JP2012242280A - Detection system, michelson interferometer, and fourier transformation spectroscopic analyzer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a detection system capable of easily detecting whether or not laser light is being emitted from a semiconductor laser in a state where one vertical mode and two vertical modes coexist.SOLUTION: A detection system includes: a fixed mirror 15; a movable mirror 16; light flux branch means 14 for dividing laser light emitted from a semiconductor laser 22 and synthesizing the laser light reflected respectively against the fixed mirror 15 and the movable mirror 16; light reception means 25 for receiving the laser light synthesized by the light flux branch means 14; and a control part 26. When the detection system performs the detection, the control part 26 moves the movable mirror 16 so as to change an optical path difference between the laser light to be reflected against the fixed mirror 15 and the laser light to be reflected against the movable mirror 16. The detection is performed based on whether or not the interference signal of the laser light to be received by the reception means 25 becomes discontinuous by a change in the contrast of the laser light.

Description

  The present invention relates to a detection system, a Michelson interferometer, and a Fourier transform spectroscopic analyzer, and in particular, a laser beam is emitted from a semiconductor laser in a state where both one longitudinal mode and two longitudinal modes are mixed. The present invention relates to a detection system for detecting whether there is a detection system, a Michelson interferometer including the detection system, and a Fourier transform spectroscopic analysis apparatus including the Michelson interferometer.

  As disclosed in U.S. Patent Application Publication No. 2004/0071173 (Patent Document 1), semiconductor lasers are widely used in applications such as testing, measurement, or analysis. In such a field, a DBR (Distributed Bragg Reflector) type semiconductor laser, a DFB (Distributed Feedback) type semiconductor laser, or the like is used as a semiconductor laser.

  In these semiconductor lasers, a semiconductor is used as an active region. The refractive index of a semiconductor varies depending on the magnitude of current that flows in the semiconductor (the density of carriers that flow into the semiconductor), the temperature of the semiconductor, and the like. For this reason, in general, the wavelength of laser light emitted from a semiconductor laser is easily affected by a change in the magnitude of a current flowing through the semiconductor or a change in the temperature of the semiconductor.

  In many applications such as sensing or spectroscopy, it is important that the semiconductor laser emits laser light in one longitudinal mode (single mode). However, there is a case where laser light is emitted from the semiconductor laser in a state where both one longitudinal mode and two longitudinal modes coexist depending on the magnitude of the current flowing in the semiconductor or the temperature of the semiconductor. In this case, it is difficult to obtain a desired result in sensing or spectroscopy using a semiconductor laser.

US Patent Application Publication No. 2004/0071173

  The present invention provides a detection system capable of easily detecting whether or not laser light is emitted from a semiconductor laser in a state where both one longitudinal mode and two longitudinal modes are mixed. It is an object of the present invention to provide a Michelson interferometer and a Fourier transform spectroscopic analyzer including the Michelson interferometer.

  The detection system based on this invention is a detection system which detects whether the laser beam is radiate | emitted from the semiconductor laser in the state where both one longitudinal mode and two longitudinal modes coexist, Comprising: 1st reflection And means for dividing the laser light emitted from the semiconductor laser into laser light directed to the first reflective means and laser light directed to the second reflective means, and the first reflective means and the second reflective means A light beam splitting unit configured to combine the laser beams reflected by each of the second reflection units, a light receiving unit configured to receive the laser light combined by the beam splitting unit, and a control unit. When detecting whether laser light is emitted from the semiconductor laser in a state where both the longitudinal mode and the two longitudinal modes are mixed The control unit is configured to change the optical path difference between the laser beam reflected by the first reflecting unit and the laser beam reflected by the second reflecting unit, and / or the second reflecting unit and / or the second reflecting unit. When the interference signal of the laser beam received by the light receiving unit becomes discontinuous due to the change in the contrast of the laser beam, the control unit has one longitudinal mode and two longitudinal modes. It is determined that laser light is emitted from the semiconductor laser in a state where both of the above are mixed.

  Preferably, the semiconductor laser is a wavelength stabilized semiconductor laser using a diffraction grating. Preferably, when it is determined that the semiconductor laser emits laser light in a state where both one longitudinal mode and two longitudinal modes are mixed, the control unit performs the above operation in one longitudinal mode. The operating current value of the semiconductor laser is changed so that the semiconductor laser emits laser light.

