JP4588601B2 - Spectroscopic method and spectroscopic apparatus - Google Patents

Description

  The present invention relates to a ring-down spectroscopic method using an optical fiber and a spectroscopic device therefor.

As is well known, in cavity ring-down spectroscopy, a cavity is formed by at least two mirrors, a substance to be inspected (sample) is introduced into the cavity, and is attenuated by light absorption of the sample in the cavity. The sample is spectrally analyzed using ring-down pulsed light. In cavity ring-down spectroscopy, an absorption coefficient at each wavelength of a sample is obtained by measuring an attenuation constant in attenuation of light intensity mainly due to light absorption, and the sample is identified and quantified. In addition, as shown in Patent Documents 3 and 4 below, pulse light is circulated through a loop fiber instead of a cavity, or pulse light is reciprocated through a straight fiber reflected at an end face, thereby improving ring-down characteristics of the pulse light. A method for obtaining absorption characteristics of a substance by measurement is known.
JP 2000-338037 A JP 2001-194299 A JP 2004-333337 A USP 6,842,548B2

However, in any of the ring-down spectroscopy methods described above, the light used is a pulse laser, and continuous light cannot be used. For this reason, a special apparatus for obtaining a pulse laser is required, and it is difficult to adjust the output of the pulse laser.
The present inventors have examined whether ring-down spectroscopy is possible using continuous light, and have completed the present invention.
Therefore, an object of the present invention is to realize ring-down spectroscopy using continuous light.

The invention of claim 1 is a spectroscopic method for measuring a light absorption property of a sample, wherein an optical fiber that guides light to a sample whose light absorption property is to be measured and a first optical transmission line that propagates continuous light are optically coupled, By reducing this optical coupling stepwise or increasing it in pulses, light that changes stepwise or in pulses is introduced into the optical fiber, and ring-down light that circulates or reciprocates through the optical fiber is externally applied. And the absorption characteristic of the sample is measured from the attenuation characteristic of the ring-down light.
According to a second aspect of the present invention, there is provided a spectroscopic method for measuring light absorption characteristics of a sample, comprising: an optical fiber that guides light to a sample whose light absorption characteristics are to be measured; and a first optical transmission line that propagates continuous light. By optically coupling and changing the polarization direction of continuous light propagating through the first optical transmission line stepwise or in pulses, only light polarized in a predetermined direction is introduced into the optical fiber, and the optical fiber is circulated or reciprocated. In this spectroscopic method, the moving ring-down light is output to the outside and the absorption characteristic of the sample is measured from the attenuation characteristic of the ring-down light.

In the above two methods, the optical fiber may be formed in a loop shape, and light may be circulated through the loop-shaped optical fiber. Alternatively, the optical fiber may be formed in a linear shape, and both end faces thereof may be reflecting surfaces. The light may be reciprocated.
A laser or LED light source can be used for the light. As the laser, any laser such as a normal semiconductor laser, other solid-state laser, or gas laser can be used. By using a wavelength tunable laser, the wavelength absorption characteristics of the sample can be measured. When a broadband supercontinuum laser is used, the wavelength absorption characteristic can be obtained by wavelength analysis of ring-down pulse light received by the light receiving element. When optical coupling is decreased stepwise, it means that the amplitude of light introduced into the optical fiber is decreased stepwise. When optically coupled in a pulsed manner, it means that the optical coupling is performed only for a short pulse period. Therefore, the amplitude of the light incident on the optical fiber becomes a step decreasing function or a pulse function. When the polarization direction is changed, there are a case where it is changed stepwise and a case where it is changed in pulses. When changing stepwise, the polarization direction is changed from a steep direction to another direction, and when changing in a pulse manner, the polarization direction is changed to a steep direction and the original polarization is changed. It means changing to wave direction or other polarization direction.

