First, in a state where the sample S to be measured is introduced from the sample supply source 13 into the sample cell 12 of the CRD unit 10, the measurement pulse light L1 and the reference pulse light L2 are generated by the light supply means 20, and the first and second pulse light L2 are generated. Output to optical paths R1 and R2. The measurement pulse light L1 is incident on the CRD unit 10 disposed on the first optical path R1, and a part of the measurement pulse light L is absorbed by the sample S to be measured. The measurement pulse light L1 is output from the CRD unit 10 as signal light M composed of a plurality of transmission pulse lights L1 _n attenuated according to the absorption of the sample S to be measured and the reflection / transmission characteristics of the pair of mirrors 11a and 11b. Is done. The signal light M is incident on the optical multiplexer 51 after receiving an optical delay so as to adjust the optical path length with the reference pulse light L2 by the measurement side delay means 31. The reference pulse light L2 output from the light supply means 20 is subjected to an optical delay so as to adjust the optical path length with the signal light M by the reference side delay means 32, and further modulated by the modulation means 40 before being optically combined. The light enters the waver 51.

  Interfering light obtained by combining the signal light M and the reference pulse light L2 by the optical multiplexer 51 is received by the pair of detectors 52 and 53. Then, an interference signal corresponding to the interference light is input to the differential amplifier 54, and the interference component is differentially amplified. When an AC signal component corresponding to the interference component among the signals output from the differential amplifier 54 is input to the digital processing circuit 60 as a data signal, the change is based on a temporal change in peak intensity included in the data signal. The absorption coefficient of the sample S to be measured is calculated. And the density | concentration etc. of the light absorption substance contained in the to-be-measured sample S are calculated | required from the absorption coefficient. In the absorption measurement apparatus 1, the measured sample S to be measured is discharged from the sample cell 12 to the waste reservoir 15 via a pipe.

In the absorption measuring apparatus 1, the measurement side delay means 31 and the reference side delay means 32 as the optical delay means are used together to change the delay time between the signal light M and the reference pulse light L2, and refer to the signal light M. The interference light obtained as a result of the interference with the pulsed light L 2 is detected by the detectors 52 and 53. Therefore, the waveform of the interference signal with respect to the delay time corresponds to the cross-correlation waveform between the signal light M and the reference pulse light L2. The rate of change of the peak intensity of the interference signal with respect to the delay time corresponds to the attenuation rate of each transmitted pulsed light L1 _n . Therefore, the time resolution in the absorption measuring apparatus 1 depends on the optical delay realized by the measurement side delay means 31 and the reference side delay means 32, that is, depends on the movement accuracy of the prisms 34 and 36.

  As described above, since the time resolution of the absorption measuring apparatus 1 mainly depends on the movement accuracy of the prisms 34 and 36, compared with the case where the signal light M is directly time-resolved and measured, There is no need for disassembly and measurement equipment (such as an oscilloscope or streak camera). Furthermore, since the time resolution of the absorption measuring apparatus 1 is determined by the mechanical accuracy of the measurement side delay means 31 and the reference side delay means 32 (movement accuracy of the prisms 34 and 36), a time resolution on the order of femtoseconds can be realized. Yes, more detailed analysis of absorption characteristics can be easily performed.

  Further, since the homodyne method for causing the signal light M having the same center frequency and the reference pulse light L2 to interfere with each other is employed, for example, when the heterodyne method is employed, the signal light and the reference pulse light having slightly different frequencies are used. Therefore, it is not necessary to control the frequency deviation between the two with high accuracy, the apparatus configuration is simplified, the absorption measuring apparatus 1 can be downsized, and the cost can be reduced.

Further, the CRDS, since it is important to obtain the attenuation factor of the peak intensity of each transmitted pulse light L1 _n, it is sufficient as long to obtain only the data near the peak position of each transmitted pulse light L1 _n. Therefore, the delay time stepwise skips, near the peak position and the reference pulsed light L2 and the transmitted pulsed light L1 _n between the measurement side delay means 31 and the reference-side delay means 32 and the signal beam M and the reference pulse light L2 It is also possible to shorten the measurement time by causing interference with.

  Furthermore, it is known that the time response of a detector that is normally used in an apparatus that applies CRDS is slow with respect to light in the far-infrared region (for example, a wavelength range of 3 to 20 μm). In an apparatus that directly time-resolves M, it is difficult to obtain the absorption characteristics of the sample S to be measured from the signal light M in the far infrared region. On the other hand, since the time resolution of the absorption measurement apparatus 1 according to the present embodiment mainly depends on the movement accuracy of the prisms 34 and 36 rather than the time response speed of the detectors 52 and 53, conventionally. It is possible to obtain the absorption characteristics of the sample S to be measured for the far-infrared region that could not be measured. When performing measurement on light in the far infrared region, a light source (for example, a quantum cascade laser) having high coherence in the far infrared region may be used as the laser light source 21.

