JP5110310B2 - Laser light generator - Google Patents

Description

  The present invention relates to a laser beam generator having a light source and a resonator.

  In general, extremely large intensity laser light propagates in a laser resonator or an external resonator (wavelength converter). For this reason, when the laser beam passes through an optical element such as a laser crystal or a wavelength conversion element in the resonator, various problems occur due to absorption of the laser beam or electric field breakdown.

  For example, in a laser crystal, energy that is not involved in laser oscillation in excitation current or excitation light generates a heat distribution, which degrades the quality of the laser light through the refractive index distribution and refractive index anisotropy. Further, the material through which the laser beam passes undergoes a chemical change with time, and the quality of the laser beam is deteriorated over time through coloring, a decrease in transmittance, and non-uniformity. Here, since the degree of deterioration of the quality of the laser light due to the chemical change of the material as described above is generally larger as the laser wavelength is shorter, visible light is larger than infrared light, and ultraviolet light is larger than visible light. .

  In order to avoid the laser beam quality deterioration due to heat-induced distortion and refractive index distribution, there is a method to reduce the temperature distribution by using a material with high thermal conductivity or reducing the amount of heat generation. . In order to reduce the chemical change, a highly reliable substance, a material with few impurities, a method of canceling the change due to the structure, or the like is used. However, when the amount of change is large, it cannot be completely removed by such a method, and in many cases, it gradually increases when used for a long time.

  Therefore, conventionally, a metal opening, slit, knife edge, or the like is used as one of the methods for reducing the quality deterioration of the laser beam in the resonator. These elements provide high intracavity losses for degraded beams and lower optical losses for desirable beam shapes (such as lower order modes) to create loss differences within the resonator. It is an element that assists so that only high-quality laser light exists.

  However, in such an element made of metal, because of the high intensity of the laser beam, the portion in contact with the laser beam path becomes a high temperature even by slight absorption. For this reason, there is a problem that the original purpose cannot be achieved because the material is deformed over time due to chemical changes such as melting, vaporization, or oxidation. In particular, if there are non-uniformities or burrs during processing in the element, the electric field of the laser beam concentrates on the part, and electric field breakdown occurs, or the tip part becomes high temperature and becomes the starting point, and the surroundings are compared. It will be altered or deformed in a short time.

  Therefore, in recent years, for example, knife edges as shown in Patent Documents 1 and 2 have been proposed.

Japanese Patent Laid-Open No. 4-158998 JP-A-8-27497

  In the above-mentioned Patent Document 1, a glass or dielectric substrate is used to ensure a precise shape, and a metal film such as chromium is deposited on such a substrate by a method such as lithography. And elements such as slits have been proposed. However, due to light absorption in the metal, the portion in contact with the optical path will be altered and deformed over a long period of time as in the conventional case.

  On the other hand, Patent Document 2 proposes an element in which openings, slits, knife edges, and the like are formed by processing a dielectric substrate such as glass or quartz without using metal. Such an element has an advantage that the material itself absorbs less light and has a high melting point, so that it is difficult to be deformed and has a longer life than a metal.

  However, the laser scattered light scattered on the rough surface irradiates the wire coating (including the flexible substrate) and polymer parts in or around the resonator for a long time, causing problems such as gas generation and polymer deformation / burning. there were. In addition, due to the presence of powerful laser light, the generated gas may adhere to the optical system through a process such as optical CVD (Chemical Vapor Deposition) and cause secondary problems. . Further, in the case of an ultraviolet resonator, there is a problem that all elements are deteriorated due to a chemical change due to spread of scattered light to the surroundings, and the efficiency of the resonator is lowered.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a laser beam generator capable of reducing quality deterioration with time in an output laser beam as compared with the prior art.

