JP2015153841A - laser light source device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact and relatively inexpensive laser light source device by improving energy utilization efficiency when amplifying pulse light with a solid amplifier and reducing heating loss of the solid amplifier.SOLUTION: A laser light source device comprises a seed light source 10; fiber amplifiers 20, 30 which amplify pulse light output from the seed light source 10 by using the gain switching method; a solid amplifier 50 which further amplifies the output from the fiber amplifiers; nonlinear optical elements 60, 70 which convert wavelength of the pulse light output from the solid amplifier; an optical switch element 40 for removing an ASE noise and a Volume Bragg Grating (VBG) 90 disposed between the fiber amplifier and the solid amplifier; and a control section 100 which controls the optical switch element 40 so as to allow the propagation of light in a light output period of the pulse light from the seed light source 10 and prevent the propagation of light in a period not in a light output period of the pulse light from the seed light source; to diffract the pulse light passed through the optical switch element 40 at the VBG 90, and guide it to the solid amplifier.

Description

  The present invention relates to a laser light source device used for various types of laser processing.

  In recent years, laser light has been used for various processes. Laser light having a wavelength in the vicinity of 532 nm to 1064 nm has high energy intensity, and is suitably used for various processing such as cutting or welding of metal or glass. In addition, laser light in the deep ultraviolet region with a wavelength of 200 nm to 350 nm is used for processing electronic materials and composite materials.

  A laser light source device that outputs laser light having a shorter wavelength than the near infrared region includes a seed light source that outputs laser light having a wavelength in the near infrared region, an optical amplifier that amplifies the laser light output from the seed light source, A nonlinear optical element that converts the wavelength of the laser light amplified by the optical amplifier into a target wavelength is provided.

  Various seed light sources are selected and various optical amplifiers are used so that laser pulse light having a pulse width of several hundred picoseconds or less and a frequency of several hundred megahertz or less and a large peak power can be obtained. Yes.

  Conventionally, a mode-locked laser with a repetition frequency of several tens of megahertz is used as such a seed light source, and a pulse light of several kilohertz is obtained by dividing the pulse light output from the seed light source. there were.

  However, since the oscillation frequency of the mode-locked laser fluctuates due to environmental factors such as temperature and vibration, and it is difficult to control the value appropriately, the oscillation frequency of the laser pulse light detected using a light receiving element etc. Therefore, there is a problem that the circuit configuration for this is complicated, and that the saturable absorber that is a component of the mode-locked laser is easily deteriorated and long-term stable driving is difficult. It was.

  Therefore, it is conceivable to use a semiconductor laser capable of controlling the oscillation frequency of pulsed light as a seed light source. The pulse energy of near-infrared pulsed light output from such a semiconductor laser is from several picojoules to several hundreds of picojoules. In order to finally obtain pulsed light having a pulse energy of a few tens of microjoules to several tens of millijoules, which is very small as a picojoule, it is necessary to amplify much more than when a conventional seed light source is used.

  As optical amplifiers therefor, fiber amplifiers such as erbium-doped fiber amplifiers and ytterbium-doped fiber amplifiers, Nd: YAG with neodymium added to yttrium aluminum garnet, and Nd: YVO4 with neodymium added to yttrium vanadate A solid-state amplifier such as is preferably used.

  Patent Documents 1 and 2 disclose an optical amplifier in which such a fiber amplifier and a solid-state amplifier are combined. As shown in Patent Documents 1 and 2, both fiber amplifiers and solid-state amplifiers are used for excitation in order to amplify light having the same wavelength as the laser light to be amplified by the pumping action in the laser active region. It is necessary to provide a light source. Usually, a semiconductor laser is used as such a light source for excitation.

JP 2011-192831 A WO2008 / 014331

  When a semiconductor laser is used as a seed light source as an alternative to a mode-locked laser, it is necessary to use a single or a plurality of fiber amplifiers and solid-state amplifiers in order to obtain a laser pulse beam having a large energy intensity.

  In this case, spontaneous emission light noise (hereinafter referred to as “ASE noise (Amplified Spontaneous Emission Noise)”) generated in the amplification process by the fiber amplifier in the previous stage is superimposed on the pulse light from the seed light source, and further chirping phenomenon and The pulse light that has been broadened by self-phase modulation or Raman scattering in the optical fiber is amplified by the solid-state amplifier in the subsequent stage, and a part of the energy of the excitation light injected into the solid-state amplifier for amplification is like this There is a problem that it is wasted in amplifying various noise components.

