JP2006133013A - Semiconductor laser absorption spectroscopic device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor laser absorption spectroscopic device capable of measuring accurately a gas concentration by enlarging sufficiently a signal-to-noise ratio even when the gas pressure of a gas to be measured is lower than 10 mbar. <P>SOLUTION: This device has two resonators comprising a current excitation type surface light emitting semiconductor laser 21 arranged in a gas cell 24 filled with ammonia gas G1 and driven by current excitation, and a concave mirror 23 arranged on the optical path of semiconductor laser light emitted from the current excitation type surface light emitting semiconductor laser 21 and in a gas cell 24. The device is equipped with the first photodiode 52 for receiving a semiconductor laser L1 irradiated toward the ammonia gas G1 and the second photodiode 55 a semiconductor laser L2 irradiated from the current excitation type surface light emitting semiconductor 21. The ammonia gas G1 concentration is measured from the emission intensities of the semiconductor laser lights L1, L2 received respectively by the first and second photodiodes 52, 55. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a semiconductor laser absorption spectrometer.

  Since there are many gas species with high absorption intensity in the near-infrared region, research on semiconductor laser absorption spectroscopy in which gas concentration and temperature are evaluated by a near-infrared semiconductor laser has been actively conducted. When performing gas concentration measurement, it is desirable to be able to sweep a wavelength of 1 nm or more in order to detect a plurality of absorption lines of a specific gas type and specify the gas concentration from information such as the intensity ratio of the absorption amount. Therefore, a wavelength sweep function (about 20 nm) using a combination of a semiconductor laser and an external resonator is conventionally used, where the oscillation wavelength of a distributed feedback (DFB) laser increases by about 1 nm as the injection current increases. Has been performed (see Non-Patent Document 1). However, the former is limited to the measurement of gas concentration at room temperature and atmospheric pressure because the wavelength sweep region is narrow. In the latter case, the wavelength sweep is performed by mechanically moving the external resonator, so that the sweep speed is low in principle.

  On the other hand, a surface emitting semiconductor laser (Vertical Cavity Surface Emitting Laser, VCSEL) has a smaller active layer volume than a conventional semiconductor laser and a distributed Bragg reflector (DBR) that performs current injection. Since the electrical resistance of the layer is high, it is known that the oscillation wavelength greatly increases to about 3 to 4 nm as the injection power increases. Furthermore, the amount of increase in wavelength per unit current is about 0.01 nm / mA for the conventional semiconductor laser, whereas the surface emitting semiconductor laser is about 0.3 to 0.4 nm / A, which is several tens of times larger. Therefore, it becomes possible to perform wavelength sweeping at a high speed. Therefore, gas concentration evaluation by semiconductor laser spectral absorption using a surface-emitting type semiconductor laser is used for concentration measurement of oxygen and ammonia (see Non-Patent Document 2 and Non-Patent Document 3).

  A conventional semiconductor laser spectral absorption method using a surface emitting semiconductor laser will be described with reference to FIG. The surface emitting semiconductor laser 101 is driven by controlling a current value and a temperature by a laser driver 102 and a temperature controller 103, respectively. The laser light L10 emitted from the surface emitting semiconductor laser 101 is collimated (parallel) light by the first lens 104, passes through the beam splitter 105, and has a pressure of 10 mbar or more filled into the gas cell 106 from one end face of the gas cell 106. It enters the measurement target gas g.

  The laser light incident on the measurement gas g once exits from the gas cell 106, is reflected in the opposite direction by the first reflecting mirror 107, passes through the gas cell 106 again, passes through the second reflecting mirror 108, and passes through the second reflecting mirror 108. After being subjected to spot size conversion by the lens 109 so as to match the light receiving diameter of the first photodiode (Photo Diode, PD) 110, the light enters the first photodiode 110.

  FIG. 19 shows the dependence of the optical output L of the laser beam L10 emitted from the surface emitting semiconductor laser 101 and the injection current I on the oscillation wavelength λ. As described above, it can be seen that the oscillation wavelength λ increases as the injection current I increases. Therefore, when the absorption line wavelength of the measurement gas and the wavelength of the laser beam do not match, the incident light to the first photodiode 110 receives almost no loss, and thus the received light intensity (current / voltage) is high. On the other hand, if the values match, the laser beam receives strong absorption when it reciprocates in the gas cell 106 and the loss increases, so the received light intensity decreases.

  FIG. 20A shows IL characteristics when the gas cell 106 is filled with ammonia gas having a pressure of 100 mbar. As described above, since the oscillation wavelength shifts to the longer wavelength side as the injection current to the surface emitting semiconductor laser 101 increases, as shown in FIG. Dips corresponding to the line wavelengths are observed (actually a larger number of dips are observed, but are omitted here for simplicity). The light absorption amount corresponding to the gas concentration can be evaluated from the area of the dip.

  FIGS. 21A and 21C show the wavelength dependence of the light absorption obtained from the result of FIG. 20A and the simulation result of the absorption line in ammonia gas, respectively. As can be seen by comparing FIG. 21A and FIG. 21C, it can be seen that the experimental result obtained from FIG. 20A and the absorption line obtained from the simulation coincide with each other with high accuracy. Thus, in semiconductor laser absorption spectroscopy in which a plurality of absorption lines must be detected within a relatively narrow wavelength band, it is necessary to accurately measure the oscillation wavelength of the semiconductor laser. Therefore, as shown in FIG. 18, the laser light L10 emitted from the surface-emitting type semiconductor laser 101 is branched by the beam splitter 105, passed through the etalon resonator 111, and received by the second photodiode 112. At this time, the received light intensity (voltage / current) greatly varies with the period of the longitudinal mode interval of the etalon resonator 111, so that the oscillation wavelength of the laser light L10 can be monitored with high resolution.

R.M. Mihalcea et al., “Diode laser sensor for measurements of CO, CO2, and CH4 in combustion flows”, Applied Optics, November 20, 1997, Vol. 36, No. 30, 8745-8552. J. Wang et al, “Oxygen measurements at high pressures with vertical cavity surface-emitting lasers”, Applied Physics B, 2001, B 72, 865-872. G. Totschnig et al., “High-speed vertical-cavity surface-emitting laser (VCSEL) absorption spectroscopy of ammonia (NH3) near 1.54 μm”, Applied Physics B, 2003, B 76, 603-608. A. Mooradian, “High brightness cavity-controlled surface emitting GaInAs lasers operating at 980 nm”, Optical Fiber Communication, 2001, PD17-1 M. A. Hadley et al, “High single-transverse-mode output from external-cavity surface-emitting laser diodes”, Applied Physics Letters, September 20, 1993, Vol. 63, No. 20, 1607-1609.

  On the other hand, in order to accurately evaluate the gas concentration based on the magnitude of the received light intensity, it is necessary to make the S / N (signal to noise) ratio of the received light intensity sufficiently large. In particular, when the gas pressure is as low as less than 10 mbar, it is difficult to ensure a high S / N ratio because the laser light intensity of the surface emitting semiconductor laser is as low as about 1 mW (single mode). Therefore, when absorption spectroscopy measurement is performed using a surface-emitting type semiconductor laser at less than 10 mbar, the dip observed in the IL characteristic becomes shallow as shown in FIG. . Therefore, a shift in absorption line wavelength is observed between the light absorption line obtained from FIG. 20B shown in FIG. 21B and the simulation result shown in FIG. Is observed weakly as a whole, it can be seen that an absorption line wavelength with a small amount of light absorption is not observed. Therefore, when the gas pressure is less than 10 mbar, the emitted light intensity of the surface emitting semiconductor laser is low, so that a sufficient S / N ratio cannot be secured in the absorption spectroscopic measurement, and the light absorption amount corresponding to the gas concentration is accurately measured. Not only can it be done, but also the absorption line wavelengths that are not observed are generated, which may cause misjudgment of gas species.

