Infrared optical parametric oscillator

Abstract

To provide an infrared light parametric oscillation device capable of obtaining convenient mid-infrared ray with high output at low cost.SOLUTION: Excitation light p generated by an excitation light source 12 that is made Nd:YAG laser laser oscillated in wavelength 1.0642 μm is made incident to a nonlinear optical device 18 of Ba2Ga8GeS16 crystal via an input mirror 16. In the nonlinear optical device 18, signal light s and idler light i in 8 to 12 μm wavelength are outputted. By an output mirror 20 reflecting the excitation light p transmitting the nonlinear optical device 18 and returning it to the nonlinear optical device 18, a double path appears, and the signal light s and the idler light i are outputted again.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an infrared optical parametric oscillator that oscillates coherent infrared light by infrared optical parametric oscillation, and is particularly suitable for oscillating infrared light (idler) in the wavelength range of 8 to 12 μm. [Background technology]

[0002] Conventionally, an optical parametric oscillator based on nonlinear optics theory has been known, which outputs coherent light beams of two different wavelengths as output light beams by inputting coherent pump light beams into the crystal of a nonlinear optical element. In general, this optical parametric oscillator is roughly composed of a pump light source, a nonlinear optical element, and a pair of reflecting mirrors arranged on both sides of the element. Note that these two coherent light beams, which are output light beams, are called signal light beam and idler light beam, and the pump light beam, signal light beam, and idler light beam satisfy the relationships shown in the following equations 1 and 2.

[0003] (Number 1) 1 / λ s +1 / λ i =1 / λ p

[0004] (Number 2) n s / λ s +n i / λ i =n p / λ p

[0005] However, λ p is the wavelength of the excitation light, λ s is the wavelength of the signal light, λ i is the wavelength of the idler light, and for nonlinear optical elements, n p is the refractive index of the excitation light, n s is the refractive index of the signal light, n i is the refractive index of the idler beam.

[0006] In a laser oscillation device having such an optical parametric oscillator, for example, a Nd:YAG (Nd 3+ :Y3Al5O 15 ) laser and uses AgGaS2 (AGS) crystals with a low damage threshold as nonlinear optical elements.

[0007] On the other hand, optical parametric oscillators can be used as light sources for in-vehicle laser radars, or for detecting toxic gases in the atmosphere, such as CH4, SO2, and CO. Therefore, in recent years, there has been interest in utilizing broadband (half-width up to about 500 nm) and coherent infrared light in the wavelength range of 8 to 12 μm, which corresponds to the atmospheric window. Accordingly, there has been a need for a device that can be miniaturized with a simple structure, and that can generate high-power infrared light in this wavelength range. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 11-95271 [Patent Document 2] JP 2003-280055 A [Patent Document 3] JP 2008-40293 A [Patent Document 4] JP 2018-31811 A Summary of the Invention [Problem to be solved by the invention]

[0009] However, conventional laser oscillators that are excited by a typical Nd:YAG laser and generate infrared light with a wavelength of 8 to 12 μm as idler light may use a single-pass optical parametric oscillator or a double-pass optical parametric oscillator. Even if a nonlinear optical element capable of high output power is obtained, the following problems remain.

[0010] That is, in a single-pass optical parametric oscillator, the pump light only pumps the nonlinear optical element once, and therefore has the drawback of low conversion efficiency into infrared light of 8 to 12 μm, which is considered to be idler light.

[0011] Furthermore, in a double-path optical parametric oscillator, simply increasing the reflectivity of one of the reflecting mirrors, the input mirror, to 90-99% at the wavelength of the pump light (1.0642 μm) and at the signal light (1.16-1.23 μm) does not result in a high output power for the idler light with a wavelength of 8-12 μm. In other words, in order to obtain a high output power for the idler light, a minimum of 100 MW / cm is required. 2 It was necessary to use an input mirror with a high damage threshold that could withstand high powers exceeding 1000kJ / s.