  In order to amplify the pulsed light to a predetermined intensity in such a situation, it is necessary to inject excessive excitation energy into the solid-state amplifier, which not only lowers the energy utilization efficiency of the solid-state amplifier but also increases heat generation, In addition, a large cooling mechanism is required, and there is a problem that the cost of parts and the like increase.

  If the frequency of the pulsed light is higher than the order of megahertz, the ASE noise is very small, so there is no problem. However, in the region where the oscillation frequency of the pulsed light is lower than 1 megahertz, the influence of the ASE noise and the like should be fully considered. I had to.

  In view of the above-described problems, an object of the present invention is to improve energy utilization efficiency when amplifying pulsed light with a solid-state amplifier, reduce heat generation loss of the solid-state amplifier, and achieve a relatively inexpensive and compact laser light source device. Is to provide

  In order to achieve the above object, a first characteristic configuration of a laser light source device according to the present invention includes a seed light source that outputs pulsed light by a gain switching method, and the seed light source as described in claim 1 of the claims. A fiber amplifier that amplifies the pulsed light output from the light source, a solid-state amplifier that amplifies the pulsed light output from the fiber amplifier, and a nonlinear optical element that wavelength-converts and outputs the pulsed light output from the solid-state amplifier; An optical switching element that is disposed between the fiber amplifier and the solid-state amplifier and that allows or blocks light propagation from the fiber amplifier to the solid-state amplifier, and the fiber amplifier. The solid-state amplification is performed by diffracting light in a specific wavelength range from pulsed light output from the fiber amplifier and disposed between the solid-state amplifier and the solid-state amplifier And the optical switching element so as to allow light to propagate during an output period of pulsed light from the seed light source and to prevent light propagation during a period different from the output period of pulsed light from the seed light source And a control unit configured to generate an output permission state that allows the output of pulsed light from the nonlinear optical element by controlling the above.

  According to the above-described configuration, when pulse light that has been broadened by self-phase modulation or Raman scattering in the optical fiber in the process of being amplified by the fiber amplifier is incident on the diffraction grating, the diffraction grating responds to each wavelength by the diffraction grating. Will occur. By extracting diffracted light in a specific wavelength range corresponding to the wavelength range of pulsed light output from the seed light source from the diffracted light, wavelength components that deviate from the allowable wavelength range that can be converted by the nonlinear optical element are removed. Become so. Therefore, the excitation energy in the solid-state amplifier is efficiently used for amplification of pulsed light in a desired wavelength region. That is, the diffraction grating functions as a noise filter that removes ASE noise and the like in the frequency domain.

  Further, the optical switching element is controlled by the control unit so as to prevent light propagation in a period different from the output period of the pulsed light from the seed light source, and during that time, propagation of ASE noise to the solid-state amplifier is prevented. It is avoided that the energy in the active region of the solid-state amplifier is wasted.

  When the optical switch element is controlled by the control unit so as to allow the propagation of light during the output period of the pulsed light from the seed light source, the output allowed state in which the pulsed light propagates from the fiber amplifier to the solid-state amplifier only during that time. The pulse light is amplified with energy efficiency, and pulse light with a large peak power is output from the nonlinear optical element. That is, the optical switch element functions as a filter that removes ASE noise in the time domain.

  By providing such a configuration, it is not necessary to supply excessive energy to the active region of the solid-state amplifier, so that a large cooling mechanism is not required, and a relatively inexpensive and small laser light source device can be realized.

  In the second feature configuration, as described in claim 2, in addition to the first feature configuration described above, the control unit prevents light from propagating during an output period of pulsed light from the seed light source. Controlling the optical switch element so as to allow the propagation of light during a period different from the output period of the pulsed light from the seed light source, thereby preventing an output stop state that blocks the output of the pulsed light from the nonlinear optical element. In that it is configured to generate.

  The optical switch element is controlled by the controller so that the propagation of the pulsed light from the fiber amplifier to the solid-state amplifier is prevented during the output period of the pulsed light from the seed light source, so nonlinear optics can be used without stopping the seed light source. An output stop state in which the output of pulsed light from the element is stopped can be realized.

  Since the optical switch element is controlled by the control unit so that the propagation of light is allowed in a period different from the output period of the pulsed light from the seed light source in the output stopped state, the ASE noise generated in the preceding fiber amplifier Is propagated to the subsequent solid-state amplifier, and the energy of the active region of the solid-state amplifier in the excited state is released by the excitation light source.