  As another means of ensuring a sufficient S / N ratio, a method of reciprocating the laser beam twice or more in the gas cell is conceivable. However, in order to reciprocate the laser beam multiple times in the gas cell, it is installed at both ends of the gas cell. Since the number of reflecting mirrors increases, the apparatus becomes complicated and expensive, and the number of optical axis adjustment points also increases, so that the measurement efficiency is significantly reduced. As described above, in the conventional semiconductor laser absorption spectrometer using the surface emitting semiconductor laser, when the gas pressure is less than 10 mbar, the S / N ratio is small (bad), and a high-accuracy measurement value cannot be obtained. As a result, there was a problem that the measurement results could be obtained.

  Therefore, the present invention has been proposed in view of the above-described problems, and even when the gas pressure of the gas to be measured is less than 10 mbar, the signal-to-noise ratio is sufficiently increased to accurately measure the gas concentration. An object of the present invention is to provide a semiconductor laser absorption spectroscopic device capable of performing

  A semiconductor laser absorption spectrometer according to a first aspect of the present invention for solving the above-described problem is a semiconductor laser absorption spectrometer that evaluates a gas concentration using absorption spectroscopy using semiconductor laser light. The semiconductor laser emitted from the semiconductor laser is used. It is characterized in that three reflecting mirrors are installed on an optical path through which light propagates, two resonators composed of two adjacent reflecting mirrors are provided, and a gas to be measured is arranged in one of the two resonators. To do.

  A semiconductor laser absorption spectroscopic device according to a second invention for solving the above-described problem is the semiconductor laser absorption spectroscopic device according to the first invention, wherein the semiconductor laser emitted from the resonator side where the measurement gas is arranged. A first photodiode for receiving light and a second photodiode for receiving the semiconductor laser emitted from a resonator side different from the resonator are provided.

  A semiconductor laser absorption spectroscopy apparatus according to a third invention for solving the above-described problem is the semiconductor laser absorption spectroscopy apparatus according to the first or second invention, wherein the semiconductor laser is driven by current excitation. It is a mold surface emitting semiconductor laser.

  A semiconductor laser absorption spectroscopic device according to a fourth invention for solving the above-described problem is the semiconductor laser absorption spectroscopic device according to the third invention, wherein the three reflections are provided in a gas container enclosing the gas to be measured. It is characterized by arranging a mirror.

  A semiconductor laser absorption spectroscopic device according to a fifth invention for solving the above-described problems is the semiconductor laser absorption spectroscopic device according to the third invention, wherein the three reflections are provided outside a gas container enclosing the gas to be measured. It is characterized by arranging a mirror.

  A semiconductor laser absorption spectroscopic device according to a sixth invention for solving the above-described problem is a semiconductor laser absorption spectroscopic device according to the first invention or the second invention, wherein the semiconductor laser is laser-excited by optical excitation. It is a surface emitting semiconductor laser.

  A semiconductor laser absorption spectrometer according to a seventh aspect of the present invention for solving the above-described problem is the semiconductor laser absorption spectrometer according to the sixth aspect of the invention, wherein the three reflections are disposed inside a gas container that encloses the gas to be measured. It is characterized by arranging a mirror.

  A semiconductor laser absorption spectroscopic device according to an eighth invention for solving the above-described problem is the semiconductor laser absorption spectroscopic device according to the sixth invention, wherein the three reflections are provided outside a gas container enclosing the gas to be measured. It is characterized by arranging a mirror.

  A semiconductor laser absorption spectrometer according to a ninth invention for solving the above-described problems is the semiconductor laser absorption spectrometer according to the first or second invention, wherein the semiconductor laser is an edge-emitting semiconductor laser. It is characterized by that.

  A semiconductor laser absorption spectrometer according to a tenth aspect of the invention for solving the above-described problem is the semiconductor laser absorption spectrometer according to the ninth aspect of the invention, wherein the three reflections are provided inside a gas container enclosing the gas to be measured. It is characterized by arranging a mirror.

  A semiconductor laser absorption spectrometer according to an eleventh aspect of the invention for solving the above-described problem is the semiconductor laser absorption spectrometer according to the ninth aspect of the invention, wherein the three reflections are provided outside the gas container enclosing the gas to be measured. It is characterized by arranging a mirror.

[Action]
In the present invention having the above-described configuration, the problems are solved as follows. The principle of the surface emitting semiconductor laser used in the semiconductor laser absorption spectrometer according to the present invention will be described below with reference to FIG. As shown in the figure, the surface emitting semiconductor laser 1 is a compound resonator type surface emitting semiconductor laser having an optical aperture 2 and a concave mirror 3 in the emission direction of a conventional surface emitting semiconductor laser. The surface emitting semiconductor laser 1 has, for example, an oscillation wavelength in a 1.55 μm band, and an n-DBR layer (having a different refractive index) having high reflectivity doped n-type on an n-InP substrate 4. A structure in which materials are alternately stacked) 5, a multiple quantum well (MQW) active layer 6, a p-DBR layer 7 having a high reflectivity, and a p-InGaAs contact layer 8 are sequentially stacked. An n-electrode 12 is stacked below the n-InP substrate 4, and a p-electrode 11 for current injection is stacked on the p-InGaAs contact layer 8. Further, an antireflection film 9 is laminated in a region surrounded by the p-InGaAs contact layer 8 in the p-DBR layer 7.

  When current is injected into the surface emitting semiconductor laser 1, laser oscillation is performed by the first resonator 13 composed of the n-DBR layer 5 and the p-DBR layer 7, and the oscillation wavelength and mode profile are as follows. , Determined by the interaction between the p-DBR layer 7 and the second resonator 14 composed of the concave mirror 3. Therefore, it is generally known that the output light intensity can be improved while maintaining the single transverse and longitudinal modes by adjusting the position of the concave mirror 3 and the optical aperture 2 and adjusting the aperture diameter of the optical aperture 2. (See Non-Patent Document 4 and Non-Patent Document 5).

  In general, the space of the second resonator 14 is usually filled with air or nitrogen gas that is transparent to the laser oscillation wavelength. This is because, when filled with an absorbing medium (solid, gas, etc.) for the laser oscillation wavelength, the optical loss in the space becomes larger than the optical gain of the multiple quantum well active layer 6, and laser oscillation cannot be obtained at all. It is. The surface-emitting type semiconductor laser 1 in the semiconductor laser absorption spectrometer according to the present invention is characterized in that, as shown in FIG. 2, the space is filled with a gas G having an absorption line near the laser oscillation wavelength. .

  Therefore, as described above, when the IL characteristic is evaluated using the fact that the oscillation wavelength of the surface emitting semiconductor laser 1 increases as the current increases, as shown in FIG. At the wavelength corresponding to the line, the optical loss in the second resonator 14 becomes large and laser oscillation cannot be obtained, so that the emission intensity cannot be obtained. On the other hand, since there is no optical loss in the second resonator 14 at a wavelength that does not correspond to the absorption line, a larger emission intensity than that of the conventional surface emitting semiconductor laser can be obtained. Therefore, when the surface emitting semiconductor laser 1 is used in the apparatus of the present invention, the signal-to-noise ratio (signal-to-noise ratio) is dramatically higher than before without increasing the number of reflectors installed at both ends of the gas cell. Therefore, highly accurate gas concentration measurement can be performed.