  Furthermore, in the absorption measuring apparatus 1, since the intensity of the interference light can be increased by increasing the intensity of the reference pulse light L2, highly sensitive measurement is possible. At this time, since the reference pulse light L2 does not pass through the sample S to be measured, the sample S to be measured is not damaged even if the intensity of the reference pulse light L2 is increased. In addition, since the differential amplifier 54 differentially amplifies the interference signal detected by the two detectors 52 and 53 to obtain the data signal, it is doubled compared to the case where the interference light is detected by one detector. As a result, the sensitivity can be improved. Further, each of the detectors 52 and 53 detects noise caused by fluorescence or scattered light from the sample S to be measured, which is known as a common mode, but these are detected to the same extent by the detectors 52 and 53. Therefore, it does not appear as a data signal after being differentially amplified by the differential amplifier 54. Therefore, a data signal in which the common mode is removed and the S / N ratio is improved can be analyzed.

  Further, since the optical path length difference between the reference pulse light L2 and the signal light M is modulated by the modulation means 40, the frequency of the AC signal component included in the interference signal is the modulation frequency and amplitude in the vibration of the piezo element 41. Depends on. Therefore, not only the modulation frequency but also the frequency of the AC signal can be changed by changing the amplitude. Therefore, when an AC signal is read from the interference signal, an AC signal corresponding to the frequency characteristic of the reading circuit can be obtained.

  In the present embodiment, the modulation unit 40 is provided. However, the modulation unit 40 is not necessarily used, and the modulation unit 40 is configured to use the optical path of the measurement pulse light L1 (and the signal light M). The optical path length difference between the signal light M and the reference pulse light L2 is disposed in at least one of the first optical path R1 that is the optical path) and the second optical path R2 that is the optical path of the reference pulse light L2. May be modulated. Further, although the laser light source 21 that outputs pulsed light is used as the pulse light source unit, for example, pulsed light may be generated from the output laser light using a laser light source that continuously oscillates.

(Second Embodiment)
The configuration of the absorption measurement device 2 according to the second embodiment shown in FIG. 3 and the configuration of the absorption measurement device 1 are mainly in that the absorption measurement device 2 uses a semiconductor laser 23 as the light supply means 20. Is different. The absorption measuring device 2 will be described focusing on this difference.

  In this absorption measuring apparatus 2, when the semiconductor laser 23 is oscillated to generate pulsed light having a specific wavelength and pulse width, one of a pair of pulsed light output simultaneously from the front end face and the rear end face of the semiconductor laser 23. Is used as measurement pulsed light L1, and the other is used as reference pulsed light L2. Thereby, the measurement pulse light L1 and the reference pulse light L2 having the same center frequency and the same phase can be easily obtained.

  Here, the operation of the absorption measuring apparatus 2 will be described. First, similarly to the first embodiment, the sample S to be measured is introduced from the sample supply source 13 into the sample cell 12 of the CRD unit 10. Then, the measurement pulse light L1 and the reference pulse light L2 are output from the semiconductor laser 23 with the sample S to be measured introduced into the sample cell 12.

  The measurement pulse light L1 becomes signal light M by passing through the CRD unit 10. Then, the signal light M receives an optical delay so that the optical path length with the reference pulse light L2 is adjusted by the measurement side delay means 31, and then is reflected by the mirror M3 and then enters the optical multiplexer 51. Further, the reference pulse light L2 output from the semiconductor laser 23 and having the same frequency as the measurement pulse light L1 is optically delayed after being subjected to an optical delay so as to adjust the optical path length with the signal light M by the reference side delay means 32. The light enters the waver 51.

  When the signal light M and the reference pulse light L2 are combined by the optical multiplexer 51, they are received by the detectors 52 and 53 as interference light, respectively. Then, an interference signal corresponding to the interference light is input to the differential amplifier 54, and the interference component included in the interference signal is differentially amplified. Subsequently, when the signal from the differential amplifier 54 is input to the digital processing circuit 60 as a data signal, the digital processing circuit 60 calculates the absorption coefficient (absorption characteristic) of the sample S to be measured. And the density | concentration etc. of the light absorption substance contained in the to-be-measured sample S are calculated | required from the absorption coefficient. In the absorption measuring apparatus 2, the measured sample S to be measured is discharged from the sample cell 12 to the waste reservoir 15 through a pipe.