[0012] However, while there are conventional reflectors made of metals such as gold and silver that have nearly 100% reflectivity for the idler light and the signal light, they have the drawback of deteriorating with use and have therefore not been practically adopted. For this reason, it is extremely difficult to manufacture reflectors with a high damage threshold as described above, and there is also the drawback of increased manufacturing costs.

[0013] In contrast, the above-mentioned Patent Documents 1 to 3 are examples of devices using parametric oscillators. For example, Patent Document 1 discloses a structure in which a quarter-wave plate is used to improve the ratio of energy converted from pump light to signal light and idler light near the degeneracy point where the wavelengths of the signal light and idler light are equal. Furthermore, Patent Document 2 discloses a device that uses an optical parametric oscillator to generate a coherent and stable output. Similarly, Patent Document 3 discloses a device that changes the angle of incidence of converted light incident on a wavelength conversion element body, reflects the light incident on the side surface of the wavelength conversion element body, and causes it to travel in a zigzag pattern within the wavelength conversion element body.

[0014] However, even in Patent Documents 1 to 3, there was no device that could provide useful mid-infrared infrared light with a wavelength of 8 to 12 μm at a low cost and with high output. 1-x CD x Although Ga2S4 crystals were used, the damage threshold of the element itself was low, so not only was it not possible to obtain high output, but it was also difficult to use for long periods of time. The present invention has been made in view of the above background, and has as its object to provide an infrared optical parametric oscillator that can provide useful, high-power mid-infrared infrared light at low cost. [Means for solving the problem]

[0015] The invention described in claim 1 that solves the above problem comprises an excitation light source that generates laser light; Ba2Ga8GeS emits coherent infrared light with a wavelength longer than that of the laser light when laser light is incident on it. 16 a nonlinear optical element that is a crystal; an input mirror disposed between the pump light source and the nonlinear optical element, which transmits the laser light and reflects coherent infrared light having a wavelength longer than that of the laser light; an output mirror that is disposed on the opposite side of the input mirror across the nonlinear optical element, and that reflects the laser light and transmits at least coherent infrared light having a wavelength longer than that of the laser light; An angle adjusting means for angle tuning the nonlinear optical element; The present invention relates to an infrared optical parametric oscillator device including:

[0016] According to the infrared optical parametric oscillator of claim 1, pumping light, which is laser light generated from a pumping light source, passes through an input mirror and is converted into Ba2Ga8GeS 16 The light is incident on a nonlinear optical element made of a crystal, which then performs optical parametric oscillation and outputs idler light, which is coherent infrared light with a longer wavelength than the laser light from the excitation light source.

[0017] The input mirror is placed between the pump light source and the nonlinear optical element, and an output mirror is placed on the opposite side of the nonlinear optical element from the input mirror. The idler light, which is a coherent infrared light, passes through this output mirror, but the laser light is reflected by this output mirror toward the nonlinear optical element.

[0018] Therefore, the nonlinear optical element outputs idler light, which is a coherent infrared ray with a longer wavelength than the laser light, by using the laser light reflected by the output mirror. In other words, in this claim, the idler light is generated twice from the nonlinear optical element as double-path optical parametric oscillation, making it possible to obtain at least high-power idler light.

[0019] The input mirror reflects the idler light, which is coherent infrared light output by the nonlinear optical element due to the laser light reflected by the output mirror, and the idler light passes through the nonlinear optical element and is transmitted through the output mirror in the same manner as the idler light described above. Furthermore, angle adjustment means equipped with a nonlinear optical element adjusts the rotation angle of the nonlinear optical element to perform angle tuning, thereby making it possible to output the idler light, which is coherent infrared light, while tunable in wavelength.

[0020] As described above, the infrared optical parametric oscillator of this claim has a simple structure that includes only an excitation light source, an input mirror, an output mirror, an angle adjustment means, etc., and by using a nonlinear optical element to generate double-pass optical parametric oscillation, it is possible to obtain approximately twice the output of a single-pass optical parametric oscillator, thereby making it possible to obtain useful mid-infrared infrared light at high output and low cost.