  According to the semiconductor laser absorption spectrometer of the first invention, a high signal-to-noise ratio is ensured not only at a normal gas pressure but also at a low gas pressure that cannot be measured by a conventional semiconductor laser absorption spectrometer. Therefore, it is possible to measure the gas concentration with high accuracy and accuracy.

  The semiconductor laser absorption spectroscopic device according to the second aspect of the invention has the same operational effects as the first aspect of the invention.

  The semiconductor laser absorption spectroscopic device according to the third aspect of the present invention has the same operational effects as the first aspect of the invention.

  According to the semiconductor laser absorption spectroscopic device of the fourth invention, the same operational effects as the first invention can be obtained.

  According to the semiconductor laser absorption spectrometer according to the fifth aspect of the invention, the same effect as the third aspect of the invention can be obtained, and without being affected by the heater that controls the temperature of the gas container filled with the gas to be measured. The driving temperature of the current excitation type surface emitting semiconductor laser can be controlled.

  According to the semiconductor laser absorption spectroscopic device of the sixth invention, the same effect as the first invention can be obtained, and an electrode and a current confinement structure such as a current excitation type surface emitting semiconductor laser are not required. There is an effect that the fabrication of the photoexcited surface emitting semiconductor laser is simplified.

  According to the semiconductor laser absorption spectroscopic device of the seventh invention, the same function and effect as the sixth invention are achieved.

  According to the semiconductor laser absorption spectroscopic device of the eighth invention, the same effect as the sixth invention can be obtained, and without being affected by the heater that controls the temperature of the gas container filled with the gas to be measured, The driving temperature of the photoexcited surface emitting semiconductor laser can be controlled.

  According to the semiconductor laser absorption spectroscopic device of the ninth invention, the same function and effect as the first invention are achieved.

  According to the semiconductor laser absorption spectroscopic device of the tenth aspect, the same function and effect as the ninth aspect are achieved.

  According to the semiconductor laser absorption spectrometer of the eleventh aspect of the invention, the same effect as that of the ninth aspect of the invention can be obtained, and without being affected by the heater that controls the temperature of the gas container filled with the gas to be measured. The driving temperature of the edge emitting semiconductor laser can be controlled.

  The best mode for carrying out the semiconductor laser absorption spectroscopic apparatus according to the present invention will be specifically described below based on examples.

  FIG. 4 is a schematic view of a semiconductor laser absorption spectrometer according to the first embodiment of the present invention. FIG. 5 is an explanatory diagram of a current-excitation surface-emitting semiconductor laser in the apparatus, and FIG. Fig. 5 (b) shows the concept when the structure is a composite resonator. FIG. 6 is a graph showing the current dependence of the optical output and oscillation wavelength in the semiconductor laser absorption spectrometer according to the first embodiment of the present invention, and FIG. 7 is a graph showing the measurement results of the apparatus, FIG. 8 is a graph showing the relationship between the light absorption amount and the oscillation wavelength. FIG. 8A shows the measurement result of the light absorption amount in the apparatus, and FIG. 8B shows the simulation result of the light absorption amount. Show.

Here, the concentration measurement of ammonia gas, which is a gas to be measured having a gas pressure of 1 mbar, will be described in detail.
As shown in FIG. 4, a semiconductor laser absorption spectroscopy apparatus 20 according to the first embodiment of the present invention includes a current excitation type surface emitting semiconductor laser (hereinafter abbreviated as current excitation type VCSEL) 21 driven by current excitation, The optical diaphragm 22 is disposed on the optical path of the semiconductor laser light oscillated from the current excitation type VCSEL 21, and the concave mirror 23 is disposed on the optical path and is opposed to the optical diaphragm 22. However, the current excitation type VCSEL 21, the optical diaphragm 22 and the concave mirror 23 are arranged in a gas cell 24 which is a gas container in which ammonia gas G1, which is a measurement gas having an absorption line wavelength near the laser oscillation wavelength described later, is sealed. Yes.

  The current excitation type VCSEL 21 and the heat sink 25 disposed adjacent to the current excitation type VCSEL 21 are fixed on the movable stage 26 by AuSn solder (not shown) or the like. The current excitation type VCSEL 21 includes a laser driver. 27 is connected. The current excitation type VCSEL 21 is driven by controlling a temperature and a current value by an electronic cooling device (not shown) built in the movable stage 26 and a laser driver 27, respectively. A temperature controller 28 is connected to the electronic cooling device, and the temperatures of the heat sink 25 and the movable stage 26 are set to the same temperature as the room temperature.

  As shown in FIG. 5A, the current excitation type VCSEL 21 has an n-InP-based DBR layer 29, InGaAsP / InGaAsP multiple quantum wells (MQW) activity on an n-InP substrate (not shown). A layer (hereinafter abbreviated as MQW active layer) 30 and a p-InP DBR layer 31 are sequentially stacked, and the MQW active layer 30 is sandwiched between an n-InP DBR layer 29 and a p-InP DBR layer 31. It has a structure.

  The n-InP-based DBR layer 29 includes an n-InP layer (not shown) and an n-InGaAsP (band gap wavelength 1.3 μm) layer (not shown) each having a thickness of ¼ of the 1.55 μm optical wavelength. The p-InP DBR layer 31 has five p-InP layers (not shown) and five p-InGaAsP layers (not shown) alternately stacked. It has a DBR structure. Such a structure in which the MQW active layer 30 is sandwiched between the semiconductor DBR layers is an advantageous structure for setting the oscillation wavelength with high accuracy.

  In addition, in order to form a current confinement structure, the periphery of the MQW active layer 30 was buried with a semi-insulating Fe—InP layer 32, and the emission diameter was set to 15 μm. A structure in which this substrate and an n-GaAs DBR layer 33 having a high thermal conductivity, that is, an n-GaAs layer and an n-AlAs layer having a thickness of 1/4 of an optical wavelength of 1.55 μm are alternately laminated is formed. By bonding the n-GaAs substrate 34 formed by thin film Wafer-fusion technology (technique for removing the InP substrate to form a thin film), it is possible to suppress a deterioration in output characteristics due to heat generated during laser driving.

An n-InP layer 35 that is a current blocking layer and a p-InGaAs layer 36 that is a current path layer are sequentially stacked on the buried structure, and then a TiO film having a thickness of 1/4 of an optical wavelength of 1.55 μm. By forming the dielectric DBR layer 37 in which ₂ and SiO ₂ are alternately stacked, high reflecting mirrors are respectively formed on both sides of the MQW active layer 30. An n-electrode 38 is formed on the n-GaAs substrate 34 side, and a p-electrode 39 is formed on the p-InGaAs layer 31. The semiconductor laser oscillates by current injection. An antireflection film 40 is formed on the n-GaAs substrate 34.

  As shown in FIG. 5, the current-excited VCSEL 21 includes a first reflector R1 having a reflectivity of 99.6%, which includes an n-GaAs DBR layer 33 and an n-InP DBR layer 29, and a p-InP system. A first resonator 41 sandwiching an MQW active layer 30 as a gain medium is formed by a second reflecting mirror R2 having a reflectivity of 90%, which is composed of a DBR layer 31 and a dielectric DBR layer 37. On the other hand, the second resonator 42 is formed by installing a concave mirror 23 having a reflectance of 99.8% as the third reflecting mirror R3 at a position opposite to the second reflecting mirror R2. The first resonator 41 and the second resonator 42 are coupled to form a coupled resonator structure.