  In this configuration, since the pair of pulsed lights simultaneously output from both end faces of the semiconductor laser 23 are used as the measurement pulsed light L1 and the reference pulsed light L2, the configuration of the absorption measuring apparatus 1 becomes simpler, and the absorption measuring apparatus. 1 can be further reduced in size. In addition, since the number of optical elements constituting the interferometer can be reduced, stable measurement tends to be possible. The effect of adopting the homodyne method is the same as that of the first embodiment. Also in the present embodiment, the modulation means 40 described in the first embodiment may be disposed in at least one of the first and second optical paths R1 and R2. In this case, the S / N ratio can be improved as in the first embodiment.

  As mentioned above, although preferred embodiment of this invention was described, it cannot be overemphasized that this invention is not limited to the said 1st and 2nd embodiment. For example, the measurement-side delay means 31 and the reference-side delay means 32 as optical delay means are delay optical systems using prisms 34 and 36 provided on the automatic stages 33 and 35, but the optical path length is variable. That's fine. For example, a reflection optical element (for example, a mirror) other than the prisms 34 and 36 can be used as long as the signal light M and the reference pulse light L2 can be reflected, and an automatic stage is used as means for moving the reflection optical element. For example, a linear movable mechanism with a rotary motor and a crank can be used. Further, although the optical path length between the signal light M and the reference pulse light L2 is adjusted by the measurement side delay means 31 and the reference side delay means 32, either one may be used as the optical delay means. Good. Furthermore, although the detection means 50 of the first and second embodiments is configured as a balanced homodyne detection system using the two detectors 52 and 53, the interference light is detected by one detector. It is also possible.

It is a figure explaining the principle of cavity ring down spectroscopy (CRDS). It is a mimetic diagram showing composition of a 1st embodiment of an absorption measuring device concerning the present invention. It is a schematic diagram which shows the structure of 2nd Embodiment of the absorption measuring device which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Absorption measuring device, 10 ... Cavity ring down (CRD) part, 11 ... Cavity, 11a, 11b ... Mirror, 20 ... Light supply means, 23 ... Semiconductor laser (light supply means), 21 ... Laser light source (pulse light source part) , 22... Optical branching unit, 31... Measurement side delay means (optical delay means), 32... Reference side delay means (optical delay means), 50. Plate, L1 ... Measurement pulse light, L1 _n ... Transmission pulse light, L2 ... Reference pulse light, M ... Signal light, R1 ... Optical path of measurement pulse light (signal light), R2 ... Optical path of reference pulse light, S ... Measured sample.

Claims (6)

Light supply means for outputting measurement pulse light and reference pulse light having the same center frequency on different optical paths, and
A sample to be measured is introduced into a cavity constituted by a pair of mirrors facing each other, and a cavity ring-down portion disposed on the optical path of the measurement pulse light,
Signal light consisting of a plurality of transmitted pulse lights output from the cavity ring-down portion in response to multiple reflection of the measurement pulse in the cavity in the cavity ring-down portion where the measurement pulse light is incident, and the reference pulse light Optical delay means for adjusting the delay time between
Detecting means for detecting interference light between the signal light and the reference pulse light by causing the signal light and the reference pulse light to interfere with each other;
Analysis means for determining absorption characteristics of the sample to be measured based on temporal changes in the intensity of the interference light detected by the detection means;
An absorption measuring device comprising: The light supply means includes
A pulse light source unit that outputs pulsed light;
A light branching unit that branches the pulsed light output from the pulsed light source unit into the measurement pulsed light and the reference pulsed light, and outputs the measurement pulsed light and the reference pulsed light on different optical paths;
The absorption measuring device according to claim 1, wherein The light supply means includes
The absorption measurement apparatus according to claim 1, wherein the absorption measurement apparatus is a semiconductor laser that outputs the measurement pulse light from one of end faces facing each other and outputs the reference pulse light from the other end face. The optical delay means is
The optical path length provided in at least one of the optical path of the said measurement pulse light and the optical path of the said reference pulse light consists of a delay optical system with which variable is possible, The any one of Claims 1-3 characterized by the above-mentioned. The absorption measuring device according to 1. Modulation means for modulating an optical path length difference between the signal light and the reference pulse light;
5. The absorption measurement apparatus according to claim 1, wherein the modulation unit is provided on an optical path of at least one of the measurement pulse light and the reference pulse light.   The absorption measurement according to claim 1, wherein the light supply unit, the cavity ring-down unit, the optical delay unit, and the detection unit are provided on the same support plate. apparatus.

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