According to a third aspect of the present invention, there is provided a spectroscopic device for measuring a light absorption characteristic of a sample. First, an optical fiber that guides light to a sample whose light absorption characteristic is to be measured; Output the optical transmission path, the optical coupling control element that reduces or increases the coupling from the first optical transmission path to the optical fiber stepwise, and ring-down light that circulates or reciprocates through the optical fiber. A spectroscopic device having a processing device for measuring the absorption characteristic of the sample from the attenuation characteristic of the ring-down light.
In this apparatus, by providing an optical coupling control element that decreases or increases the coupling from the first optical transmission line to the optical fiber in a stepwise manner, the amplitude changes from a continuous light to a step decreasing function or a pulse function. It is characterized in that light is incident on an optical fiber.

According to a fourth aspect of the present invention, there is provided a spectroscopic device for measuring a light absorption characteristic of a sample. First, an optical fiber that guides light to a sample whose light absorption characteristic is to be measured; An optical transmission line; a polarization control element that changes the polarization direction of continuous light propagating through the first optical transmission line in a stepwise or pulse manner; and an optical coupling element that splits light polarized in a predetermined direction into an optical fiber. And a processing device that outputs ring-down light that circulates or reciprocates through the optical fiber to the outside and measures the absorption characteristics of the sample from the attenuation characteristics of the ring-down light.
This device changes the polarization direction of continuous light stepwise or in a pulse manner so that only light polarized in a predetermined direction is guided to the optical fiber, and the amplitude changes in a step decreasing function or a pulse function. It is characterized in that light is incident on an optical fiber.

  The invention according to claim 5 further includes a first polarizer that is provided in front of the incident side of the light receiving element provided at one end of the first optical transmission line and allows only light polarized in a predetermined direction to pass therethrough. The spectroscopic device according to claim 4.

The invention described in claim 6 further includes a second polarizer that is provided in front of the incident side of the optical coupling element in the first optical transmission line and polarizes continuous light in a direction different from a predetermined direction. The spectroscopic device according to item 4 or claim 5.
The invention according to claim 7 is characterized in that the ring-down light is output to the first optical transmission line by an optical coupling element in the optical fiber. It is a spectroscopic device.

  According to the eighth aspect of the present invention, ring-down light is output to a second optical transmission line different from the first optical transmission line by another optical coupling element disposed at a position different from the optical coupling element in the optical fiber. The spectroscopic device according to claim 3, wherein a processing device is connected to the second optical transmission line.

In the method of claim 1, the coupling between the first optical transmission line for propagating continuous light and the optical fiber is changed stepwise or in pulses. Therefore, in the optical fiber, the light amplitude can be reduced stepwise or light that changes in a pulse manner can be introduced. In the method of claim 2, the polarization direction of the continuous light propagating through the first optical transmission line is changed stepwise or pulsewise. The first optical transmission line and the optical fiber are optically coupled so that only light polarized in a predetermined direction is introduced from the first optical transmission line into the optical fiber. Thereby, only the light polarized in a predetermined direction is introduced into the optical fiber. That is, in the optical fiber, pulsed light polarized in a predetermined direction is introduced, or continuous light polarized in a predetermined direction decreases stepwise.
In this aspect, the light circulates or reciprocates through the optical fiber, and the amplitude of the light is attenuated by the absorption of the sample. The ring-down light is output to the outside, and the absorption characteristic of the sample can be measured from the attenuation characteristic of the ring-down light. If the wavelength of the continuous light is changed, the wavelength absorption characteristic of the sample can be obtained. This enables sample identification analysis.