  The semiconductor laser light is emitted from one side of the first reflecting mirror R1 and one side of the third reflecting mirror R3, and the first photodiode 52 (see FIG. 4) is output from the third reflecting mirror R3. The semiconductor laser light L1 emitted to the side is adjusted so that the output light intensity is about 20 times that of the semiconductor laser light L2 emitted from the first reflecting mirror R1 to the second photodiode 55 (see FIG. 4) side. ing.

  On the other hand, the gas cell 24 has a length of about 40 cm, is made of a material such as quartz having a high temperature resistance of 1000 ° C. or higher, and is transparent to the semiconductor laser light emitted from the current excitation type VCSEL 21. Is used. Both end surfaces of the gas cell 24 are processed obliquely at an angle of about 1 to 7 degrees so that the influence of the reflection of the semiconductor laser light on the end surface is minimized. Further, as shown in FIG. 4, the temperature of the ammonia gas G1 in the gas cell 24 is adjusted to be constant by a heater 43 provided around the gas cell 24, and the gas pressure of the ammonia gas G1 in the gas cell 24 is adjusted. Is monitored by a gas pressure gauge 44 provided at the gas outlet 24 a of the gas cell 24.

  First, the gas cell 24 is filled with the ammonia gas G1 after the gas inlet 24b of the gas cell 24 is closed and a vacuum pump (not shown) is connected to the gas outlet 24a to evacuate the gas cell 24. Close the gas outlet 24a. Subsequently, a container (cylinder) containing ammonia gas G1 is connected to the gas inlet 24b, the gas inlet 24b is opened, and the gas pressure gauge 44 is filled with the ammonia gas G1 until a gas pressure of 1 mbar is obtained. Close the inlet 24b. The temperature of the heater 43 is set to the same temperature as the room temperature.

  The optical aperture 22 and the concave mirror 23 are installed on movable stages 45 and 46, respectively. XYZ axis stage controllers 47, 48, and 49 are connected to the movable stages 26, 45, and 46, respectively, and the positions of the current excitation type VCSEL 21, the optical diaphragm 22, and the concave mirror 23 can be adjusted. A composite resonator 50 in which two resonators including a current excitation type VCSEL 21, an optical aperture 22 and a concave mirror 23 are coupled is formed. In the coupled resonator 50, a single transverse mode can be realized by adjusting each position. Vertical mode has been implemented. Since the concave mirror 23 having a curvature radius of 10 cm is used, the movable stages 26, 45, and 46 are finely adjusted by the XYZ axis stage controllers 47, 48, and 49 with the distance between the concave mirror 23 and the current excitation type VCSEL 21 being about 10 cm as a guide. A single transverse and longitudinal mode of the semiconductor laser light is realized.

  A lens 51 is disposed relative to one end of the gas cell 24 in the optical path through which the semiconductor laser light emitted from the current excitation type VCSEL 21 propagates, and a first photodiode (Photo Diode, PD) 52 is arranged. A lens 53 is disposed relative to the other end of the gas cell 24 in the optical path, an etalon resonator 54 is disposed relative to the lens 53, and a second photodiode 55 is disposed relative to the etalon resonator 54. Is arranged.

  When the wavelength of the semiconductor laser light L1 emitted from the current excitation type VCSEL 21 does not coincide with the absorption line of the ammonia gas G1, it enters the first photodiode 52 through one end of the gas cell 24 and the lens 51. The light emission intensity (voltage / current) is recorded in the photodiode 52. When the absorption line of the ammonia gas G1 has the same wavelength, the semiconductor laser light L1 is absorbed by the ammonia gas G1. From the opposite side of the current excitation type VCSEL 21, semiconductor laser light L2 having an output light intensity of about 1/20 of the semiconductor laser light L1 is emitted at the same wavelength. The semiconductor laser light L2 is incident on the second photodiode 55 through the heat sink 25 and the through holes 25a and 26a of the movable stage 26, the lens 53, and the etalon resonator 54, and the oscillation wavelength is monitored with high resolution. .

  As shown in FIG. 6, in the semiconductor laser absorption spectroscopic device 20, the oscillation wavelength of the semiconductor laser light gradually increases in proportion to the increase in current, and the output intensity of the semiconductor laser light changes at a predetermined rate. Moreover, it was confirmed by the optical spectrum measurement and the far field pattern measurement that the emitted light from the current excitation type VCSEL 21 has a good single transverse mode and longitudinal mode property. As shown in FIG. 7 (actually, a dip larger than that shown in the figure was observed, but only a representative dip having a large amount of absorption is shown here), the semiconductor laser absorption spectrometer 20 has a very large dip. It is deep and its shape is acute, so it can be seen that data having a high S / N ratio and wavelength accuracy were obtained even though the gas pressure was as low as 1 mbar. As shown in FIG. 8, the light absorption amount obtained by the semiconductor laser absorption spectroscopic device 20 and the light absorption amount obtained by the simulation are in good agreement with each other without any deviation of the absorption line wavelength. It can be seen that the wavelength was observed.

  Thus, according to the semiconductor laser absorption spectrometer 20 having the composite resonator 50, a high S / N ratio can be ensured even when the ammonia gas pressure is less than 10 mbar, so that accurate gas concentration measurement can be realized. It becomes possible.

  In the above description, the ammonia gas G1 is used as the gas to be measured. However, any gas may be used as long as it has an absorption line wavelength near the oscillation wavelength of the semiconductor laser light. The same effect as that of the concentration measurement is obtained.

  The semiconductor laser absorption spectrometer according to the second embodiment will be described below with reference to the drawings.

  FIG. 9 is a schematic diagram of a semiconductor laser absorption spectrometer according to the second embodiment of the present invention. The semiconductor laser absorption spectroscopic apparatus according to the second embodiment is obtained by changing the arrangement positions of the current excitation type VCSEL, the optical diaphragm and the concave mirror in the semiconductor laser absorption spectroscopic apparatus according to the first embodiment described above. Has the same configuration as the semiconductor laser absorption spectrometer. About these structures, the code | symbol same as the semiconductor laser absorption spectroscopy apparatus which concerns on the said 1st Example is attached, and the description is abbreviate | omitted about the same code | symbol.

  The semiconductor laser absorption spectrometer 56 according to the second embodiment of the present invention has a current excitation type VCSEL 21, an optical aperture 22 and a concave mirror 23 arranged outside the gas cell 57, and is emitted from one of the current excitation type VCSELs 21. The semiconductor laser light L1 enters the first photodiode 52 through the gas cell 54, the optical aperture 22, the concave mirror 23, and the lens 51. The semiconductor laser light L2 emitted from the other side of the current excitation type VCSEL 21 enters the second photodiode 55 through the heat sink 25 and the through holes 25a and 26a of the movable stage 26, the lens 53, and the etalon resonator 54.

  Both end faces of the gas cell 57 are processed obliquely at an angle of about 1 to 7 degrees so as to minimize the influence of reflection of the semiconductor laser light on the end faces. Therefore, according to the semiconductor laser absorption spectroscopic apparatus 56 according to the second embodiment, the same operational effects as the semiconductor laser absorption spectroscopic apparatus 20 according to the first embodiment are exhibited. Further, since the current excitation type VCSEL 21 is disposed outside the gas cell 57, there is an advantage that the driving temperature of the current excitation type VCSEL 21 can be controlled without being affected by the heater 43 that controls the temperature of the gas cell 57. .