  Preferably, the optical path difference between the laser light reflected by the first reflecting means and the laser light reflected by the second reflecting means is predetermined by the movement of the first reflecting means and / or the second reflecting means. The control unit stores in advance the coherence distance of the laser light in a state in which the semiconductor laser is emitted in two longitudinal modes, and the detection system has 1 When detecting whether or not laser light is emitted from the semiconductor laser in a state where both of the two longitudinal modes and the two longitudinal modes are mixed, the control unit has the maximum value of the optical path difference as described above. The first reflecting means and / or the second reflecting means is moved so as to be longer than the coherence distance, and the light receiving means is moved until the optical path difference changes from a predetermined value to the maximum value. When the interference signal of the received laser beam becomes discontinuous due to a change in the contrast of the laser beam, the control unit is in a state where both one longitudinal mode and two longitudinal modes are mixed. Thus, it is determined that laser light is emitted from the semiconductor laser.

  A Michelson interferometer according to the present invention includes the detection system according to the present invention, and a detector that detects the laser light combined by the light beam splitting means as interference light, and the first reflecting means includes: It is a fixed mirror, and the second reflecting means is a moving mirror.

  Preferably, the optical path correction device further corrects the inclination of the fixed mirror, the light receiving means includes two or more light receiving elements, and the control unit transmits laser light received by each of the two or more light receiving elements. The signal phases are compared with each other, and the optical path correction device is driven to correct the tilt of the fixed mirror so that there is no difference between the signal phases.

  The Fourier transform spectroscopic analyzer based on this invention is provided with the calculating part which calculates the spectrum of the said interference light which the said detector detected, and the output part which outputs the said spectrum obtained by the said calculating part.

  According to the present invention, a detection system capable of easily detecting whether or not laser light is emitted from a semiconductor laser in a state where both one longitudinal mode and two longitudinal modes coexist, and its detection A Michelson interferometer equipped with the system and a Fourier transform spectroscopic analyzer equipped with the Michelson interferometer can be obtained.

It is a figure which shows typically the Michelson interferometer provided with the detection system in embodiment, and the Fourier-transform spectroscopy analyzer provided with the Michelson interferometer. It is a front view which shows the structure of the reference detector used for the detection system in embodiment. (A) is a figure which shows the time-dependent change of the intensity | strength of a part of interference light which the reference detector used for the detection system in embodiment detected. (B) is a figure which shows the time-dependent change of the intensity | strength of the remainder of the interference light which the reference detector used for the detection system in embodiment detected. It is a figure which shows the relationship between the wavelength of a laser beam, and the intensity | strength of a laser beam in case the reference light source is radiate | emitting a laser beam by two longitudinal modes. It is a figure which shows the relationship between the optical path difference formed with the laser beam radiate | emitted from a reference light source, and the interference light intensity | strength of the laser beam. It is the figure which showed the interference signal and signal intensity | strength detected by the light receiving element in case the reference light source is radiating | emitting a laser beam by one longitudinal mode as a relationship between time and a signal voltage. When the reference light source emits laser light in a state where one longitudinal mode and two longitudinal modes are mixed, the interference signal detected by the light receiving element and the signal intensity are related to time and the signal voltage. It is the figure shown as. It is the figure which showed the relationship between the drive current value added to a reference light source, and the wavelength of the laser beam radiate | emitted from a reference light source.

  Embodiments based on the present invention will be described below with reference to the drawings. In the description of the embodiments, when referring to the number, amount, and the like, the scope of the present invention is not necessarily limited to the number, amount, or the like unless otherwise specified. In the description of the embodiments, the same parts and corresponding parts are denoted by the same reference numerals, and redundant description may not be repeated.

[Embodiment]
(Fourier transform spectroscopic analyzer 100 / Michelson interferometer 10)
With reference to FIG. 1, a Fourier transform spectroscopic analyzer 100 in the embodiment will be described. The Fourier transform spectroscopic analysis apparatus 100 includes a Michelson interferometer 10, a calculation unit 20, and an output unit 30. The Michelson interferometer 10 includes a spectroscopic optical system 11, a reference optical system 21 as a detection system, and an optical path correction device 28.

(Spectral optical system 11)
The spectroscopic optical system 11 includes a light source 12, a collimating optical system 13, a beam splitter 14 (light beam splitting means), a fixed mirror 15 (first reflecting means), a moving mirror 16 (second reflecting means), a condensing optical system 17, and a detection. And a translation mechanism 19.