In the device invention of claim 3, since the optical coupling control element for decreasing or increasing the coupling from the first optical transmission line to the optical fiber in a stepwise manner is provided, the amplitude of light is stepwise in the optical fiber. It is possible to introduce light that is reduced or pulsed. In the device invention of claim 4, the polarization direction of the continuous light propagating through the first optical transmission line can be changed stepwise or pulsed by the polarization control element. Further, only the light polarized in a predetermined direction is branched into the optical fiber by the optical coupling element.
Therefore, in an optical fiber, continuous light can be reduced stepwise or pulsed light can be propagated. In other words, in the present invention, pulsed light polarized in a predetermined direction or light that decreases in steps is obtained by the polarization control element and the optical coupling element.
In Claims 3 and 4, this light circulates or reciprocates through the optical fiber, and the amplitude of the pulsed light is attenuated by light absorption by the sample, whereby ring-down light is obtained. The ring-down light is output to the outside, and the absorption characteristic of the sample is measured from the attenuation characteristic of the ring-down light by the processing device. If the wavelength of the continuous light introduced into the first optical transmission line is changed, the wavelength absorption characteristic of the sample can be obtained. This enables sample identification analysis.

In the device invention of claim 5, since the first polarizer that is provided in front of the light receiving element provided at one end of the first optical transmission line and passes only light polarized in a predetermined direction is provided, Only the ring-down light polarized in the predetermined direction can be detected by the light receiving element. When changing stepwise, in the first optical transmission line, the light that has passed through the polarization control element propagates polarized light in a predetermined direction, and after the step change, the polarization differs from the predetermined direction. Wave direction. When the pulse is changed, the light that has passed through the polarization control element in the first optical transmission line propagates the light that is pulse-polarized in a fixed direction, and is different from the predetermined direction in other time intervals. Light polarized in the direction propagates.
Therefore, in the measurement period of the ring-down light, the light that has passed through the polarization control element with the light from the light source does not include the light polarized in a predetermined direction, so the continuous light from the light source is the first polarizer. And is not received by the light receiving element, so that the continuous light does not hinder the reception of the ring-down light.

  In the device invention of claim 6, the continuous light is polarized in a direction different from the predetermined direction by the second polarizer provided in front of the incident side of the optical coupling element in the first optical transmission line. For example, if polarized light in a predetermined direction is P-polarized light, polarized light in a different direction is S-polarized light. It is sufficient that the polarization directions are different, and the polarization directions are not necessarily different by 90 degrees. As a result, the test control P-polarized light or the pulsed P-polarized light can be obtained by the polarization control element. In the first polarizer, light polarized in a direction different from a predetermined direction (for example, S-polarized light) is blocked. For example, only P-polarized ring-down light is allowed to pass through the first polarizer to be received by the light receiving element. It can be made incident.

  In the device invention of claim 7, ring-down light is output to the first optical transmission line by an optical coupling element in the optical fiber. In other words, the optical coupling element for introducing light into the optical fiber and the optical coupling element for deriving ring-down light from the optical fiber are used in common, and this can be realized by using a directional optical coupling element. .

  In the device invention of claim 8, the ring-down light is output to the second optical transmission line different from the first optical transmission line by another optical coupling element arranged at a position different from the optical coupling element in the optical fiber. Yes. Accordingly, since continuous light does not enter the light receiving element, ring-down light derived from the optical fiber can be reliably received by the light receiving element.

  The present invention will be described based on specific examples, but the present invention is not limited to the following examples.

  As shown in FIG. 1, the first optical transmission line 12 for introducing light is optically coupled to the loop optical fiber 10 by a directional optical coupling element 36. A sample 40 is inserted into the transmission path of the loop-shaped optical fiber 10. The sample 40 is provided in a space between the end faces by cutting the optical fiber 10 so that the end faces face each other. The sample 40 is configured to pass light. The first optical transmission line 12 is composed of an optical fiber. A laser device 30 capable of outputting continuous laser light is connected to one end of the optical fiber, and the other end is received by a light receiving element 32 and a light receiving element 32. A processing unit 34 is provided for calculating an attenuation coefficient from the ring-down pulse. The processing device according to the claims includes a light receiving element 32 and a processing device 34.