  The semiconductor laser absorption spectrometer according to the third embodiment will be described below with reference to the drawings.

  FIG. 10 is a schematic view of a semiconductor laser absorption spectroscopic apparatus according to a third embodiment of the present invention, and FIG. 11 is a structural diagram of an optically pumped surface emitting semiconductor laser in the apparatus. The semiconductor laser absorption spectroscopic device according to the third embodiment is obtained by replacing the current excitation type VCSEL in the semiconductor laser absorption spectroscopic device according to the first embodiment described above with a light excitation type surface emitting semiconductor laser. It has the same configuration as the semiconductor laser absorption spectrometer. About these structures, the same code | symbol as the semiconductor laser absorption spectroscopy apparatus which concerns on the said 1st Example is appended.

Here, the concentration measurement of ammonia gas, which is a gas to be measured having a gas pressure of 1 mbar, will be described in detail.
As shown in FIG. 10, a semiconductor laser absorption spectroscopic device 58 according to a third embodiment of the present invention includes an optically pumped surface emitting semiconductor laser (hereinafter, optically pumped VCSEL) that oscillates with pumping light having a wavelength shorter than the oscillation wavelength. 59, an optical diaphragm 22 disposed on the optical path of the semiconductor laser light oscillated by the optically pumped VCSEL 59, and a concave mirror 23 disposed on the optical path and opposed to the optical diaphragm 22. Have However, the photoexcited VCSEL 59, the optical aperture 22, and the concave mirror 23 are disposed in a gas cell 24 that is a gas container that encloses ammonia gas G1, which is a measurement gas having an absorption line wavelength near a laser oscillation wavelength, which will be described later. .

  The photoexcited VCSEL 59 and the heat sink 25 disposed adjacent to the photoexcited VCSEL 59 are fixed on the movable stage 26 by AuSn solder (not shown) or the like, and a laser driver 60 is connected to the photoexcited VCSEL 59. Has been. The photoexcited VCSEL 59 is driven by controlling the temperature and the current value by an electronic cooling device (not shown) built in the movable stage 26 and a laser driver 60, respectively. The temperatures of the heat sink 25 and the movable stage 26 are set to the same temperature as the room temperature.

  As shown in FIG. 11, in the photoexcited VCSEL 59, an InP layer 61, an InGaAsP / InGaAsP multiple quantum well active layer (MQW active layer) 62, an InP layer 61, and an InP-based DBR layer 63 are formed on an InP substrate (not shown). Are formed sequentially. The InP-based DBR layer 63 includes an n-InP layer (not shown) and an n-InGaAsP (band gap wavelength 1.3 μm) layer (not shown) each having a thickness of ¼ of the 1.55 μm optical wavelength. It has a DBR structure in which five pairs are stacked.

The thinned substrate by removing the InP substrate and the high thermal conductivity GaAs-based DBR layer 64 (a layer in which GaAs layers and AlAs layers having a thickness of 1/4 of the optical wavelength of 1.55 μm are alternately laminated) By bonding the GaAs substrate 65 on which is formed by thin film Wafer-fusion technology, it becomes a structure that suppresses deterioration of output characteristics due to heat generation during laser driving. A dielectric DBR layer 66 in which TiO ₂ and SiO ₂ having a thickness of 1/4 of the 1.55 μm optical wavelength are alternately formed is formed on the InP-based DBR layer 63, and is formed on both sides of the MQW active layer 62. A highly reflective mirror is formed. Further, an antireflection film 67 is formed on the GaAs substrate 65.

  The photoexcited VCSEL 59 includes a first reflecting mirror R4 having a reflectance of 99.6% made of a GaAs-based DBR layer 64, and a second reflecting mirror having a reflectance of 90% made of an InP-based DBR layer 63 and a dielectric DBR layer 66. The first resonator sandwiching the MQW active layer 62 as a gain medium is formed by the reflecting mirror R5. On the other hand, a concave mirror 23 having a reflectance of 99.8% is installed as a third reflecting mirror R6 at a position facing the second reflecting mirror R5, thereby forming a second resonator. The first resonator and the second resonator are coupled to form a coupled resonator structure.

  As shown in FIG. 10, the oscillation of the semiconductor laser light by optical excitation has a wavelength shorter than the oscillation wavelength of the optical excitation type VCSEL 59 and is excited by the excitation light L3 oscillated from the optical excitation light source 68 to oscillate the semiconductor laser light. . Here, an edge-emitting semiconductor laser that oscillates at 980 nm is used as the optical excitation light source 68. The pumping light L3 oscillated from the optical pumping light source 68 is an optical fiber 70 (connected to a first port 69a of a wavelength division multiplexing (WDM) filter 69 and a second port 69b of the WDM filter 69 ( 11), the lens 53 converts the spot size into a diameter of 20 μm and irradiates the photoexcited VCSEL 59.

  Laser oscillation is generated by the excitation light L3, the semiconductor laser light L4 is emitted from the concave mirror 23 side, and the semiconductor laser light L5 is emitted from the opposite GaAs substrate 61 (see FIG. 11) side. The semiconductor laser light L5 enters the second port 69b of the WDM filter 69 through the optical fiber 70, passes through the etalon resonator 54 through the third port 69c, and enters the second photodiode 52. To do. At this time, due to the action of the WDM filter 67, the semiconductor laser light L5 incident from the second port 67b is not emitted from the first port 67a. Further, the excitation light L3 incident from the first port 67a is not emitted from the third port 67c.

  In such a photo-excited VCSEL 59, it is not necessary to form an electrode and a current confinement structure necessary for current driving, so that the manufacturing process can be greatly omitted, and it can be easily manufactured. The semiconductor laser light is emitted from both sides of the first reflecting mirror R4 and the second reflecting mirror R5, and the semiconductor laser light L4 emitted from the third reflecting mirror R6 is emitted from the first reflecting mirror R4. The output light intensity is adjusted to about 20 times that of the semiconductor laser light L5.

  On the other hand, the gas cell 24 has a length of about 40 cm, is made of a material such as quartz having a high temperature resistance of 1000 ° C. or higher, and is made of a material that is transparent to the semiconductor laser light emitted from the photoexcited VCSEL 59. Used. Both end faces of the gas cell 24 are processed obliquely at an angle of about 1 to 7 degrees so that the influence of the reflection of the semiconductor laser light on the end face is minimized. The temperature of the ammonia gas G1 in the gas cell 24 is adjusted to be constant by a heater 43 provided around the gas cell 24, and the gas pressure of the ammonia gas G1 in the gas cell 24 is adjusted to the gas outlet of the gas cell 24. It is monitored by a gas pressure gauge 44 provided at 24a.

  For filling the gas cell 24 with the ammonia gas G1, as in the first embodiment, a vacuum pump (not shown) is first connected to the gas outlet 24a with the gas inlet 24b of the gas cell 24 closed. After evacuating the gas cell 24, the gas outlet 24a is closed. Subsequently, a container (cylinder) containing ammonia gas G1 is connected to the gas inlet 24b, the gas inlet 24b is opened, and the gas pressure gauge 44 is filled with the ammonia gas G1 until a gas pressure of 1 mbar is obtained. Close the inlet 24b. The temperature of the heater 43 is set to room temperature.