  As a result, even when the optical switch element is controlled by the control unit so that the pulsed light from the seed light source propagates from the fiber amplifier to the solid-state amplifier after the output is stopped, the pulsed light is output from the nonlinear optical element. Giant pulses are not generated and the solid-state amplifier and the nonlinear optical element are not damaged.

  When the output is restarted after temporarily stopping the output of pulsed light, if excessive energy is accumulated in the solid-state laser medium, the solid-state laser medium will generate excessive heat, resulting in a temperature rise and beam propagation characteristics. However, according to the above configuration, excessive heat generation of the solid-state laser medium is suppressed, so that the beam propagation characteristics immediately after restarting the output can be adversely affected. The quality of the object to be processed using the laser pulse light is not adversely affected.

  Even if ASE noise propagated and amplified in the solid-state amplifier during a period different from the output period of the pulse light from the seed light source is incident on the nonlinear optical element, the intensity is inherently low and the wavelength conversion characteristic of the nonlinear optical element However, ASE noise in a wide wavelength band is not output as light having a large peak power. In addition, since the ASE noise output from the fiber amplifier is not amplified to light with such a large peak power, peripheral optical parts including the switch element are not damaged even if blocked by the optical switch element. .

  The third characteristic configuration is that, as described in the third aspect, in addition to the first or second characteristic configuration described above, the diffraction grating is configured by a volume Bragg grating.

  The pulse light that has been broadened in the process of being amplified by the fiber amplifier is diffracted by a volume Bragg grating (hereinafter also referred to as “VBG”) and guided to a solid-state amplifier. In the diffracted light narrowed to a specific wavelength range by the VBG, the wavelength component deviating from the allowable wavelength range that can be converted by the nonlinear optical element is effectively removed. VBG is excellent in diffraction efficiency and high accuracy compared with a general-purpose diffraction grating, and can be used very suitably. For example, when a reflective VBG is used, only diffracted light in a desired wavelength region is reflected, and there is an advantage that a filter mechanism for selecting diffracted light in a desired wavelength region is not required.

  In the fourth feature configuration, as described in claim 4, in addition to the third feature configuration described above, the pulse light output from the fiber amplifier is reflected toward the volume Bragg grating, Alternatively, a reflection mirror is further provided that reflects light in a specific wavelength range diffracted by the volume Bragg grating toward the solid-state amplifier.

  In order to diffract pulse light in a desired wavelength range, fine adjustment of the diffraction angle of VBG is necessary. Even in such a case, it is possible to easily and surely align the optical axis of the diffracted light with the target optical axis by providing the reflecting mirror in the front stage or the rear stage of the VBG.

  In the fifth feature configuration, as described in claim 5, in addition to any of the first to fourth feature configurations described above, light in a wavelength range including the specific wavelength range in the subsequent stage of the fiber amplifier. It is in the point provided with the band pass filter which permeate | transmits.

  The bandwidth of the pulse light output from the seed light source is increased in the process of being amplified by the fiber amplifier, and even if ASE noise is superimposed on the pulse light, the spectrum width is limited to the wavelength range including the specific wavelength range by the bandpass filter. As a result, the influence on the subsequent amplifier can be reduced. For example, even when a plurality of fiber amplifiers are provided, the ASE noise superimposed on the pulse light in the process of being amplified by the preceding fiber amplifier is removed to some extent and input to the subsequent fiber amplifier, so that the overall energy efficiency is improved.

  In the sixth feature configuration, in addition to any one of the first to fifth feature configurations described above, the optical switch element includes a dynamic optical element or an electro-optic element. It is in the point comprised by the optical element.

  Dynamic optical elements such as an acousto-optic element that turns on or off first-order diffracted light when an ultrasonic transducer is turned on or off as an optical switch element, or an electro-optic element that turns on or off light by an electric field using intensity modulation of EO modulation It is preferable to use it.

  In the seventh feature configuration, as described in claim 7, in addition to any of the first to sixth feature configurations described above, the seed light source is configured by a DFB laser, and the control unit is configured by the DFB. The laser is configured to be driven at a frequency of several megahertz or less and with a pulse width of several hundred picoseconds or less.