  The light source 12 includes a light emitting element such as a lamp having a color temperature of 2900K, and emits lamp light such as infrared light. The lamp light emitted from the light source 12 is introduced into an optical path combining mirror 23 in the reference optical system 21 (details will be described later), and is combined with the laser light emitted from the reference light source 22 (details will be described later). The combined light formed by combining the lamp light and the laser light is emitted from the optical path combining mirror 23, converted into parallel light by the collimating optical system 13, and then introduced into the beam splitter 14. The beam splitter 14 is composed of a half mirror or the like, and can branch light of an arbitrary wavelength at an arbitrary ratio by design. The beam splitter 14 may be configured using an optical thin film, a polarizing plate, or a combination of these. The combined light (incident light) introduced into the beam splitter 14 is split into two light beams.

  One of the divided combined lights (including laser light) is directed to the fixed mirror 15 and irradiated onto the fixed mirror 15. The combined light (reflected light) reflected by the fixed mirror 15 passes through substantially the same optical path as before the reflection and is irradiated again to the beam splitter 14. The other of the divided synthesized light (including laser light) is directed to the movable mirror 16 and is irradiated on the movable mirror 16. The combined light (reflected light) reflected by the movable mirror 16 passes through substantially the same optical path as before reflection and is irradiated again to the beam splitter 14. The reflected light from the fixed mirror 15 and the reflected light from the movable mirror 16 are combined (superposed) by the beam splitter 14.

  Here, when the other of the divided combined light is reflected by the movable mirror 16, the movable mirror 16 is reciprocated in the direction of the arrow AR while being kept parallel by the parallel movement mechanism 19. The speed of the movable mirror 16 is, for example, 100 m / sec. Due to the reciprocating movement of the movable mirror 16, a difference in optical path length (hereinafter also referred to as an optical path difference) occurs between the reflected light from the fixed mirror 15 and the reflected light from the movable mirror 16.

  Specifically, the optical path length of the combined light (including the laser light) that is split by the beam splitter 14 and irradiated again to the beam splitter 14 after being reflected by the fixed mirror 15 is represented by (L1 × 2). The optical path length of the combined light (including laser light) that is split by the beam splitter 14 and irradiated again to the beam splitter 14 after being reflected by the movable mirror 16 is represented by (L2 × 2).

  Therefore, the optical path difference between the combined light reflected by the fixed mirror 15 and the combined light reflected by the movable mirror 16 is represented by | (L2 × 2) − (L1 × 2) |. The reflected light from the fixed mirror 15 and the reflected light from the movable mirror 16 are combined with the beam splitter 14 to form interference light.

  Depending on the position of the movable mirror 16, the optical path difference | (L2 × 2) − (L1 × 2) | changes periodically. The intensity of light as interference light also changes continuously according to the optical path difference. For example, when the optical path difference is an integral multiple of the wavelength of the light emitted from the collimating optical system 13 to the beam splitter 14, the intensity of the light as interference light is maximized.

  The light that forms the interference light is applied to the sample S through the condensing optical system 17 and the optical path separation mirror 24. Specifically, the light combined by the beam splitter 14 is emitted as interference light from the beam splitter 14 and then condensed by the condensing optical system 17. The light condensed by the condensing optical system 17 is introduced into an optical path separation mirror 24 in a reference optical system 21 (details will be described later) as a detection system. One of the interference lights divided by the optical path separation mirror 24 is irradiated on the sample S. The other of the interference lights divided by the optical path separation mirror 24 is introduced into a reference detector 25 described later. The detector 18 detects the synthesized light (including laser light) that has passed through the sample S as an interference pattern (interferogram). This interference pattern is sent to a calculation unit 20 including a CPU (Central Processing Unit) and the like. The computing unit 20 converts the collected (sampled) interference pattern from an analog format to a digital format, and further performs a Fourier transform on the converted data.

  A spectral distribution indicating the light intensity for each wave number (= 1 / wavelength) of light (interference light) transmitted through the sample S is calculated by Fourier transform. The data after the Fourier transform is output to another device through the output unit 30 or displayed on a display or the like. Based on this spectral distribution, the characteristics (eg, material, structure, or amount of components) of the sample S are analyzed.

(Reference optical system 21)
The reference optical system 21 including a function as a detection system includes a collimating optical system 13, a beam splitter 14, a fixed mirror 15, a moving mirror 16, a condensing optical system 17, a reference light source 22 (semiconductor laser), an optical path synthesis mirror 23, an optical path. A separation mirror 24, a reference detector 25 (light receiving means), and a control unit 26 are included. The collimating optical system 13, the beam splitter 14, the fixed mirror 15, the moving mirror 16, and the condensing optical system 17 are common to both the spectroscopic optical system 11 and the reference optical system 21.