[0021] The invention of claim 2 uses an Nd:YAG laser as the excitation light source and Ba2Ga8GeS 16 An infrared optical parametric oscillator device as described in claim 1, wherein the cut angles of the crystal in the crystal are θ=40 to 50°, φ=0° or 90° (where θ and φ are polar coordinates and are angles from the z (=c) axis and the x (=a) axis, respectively).

[0022] Therefore, according to this claim, by using an Nd:YAG laser as the excitation light source, it is possible to output laser light with a wavelength of 1.0642 μm, and by using Ba2Ga8GeS as the nonlinear optical element as in claim 1, 16 By using a crystal, it is possible to parametrically oscillate idler light with a wavelength of 2.1 to 12 μm, which makes it possible to obtain high-power idler light, which is a useful mid-infrared infrared light in the 8 to 12 μm range within the 2.1 to 12 μm range, at low cost.

[0023] Furthermore, in this claim, the nonlinear optical element is a Ba2Ga8GeS crystal with a cut angle of θ=40 to 50° and φ=0° or 90° (where θ and φ are polar coordinates, and are angles from the z (=c) axis and the x (=a) axis, respectively). 16 By forming it into a crystal, it is possible to obtain crystals of a more appropriate shape, which results in a further increase in the output of mid-infrared infrared light in the range of 8 to 12 μm.

[0024] The invention of claim 3 is the infrared optical parametric oscillator according to claim 1 or 2, in which the input mirror is made of fused silica and the output mirror is made of ZnSe. Therefore, according to this claim, unlike input mirrors and output mirrors made of metals such as gold and silver, not only is there no increase in manufacturing costs, but they are also less likely to deteriorate with use, resulting in a higher damage threshold.

[0025] The invention of claim 4 is characterized in that the angle adjustment means is a rotation stage that mounts a nonlinear optical element and can rotate the nonlinear optical element; a sensor for measuring the rotation angle of the nonlinear optical element; a control means for controlling the amount of rotation of the rotary stage based on the measurement value of the sensor to maintain the nonlinear optical element within a predetermined angle range; The infrared optical parametric oscillator according to any one of claims 1 to 3, further comprising:

[0026] Therefore, according to this claim, the nonlinear optical element can be maintained within a predetermined angular range, making it possible to more appropriately and specifically tune the angle of the nonlinear optical element, and making it easier to parametrically oscillate idler light of a target wavelength using this nonlinear optical element.

[0027] The invention of claim 5 is an infrared optical parametric oscillator according to any one of claims 1 to 4, in which an isolator is arranged between the pumping light source and the input mirror to exclude laser light returning from the nonlinear optical element and prevent it from entering the pumping light source. Therefore, according to this claim, the isolator eliminates the laser light that returns to the pump light source side due to double-path optical parametric oscillation, preventing the laser light from entering the pump light source, thereby increasing the durability of the device. [Effects of the Invention]

[0028] The present invention has the excellent effect of providing an infrared optical parametric oscillator that can generate useful, high-power mid-infrared infrared radiation at low cost. [Brief explanation of the drawings]

[0029] [Figure 1]1 is a schematic diagram illustrating an embodiment of an infrared optical parametric oscillator according to the present invention. [Figure 2] FIG. 10 is a graph showing the output characteristics of signal light and idler light based on angle tuning of a Ba2Ga8GeS16 crystal applied to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0030] An embodiment of an infrared optical parametric oscillator according to the present invention will be described below with reference to the drawings. As shown in Fig. 1, an infrared optical parametric oscillator 10 according to this embodiment has a pump light source 12 that generates pump light p by laser oscillation at a wavelength of 1.0642 µm. In this embodiment, an Nd:YAG laser with an average output of 2.4 W (output per pulse: 80 mJ, pulse width: 5 ns) is used as the pump light source 12. At a position on the optical axis L that is the optical path of the pump light p and adjacent to the pump light source 12, which is the basic light source, to the right in Fig. 1, is an isolator 14, which is a beam splitter that allows the pump light p, which is laser light generated by the pump light source 12, to pass at least from left to right in Fig. 1.