  By applying a gain switching method using a DFB laser as a seed light source, pulse light that oscillates in a single longitudinal mode and has a higher intensity than that in a steady state can be obtained. According to the gain switching method, it is possible to easily generate pulsed light having a desired pulse width of several hundred picoseconds or less at a desired frequency of several megahertz or less including single pulsed light. By using the above-described optical switch element, it becomes possible to efficiently obtain pulsed light having a high average output and a desired wavelength.

  As described above, according to the present invention, it is possible to improve the energy use efficiency when amplifying pulsed light with a solid-state amplifier and reduce the heat loss of the solid-state amplifier, thereby providing a relatively inexpensive and compact laser light source device. I was able to do that.

Block diagram of laser light source device (A) is an explanatory diagram of frequency characteristics and time axis characteristics of narrow-band pulsed light oscillated from a seed light source, and (b) and (c) are diagrams of pulsed light whose bandwidth has been widened by self-phase modulation or Raman scattering of a fiber amplifier. Explanatory diagram of frequency characteristics and time axis characteristics, (d) is an explanatory diagram of frequency characteristics and time axis characteristics of pulsed light that has been narrowed by VBG and reduced ASE noise, and (e) is narrow band by a bandpass filter. Of frequency characteristics of pulsed light with reduced ASE noise (A) is an explanatory diagram of pulsed light periodically oscillated from the seed light source, (b) is an explanatory diagram of pulsed light superimposed with ASE noise in the first-stage fiber amplifier, and (c) is an ASE in the subsequent-stage fiber amplifier. An explanatory diagram of pulsed light on which noise is superimposed, (d) is an explanatory diagram of pulsed light passing through the optical switch element in synchronization with the oscillation cycle of the seed light source in the time domain, and (e) is an oscillation cycle of the seed light source in the time domain. FIG. 5F is an explanatory diagram of ASE noise that passes through the optical switch element before and after, and FIG. 8F is an explanatory diagram of pulsed light that is amplified by the solid-state amplifier through the optical switch element in synchronization with the oscillation period of the seed light source in the time domain. Timing chart explaining the output timing of the trigger signal that drives the seed light source and the gate signal that drives the optical switch element, corresponding to the output stop state and output permission state of the optical pulse (A) is explanatory drawing of the pulse energy characteristic after wavelength conversion which contrasted the case where an optical switch element is used, and the case where an optical switch element is not used, (b) is the case where an optical switch element is used, and an optical switch Explanatory diagram of average power characteristics after wavelength conversion compared with the case where no element is used (A) is explanatory drawing of the output characteristic which contrasted the case where VBG is used with respect to the case where it does not use with respect to the pulse light of wavelength 1064nm amplified with the fiber amplifier, (b) is VBG with respect to the same pulse light. An explanatory view of spectrum characteristics comparing the case of using and not using, (c) is an explanatory view of the conversion efficiency of harmonics comparing the case of using VBG and the case of not using the same pulse light, (D) is an explanatory diagram of the output characteristics of harmonics comparing the case of using VBG with the case of not using the same pulsed light (A) is explanatory drawing of the pulse energy characteristic after the wavelength conversion which contrasted the case where VBG is used, and the case where it is not used, (b) is the average after wavelength conversion which contrasted the case where it uses and the case where VBG is not used Illustration of power characteristics Block diagram of a laser light source device showing another embodiment Timing chart for explaining the output timing of the trigger signal for driving the seed light source and the gate signal for driving the optical switch element corresponding to the output stop state and the output allowable state of the light pulse of the laser light source device showing another embodiment

Hereinafter, embodiments of a laser light source device according to the present invention will be described.
FIG. 1 shows an exemplary configuration of a laser light source device 1 according to the present invention. The laser light source device 1 includes a light source unit 1A, a fiber amplification unit 1B, a solid amplification unit 1C, and a wavelength conversion unit 1D arranged along the optical axis L, and further includes a control unit 100 that controls the light source unit 1A and the like. It is prepared for.

  The light source unit 1A includes a seed light source 10, a seed light source driver D1, an optical isolator ISL1, and the like. The fiber amplifying unit 1B includes two-stage fiber amplifiers 20 and 30 each having excitation light sources 21 and 31 and multiplexers 22 and 32 each composed of a laser diode, optical isolators ISL2 and ISL3, and an optical switch element. 40, VBG90, reflection mirror M1 and the like.

  The solid-state amplifier 1C includes a solid-state amplifier 50, reflection mirrors M2 and M3, a lens L1, a collimator CL2, and the like. The wavelength conversion unit 1D includes a first wavelength conversion unit 1E and a second wavelength conversion unit 1F, and includes nonlinear optical elements 60 and 70, respectively. The optical switch element 40, the VBG 90, and the reflection mirror M1 provided in the fiber amplifier 1B may be incorporated in the solid amplifier 1C.