  The reference light source 22 is composed of a light emitting element such as a semiconductor laser, and emits laser light (wavelength is, for example, 300 nm to 1100 nm) such as red light. As the reference light source 22, a wavelength stabilized semiconductor laser using a diffraction grating such as a VHG (Volume Holographic Grating) type semiconductor laser or an FBG (Fiber Bragg Grating) type semiconductor laser may be used. Further, as the reference light source 22, a VCSEL (Vertical Cavity Surface Emitting LASER) may be used.

  As described above, the laser light emitted from the reference light source 22 is introduced into the optical path synthesis mirror 23. The optical path combining mirror 23 is composed of a half mirror or the like. The lamp light from the light source 12 passes through the optical path combining mirror 23. Laser light from the reference light source 22 is reflected by the optical path combining mirror 23.

  The lamp light from the light source 12 and the laser light from the reference light source 22 are emitted from the optical path combining mirror 23 onto the same optical path in a state where they are combined by the optical path combining mirror 23. The combined light emitted from the optical path combining mirror 23 is converted into parallel light by the collimating optical system 13 and then introduced into the beam splitter 14 and split into two light beams.

  As described above, one of the divided combined lights is irradiated on the fixed mirror 15 and again irradiated on the beam splitter 14 as reflected light. The other of the divided combined light is irradiated on the movable mirror 16 and again irradiated on the beam splitter 14 as reflected light. The reflected light from the fixed mirror 15 and the reflected light from the movable mirror 16 are combined with the beam splitter 14 to form interference light. If the above-described optical path length difference | (L2 × 2) − (L1 × 2) | can be formed, the fixed mirror 15 (first reflecting means) and the moving mirror 16 (second reflecting means) are relatively The fixed mirror 15 and the movable mirror 16 may both be configured to be movable.

  As described above, the light forming the interference light is irradiated to the sample S through the condensing optical system 17 and the optical path separation mirror 24. Specifically, the light combined by the beam splitter 14 is emitted as interference light from the beam splitter 14 and then condensed by the condensing optical system 17. The light condensed by the condensing optical system 17 is introduced into the optical path separation mirror 24 in the reference optical system 21. The optical path separation mirror 24 is constituted by a half mirror or the like, and one of the lights divided by the optical path separation mirror 24 is irradiated on the sample S. The other of the lights divided by the optical path separation mirror 24 is introduced into the reference detector 25.

  The light emitted from the light source 12 and introduced into the optical path separating mirror 24 through the optical path combining mirror 23, the collimating optical system 13, the beam splitter 14, the fixed mirror 15, the moving mirror 16, and the condensing optical system 17 is reflected by the optical path separating mirror 24. Transparent. As described above, this light (interference light) that has passed through the optical path separation mirror 24 further passes through the sample S and is then detected by the detector 18.

  On the other hand, the light emitted from the reference light source 22 and introduced into the optical path separation mirror 24 through the optical path synthesis mirror 23, the collimating optical system 13, the beam splitter 14, the fixed mirror 15, the moving mirror 16, and the condensing optical system 17 Reflected by the separation mirror 24. Reflected light (interference light) from the optical path separation mirror 24 is detected as an interference pattern by a reference detector 25 constituted by a quadrant sensor or the like.

  The interference pattern of the interference light is sent to the control unit 26 including a CPU and the like. The control unit 26 processes a signal based on the collected interference pattern and calculates the intensity of the reflected light emitted from the optical path separation mirror 24. The control unit 26 can generate a signal indicating the sampling timing in the calculation unit 20 based on the intensity of the reflected light from the optical path separation mirror 24. A signal indicating the sampling timing in the arithmetic unit 20 can be generated by a known means.

  Based on the intensity of the reflected light from the optical path separation mirror 24, the control unit 26 determines the inclination of the light between the two optical paths (the relative inclination between the reflected light from the fixed mirror 15 and the reflected light from the movable mirror 16). It can also be calculated. For example, the inclination of light between the two optical paths is calculated as follows.

  With reference to FIG. 2, the reference detector 25 comprised from a 4-part dividing sensor has the four light receiving elements E1-E4. The light receiving elements E1 to E4 are adjacent to each other in the counterclockwise direction. Reflected light from the optical path separation mirror 24 is irradiated onto the region constituted by the light receiving elements E1 to E4. The center of the region constituted by the light receiving elements E1 to E4 and the center of the spot D of the reflected light from the optical path separation mirror 24 are substantially coincident.