  The optical diaphragm 22 and the concave mirror 23 are installed on movable stages 45 and 46, respectively. XYZ axis stage controllers 47, 48, and 49 are connected to the movable stages 26, 45, and 46, and the positions of the light excitation type VCSEL 59, the optical diaphragm 22, and the concave mirror 23 can be adjusted. A composite resonator 71 is formed by combining two resonators including an optically pumped VCSEL 59, an optical aperture 22, and a concave mirror 23. In the composite resonator 71, by adjusting each position, a single transverse mode and a single longitudinal mode are formed. Mode is being performed. Since the concave mirror 23 having a curvature radius of 10 cm is used, the movable stages 26, 45, and 46 are finely adjusted by the XYZ axis stage controllers 47, 48, and 49 with the distance between the concave mirror 23 and the photoexcited VCSEL 59 as a guideline. A single transverse and longitudinal mode of the semiconductor laser light is realized.

  A lens 51 is disposed opposite to one end of the gas cell 24 in the optical path through which the semiconductor laser light emitted from the optically pumped VCSEL 59 propagates, and the first photodiode 52 of the gas cell 24 faces the lens 51. Has been placed. A lens 53 is disposed relative to the other end of the gas cell 24 in the optical path, an etalon resonator 54 is disposed relative to the lens 53, and a second photodiode 55 is disposed relative to the etalon resonator 54. Is arranged.

  The semiconductor laser light L4 emitted from the photoexcited VCSEL 59 enters the first photodiode 52 through one end of the gas cell 24 and the lens 48 when the wavelength does not match the absorption line of the ammonia gas G1. The light emission intensity (voltage / current) is recorded in the photodiode 52. When the wavelength of the absorption line of the ammonia gas G1 matches, the semiconductor laser light L4 is absorbed by the ammonia gas G1. From the opposite side of the photoexcited VCSEL 59, the semiconductor laser light L5 having an output light intensity of about 1/20 of the semiconductor laser light L4 is emitted at the same wavelength. The semiconductor laser light L5 is incident on the second photodiode 55 through the heat sink 25 and the through holes 25a and 26a of the movable stage 26, the lens 53, the optical fiber 70, the WDM filter 69, and the etalon resonator 54, and has high resolution. The oscillation wavelength is monitored at.

  In the semiconductor laser absorption spectroscopic device 58, as shown in FIG. 6, the oscillation wavelength of light gradually increases in proportion to the increase in current, and the output intensity of light changes at a predetermined rate. Moreover, it was confirmed by the optical spectrum measurement and the far field pattern measurement that the emitted light from the photoexcited VCSEL 59 has a good single transverse mode and longitudinal mode property. As shown in FIG. 7 (in fact, a dip larger than that shown in the figure was observed, but here, only a representative dip having a large amount of absorption is shown), the semiconductor laser absorption spectrometer 58 has a very large dip. It is deep and its shape is acute, so it can be seen that data having a high S / N ratio and wavelength accuracy were obtained even though the gas pressure was as low as 1 mbar. As shown in FIG. 8, the light absorption amount obtained by the semiconductor laser absorption spectroscopic device 58 and the light absorption amount obtained by the simulation are in good agreement with each other without any deviation of the absorption line wavelength. It can be seen that.

  As described above, according to the semiconductor laser absorption spectroscopic device 58 having the composite resonator 71, a high S / N ratio can be ensured even when the ammonia gas pressure is less than 10 mbar, so that accurate gas concentration measurement can be realized. It becomes possible. Further, the use of the photoexcited VCSEL 59 eliminates the need for an electrode and a current confinement structure, and thus has an effect of simplifying the fabrication of the surface emitting semiconductor laser.

  In the above description, ammonia gas is used as the measurement gas. However, any gas may be used as long as it has an absorption line wavelength near the oscillation wavelength of the semiconductor laser light. Has the same effect as measurement.

  The semiconductor laser absorption spectrometer according to the fourth embodiment will be described below with reference to the drawings.

  FIG. 12 is a schematic diagram of a semiconductor laser absorption spectrometer according to the fourth embodiment of the present invention. The semiconductor laser absorption spectrometer according to the fourth embodiment is obtained by changing the arrangement positions of the optically pumped VCSEL, the optical diaphragm, and the concave mirror in the semiconductor laser absorption spectrometer according to the third embodiment described above. It has the same configuration as the semiconductor laser absorption spectrometer. About these structures, the same code | symbol as the semiconductor laser absorption spectroscopy apparatus which concerns on the said 3rd Example is attached, and the description is abbreviate | omitted about the same code | symbol.

  A semiconductor laser absorption spectroscopic apparatus 72 according to the fourth embodiment of the present invention has a light-excited VCSEL 59, an optical diaphragm 22 and a concave mirror 23 arranged outside a gas cell 73, and a semiconductor laser emitted from one of the light-excited VCSELs 59. The light L4 enters the first photodiode 52 through the gas cell 73, the optical diaphragm 22, the concave mirror 23, and the lens 51. The semiconductor laser light L5 emitted from the other of the optically pumped VCSEL 59 passes through the heat sink 25 and the through holes 25a and 26a of the movable stage 26, the lens 53, the WDM filter 69, and the etalon resonator 54, and then enters the second photodiode 55. Incident.

  Both end faces of the gas cell 73 are processed obliquely at an angle of about 1 to 7 degrees so as to minimize the influence of reflection of the semiconductor laser light on the end faces. Therefore, according to the semiconductor laser absorption spectroscopic apparatus 72 according to the fourth embodiment, the same operational effects as the semiconductor laser absorption spectroscopic apparatus 58 according to the third embodiment are exhibited. Further, since the photoexcited VCSEL 59 is disposed outside the gas cell 73, there is an advantage that the driving temperature of the photoexcited VCSEL 59 can be controlled without being affected by the heater 43 that controls the temperature of the gas cell 73.

  The semiconductor laser absorption spectrometer according to the fifth embodiment will be described below with reference to the drawings.

  FIG. 13 is a schematic diagram of a semiconductor laser absorption spectrometer according to a fifth embodiment of the present invention, FIG. 14 is a graph showing the current dependence of the optical output and oscillation wavelength in the device, and FIG. FIG. 16 is a graph showing the relationship between the light absorption amount and the oscillation wavelength, and FIG. 16A shows the measurement result of the light absorption amount in the device. 16 (b) shows the simulation result of the light absorption amount. The semiconductor laser absorption spectrometer according to the fifth embodiment is obtained by replacing the current-excited VCSEL in the semiconductor laser absorption spectrometer according to the first embodiment described above with an edge-emitting semiconductor laser. It has the same configuration as the semiconductor laser absorption spectrometer. About these structures, the same code | symbol as the semiconductor laser absorption spectroscopy apparatus which concerns on the said 1st Example is appended.

Here, the concentration measurement of ammonia gas, which is a gas to be measured having a gas pressure of 1 mbar, will be described in detail.
As shown in FIG. 13, a semiconductor laser absorption spectrometer 74 according to a fifth embodiment of the present invention includes an edge-emitting semiconductor laser 75 and an edge-emitting semiconductor laser 75 that are used in the current optical fiber communication network. The optical aperture 22 is disposed on the optical path of the semiconductor laser light oscillated by the optical path, and the concave mirror 23 is disposed on the optical path and is disposed opposite to the optical aperture 22. However, the edge-emitting semiconductor laser 75, the optical aperture 22, and the concave mirror 23 are disposed in a gas cell 24, which is a gas container that encloses ammonia gas G1, which is a measurement gas having an absorption line wavelength near a laser oscillation wavelength, which will be described later. Has been.