The first laser light generating apparatus of the present invention, an excitation light source that emits excitation light is configured to include a knife edge and a laser crystal made of dielectric, the laser resonator to generate an output laser beam by resonating an excited light It is equipped with a vessel. The knife edge has a plurality of optical smooth surfaces that transmit laser light in the laser resonator and are not parallel to each other, and refract at least part of the incident laser light on the optical smooth surfaces. The refracted light is separated from the main beam.
A second laser beam generator according to the present invention includes a fundamental wave light source that emits a laser beam as a fundamental wave, a knife edge made of a dielectric, and a wavelength conversion crystal, and converts the wavelength by resonating the fundamental wave. And a wavelength converter that generates an output laser beam by performing the above. Further, the knife edge has a plurality of optical smooth surfaces that are non-parallel to each other through which the laser light in the wavelength converter is transmitted, and refracts at least part of the incident laser light on the optical smooth surfaces, The refracted light is separated from the main beam.

In the laser beam generator of the present invention, since the knife edge is made of a dielectric, unlike the conventional metal one, the incident laser beam is not absorbed at the knife edge. Therefore, the temporal change of the knife edge due to the heat generation due to such absorption can be suppressed. Further, the laser light incident surface (transmission surface) at the knife edge is a plurality of non-parallel optical smooth surfaces, and at least a part of the incident laser light on the optical smooth surfaces is refracted. For this reason, the light (refracted light) separated from the main beam travels in a certain direction. Accordingly, the generation of scattered light is reduced as compared with the case where the optical rough surface is separated as in the prior art, and the optical element in the resonator (laser resonator or wavelength converter) due to such scattered light is timed. Deterioration is suppressed.

According to the laser beam generator of the present invention, since the knife edge is made of a dielectric, it is possible to suppress changes in the knife edge over time due to heat generation due to absorption of the laser beam. Also, the laser light incident surface (transmission surface) at the knife edge is a plurality of non-parallel optical smooth surfaces, and at least a part of the incident laser light on the optical smooth surfaces is refracted. Therefore, it is possible to suppress deterioration over time of the optical element in the resonator (laser resonator or wavelength converter) due to scattered light. Therefore, it is possible to reduce the quality deterioration with time in the output laser light as compared with the conventional case.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows the overall configuration of a laser beam generator (laser beam generator 1) according to an embodiment of the present invention. This laser beam generator 1 is a laser beam (wavelength-converted beam L12; for example, a laser beam in the green wavelength region) that has undergone wavelength conversion with respect to the laser beam (for example, the laser beam in the red wavelength region) as the fundamental wave L11. Is output to the outside. The laser beam generator 1 includes a fundamental wave laser 11, an RF signal source 12, a phase modulator 13, a mode matching lens 14, an external resonator 15, and a lens 16.

  The fundamental wave laser 11 (fundamental wave light source) includes a light source (laser light source) that emits laser light as the fundamental wave L11. As the fundamental wave L11, for example, laser light in the infrared wavelength region to the ultraviolet wavelength region (for example, a wavelength region of about 2000 nm to 250 nm) is used. In addition, as a light source that emits laser light in the visible wavelength region and in the ultraviolet wavelength region from such an infrared wavelength region, for example, a laser material in which rare earth ions such as neodymium, yttrium and erbium are doped into a crystal, glass, fiber or the like A laser light source such as Nd: YAG, Nd: YVO4, Yb: YAG, Yb fiber, Er fiber or the like, or an external cavity semiconductor laser or DFB (Distributed Feedback) semiconductor laser with a narrowed line width, and those Harmonics (sum frequency, second harmonic, fourth harmonic, etc.) are used.

  The RF signal source 12 supplies a carrier (RF signal) electrically amplified as necessary to the phase modulator 13. A part of such an RF signal is used as a local oscillator when the error signal of the external resonator 15 is demodulated. In many cases, the output from the RF signal source 12 is sufficient, but in order to ensure a sufficiently large S / N of the error signal of the external resonator 15, an electric signal amplifier or the like is provided between the phase modulator 13 and the like. It is also effective to put in.