  The light receiving elements E <b> 1 to E <b> 4 detect the intensity of the reflected light emitted from the optical path separation mirror 24 to each region. The intensity of the reflected light from the optical path separation mirror 24 is detected as a phase signal that changes with time, for example, as shown in FIGS. 3 (A) and 3 (B).

  Each horizontal axis of FIG. 3 (A) and FIG. 3 (B) indicates the passage of time (unit: second). The vertical axis in FIG. 3A indicates the sum of the light intensity detected by the light receiving element E1 and the light intensity detected by the light receiving element E2 as intensity A1 (relative value). The vertical axis in FIG. 3B indicates the sum of the light intensity detected by the light receiving element E3 and the light intensity detected by the light receiving element E4 as intensity A2 (relative value).

  As shown in FIGS. 3A and 3B, it is assumed that there is a phase difference Δ between the intensity A1 and the intensity A2. Based on the phase difference Δ, the inclination of the light between the two optical paths (the relative inclination between the reflected light from the fixed mirror 15 and the reflected light from the movable mirror 16) is calculated. Other phase differences Δ can be obtained by other combinations of the light receiving elements E1 to E4 (for example, combinations of the light receiving elements E1 and E4 and the light receiving elements E2 and E3). Based on the above phase difference Δ and other phase differences Δ, the direction (vector) of the inclination of light between the two optical paths can also be calculated.

(Optical path correction device 28)
The optical path correction device 28 determines the attitude of the fixed mirror 15 (angle with respect to the beam splitter 14) based on the detection result in the control unit 26 (relative inclination between the reflected light from the fixed mirror 15 and the reflected light from the moving mirror 16). ). By this adjustment, the optical path of the reflected light at the fixed mirror 15 is corrected, and the inclination of the light between the two optical paths can be eliminated (or reduced). By providing the optical path correction device 28 in the Michelson interferometer 10, it becomes possible to generate interference light with higher accuracy.

(Detection system)
The detection system will be described with reference to FIG. 1 again. The detection system uses laser light emitted from the reference light source 22 in the reference optical system 21 as a detection target.

  The detection system according to the embodiment detects whether or not laser light is emitted from the reference light source 22 in a state where both one longitudinal mode and two longitudinal modes are mixed. When laser light is emitted from the reference light source 22 in a state where both one longitudinal mode and two longitudinal modes are mixed, the operation accuracy in the optical path correction device 28 (accuracy of tilt correction with respect to the fixed mirror 15) is improved. It will decline.

  Specifically, the detection system includes a reference light source 22, a fixed mirror 15, a movable mirror 16, a beam splitter 14, a reference detector 25, and a control unit 26.

  As described above, the laser light emitted from the reference light source 22 and divided by the beam splitter 14 and reflected by the fixed mirror 15, and the laser light emitted from the reference light source 22 and divided by the beam splitter 14 and reflected by the movable mirror 16. An optical path difference | (L2 × 2) − (L1 × 2) | This optical path difference | (L2 × 2) − (L1 × 2) | is configured to periodically change as the movable mirror 16 moves.

  Referring to FIG. 4, as described at the beginning, one longitudinal mode and two longitudinal modes are changed depending on the magnitude of the current flowing through the semiconductor constituting the reference light source 22 or the temperature of the semiconductor constituting the reference light source 22. Laser light may be emitted from the reference light source 22 in a state where both modes are mixed.

  FIG. 4 shows the relationship between the wavelength of the laser beam and the intensity of the laser beam when the reference light source 22 emits the laser beam in two longitudinal modes. As shown in FIG. 4, when the reference light source 22 emits laser light in two longitudinal modes, the wavelength-intensity characteristic represented by the peak curve M1 in FIG. 4 and the peak curve in FIG. The wavelength-intensity characteristic represented by M2 coexists (competes).

  The control unit 26 (see FIG. 1) in the detection system stores in advance the coherence distance (for example, 1 mm) of the laser light in a state where the reference light source 22 emits in two longitudinal modes (the state shown in FIG. 4). Yes. As described above, the laser light emitted from the reference light source 22 is split by the beam splitter 14. As a condition for the two divided laser beams to interfere with each other when the two divided laser beams (synthesized light) are synthesized again, the optical path difference between the two laser beams | (L2 × 2) − (L1 × 2) When | exceeds a certain value, the two laser beams do not form interference light with each other. This certain value is the coherence distance of the laser light emitted from the reference light source 22 and is stored in advance in the control unit 26 as a characteristic value inherent to the reference light source 22.