  Laser pulse light with a wavelength of 1064 nm output from the seed light source 10 (hereinafter also simply referred to as “pulse light”) is amplified by the two-stage fiber amplifiers 20 and 30 and further amplified to a desired level by the one-stage solid-state amplifier 50. Is done. The pulsed light amplified by the solid-state amplifier 50 is wavelength-converted to a wavelength of 532 nm by the nonlinear optical element 60 and further wavelength-converted to a wavelength of 266 nm by the nonlinear optical element 70 and output.

  The number of fiber amplifiers and solid-state amplifiers is not particularly limited, and may be set as appropriate in order to obtain a desired amplification factor for pulsed light. For example, three fiber amplifiers may be cascaded, and two solid state amplifiers may be cascaded in the subsequent stage.

  A distributed feedback laser diode (hereinafter referred to as “DFB laser”) that outputs a single longitudinal mode laser beam is used as the seed light source 10, and is controlled by a control signal output from the control unit 100 to which the gain switching method is applied. From the DFB laser, pulse light having a desired pulse width of several hundred picoseconds or less is output at a desired frequency of one shot or several megahertz or less.

  Pulse light having a pulse energy of several picojoules to several hundred picojoules output from the seed light source 10 is finally pulsed by the fiber amplifiers 20 and 30 and the solid-state amplifier 50 with a pulse energy of several tens of microjoules to several tens of millijoules. After being amplified to light, it is converted into deep ultraviolet rays having a wavelength of 266 nm by being input to the two-stage nonlinear optical elements 60 and 70.

  The pulsed light output from the seed light source 10 is input to the first-stage fiber amplifier 20 via the optical isolator ISL1 and amplified. As the fiber amplifiers 20 and 30, rare earth-doped optical fibers such as ytterbium (Yb) -doped fiber amplifiers pumped by a pumping light source 21 having a predetermined wavelength (for example, 975 nm) are used. Since the lifetime of the inversion distribution of the fiber amplifier 20 is in the order of milliseconds, the energy excited by the excitation light source 21 is efficiently transferred to pulsed light having a frequency of 1 kilohertz or more.

  The pulse light amplified by about 30 dB by the first-stage fiber amplifier 20 is input to the subsequent-stage fiber amplifier 30 via the optical isolator ISL2 and amplified by about 25 dB. The pulsed light amplified by the subsequent fiber amplifier 30 is beam-shaped by the collimator CL1, passes through the optical isolators ISL3 and ISL4, and is then guided to the solid-state amplifier 50 to be amplified by about 25 decibels.

  In the present embodiment, the pulse light output from the fiber amplifier 30 is beamed by the collimator CL1 immediately before the incident surface of the solid amplifier 50 so as to be efficiently amplified with respect to the thermal lens effect generated in the solid amplifier 50. Beam-shaped so that the waist is located.

  Between the collimator CL and the solid-state amplifier 50, an optical isolator ISL3, an acoustooptic modulator AOM (Acousto-Optic Modulator) that incorporates an acoustooptic element and functions as the optical switch element 40, a VBG90 that is an example of a diffraction grating, and a pair The reflection mirrors MR1 and MR2 are arranged, and an optical isolator ISL4 for guiding the pulse light amplified by the solid-state amplifier 50 to the wavelength converter 60 is arranged between the reflection mirrors MR1 and MR2.

  The optical isolators ISL1 to ISL4 described above are polarization-dependent optical isolators that block the return light by rotating the polarization plane in the reverse direction and the reverse direction using the magneto-optic effect, Each optical element disposed on the upstream side along the optical axis is provided for avoiding thermal destruction by high-intensity return light.

  As the solid-state amplifier 50, a solid-state laser medium such as Nd: YVO4 crystal or Nd: YAG crystal is preferably used. The solid-state laser medium is configured to be excited by the excitation light output from the excitation light source 51 including a laser diode having an emission wavelength of 808 nm or 888 nm and beam-formed by the collimator CL2.

  The pulsed light that has passed through the optical switch element 40 is diffracted by the VBG 90, is incident on the solid-state amplifier 50 through the reflection mirrors MR1 and MR2, is amplified, and is further reflected by the reflection mirror MR3 and re-applied to the solid-state amplifier 50. Incident and amplified again. That is, it is configured to be amplified on the forward path and the return path of the solid-state amplifier 50, respectively. The lens L1 is for beam shaping.