Phase modulator 13 is for adding the sideband wavelength lambda ₁ of the laser beam (fundamental wave L11). The phase modulator 13 is provided to perform locking using the FM sideband method in the external resonator 15 at the subsequent stage. For example, when the RF signal generated by the RF signal source 12 is supplied to the phase modulator 13, the laser light that has passed through the phase modulator 13 is subjected to phase modulation corresponding to the RF frequency. Specifically, when the carrier frequency f1 is supplied from the RF signal source 12 to the phase modulator 13, a side band is added around the frequency f _L of the laser light L11 that passes through the phase modulator 13, and f _L Light having a frequency such as ± f1 is generated. The number of phase modulators 13 to be installed is preferably one in terms of cost and reliability. Further, a phase modulator may be added to the laser light L12 after wavelength conversion.

  The mode matching lens 14 is an optical element that is used together with a mirror (not shown) or the like and adjusts so that the laser beam (fundamental wave L11) spatially overlaps the natural mode of the external resonator 15 (mode matching).

The external resonator 15 generates wavelength-converted light L12 as output laser light by resonating laser light (fundamental wave L11) having a wavelength λ ₁ and performing wavelength conversion. That is, the external resonator 15 functions as a wavelength converter (specifically, a bow-tie wavelength resonator). The external resonator 15 includes, for example, four mirrors 151a to 151d, a wavelength conversion crystal 152 is disposed between the mirrors 151a and 151b, and a knife described later between the mirrors 151c and 151d. Edges 153a and 153b are provided. The external resonator 15 is provided with beam dumps 154a and 154b which will be described later. The wavelength conversion crystal 152 is a non-linear optical element, and converts the wavelength of incident light to, for example, ½. The wavelength conversion crystal 152 is made of, for example, an LBO (LiB ₃ O ₅ ) crystal.

In such an external resonator 15, the mode match and the impedance match are compatible, and the optical path length of the circuit (resonator circuit length) resonates at a certain value, and the optical path length changes by the wavelength λ _1. Every time you do it, you get a resonance. For this reason, although not shown, a servo mechanism for holding resonance is provided, and at least one of the mirrors 151a to 151d is provided with optical path length varying means such as a VCM element or a PZT element. As a result, in combination with an error signal obtained by demodulating using a local oscillator after PD detection of the reflected light of the resonator, servo control is performed so that the resonator loop length becomes an integral multiple of the wavelength, and the resonance state is maintained ( Locked). Note that a method for performing wavelength conversion while maintaining the resonance state of the laser light to which such a sideband is added is a so-called FM sideband method.

  In this way, in the external resonator 15, the fundamental wave L11 from the fundamental laser 11 passes through the wavelength conversion crystal 152 while being reflected by the mirrors 151a to 151d, so that the wavelength from the fundamental wave L11 to the wavelength converted light L12 is increased. Conversion is made. Specifically, for example, from a laser beam (fundamental wave L11) in the near-infrared wavelength region to, for example, a laser beam (wavelength converted light L12 composed of a double wave) in a green wavelength region (a wavelength region of about 500 nm to 550 nm). Wavelength conversion is performed.

  Here, the knife edges 153a and 153b are made of a dielectric, and refract at least part of the incident laser light to separate the refracted light from the main beam. That is, it is an optical element for obtaining a desired mode such as a fundamental mode by removing higher-order modes in the main beam. Further, as such a dielectric material, a material having a high melting point is desirable because it is transparent at the wavelength used and has almost no absorption (having a light absorption coefficient of, for example, 1% / mm or less in the wavelength region of incident laser light). Specifically, oxide dielectrics such as quartz (synthetic quartz) and sapphire, and fluoride dielectrics such as magnesium fluoride and calcium fluoride satisfy this condition. Further, glass may be used depending on use conditions. Such knife edges 153a and 153b are produced by cutting a dielectric member with a tool such as an ultrasonic cutter, a diamond cutter or a multi-blade saw, and then performing simple optical polishing on the end face. At this time, the surface accuracy and surface roughness of the polishing are not required to be as high as the polishing level required for normal laser light because the transmitted light or reflected light is not used by resonance or output. In particular, when glass having a low melting point is used, it can be molded by a mold such as metal in mass production. The detailed configuration of the knife edges 153a and 153b will be described later.