  When the reference light source 22 emits laser light in one longitudinal mode, the wavelength range D1 (see FIG. 4) is a coherent wavelength range. When the reference light source 22 emits laser light in two longitudinal modes, a peak interval D2 (see FIG. 4) between the peak curve M1 and the peak curve M2 is generated, and is emitted from the reference light source 22. The coherence distance of laser light is shortened.

  FIG. 5 is a diagram showing the relationship between the optical path difference | (L2 × 2) − (L1 × 2) | formed in the laser light emitted from the reference light source 22 and the intensity of the laser light. When the reference light source 22 emits laser light in one longitudinal mode (see the solid line in FIG. 5), the intensity (contrast) of the laser light detected by the reference detector 25 is high. Even if the optical path difference is increased due to the movement of the movable mirror 16, a high contrast can be obtained (the contrast hardly changes in a practical range, for example, 50 cm or less), so that the light emitted from the reference light source 22 is Interference light can be formed.

  On the other hand, when the reference light source 22 emits laser light in two longitudinal modes (see the dotted line in FIG. 5), the intensity (contrast) of the laser light detected by the reference detector 25 is low. When the optical path difference increases due to the movement of the movable mirror 16 (see the regions RR1 and RR2 in the figure), the contrast of the laser light is further lowered, and the light emitted from the reference light source 22 cannot form interference light.

  The detection system uses this principle. When the detection system detects whether or not the laser beam is emitted from the reference light source 22 in a state where both one longitudinal mode and two longitudinal modes are mixed, the optical path difference between the two laser beams | The movable mirror 16 is reciprocated so that the maximum value of (L2 × 2) − (L1 × 2) | can detect the contrast fluctuation due to the shortened coherence distance of the reference light source 22.

(In the case of one vertical mode)
6 shows the interference signal P1 (relative value) detected by the light receiving elements E1 and E2 (see FIG. 2) and the light receiving elements E3 and E3 when the reference light source 22 emits laser light in one longitudinal mode. The interference signal R1 (relative value) detected by E4 (see FIG. 2) and the intensity S1 (relative value) of the signal detected by any of the light receiving elements E1 to E4 are expressed as the relationship between time and signal voltage. FIG.

  As shown in FIG. 6, when the reference light source 22 emits laser light in one longitudinal mode, the interference signals P1 and R1 are detected as substantially continuous (stable) values. The signal intensity S1 is also detected as a substantially continuous (stable) value with a predetermined value. In other words, the signal strength S1 draws a stable and gentle envelope. In this case, the control unit 26 determines that the laser light is emitted from the reference light source 22 in one vertical mode.

  Note that the control unit 26 can determine that the laser light is emitted from the reference light source 22 in one longitudinal mode based only on the signal strength S1. In the present embodiment, the reference detector 25 is composed of four light receiving elements E1 to E4. However, for the purpose of the determination, the reference detector 25 may be composed of one light receiving element. .

(In the case of two vertical modes)
FIG. 7 is detected by the light receiving elements E1 and E2 (see FIG. 2) when the reference light source 22 emits laser light in a state where both one longitudinal mode and two longitudinal modes are mixed. The interference signal P2 (relative value), the interference signal R2 (relative value) detected by the light receiving elements E3 and E4 (see FIG. 2), and the intensity S2 (relative) of the signal detected by any of the light receiving elements E1 to E4 Value) as a relationship between time and signal voltage.

  As shown in FIG. 7, until the optical path difference | (L2 × 2) − (L1 × 2) | between the two laser beams changes from a predetermined value to the maximum value, the interference signals P2 and R2 are It can be seen that it is detected as an unstable value. It can be seen that the intensity S2 of the signal is discontinuous (spike-like) by changing the contrast of the laser beam (see the portion surrounded by the dotted line in the figure).

  This is because the high contrast state (the reference light source 22 emits laser light in one longitudinal mode) and the low contrast state (the reference light source 22 has both one longitudinal mode and two longitudinal modes). The state in which the laser light is emitted in the state of being in a state of being mixed means that they are mixed (alternating at high speed alternately). In this case, the control unit 26 determines that the laser light is emitted from the reference light source 22 in a state where both one longitudinal mode and two longitudinal modes are mixed.

  As in the case of one longitudinal mode, based on only the signal strength S2, the control unit 26 emits laser light from the reference light source 22 in a state where both one longitudinal mode and two longitudinal modes are mixed. Can be determined to be emitted. In the present embodiment, the reference detector 25 is composed of four light receiving elements E1 to E4. However, for the purpose of the determination, the reference detector 25 may be composed of one light receiving element. .