  The first optical transmission line 12 is provided with a directional optical coupling element 36 that optically couples the loop-shaped optical fiber 10 and the first optical transmission line 12. A second polarizer 21 is provided in front of the directional optical coupling element 36 on the laser light incident side, and a first polarizer 22 is provided in front of the light receiving element 32 on the laser light incident side. A Faraday polarizer 23 which is a polarization control element is provided in front of the directional optical coupling element 36 on the laser light incident side. For example, the second polarizer 21 is an element that outputs only the S-polarized light component. The Faraday polarizer 23 is an element that applies a magnetic field in the transmission path direction according to a control signal from the processing device 34, rotates the polarization by 90 degrees, and changes the polarization from, for example, S polarization to P polarization. The directional optical coupling element 36 is an element that branches only the P-polarized light to the optical fiber 10 only in the traveling direction. The first polarizer 22 is an element that allows only light polarized in a predetermined direction, for example, P-polarized light to pass therethrough.

  The continuous laser light output from the laser device 30 enters the second polarizer 21, and only the S-polarized component is output to the first optical transmission line 12. The S-polarized continuous laser light passes through the Faraday polarizer 23 to which no magnetic field is applied, and enters the directional optical coupling element 36. However, since the directional optical coupling element 36 branches only the P-polarized light to the optical fiber 10, no laser light is output to the optical fiber 10 in this state. The S-polarized continuous laser light that has passed through the directional optical coupling element 36 is incident on the first polarizer 22, but the first polarizer 22 passes only the P-polarized light. It does not enter the light receiving element 32. Therefore, the continuous laser light output from the laser device 30 does not enter the light receiving element 32 and does not prevent the light receiving element 32 from receiving the ring-down pulse light.

  When a pulse magnetic field is applied to the Faraday polarizer 23 by the pulse control signal output from the processing device 34, the laser light passing through the Faraday polarizer 23 during this application period has a 90-degree phase from S-polarized light to P-polarized light. Rotate. That is, pulse P-polarized light is obtained at the output of the Faraday polarizer 23, and is continuously S-polarized light outside that period. The pulsed P-polarized laser light is incident on the directional optical coupling element 36, branched to the optical fiber 10, and circulated through the optical fiber 10 clockwise in the drawing. Each time it circulates, light absorption occurs in the sample, and the amplitude of the pulsed P-polarized laser light decreases sequentially. That is, P-polarized ring-down pulsed light is obtained. Each time this ring-down pulse light circulates, a part of the light is branched to the first optical transmission line 12 via the directional optical coupling element 36. Since it is P-polarized light, it is partially branched to the first optical transmission line 12 side by the directional optical coupling element 36 and enters the first polarizer 22. Since the first polarizer 22 passes only P-polarized light, the ring-down pulse light is incident on the light receiving element 32.

  By measuring the ring-down time constant of the P-polarized ring-down pulsed light with the light receiving element 32 and the processing device 34, it is possible to measure the attenuation coefficient of the sample at the wavelength of the laser light. By performing this measurement while changing the wavelength of the continuous laser light, the wavelength absorption characteristics of the sample can be obtained, and the atomic and molecular structure of the sample can be specified.

For example, if the total length of the optical fiber 10 is 6 cm, a ring-down pulse is output every 2 × 10 ⁻¹⁰ sec, so the frequency of the control signal applied from the processing device 34 to the Faraday polarizer 23, that is, the pulse P If the repetition frequency of polarized laser light is 50 MHz (period 2 × 10 ⁻⁸ ec), 100 ring-down pulses can be allowed during one pulse period. If the repetition frequency is 5 MHz, 1000 ring-down pulses can be allowed. If the total length of the optical fiber 10 is 6 m, a ring-down pulse is output every 2 × 10 ⁻⁸ ec. Therefore, if 100 ring-down pulses are allowed during one pulse period, the pulse period is If it is necessary to set the frequency to 500 kHz and 1000 ring-down pulses are allowed during one pulse period, the pulse period needs to be 50 kHz.