  Further, the beam dumps 154a and 154b take in the refracted light from the knife edges 153a and 153b (the light beam indicated by the broken line in FIG. 1), so that the refracted light is transmitted to other resonators 15 in the external resonator 15. It is an optical member for preventing the optical element (wavelength conversion element 152, mirrors 151a to 151d, etc.) from being irradiated. Specifically, it is an element capable of reducing the light emitted to the outside by allowing a beam to enter the inside from a narrow entrance and scattering and absorbing the inside. However, when only one of the knife edges 153a and 153b is arranged, only one of the beam dumps 154a and 154b may be provided correspondingly. In addition, since the external resonator 15 is a bow-tie resonator here, the traveling direction of the resonating light is easily unidirectional, and the number of necessary beam dumps can be reduced.

  Next, a detailed configuration of the knife edges 153a and 153b will be described with reference to FIGS. FIG. 2 shows a detailed configuration example of the knife edges 153a and 153b, FIG. 2 (A) is a plan configuration example, and FIG. 2 (B) is along the line II-II in FIG. 2 (A). Each arrow cross-section configuration example is shown. FIG. 3 (A) is an enlarged view of the portion P1 in FIG. 2 (B).

  As shown in FIGS. 2A, 2B, and 3A, the knife edges 153a, 153b are respectively the end surfaces S1 and S21, S22 facing each other, and the end surfaces S3 and S4 facing each other. And have. Of these, the end surfaces S1 and S21 are parallel to each other, and the end surfaces S3 and S4 are also parallel to each other. On the other hand, the end faces S1 and S22 are not parallel to each other, and the inclination angle α (depending on the optical path design such as the refractive index of the material, the resonator size, and the position of the beam dump between the end faces S1 and S22, for example, 5 to 15 °). That is, the end surface S22 is an inclined surface with respect to the end surface S1 (inclined surface S22). In addition, between the end surfaces S3 and S4, an angle β (similarly depending on the design, for example, about 60 ° to 120 °) is formed. Thus, each of the knife edges 153a and 153b has the inclined surface S22 having the inclination angle α formed at the end of the rectangular (square) double-sided parallel plate of the dielectric.

  Among these end faces, two end faces S1 and S22 that are non-parallel to each other are end faces through which the laser light (laser beam LB) in the external resonator 15 is transmitted, as shown in FIG. 4, for example. It is an optical smooth surface (optical smooth surface). Specifically, the vicinity of the end face of the portion through which the laser beam LB passes is a glossy surface by polishing or cleavage.

  In addition, the cross-sectional shape in knife edge 153a, 153b is not restricted to what was shown to FIG. 3 (A), For example, you may become cross-sectional shape as shown to FIG. 3 (B)-(F). . Specifically, in FIGS. 3B and 3E, the angle β is an obtuse angle, and in FIGS. 3C and 3F, the angle β is an acute angle, and FIG. Then, as in FIG. 3A, the angle β is a right angle. 3D to 3F, an end surface S23 (inclined surface S23) is formed instead of the end surfaces S21 and S22 in FIGS. 3A to 3C.