[0031] 1, an input mirror 16 made of fused silica, such as quartz glass or fused silica, is located to the right of the isolator 14 on the optical axis L, and a dielectric multilayer film 16A is coated on the right end face of the input mirror 16. The transmittance T of the dielectric multilayer film 16A at a wavelength of 1.0642 μm is approximately 98%, and the reflectance R is also approximately 98% in the wavelength range of 1.16 to 1.42 μm, so the input mirror 16 itself has similar transmittance and reflectance.

[0032] It is also possible to consider that input mirror 16 has high reflectivity even for mid-infrared infrared wavelengths of 8 to 12 μm. Therefore, input mirror 16 can transmit excitation light p with a wavelength of 1.0642 μm and reflect infrared rays with predetermined wavelengths of 1.17 to 1.23 μm and 8 to 12 μm.

[0033] At a position adjacent to the input mirror 16 on the right side of the optical axis L, a Ba2Ga8GeS 16 The nonlinear optical element 18 formed of a crystal, for example, 15 mm in length, is disposed. 16 The crystal was grown by the Bridgman-Stockbarger method, and the transmittance range of visible light and infrared light is 0.41 to 12.1 μm. 16 The cut angles of the crystal are θ=40 to 50°, φ=0° or 90° (where θ and φ are polar coordinates and are angles from the z (=c) axis and x (=a) axis, respectively).

[0034] Furthermore, in this embodiment, when pump light p with a wavelength of 1.0642 μm that has passed through input mirror 16 is incident on this nonlinear optical element 18, signal light s and idler light i, which are coherent infrared rays with wavelengths longer than that of the pump light p and different from each other, are output. Here, in this embodiment, the signal light s has a wavelength of 1.16 to 1.23 μm, and the idler light i has a wavelength of 8 to 12 μm.

[0035] Both end faces of this nonlinear optical element 18 are not only optically polished but also coated with an anti-reflection film 18A that has a high transmittance T of approximately 98% at wavelengths of 1.0642 μm and 1.16 to 1.32 μm. However, this anti-reflection film 18A can maintain a transmittance T of approximately 98% up to a wavelength of 1.42 μm.

[0036] On the other hand, this Ba2Ga8GeS 16 The crystal is a semiconductor that belongs to the point group "point group 6mm". 16 The nonlinear optical constant of the crystal is almost the same as that of the conventional AgGa2S4 crystal (d 15 ≒13 pm / V), but the damage threshold at a wavelength of 1.0642 μm is said to be about 20 times that of this AgGaS2 crystal.

[0037] The Ba2Ga8GeS is excited by the excitation light p from the Nd:YAG laser, which is the excitation light source 12. 16 The conversion efficiency of crystals currently achieved is limited to 3-5% (depending on the wavelength) due to the long wavelength of the idler light i. However, if it becomes possible to coat the crystal with an anti-reflection film with a high damage threshold at wavelengths of 8-12 μm, a high output of 400 kW peak power (500 mW average power) at 30 Hz with an average input of 4 W will be achievable.

[0038] On the other hand, an output mirror 20 made of ZnSe is disposed adjacent to the nonlinear optical element 18 on the right side along the optical axis L. In this embodiment, in order to make the pumping light p double-pass, the incident end face of the output mirror 20 is coated with a dielectric multilayer film 20A that not only has a high reflectance R of approximately 98% at a wavelength of 1.0642 μm, but also has a reflectance R of approximately 80 to 90% in the wavelength range of 1.15 to 1.42 μm. In addition, the exit end face of the output mirror 20 is coated with an anti-reflection film 20B that has a transmittance T of approximately 90 to 98% in the wavelength range of 8 to 12 μm.