On the other hand, the pulse width of the pulsed P-polarized laser light needs to be shorter than the period of the ring-down pulse. Therefore, when the total length of the optical fiber 10 is 6 cm, it may be shorter than 2 × 10 ⁻¹⁰ sec. Necessary. Further, when the total length of the optical fiber 10 is 6 m, the pulse width of the laser light should be shorter than 2 × 10 ⁻⁸ ec. Therefore, shortening the pulse width of the laser light leads to shortening the overall length of the optical fiber 10, and the device configuration can be reduced in size.

  In addition, since the measurement system itself is attenuated, in reality, the ring-down characteristic of the pulsed P-polarized laser beam when no sample is present is measured as a reference characteristic, and the pulsed P-polarized laser when the sample is measured. The absorption coefficient of the sample is measured using the attenuation characteristic of the deviation of the light ring-down characteristic from the reference characteristic. The absorption coefficient may be calculated from an exponential decay coefficient when the horizontal axis is the number of ringdowns and the vertical axis is the amplitude of the ringdown pulse. Further, the wavelength absorption characteristic can be obtained by changing the wavelength of the laser beam and measuring the attenuation coefficient of the ring-down characteristic in the same manner. Even if the absolute value of the absorption coefficient is unknown, the sample can be identified if the relative absorption characteristic is obtained as the wavelength characteristic.

  In the above embodiment, the directional optical coupling element 36 is generally well known. With this directional coupling element, a ring-down pulse of laser light can be extracted to the light receiving element 32. Further, the intensity of light circulating through the optical fiber 10 can be adjusted by changing the coupling rate. Thereby, since the attenuation width of the light received by the light receiving element 32 can be adjusted, the attenuation coefficient can be measured with the same dynamic range, and the accuracy can be improved.

Next, a second embodiment which is a specific embodiment of the present invention will be described. In FIG. 2, the configuration of the first optical transmission line 12, the loop-shaped optical fiber 10, the insertion position of the sample 40, the laser device 30, the light receiving element 32, and the processing device 34 is the same as that of the first embodiment.
In this embodiment, the laser light input system and the laser light output system for the optical fiber 10 are separated. The input system is substantially the same as that of the first embodiment except that a terminal 24 that does not transmit or reflect light is used instead of the first polarizer 22. As a newly provided laser beam output system, a second directional optical coupling element 37 optically coupled to the optical fiber 10, a second optical transmission line 13 coupled to the optical fiber 10 by the second directional optical coupling element 37, A termination terminal 25 is provided. The light receiving element 32 is connected to one end of the second optical transmission line 13.

  In this embodiment, the method for guiding the pulsed P-polarized laser light to the optical fiber 10 is the same as that in the first embodiment. The ring-down pulse light circulating through the optical fiber 10 enters the light receiving element 32 via the second directional optical coupling element 37 and the second optical transmission path 13. In this case, since the input system and the output system are separated, it is not necessary to use a polarizer or a polarizing directional coupling element for the second optical transmission line 13 that is the output system.

  In the above embodiment, the optical fiber 10 is configured in a loop shape, but it may be a straight line or a curved line as shown in FIG. That is, the linear optical fiber 100 is coupled to the first optical transmission line 12 by the directional optical coupling element 36. Then, both ends of the optical fiber 100 are mirror surfaces 42 and 43 so as to reflect light. Even in this case, pulsed P-polarized laser light traveling back and forth through a linear or curved optical fiber 100 that is not a loop can be output to the light receiving element 32 side. At this time, only the ring-down pulse light propagating through the optical fiber 100 toward the sample 40 can be output to the first optical transmission line 12 and incident on the light receiving element 32 by the function of the directional optical coupling element 36. Other configurations are the same as those of the first embodiment.