  With such a configuration, at the knife edges 153a and 153b, for example, as shown in FIG. 4, by refracting at least part of the incident laser light (laser beam LB) on the end surfaces S21 and S1 made of an optically smooth surface, The refracted light (reflected light LR) is separated from the main beam. At this time, since the end surfaces S21 and S1 are optically smooth surfaces, the scattering of the laser light at these portions is reduced, and the irradiation of the scattered light to the surroundings is suppressed. Moreover, since the refraction angle and reflection angle at this time can be set at the time of design, light can be deflected in the intended direction. When the incident beam (laser beam LB) returns to the optical axis LO, the optical element is damaged or the operation of the fundamental laser 11 becomes unstable. Therefore, the incident direction of the laser beam LB and the incident surface ( The end surface S22) is preferably inclined (not vertical). Thereby, the effect as a knife edge can be utilized, preventing the reflected light to optical axis LO vicinity.

  Such knife edges 153a and 153b function as, for example, an optical slit (slit part) 153-1 as shown in FIG. 5 or an optical aperture (opening part) 153-2 as shown in FIG. It is also possible to configure as described above. FIG. 5A illustrates a planar configuration example of the optical slit 153-1, and FIG. 5B illustrates a cross-sectional configuration example taken along the line III-III in FIG. 5A. It is a thing. 6A illustrates a planar configuration example of the optical aperture 153-2, and FIG. 6B illustrates a cross-sectional configuration example taken along line IV-IV in FIG. 6A. It represents.

  Here, in the optical slit 153-1 illustrated in FIG. 5, a slit having a width D is formed between the end surface S3 of the knife edge 153a and the end surface S3 of the knife edge 153b. Further, in the optical aperture 153-2 shown in FIG. 6, a circular opening having a diameter D surrounded by the end face S3 is formed. In addition, the shape of the opening may be an ellipse, a square, a rectangle, or the like.

  In FIG. 5, the width D of the slit is set to have a size of about 1 to 3 times the diameter 2W of the laser beam passing through this portion, for example. In FIG. 6, the appropriate ratio varies depending on design parameters such as gain and resonator loss, but the diameter D is set so that the fundamental mode is transmitted with low loss and a large loss is given to the lateral high-order mode. . Thereby, the scattering of the laser light around the opening is reduced, and the amount of scattered light irradiated to the surroundings can be suppressed. Further, the laser beam that is lost is diffracted in a certain direction by the inclined surface S22 formed around the opening.

  Next, the operation and effect of the laser beam generator 1 of the present embodiment will be described.

  In this laser beam generator 1, when the laser beam as the fundamental wave L 11 is emitted from the fundamental wave laser 11, the fundamental wave L 11 passes through the phase modulator 13. At this time, the sideband as described above is added to the fundamental wave L11 in the phase modulator 13 based on the RF signal supplied from the RF signal source 12.

Here, in general, how much δ ′ corresponds to the sideband frequency (side band) frequency f _b (f _b = f1, f2,...) Added by the phase modulator 13 is f _b = cδ ′ / 2πL (c: speed of light in vacuum). Since the polarities of the upper sideband and the lower sideband are reversed, the RF component contained in the resonator reflected light near the resonance point (reflectance minimum point) gives an error signal when detected by the local oscillator. After the phase of the local oscillator is matched and the center of resonance and the zero point of the error signal are matched, the resonator length control means is driven by the servo circuit and locked to the resonance point. When locked, the apparent reflectance is significantly reduced, and most of the light incident on the external resonator 15 is injected into the inside. At the same time, in the external resonator 15, light having a power much larger than that of the incident fundamental wave L <b> 11 circulates, so that the conversion efficiency in the wavelength conversion crystal 152 placed in the external resonator 15 is increased.

  The fundamental wave L11 to which the sideband is added by the phase modulator 13 is input to the external resonator 15 through the mode matching lens 14. In the external resonator 15, the fundamental wave L11 is resonated by circulating between the mirrors 151a to 151d, and wavelength-converted to ½ by passing through the wavelength conversion crystal 152 in the process. Thereby, the power of the circulating light inside the external resonator 15 is increased, and the wavelength conversion efficiency of the fundamental wave L11 is increased. At this time, the external resonator 15 is locked by the error signal using the sideband. The wavelength-converted light (second harmonic) L12 that is the laser light wavelength-converted in this way is output from the external resonator 15. The wavelength-converted light L12 is output to the outside as output laser light through the lens 16.