[0039] As a result of the above, a portion of the signal light s and most of the idler light i are transmitted through the output mirror 20 and output as shown in Figure 1. Furthermore, most of the pump light p, which is laser light, is reflected by the dielectric multilayer film 20A of the output mirror 20 and returns to the nonlinear optical element 18, making a round trip (double pass) through the nonlinear optical element 18. Furthermore, the pump light p that has not been phase-matched after passing through the nonlinear optical element 18 in the reverse direction is transmitted through the input mirror 16 and is reflected upward in Figure 1 by the isolator 14 and separated.

[0040] When the signal light s and the idler light i pass through the nonlinear optical element 18 again, they are output again, but the coherent infrared light of these two wavelengths is also reflected by the input mirror 16, returns to the nonlinear optical element 18, and passes through, with a portion of the signal light s and a majority of the idler light i finally passing through the output mirror 20.

[0041] On the other hand, below the nonlinear optical element 18, a rotary stage 24 is installed, which is rotated by a motor 26 such as a servo motor or a stepping motor. The rotary stage 24 carries the nonlinear optical element 18, and the nonlinear optical element 18 can be rotated around its x (= a) axis.

[0042] In addition, an angle sensor 28 that measures the rotation angle of the nonlinear optical element 18 is attached to the nonlinear optical element 18, and a controller 30, which is a control means connected to this angle sensor 28 and the motor 26, adjusts the rotation angle of the motor 26 based on the measurement value of the angle sensor 28, thereby controlling the rotation amount of the rotation stage 24 and making it possible to maintain the nonlinear optical element 18 within a predetermined angle range, thereby enabling angle tuning.

[0043] In other words, the rotation stage 24, motor 26, angle sensor 28, and controller 30 constitute the angle adjustment device 22, which is an angle adjustment means for tuning the angle of the nonlinear optical element 18. As a result, the infrared optical parametric oscillator 10 of this embodiment can ensure an angle accuracy of, for example, ±0.03° or less.

[0044] Next, the operation of the infrared optical parametric oscillator 10 of this embodiment will be described. In the infrared optical parametric oscillator 10 according to this embodiment, pump light p, which is laser light generated by the pump light source 12, which is an Nd:YAG laser, travels along the optical axis L and passes through the isolator 14 and the input mirror 16 to generate Ba2Ga8GeS 16 The light is incident on a nonlinear optical element 18 made of a crystal. This nonlinear optical element 18 performs optical parametric oscillation to output signal light s and idler light i, which are coherent infrared rays with wavelengths longer than that of the pump light p and different from each other.

[0045] The input mirror 16 is disposed between the pumping light source 12 and the nonlinear optical element 18, and an output mirror 20 is disposed on the opposite side of the nonlinear optical element 18 from the input mirror 16. A portion of the signal light s and most of the idler light i are transmitted through the output mirror 20, but the pumping light p is reflected by the output mirror 20 toward the nonlinear optical element 18 along the optical axis L.

[0046] Therefore, the nonlinear optical element 18 outputs the signal light s and the idler light i in the same manner due to the pump light p reflected by the output mirror 20. Since the input mirror 16 also reflects the coherent infrared rays of these two wavelengths, these infrared rays pass through the nonlinear optical element 18 and are output after passing through the output mirror 20 in the same way as the signal light s and idler light i described above.

[0047] That is, in this embodiment, the signal light s and the idler light i are doubly generated from the nonlinear optical element 18 to form a double-pass optical parametric oscillation, making it possible to obtain high output power at least from the idler light i. The returning pump light p passes through the nonlinear optical element 18, but the isolator 14 arranged between the pump light source 12 and the input mirror 16 rejects this passing pump light p to the upper side in FIG. 1, so that the pump light p does not enter the pump light source 12.