The present embodiment excludes the first polarizer 22, the second polarizer 21, and the Faraday polarizer 23 which is a polarization control element in the configuration of the second embodiment, and instead of the directional optical coupling element 36, the optical coupling control is performed. It is characterized in that a piezo drive coupling rate variable coupler 136 as an element is provided. Other configurations are the same as those of the second embodiment. The piezo drive coupling rate variable coupler 136 is an element that controls the coupling rate by using an electro-optic effect, and is an element that can control the optical coupling rate by applying a voltage. By applying a pulse voltage to the piezo drive coupling rate variable coupler 136 to increase the coupling rate in a pulse manner, pulsed light can be incident on the optical fiber 10. The fact that the ring-down characteristic of the pulsed light is detected by the light receiving element 32 is the same as in the second embodiment.
The optical coupling control element may be an optical switch instead of the piezo drive coupling rate variable coupler. That is, even if the optical switch element that can connect and disconnect the optical fiber 10 from the first optical transmission line 12 at a high speed is used, pulsed light or step-reduced light can be incident on the optical fiber 10.

[Modification]
In all the embodiments described above, the light propagating through the optical fibers 10 and 100 may be replaced with pulsed light, and may be light that decreases in steps. In this case, in the first to third embodiments, a continuous magnetic field is applied to the Faraday polarizer 23 by a continuous control signal output from the processing device 34. As a result, the S-polarized continuous laser light output from the second polarizer 21 is converted into P-polarized light by the Faraday polarizer 23. P-polarized laser light is incident on the optical fibers 10 and 100 via the directional optical coupling element 36. Next, the continuous control signal is cut off, and the application of the magnetic field to the Faraday polarizer 23 is stopped. Then, the output of the Faraday polarizer 23 becomes S-polarized continuous laser light, and this light does not enter the optical fibers 10 and 100. Therefore, in the optical fibers 10 and 100, the amplitude of the P-polarized laser light is decreased stepwise. It is possible to measure the absorptance of the sample by detecting the ring-down light of this step-decreasing light and measuring the attenuation constant.

  In the fourth embodiment, the coupling ratio between the first optical transmission line 12 and the optical fiber 10 is increased by the piezo drive coupling ratio variable coupler 136 in the initial state, and continuous laser light is incident on the optical fibers 10 and 100. Let Next, the piezo drive coupling rate variable coupler 136 is controlled to reduce the coupling rate between the first optical transmission line 12 and the optical fiber 10 stepwise. Then, the continuous laser light incident on the optical fibers 10 and 100 is blocked stepwise. It is possible to measure the absorptance of the sample by detecting the ring-down light of this step-decreasing light and measuring the attenuation constant.

  In all embodiments, an optical amplifier such as a fiber amplifier may be inserted into the optical fibers 10 and 100 to amplify the laser light. For example, when the sample 40 is not present, the amplification factor of the optical amplifier is set so that there is no attenuation of the ring-down light, the sample 40 is installed, and the attenuation constant of the ring-down light is measured. Only the absorption coefficient can be obtained accurately. Further, the amplification factor of the optical amplifier may be feedback controlled so that ring-down light is not attenuated, and the light absorption coefficient of the sample may be measured from this amplification factor. In this case, since the absorption coefficient can be measured with the amplitude of the light incident on the sample being constant, the nonlinear effect can be eliminated, and the absorption coefficient with respect to the light intensity can be accurately measured. it can. In other words, if the above measurement is performed while changing the intensity of the laser beam, the nonlinear characteristic of the absorption coefficient of the sample can be obtained.

  In all the embodiments, an optical switch may be used instead of the directional optical coupling element 36. That is, the mode in which the first optical transmission line 12 and the optical fibers 10 and 100 are coupled in the light propagation direction, the mode in which the optical fibers 10 and 100 are closed, and the light propagated through the optical fibers 10 and 100 are You may use the optical switch which can switch the mode propagated to the downstream of 1 optical transmission path 12. FIG. It is good also as an optical switch element which switches a switch terminal synchronizing with the period of ringdown pulse light.