At this time, for example, when a wavelength of 1064 nm is used as the wavelength λ ₁ , laser light (wavelength converted light) L 12 having a wavelength λ ₂ of 532 nm is output by wavelength conversion in the external resonator 15.

  At this time, in the external resonator 15 of the present embodiment, since the knife edges 153a and 153b are made of a dielectric, unlike the conventional metal ones, the incident laser light is transmitted at the knife edges 153a and 153b. Not absorbed. Therefore, changes with time of the knife edges 153a and 153b due to heat generation due to such absorption can be suppressed. That is, unlike a metal having a large absorption, there is no increase in temperature due to absorption and the accompanying evaporation or melting. Therefore, even when used for a long time, the knife edges 153a and 153b are not deformed and the performance does not change. Further, deterioration of optical elements (wavelength conversion crystal 152, mirrors 151a to 151d, etc.) in the external resonator 15 due to adhesion / deposition of metal scattered by evaporation / melting is avoided.

  Further, as shown in FIGS. 2 and 3, for example, the laser light incident surfaces (transmission surfaces) S1 and S22 at the knife edges 153a and 153b are non-parallel optical smooth surfaces. As shown in the above, at least a part of the laser beam (laser beam LB) incident on the optical smooth surface is refracted. Thereby, the light (refracted light; reflected light LR) separated from the main beam travels in a certain direction. Therefore, the generation of scattered light is reduced as compared with the case of separation on a conventional optical rough surface, and the optical elements (such as the wavelength conversion crystal 152 and the mirrors 151a to 151d, etc.) in the external resonator 15 caused by such scattered light. ) Over time. Specifically, the coating of the wire existing around the knife edges 153a and 153b, the polymer material, and other optical elements may be irradiated with laser light that is diffracted or scattered and burned out, or gas may be generated. Be suppressed (or avoided). Also, for example, when the incident laser light is ultraviolet light, it can be chemically altered by being irradiated for a long time without any problem for a short time, or the generated gas can be produced on the optical axis of the ultraviolet light by a process such as laser CVD. It is possible to avoid depositing on optical components in the vicinity.

  Further, since the beam dumps 154a and 154b are provided in the external resonator 15, the refracted light from the knife edges 153a and 153b (light rays indicated by broken lines in FIG. 1) is taken in, so that Irradiation of other refracted light to other optical elements (such as the wavelength conversion element 152 and the mirrors 151a to 151d) in the external resonator 15 is completely avoided.

  As described above, in this embodiment, since the knife edges 153a and 153b are made of a dielectric, it is possible to suppress temporal changes of the knife edges 153a and 153b caused by heat generation due to absorption of laser light. it can. In addition, the laser light incident surfaces (transmission surfaces) S1, S21 and the like at the knife edges 153a and 153b are non-parallel optical smooth surfaces, and the incident laser light (laser beam LB) incident on these optical smooth surfaces is also provided. Since at least a part of the light is refracted, deterioration with time of the optical element (such as the wavelength conversion crystal 152) in the external resonator 15 due to scattered light can be suppressed. Therefore, it is possible to reduce the quality deterioration with time in the output laser light as compared with the conventional case.

  Further, by using a dielectric, not only the deterioration of the knife edges 153a and 153b itself can be reduced, but also the deterioration of the polymer used in other parts of the optical system and wiring of the electric circuit can be prevented. Moreover, the lifetime of the entire optical system can be significantly extended by preventing gas generation due to polymer degradation.

  In addition, the cross-sectional shape in knife edge 153a, 153b is not restricted to what was demonstrated in this Embodiment (what was shown to FIG. 3 (A)-(F)), For example, FIG. 7 (A)-(F The cross-sectional shape as shown in FIG. That is, instead of the end surface S1, the end surface S11 and the end surface S12 (inclined surface S12) are formed, or the end surface S13 (inclined surface S13) is formed, so that both surfaces of the incident laser light transmission surface are inclined. You may make it become a surface.