[0048] Furthermore, the nonlinear optical element 18 is mounted on a rotation stage 24 that is rotated by a motor 26, thereby enabling the nonlinear optical element 18 to rotate. An angle sensor 28 measures the rotation angle of the nonlinear optical element 18, and a controller 30 adjusts the rotation angle of the motor 26 based on the measurement value of the angle sensor 28. This allows the amount of rotation of the rotation stage 24 to be controlled to maintain the nonlinear optical element 18 within a predetermined angle range, thereby enabling angle tuning of the nonlinear optical element 18 to a preset target angle.

[0049] As described above, the infrared optical parametric oscillator 10 of this embodiment achieves approximately twice the output of a single-pass optical parametric oscillator due to the double-pass optical parametric oscillation achieved by the nonlinear optical element 18. Furthermore, this embodiment not only has a simple and compact structure that includes only the pump light source 12, input mirror 16, output mirror 20, angle adjustment device 22, etc., but also, by using an Nd:YAG laser as the pump light source 12 as described above, it is able to output pump light p with a wavelength of 1.0642 μm.

[0050] The nonlinear optical element 18 is made of Ba2Ga8GeS 16 By using a crystal, it is possible to optically parametrically oscillate signal light s with a wavelength of 1.17 to 1.23 μm and idler light i with a wavelength of 8 to 12 μm. Furthermore, by placing nonlinear optical element 18 on rotation stage 24 and rotating it with high precision using controller 30, it becomes possible to accurately tune the angle of nonlinear optical element 18, and it becomes possible to optically parametrically oscillate idler light i with a particularly required wavelength within the wavelength range of 8 to 12 μm.

[0051] As a result, the infrared optical parametric oscillator 10 of this embodiment can generate useful mid-infrared infrared radiation at high output and low cost, which can be used as a light source for automotive laser radar or for detecting toxic gases such as CH4, SO2, and CO in the atmosphere.

[0052] Furthermore, in this embodiment, the input mirror 16 is made of fused silica and the output mirror 20 is made of ZnSe. This not only prevents the manufacturing costs from increasing, as opposed to input mirror 16 and output mirror 20 made of metals such as gold or silver, but also makes them less susceptible to deterioration with use, resulting in a higher damage threshold.

[0053] Next, the Ba2Ga8GeS used in this embodiment 16 The results of the crystal experiments will be specifically explained using the graph in FIG. 2 and Table 1. The excitation light p, which is a laser beam with a wavelength of 1.0642 μm, was applied by a Nd:YAG laser to the crystal, and the angle of the crystal was tuned in the range of 43.4° to 41.9°. The size of the Ba2Ga8GeS crystal was 10 mm x 10 mm x 15 mm. 16 Experimental results showed that the idler light i was phase-matched in the wavelength range of 8 to 12 μm when incident on the crystal.

[0054] Specifically, the phase matching angle θ, which is the angle of the crystal, is rotated around the x (= a) axis in the range of 43.4° to 41.9°, and data taken at measurement points M1 to M8 and M11 to M18 is shown in the graph in Figure 2. Here, measurement points M1 and M11 are set to the same angle, and measurement points M2 to M8 and M12 to M18 are set to the same angle. In this case, the phase matching angle θ decreases from 43.4° at measurement points M1 and M11, reaches a minimum of 41.9° at measurement points M5 and M15, and then increases to 42.3° at measurement points M8 and M18.

[0055] Based on this graph, this Ba2Ga8GeS 16 Signal light s of each wavelength λs was generated from the crystal, and light with wavelengths from 1.2275 μm to 1.1677 μm was obtained at measurement points M1 to M8 (due to space limitations, only measurement points M1, M5, and M8 are shown in the graph in Figure 2). Idler light i of each wavelength λi was also generated from the crystal, and light with wavelengths from 7.9994 μm to 12.0064 μm was obtained at measurement points M11 to M18.

[0056] The signal light s with wavelength λs and the idler light i with wavelength λi corresponding to each phase matching angle θ at each of the measurement points M1 to M8 and each of the measurement points M11 to M18 are specifically shown in Table 1 below. In Table 1, the "wavelength of the signal light s" is represented as wavelength λs, and the "wavelength of the idler light i" is represented as wavelength λi. Meanwhile, the solid line in the graph of Fig. 2 is the logical curve C calculated using the Sellmeier equation constructed by the inventors, and agreed with the experimental value within a range of ±0.2°.