  INDUSTRIAL APPLICABILITY The present invention is effective for spectroscopic analysis of liquids with small light absorption, biological materials such as gas, DNA, protein, and solids such as organic, inorganic materials, and thin films.

The block diagram which showed the apparatus which concerns on the specific Example 1 of this invention. The block diagram which showed the apparatus which concerns on the specific Example 2 of this invention. The block diagram which showed the apparatus which concerns on the specific Example 3 of this invention. The block diagram which showed the apparatus which concerns on the specific Example 4 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10,100 ... Optical fiber 21 ... 2nd polarizer 22 ... 1st polarizer 23 ... Faraday polarizer 12 ... 1st optical transmission path 13 ... 2nd optical transmission path 36, 37 ... Directional optical coupling element 136 ... Piezo drive coupling Variable rate coupler

Claims (8)

In a spectroscopic method for measuring the light absorption characteristics of a sample,
By optically coupling an optical fiber that guides light to a sample whose light absorption characteristics are to be measured and a first optical transmission path that propagates continuous light, the optical coupling is changed stepwise or in a pulse manner. In addition, light that changes in a pulsed manner is introduced into the optical fiber, ring-down light that circulates or reciprocates through the optical fiber is output to the outside, and the absorption characteristics of the sample are measured from the attenuation characteristics of the ring-down light. Spectroscopic method characterized by the above. In a spectroscopic method for measuring the light absorption characteristics of a sample,
An optical fiber that guides light to a sample whose light absorption characteristic is to be measured and a first optical transmission path that propagates continuous light are optically coupled, and the polarization direction of continuous light that propagates through the first optical transmission path is stepwise or By changing in a pulse manner, only the light polarized in a predetermined direction is introduced into the optical fiber, and ring-down light that circulates or reciprocates through the optical fiber is output to the outside. A spectroscopic method characterized by measuring absorption characteristics. In a spectroscopic device that measures the light absorption characteristics of a sample,
An optical fiber that directs light to the sample whose light absorption characteristics are to be measured;
A first optical transmission line that is optically coupled to the optical fiber and propagates continuous light;
An optical coupling control element for decreasing or pulsingly increasing the coupling from the first optical transmission line to the optical fiber;
A spectroscopic device comprising: a processing device that outputs ring-down light that circulates or reciprocates through the optical fiber and measures the absorption characteristics of the sample from the attenuation characteristics of the ring-down light. In a spectroscopic device that measures the light absorption characteristics of a sample,
An optical fiber that directs light to the sample whose light absorption characteristics are to be measured;
A first optical transmission line that is optically coupled to the optical fiber and propagates continuous light;
A polarization control element that changes the polarization direction of continuous light propagating through the first optical transmission path in a stepwise manner or in a pulse manner;
An optical coupling element for branching light polarized in a predetermined direction into the optical fiber;
A spectroscopic device comprising: a processing device that outputs ring-down light that circulates or reciprocates through the optical fiber and measures the absorption characteristics of the sample from the attenuation characteristics of the ring-down light.   The spectroscope according to claim 4, further comprising: a first polarizer that is provided in front of an incident side of a light receiving element provided at one end of the first optical transmission path and transmits only light polarized in the predetermined direction. apparatus.   6. The device according to claim 4, further comprising: a second polarizer that is provided in front of an incident side of the optical coupling element in the first optical transmission line and polarizes the continuous light in a direction different from the predetermined direction. The spectroscopic device described.   The spectroscopic device according to claim 4, wherein the ring-down light is output to the first optical transmission line by the optical coupling element in the optical fiber. The other optical coupling element disposed at a position different from the optical coupling element in the optical fiber causes the ring-down light to be output to a second optical transmission line different from the first optical transmission line, and this second optical transmission line The spectroscopic apparatus according to claim 3, wherein the processing apparatus is connected to the spectroscopic apparatus.

Images