(Modification)
Next, a modified example of the present invention will be described. In addition, about the component similar to the said embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted suitably.

  FIG. 8 shows the overall configuration of a laser beam generator (laser beam generator 2) according to a modification of the present invention. This laser beam generator 2 generates an output laser beam L22 and outputs it to the outside by irradiating a laser crystal 252 with excitation light L21 and causing laser oscillation. The laser light generator 2 includes an excitation light source 21, a matching lens 24, a laser resonator 25, and a lens 26.

  The excitation light source 21 is a light source that emits excitation light L21. As such an excitation light source 21, for example, a laser that outputs second harmonics such as an Nd: YAG laser, an Nd: YLF laser, a Yb fiber laser, an Er fiber laser, or the like, or a high-power semiconductor laser, and its output are used. An amplified laser, a high-power semiconductor laser coupled to a multimode fiber, and in some cases, lamp light such as LED or Xe can be used.

  The matching lens 24 is an optical element that is used together with a mirror (not shown) as necessary, and adjusts the excitation light L21 so that it substantially overlaps the natural mode of the laser resonator 25 (mode matching).

  The laser resonator 25 includes mirrors 251a to 251d, a laser crystal 252, knife edges 253a and 253b, and beam dumps 254a to 254d. The laser resonator 25 generates output laser light Lout by resonating incident excitation light L21.

  The mirrors 251a to 251d correspond to the mirrors 151a to 151d in the external resonator 15 of the above embodiment. As the laser crystal 252, for example, Nd: YAG, Nd: YLF, Cr: LiSAF, Ti: sapphire, Nd: Glass, Nd: ceramic, Yb: ceramic, or the like can be used.

  The knife edges 253a and 253b and the beam dumps 254a to 254d correspond to the knife edges 153a and 153b and the beam dumps 154a and 154b in the external resonator 15, respectively.

  In such a laser resonator 25, for example, as the output is increased by the excitation light L21 from a semiconductor laser or the like, the light emitting region is increased. Therefore, when the laser beam 252 is irradiated with the excitation light L 21, the irradiation region is often larger than the fundamental mode oscillation region of the laser resonator 25. In this case, the oscillating laser beam (output laser beam Lout) oscillates not only in the transverse basic mode but also in the spatially expanded transverse higher-order mode at the same time, and the condensing characteristic of the laser beam is lowered. In many cases, the brightness is lowered and the purpose cannot be achieved. Therefore, by installing knife edges (slits, openings) 253a and 253b in the laser resonator 25 to oscillate only the transverse fundamental mode, the energy from the excitation light L11 is selectively injected into the transverse fundamental mode. Is effective. In addition, such knife edge 253a, 253b installation place is not limited to one place.

  However, in the laser resonator 25 of this modification, since the laser light is incident on the knife edges 253a and 253b from both directions, the cross-sectional shapes thereof are as shown in FIGS. 7A to 7F described above. It has become a thing. Accordingly, unlike the case of the external resonator 15, four beam dumps 254 a to 254 d are provided in the laser resonator 25. When only one of the knife edges 253a and 253b is arranged, only one of the beam dumps 254a and 254b and the beam dumps 254c and 254d is provided correspondingly. What should I do?

  In the laser beam generator 2 of this modification, since the knife edges 253a and 253b described above are provided in the laser resonator 25, the same effect can be obtained by the same operation as in the above embodiment. That is, it is possible to reduce the deterioration of the quality of the output laser light over time as compared with the conventional case.

  Although the present invention has been described with reference to the embodiment and the modification examples, the present invention is not limited to the embodiment and the like, and various modifications can be made.

  For example, in the above-described embodiment and the like, the locking in the external resonator has been described by taking the example using the FM sideband method as an example, but the present invention is not limited to this, and other methods such as the Hansch-Couillaud method, Dither, etc. Method, fringe side locking, etc. may be used.