  The control unit 26 may drive a warning unit 27 (see FIG. 1) connected to the control unit 26 to make the user recognize the mixed state. The warning by the warning unit 27 recognizes that the operation accuracy (accuracy of tilt correction with respect to the fixed mirror 15) in the optical path correction device 28 (see FIG. 1) may be reduced.

  In this case, the user may change the operating current value of the reference light source 22 so that the reference light source 22 emits laser light in one vertical mode. The reference light source 22 may emit laser light in one longitudinal mode by adjusting the temperature of the reference light source 22.

  Further, the control unit 26 may change the operating current value of the reference light source 22. When the control unit 26 determines that the laser light is emitted from the reference light source 22 in a state where both one vertical mode and two vertical modes are mixed, the control unit 26 determines the operating current value of the reference light source 22. Increase or decrease.

FIG. 8 is a diagram showing the relationship between the drive current value applied to the reference light source 22 and the wavelength of the laser light emitted from the reference light source 22. If the current value applied to the reference light source 22 is lower than the current value A _1, from the reference light source 22 laser beam is emitted in a single longitudinal mode. When the current value applied to the reference light source 22 is not less than the current value A _{1 and not} more than the current value A ₂ , laser light is emitted from the reference light source 22 in two longitudinal modes.

Similarly, when the current value applied to the reference light source 22 is larger than the current value A ₂ and lower than the current value A ₃ , laser light is emitted from the reference light source 22 in one longitudinal mode. When the current value applied to the reference light source 22 is not less than the current value A _{3 and not} more than the current value A ₄ , laser light is emitted from the reference light source 22 in two longitudinal modes. In the reference light source 22, such a behavior is repeated as the drive current value is increased or decreased as an inherent characteristic of the reference light source 22.

Therefore, when the control unit 26 determines that the laser light is emitted from the reference light source 22 in a state where both one longitudinal mode and two longitudinal modes are mixed, as the control unit 26, for example, reference The drive current value for the light source 22 may be set to the current value A ₅ in the middle of the current value A ₂ and the current value A ₃ , and the temperature of the reference light source 22 may be controlled to be constant. This control enables the reference light source 22 to emit laser light in one vertical mode.

As the selection of the current value A _5, the control unit 26, for example, increase or decrease the operating current value within a predetermined range, based on the light intensity reference detector 25 (see FIG. 1) is received, said current value Each value of A ₁ , A ₂ , A ₃ , A ₄ (interval between values) is acquired. On top of that, the control unit 26, a driving current value for the reference light source 22 may be set to exactly the current value A ₅ in the middle of the current value A ₂ and the current value A _3. By reference light source 22 at a current value A ₅ is driven, the reference light source 22 makes it possible to emit a laser beam in one longitudinal mode, the posture of the optical path compensating device 28 is fixed mirror 15 based on the exact upward Can be corrected.

[Modification of Embodiment]
In the above-described embodiment, the detection system has been described based on an example of an embodiment in which the detection system is applied to the Michelson interferometer 10 and the Fourier transform spectroscopic analyzer 100. The detection system in the present invention can be applied to the following modes.

  For example, when the detection system detects whether or not laser light is emitted from the semiconductor laser in a state where both one longitudinal mode and two longitudinal modes are mixed (control operation is started), control is performed. The unit 26 changes the optical path difference between the laser beam reflected by the fixed mirror 15 (a member corresponding to the fixed mirror 15) and the laser beam reflected by the movable mirror 16 (the corresponding member). In this case, for example, the control unit 26 moves the movable mirror 16 so that the optical path difference changes, and does not move the fixed mirror 15. Before and after the control unit 26 moves the movable mirror 16, the movable mirror 16 does not need to be operated so that the optical path difference periodically changes. For example, after the stationary state, the movable mirror 16 is moved by a predetermined distance. Then, it may be in a stationary state again.

  When the laser light is emitted from the reference light source 22 in a state where both one longitudinal mode and two longitudinal modes are mixed after the optical path difference is changed, the light is received by the reference detector 25. The laser signal becomes discontinuous as the intensity (contrast) of the laser light changes. When the signal becomes discontinuous, the control unit 26 can determine that the laser light is emitted from the reference light source 22 in a state where both one longitudinal mode and two longitudinal modes are mixed. . Thus, the detection system according to the present invention is not limited to the case where the optical path difference changes periodically as in the above-described embodiment, and the case where the optical path difference does not change periodically. It can also be applied to. For the same reason, the detection system according to the present invention can also be applied to the case where the optical path difference changes aperiodically within a predetermined range.