  The edge-emitting semiconductor laser 75 and the heat sink 25 disposed adjacent to the edge-emitting semiconductor laser 75 are fixed on the movable stage 26 by AuSn solder (not shown), and the edge-emitting semiconductor laser. A laser driver 76 is connected to 75. The edge-emitting semiconductor laser 75 is driven by controlling the temperature and the current value by an electronic cooling device (not shown) built in the movable stage 26 and a laser driver 76, respectively. A temperature controller 28 is connected to the electronic cooling device, and the temperatures of the heat sink 25 and the movable stage 26 are set to the same temperature as the room temperature.

  The edge-emitting semiconductor laser 75 is formed by sequentially forming an n-InP clad layer, an InGaAsP / InGaAsP multiple quantum well active layer (MWQ active layer), a p-InP clad layer, and a contact layer on an n-InP substrate. A mesa stripe having a width of 1 μm is processed by a mask and photolithography, and the periphery of the protrusion formed by the mesa stripe is buried with a semi-insulating Inp layer. An n-electrode is formed on the n-InP substrate side, a p-electrode is formed on the contact layer, an antireflection film is formed on the end surface on the concave mirror 23 side, and a reflectance is formed on the other end surface. A Fabry-Perot type semiconductor laser (resonator length: 500 μm), which is a 95% highly reflective film, is formed, and laser oscillation occurs by current injection.

  The edge-emitting semiconductor laser 75 has a reflectivity of 1% consisting of a first reflecting mirror made of a highly reflective film formed on the end face of the edge-emitting semiconductor laser 75 and an antireflection film formed on the other end face. The second reflector has a first resonator sandwiching the MQW active layer as a gain medium. On the other hand, a second resonator is formed by installing a concave mirror 23 having a reflectivity of 90% as a third reflecting mirror at a position opposite to the second reflecting mirror. The first resonator and the second resonator are coupled to form a coupled resonator structure.

  Semiconductor laser light is emitted from one side of the first reflecting mirror and one side of the third reflecting mirror, respectively, and the semiconductor laser light L6 emitted from one side of the third reflecting mirror is The output light intensity is adjusted to about 20 times that of the semiconductor laser light L7 emitted from the first reflecting mirror.

  On the other hand, the gas cell 24 has a length of about 40 cm, is made of a material such as quartz having a high temperature resistance of 1000 ° C. or higher, and is transparent to the semiconductor laser light emitted from the edge-emitting semiconductor laser 75. A certain material is used. Both end faces of the gas cell 24 are processed obliquely at an angle of about 1 to 7 degrees so that the influence of the reflection of the semiconductor laser light on the end face is minimized. The temperature of the ammonia gas G1 in the gas cell 24 is adjusted to be constant by a heater 43 provided around the gas cell 24, and the gas pressure of the ammonia gas G1 in the gas cell 24 is adjusted to the gas outlet of the gas cell 24. It is monitored by a gas pressure gauge 44 provided at 24a.

  As in Example 1 described above, the ammonia gas G1 is charged into the gas cell 24 by first connecting a vacuum pump (not shown) to the gas outlet 24a with the gas inlet 24b of the gas cell 24 closed. After evacuating the gas cell 24, the gas outlet 24a is closed. Subsequently, a container (cylinder) containing ammonia gas G1 is connected to the gas inlet 24b, the gas inlet 24b is opened, and the gas pressure gauge 44 is filled with the ammonia gas G1 until a gas pressure of 1 mbar is obtained. Close the inlet 24b. The temperature of the heater 43 is set to room temperature.

  The optical diaphragm 22 and the concave mirror 23 are installed on movable stages 45 and 46, respectively. XYZ axis stage controllers 47, 48, and 49 are connected to the movable stages 26, 45, and 46, and the positions of the edge-emitting semiconductor laser 75, the optical diaphragm 22, and the concave mirror 23 can be adjusted. A composite resonator 79 in which two resonators composed of an edge-emitting semiconductor laser 75, an optical aperture 22, and a concave mirror 23 are coupled is formed. In the composite resonator 79, by adjusting each position, a single transverse mode is obtained. Single vertical mode has been implemented. Since the concave mirror 23 having a radius of curvature of 10 cm is used, the movable stages 26, 45 and 46 are finely adjusted by the XYZ axis stage controllers 47, 48, and 49 with the distance between the concave mirror 23 and the edge-emitting semiconductor laser 75 as a guideline of about 10 cm. Thus, single horizontal and vertical modes are realized.

  A lens 51 is disposed opposite to one end of the gas cell 24 in the optical path in which the semiconductor laser light emitted from the edge-emitting semiconductor laser 75 propagates, and the first photo of the gas cell 24 is opposed to the lens 51. A diode 52 is disposed. A lens 53 is disposed relative to the other end of the gas cell 24 in the optical path, an etalon resonator 54 is disposed relative to the lens 53, and a second photodiode 55 is disposed relative to the etalon resonator 54. Is arranged.

  The semiconductor laser light L6 emitted from the edge emitting semiconductor laser 75 is incident on the first photodiode 52 through the lens 51 and one end of the gas cell 24 when the wavelength does not match the absorption line of the ammonia gas G1. The light emission intensity (voltage / current) is recorded in the photodiode 52. When the wavelength matches the absorption line of the ammonia gas G1, the laser light is absorbed by the ammonia gas G1. From the opposite side of the edge emitting semiconductor laser 75, the semiconductor laser light L7 having an output light intensity of about 1/20 of the semiconductor laser light L6 is emitted at the same wavelength. The semiconductor laser light L7 enters the second photodiode 55 through the lens 53 and the etalon resonator 54, and the oscillation wavelength is monitored with high resolution.

  In the semiconductor laser absorption spectrometer 74, as shown in FIG. 14, the oscillation wavelength of the semiconductor laser light gradually increases in proportion to the increase in current, and the output intensity of the semiconductor laser light gradually increases. Moreover, it was confirmed by the optical spectrum measurement and the far field pattern measurement that the emitted light from the edge-emitting semiconductor laser 75 has a good single transverse mode and longitudinal mode property. As shown in FIG. 15 (actually, a dip larger than that shown in the figure was observed, but only a representative dip having a large amount of absorption is shown here), the semiconductor laser absorption spectrometer 74 has a very large dip. It is deep and its shape is acute, so it can be seen that data having a high S / N ratio and wavelength accuracy were obtained even though the gas pressure was as low as 1 mbar. As shown in FIG. 16, the light absorption amount obtained by the semiconductor laser absorption spectroscopic device 74 and the light absorption amount obtained by the simulation are in good agreement with each other without any deviation of the absorption line wavelength. It can be seen that.

  As described above, according to the semiconductor laser absorption spectroscopic device 74 having the composite resonator 79, even when the ammonia gas G1 is less than 10 mbar, a high S / N ratio can be ensured, so that accurate gas concentration measurement can be realized. It becomes possible.

  In the above description, ammonia gas is used as the gas to be measured. However, any gas may be used as long as it has an absorption line wavelength near the laser oscillation wavelength. There are various effects.

  The semiconductor laser absorption spectrometer according to the sixth embodiment will be described below with reference to the drawings.