  Further, in the above-described embodiment and the like, the case where each resonator includes four mirrors has been described, but the structure of each resonator is not limited to this and can be changed as appropriate. For example, the configuration of each resonator is not limited to the bow-tie resonator as shown in FIGS. 1 and 8, but is a standing wave resonator, a V-shaped resonator, a Z-type resonator, or a more complicated structure. It may be a shaped resonator. Further, the location and the number of knife edges (slits, openings) are not limited to the illustrated example. For example, the number of mirrors may be 1 to 3 or 5 or more. In addition to such a mirror, an element such as a prism may be used.

It is a figure showing the whole structure of the laser beam generator which concerns on one embodiment of this invention. It is the top view and sectional drawing showing an example of the detailed structure of the knife edge shown in FIG. It is sectional drawing which expanded and represented a part of example of a structure of a knife edge. It is sectional drawing for demonstrating the effect | action of the knife edge shown in FIG. It is the top view and sectional drawing showing the structural example of the slit part comprised by the knife edge shown in FIG. It is the top view and sectional drawing showing the structural example of the opening part comprised by the knife edge shown in FIG. It is sectional drawing which expanded and represented a part of other structural example of the knife edge. It is a figure showing the whole structure of the laser beam generator which concerns on the modification of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1, 2 ... Laser beam generator, 11 ... Fundamental laser, 12 ... RF signal source, 13 ... Phase modulator, 14 ... Mode matching lens, 15 ... External resonator, 151a-151d ... Mirror, 152 ... Wavelength conversion crystal 153a, 153b ... knife edge, 153-1 ... optical slit, 153-2 ... optical aperture, 154a, 154b ... beam dump, 16 ... lens, 21 ... excitation light source, 24 ... matching lens, 25 ... laser resonator, 251a 251d ... mirror, 252 ... laser crystal, 253a, 253b ... knife edge, 254a-254d ... beam dump, 26 ... lens, L11 ... fundamental wave, L12 ... wavelength conversion light, L21 ... excitation light, L22 ... output laser light, S1, S11, S12, S13, S21, S22, S23, S3, S4... End face, S12, S13 S22, S23: inclined surface, α: inclined angle, β: angle between end surfaces, LO: optical axis, LB: laser beam (incident laser light), LR: reflected light (refracted light), D: slit width (opening) Diameter).

Claims (6)

An excitation light source that emits excitation light ;
Is configured to include a knife edge and a laser crystal made of a dielectric material, and a laser resonator for generating an output laser beam by resonating the excitation light,
The knife edge has a plurality of optical smooth surfaces that transmit laser light in the laser resonator and are non-parallel to each other, and refract at least part of the incident laser light on the optical smooth surfaces. Laser beam generator that separates refracted light from main beam. A fundamental light source that emits laser light as a fundamental wave;
A wavelength converter configured to include a knife edge made of a dielectric and a wavelength conversion crystal, and generate output laser light by performing wavelength conversion by resonating the fundamental wave;
With
The knife edge has a plurality of optical smooth surfaces that transmit the laser light in the wavelength converter and are non-parallel to each other, and refract at least part of the incident laser light to the optical smooth surfaces. Separate refracted light from main beam
Laser light generator. The laser beam generator according to claim 1 or 2 , wherein the knife edge is made of an oxide, glass, or fluoride having a light absorption coefficient of 1% / mm or less in the wavelength region of the incident laser beam. . The laser beam generator according to claim 3 , wherein the knife edge is made of quartz, sapphire, magnesium fluoride, or calcium fluoride. The laser beam generator according to any one of claims 1 to 4, wherein the knife edge is configured to function as an optical slit or an optical aperture. The laser beam generator according to any one of claims 1 to 5 , wherein the laser resonator or the wavelength converter includes an optical member for taking in refracted light from the knife edge.

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