[0057] [Table 1]

[0058] Furthermore, the results of this experiment showed that the wavelength width (bandwidth) of the idler light i reached approximately 110 nm when the wavelength λi of the idler light i was 8.50 μm, and approximately 800 nm when it was 11.0 μm. Therefore, it was confirmed that using the idler light i with a wide bandwidth is extremely effective in detecting toxic gases in the atmosphere.

[0059] The greatest feature of the infrared optical parametric oscillator 10 of this embodiment is that, when pumped by a common and inexpensive Nd:YAG laser, phase matching is possible over a long wavelength range of 8 to 12 μm and a wide wavelength band, which was impossible with conventional chemical crystals, using Ba2Ga8GeS 16 This was made possible for the first time by using crystals.

[0060] Furthermore, in the above embodiment, not only the idler light i but also the signal light s is transmitted through the output mirror 20 and output from the infrared optical parametric oscillator 10, but it is also possible to guide only the idler light i that is actually used outside the device. Also, in the above embodiment, the input mirror 16 is made of fused silica and the output mirror 20 is made of ZnSe, but other well-known materials may be used for the input mirror 16 and the output mirror 20 as long as they have a high damage threshold. Meanwhile, in the above embodiment, the angle sensor 28 that measures the rotation angle is attached to the nonlinear optical element 18, but this angle sensor 28 may also be attached directly to the rotation stage 24.

[0061] Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and can be implemented in various modified forms without departing from the spirit of the present invention. [Industrial Applicability]

[0062] The present invention can be applied to various technical fields that require high-power infrared rays, such as light sources for automotive laser radars and for detecting toxic gases in the atmosphere, as well as other technical fields such as industrial applications. [Explanation of symbols]

[0063] 10. Infrared optical parametric oscillator 12 Excitation light source 14 Isolator 16 Input mirror 18 Nonlinear optical elements 20 Output mirror 22 Angle adjustment device 24 Rotating Stage 26 Motor 28 Angle Sensor 30 Controllers p excitation light s Signal light i Idler light

Claims

1. an excitation light source that generates laser light; Ba emits coherent infrared light with a wavelength longer than that of the laser light when it is incident on the device. 2 Ga 8 GeS 16 a nonlinear optical element that is a crystal; an input mirror disposed between the pump light source and the nonlinear optical element, which transmits the laser light and reflects coherent infrared light having a wavelength longer than that of the laser light; an output mirror that is disposed on the opposite side of the input mirror across the nonlinear optical element, and that reflects the laser light and transmits at least coherent infrared light having a wavelength longer than that of the laser light; An angle adjusting means for angle tuning the nonlinear optical element; An infrared optical parametric oscillator comprising:

2. The excitation light source is a Nd:YAG laser, and Ba 2 Ga 8 GeS 16 2. The infrared optical parametric oscillator according to claim 1, wherein the cut angles of the crystal are θ=40 to 50°, φ=0° or 90° (where θ and φ are polar coordinates and are angles from the z (=c) axis and the x (=a) axis, respectively).

3. 3. An infrared optical parametric oscillator according to claim 1, wherein the input mirror is made of fused silica and the output mirror is made of ZnSe.

4. The angle adjustment means a rotation stage that mounts a nonlinear optical element and can rotate the nonlinear optical element; a sensor for measuring the rotation angle of the nonlinear optical element; a control means for controlling the amount of rotation of the rotary stage based on the measurement value of the sensor to maintain the nonlinear optical element within a predetermined angle range; 4. The infrared optical parametric oscillator according to claim 1, further comprising:

5. 5. An infrared optical parametric oscillator according to claim 1, wherein an isolator is disposed between the pumping light source and the input mirror to exclude laser light returning from the nonlinear optical element and prevent it from entering the pumping light source.

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