  FIG. 17 is a schematic view of a semiconductor laser absorption spectrometer according to the sixth embodiment of the present invention. The semiconductor laser absorption spectrometer according to the sixth embodiment is obtained by changing the arrangement positions of the edge-emitting semiconductor laser, the optical diaphragm, and the concave mirror in the semiconductor laser absorption spectrometer according to the fifth embodiment described above. Other than that, it has the same configuration as the semiconductor laser absorption spectrometer. About these structures, the code | symbol same as the semiconductor laser absorption spectroscopy apparatus which concerns on the said 1st Example is attached, and the description is abbreviate | omitted about the same code | symbol.

  A semiconductor laser absorption spectroscopic device 77 according to the sixth embodiment of the present invention has an edge emitting semiconductor laser 75, an optical aperture 22 and a concave mirror 23 arranged outside a gas cell 78. The semiconductor laser light L6 emitted from one side passes through the gas cell 78, the optical aperture 22, the concave mirror 23, and the lens 51 and enters the first photodiode 52. The semiconductor laser light L 7 emitted from the other of the edge-emitting semiconductor laser 75 enters the second photodiode 55 through the lens 53 and the etalon resonator 54.

  Both end surfaces of the gas cell 76 are processed obliquely at an angle of about 1 to 7 degrees so as to minimize the influence of reflection of the semiconductor laser light on the end surface. Therefore, according to the semiconductor laser absorption spectroscopic apparatus 77 according to the sixth embodiment, the same operational effects as the semiconductor laser absorption spectroscopic apparatus 74 according to the fifth embodiment are exhibited. Furthermore, since the edge-emitting semiconductor laser 75 is disposed outside the gas cell 78, the driving temperature of the edge-emitting semiconductor laser 75 can be controlled without being affected by the heater 43 that controls the temperature of the gas cell 78. There is an advantage.

  The present invention can be used in a semiconductor laser absorption spectrometer.

1 is a schematic view of a semiconductor laser absorption spectrometer according to an embodiment of the present invention. It is explanatory drawing of the composite resonator structure in the semiconductor laser absorption spectroscopy apparatus which concerns on one Embodiment of this invention. It is a graph which shows the relationship between the injection current and the optical output in the semiconductor laser absorption spectroscopy apparatus which concerns on one Embodiment of this invention. 1 is a schematic diagram of a semiconductor laser absorption spectrometer according to a first embodiment of the present invention. It is explanatory drawing of the current excitation type | mold surface emitting semiconductor laser in the semiconductor laser absorption spectroscopy apparatus based on 1st Example of this invention. It is a graph which shows the current dependence of the optical output and oscillation wavelength in the semiconductor laser absorption spectrometer which concerns on the 1st Example of this invention. It is a graph which shows the measurement result by the semiconductor laser absorption spectrometer which concerns on 1st Example of this invention. It is a graph which shows the relationship between the light absorption amount and oscillation wavelength in the measurement result by the semiconductor laser absorption spectrometer which concerns on 1st Example of this invention, and simulation. It is the schematic of the semiconductor laser absorption spectroscopy apparatus which concerns on the 2nd Example of this invention. It is the schematic of the semiconductor laser absorption spectroscopy apparatus which concerns on the 3rd Example of this invention. FIG. 6 is a structural diagram of an optically pumped surface emitting semiconductor laser in a semiconductor laser absorption spectrometer according to a third embodiment of the present invention. It is the schematic of the semiconductor laser absorption spectroscopy apparatus which concerns on the 4th Example of this invention. It is the schematic of the semiconductor laser absorption spectroscopy apparatus which concerns on the 5th Example of this invention. It is a graph which shows the current dependence of the optical output and oscillation wavelength in the semiconductor laser absorption spectrometer which concerns on the 5th Example of this invention. It is a graph which shows the measurement result by the semiconductor laser absorption spectrometer which concerns on the 5th Example of this invention. It is a graph which shows the measurement result by the semiconductor laser absorption spectrometer which concerns on the 5th Example of this invention, and the relationship between the light absorption amount and oscillation wavelength in simulation. It is the schematic of the semiconductor laser absorption spectroscopy apparatus which concerns on the 6th Example of this invention. It is the schematic of the conventional semiconductor laser absorption spectroscopy apparatus. It is a graph which shows the relationship between the injection current and optical output in the conventional semiconductor laser absorption spectroscopy apparatus. It is a graph which shows the measurement result by the conventional semiconductor laser absorption spectroscopy apparatus. It is a graph which shows the measurement result by the conventional semiconductor laser absorption spectroscopy apparatus, and the relationship between the light absorption amount and oscillation wavelength in simulation.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Surface emitting semiconductor laser 2 Optical aperture 3 Concave mirror 4 n-InP substrate 5 n-DBR layer 6 Multiple quantum well active layer (MQW active layer)
7 p-DBR layer 8 p-InGaAs contact layer 9 antireflection film 11 p electrode 12 n electrode 13 first resonator 14 second resonator

Claims (11)

In a semiconductor laser absorption spectrometer that evaluates gas concentration using absorption spectroscopy using semiconductor laser light,
Three reflecting mirrors are installed on an optical path through which the semiconductor laser light emitted from the semiconductor laser propagates, and two resonators composed of two adjacent reflecting mirrors are provided, and one of the two resonators is covered. A semiconductor laser absorption spectroscopic apparatus, characterized in that a measurement gas is arranged. The semiconductor laser absorption spectrometer according to claim 1.
A first photodiode for receiving the semiconductor laser light emitted from the resonator side where the measurement gas is disposed;
A semiconductor laser absorption spectroscopic apparatus comprising: a second photodiode that receives the semiconductor laser emitted from a resonator side different from the resonator. The semiconductor laser absorption spectrometer according to claim 1 or 2,
The semiconductor laser absorption spectroscopic apparatus, wherein the semiconductor laser is a current excitation type surface emitting semiconductor laser driven by current excitation. The semiconductor laser absorption spectrometer according to claim 3,
3. A semiconductor laser absorption spectroscopic apparatus, wherein the three reflecting mirrors are arranged inside a gas container that encloses the gas to be measured. The semiconductor laser absorption spectrometer according to claim 3,
3. A semiconductor laser absorption spectroscopic apparatus, wherein the three reflecting mirrors are arranged outside a gas container that encloses the gas to be measured. The semiconductor laser absorption spectrometer according to claim 1 or 2,
The semiconductor laser absorption spectroscopic apparatus, wherein the semiconductor laser is an optically pumped surface emitting semiconductor laser that oscillates by optical excitation. The semiconductor laser absorption spectrometer according to claim 6,
A semiconductor laser absorption spectroscopic apparatus, wherein the three reflecting mirrors are arranged inside a gas container that encloses the gas to be measured. The semiconductor laser absorption spectrometer according to claim 6,
3. A semiconductor laser absorption spectroscopic apparatus, wherein the three reflecting mirrors are arranged outside a gas container that encloses the gas to be measured. The semiconductor laser absorption spectrometer according to claim 1 or 2,
The semiconductor laser absorption spectroscopic apparatus, wherein the semiconductor laser is an edge-emitting semiconductor laser. The semiconductor laser absorption spectrometer according to claim 9,
A semiconductor laser absorption spectroscopic apparatus, wherein the three reflecting mirrors are arranged inside a gas container that encloses the gas to be measured. The semiconductor laser absorption spectrometer according to claim 9,
3. A semiconductor laser absorption spectroscopic apparatus, wherein the three reflecting mirrors are arranged outside a gas container that encloses the gas to be measured.

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