  Further, the control unit 26 detects whether or not the laser signal received by the reference detector 25 has become discontinuous. Based on the detected information, the control unit 26 can determine whether or not laser light is emitted from the semiconductor laser in a state where both one longitudinal mode and two longitudinal modes are mixed. For this reason, the control unit 26 does not necessarily need to store in advance the coherence distance of the laser light in a state where the semiconductor laser emits in two longitudinal modes.

  As mentioned above, although embodiment based on this invention was described, embodiment disclosed this time is an illustration and restrictive at no points. The technical scope of the present invention is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  DESCRIPTION OF SYMBOLS 10 Michelson interferometer, 11 Spectroscopic optical system, 12 Light source, 13 Collimating optical system, 14 Beam splitter (light beam splitting means), 15 Fixed mirror (1st reflection means), 16 Moving mirror (2nd reflection means), 17 Collection Optical optical system, 18 detector, 19 translation mechanism, 20 calculation unit, 21 reference optical system (detection system), 22 reference light source (semiconductor laser), 23 optical path synthesis mirror, 24 optical path separation mirror, 25 reference detector (light reception) Means), 26 control unit, 27 warning unit, 28 optical path correction device, 30 output unit, 100 Fourier transform spectroscopic analysis device, E1-E4 light receiving element, S sample.

Claims (7)

A detection system for detecting whether or not laser light is emitted from a semiconductor laser in a state where both one longitudinal mode and two longitudinal modes are mixed,
A first reflecting means and a second reflecting means;
The laser beam emitted from the semiconductor laser is divided into a laser beam directed to the first reflecting unit and a laser beam directed to the second reflecting unit, and reflected to each of the first reflecting unit and the second reflecting unit. A beam splitting means for synthesizing the laser beam,
A light receiving means for receiving the laser beam synthesized by the light beam branching means;
A control unit,
When the detection system detects whether or not laser light is emitted from the semiconductor laser in a state where both one longitudinal mode and two longitudinal modes are mixed,
The controller may be configured to change the optical path difference between the laser light reflected by the first reflecting means and the laser light reflected by the second reflecting means, and / or the second reflecting means. Move the means,
When the interference signal of the laser beam received by the light receiving means becomes discontinuous due to a change in the contrast of the laser beam, the control unit includes both one longitudinal mode and two longitudinal modes. It is determined that laser light is emitted from the semiconductor laser in a state where
Detection system. The semiconductor laser is a wavelength stabilized semiconductor laser using a diffraction grating,
The detection system according to claim 1. When it is determined that the semiconductor laser emits laser light in a state where both one longitudinal mode and two longitudinal modes are mixed, the control unit causes the semiconductor laser to operate in one longitudinal mode. Changing the operating current value of the semiconductor laser to emit laser light,
The detection system according to claim 1 or 2. The optical path difference between the laser light reflected by the first reflecting means and the laser light reflected by the second reflecting means is within a predetermined range by movement of the first reflecting means and / or the second reflecting means. Configured to change in
The controller stores in advance the coherence distance of the laser light in a state where the semiconductor laser is emitted in two longitudinal modes,
When the detection system detects whether or not laser light is emitted from the semiconductor laser in a state where both one longitudinal mode and two longitudinal modes are mixed,
The control unit moves the first reflecting means and / or the second reflecting means so that the maximum value of the optical path difference is longer than the coherence distance,
In the case where the interference signal of the laser beam received by the light receiving means becomes discontinuous due to a change in the contrast of the laser beam before the optical path difference changes from a predetermined value to the maximum value, The control unit determines that laser light is emitted from the semiconductor laser in a state where both one longitudinal mode and two longitudinal modes are mixed.
The detection system according to claim 1. The detection system according to any one of claims 1 to 3,
A detector for detecting the laser light synthesized by the light beam splitting means as interference light,
The first reflecting means is a fixed mirror;
The second reflecting means is a movable mirror;
Michelson interferometer. An optical path correction device that corrects the tilt of the fixed mirror;
The light receiving means includes two or more light receiving elements,
The controller compares the signal phases of the laser beams received by each of the two or more light receiving elements, drives the optical path correction device so that there is no difference between the signal phases, and Correct the tilt,
The Michelson interferometer according to claim 5. Michelson interferometer according to claim 5 or 6,
A calculation unit for calculating a spectrum of the interference light detected by the detector;
An output unit that outputs the spectrum obtained by the arithmetic unit,
Fourier transform spectroscopic analyzer.