  The pulse light amplified by the solid-state amplifier 50 is reflected by the reflection mirror MR2 and the optical isolator ISL4, is incident on the nonlinear optical elements 60 and 70 of the wavelength converter 1D, is converted to a desired wavelength, and is output.

The first wavelength conversion unit 1E incorporates an LBO crystal (LiB ₃ O ₅ ) that is a nonlinear optical element 60, and the second wavelength conversion unit 1F incorporates a CLBO crystal (CsLiB ₆ O ₁₀ ) that is a nonlinear optical element 70. It is. The pulse light having a wavelength of 1064 nm output from the seed light source 10 is wavelength-converted to a wavelength of 532 nm by the nonlinear optical element 60, and further wavelength-converted to a wavelength of 266 nm by the nonlinear optical element 70.

  The reflection mirrors M4 and M8 function as a filter for separating pulsed light with a wavelength of 1064 nm output from the nonlinear optical element 60, and the reflection mirror M6 is for separating pulsed light with a wavelength of 532 nm output from the nonlinear optical element 70. Each of the separated pulse lights is attenuated by an optical damper.

The second wavelength conversion unit 1F is provided with a stage 71 that is a scanning mechanism that moves a CLBO crystal (CsLiB ₆ O ₁₀ ) in a plane orthogonal to the optical axis. For lowering the ultraviolet When is irradiated to the same position long CLBO crystal (CsLiB ₆ O ₁₀₎ in the degradation and the wavelength converted output of the intensity distribution generated optical damage, CLBO crystal in a predetermined time (CsLiB ₆ O ₁₀₎ This is to shift the irradiation position of the pulsed light on the.

  The control unit 100 is configured by a circuit block including an FPGA (Field Programmable Gate Array) and peripheral circuits, and drives a plurality of logic elements based on a program stored in advance in a memory in the FPGA. For example, the blocks constituting the block are sequentially controlled. In addition to the FPGA, the control unit 100 may be configured with a microcomputer, a peripheral circuit such as a memory and an IO, or a programmable logic controller (PLC). .

  Specifically, the control unit 100 outputs a trigger signal having a predetermined pulse width to the driver D1 of the DFB laser that is the seed light source 10 in order to cause the seed light source 10 to emit light using the gain switching method. When a pulse current corresponding to the trigger signal is applied from the drive circuit to the DFB laser, relaxation oscillation occurs, and only the first wave having the highest emission intensity immediately after the start of light emission due to relaxation oscillation consists of the second and subsequent sub-pulses. A pulsed laser beam not included is output. The gain switching method refers to a method of generating pulsed light having a short pulse width and high peak power using such relaxation oscillation.

  Further, the control unit 100 outputs a gate signal to the RF driver D2 that drives the acousto-optic modulator AOM that is the optical switch element 40. A diffraction grating is generated in a crystal constituting the acoustooptic device by a transducer (piezo conversion device) to which a high frequency signal is applied from the RF driver D2, and diffracted light of pulsed light incident on the acoustooptic device is incident on the VBG 90. When the RF driver D2 is stopped, the pulsed light incident on the acoustooptic device passes through without being diffracted and does not enter the VBG 90. The light that has passed through the acoustooptic device when the RF driver D2 is stopped is attenuated by an optical damper.

  When the optical switch element 40 is turned on by the gate signal, the diffracted light enters the VBG 90 from the fiber amplifier 30 and propagates to the solid-state amplifier 50 via the reflection mirrors M1 and M2. When the optical switch element 40 is turned off by the gate signal, propagation of light from the fiber amplifier 30 to the solid-state amplifier 50 through the VBG 90 is blocked.

Further, the control unit 100 controls the stage 71 to move stepwise in order to shift the irradiation position of the pulsed light to the CLBO crystal (CsLiB ₆ O ₁₀ ) at a predetermined time. For example, the control unit 100 monitors the intensity of the wavelength-converted ultraviolet rays, and when the monitored intensity history matches a predetermined pattern, the control unit 100 moves the stage 71 to irradiate the CLBO crystal (CsLiB ₆ O ₁₀ ) with pulsed light. Shift position.

  The stage 71 is controlled by the control unit 100 via the motor driver D3 and / or the Y-direction moving motor so that the stage 71 can move on the XY plane perpendicular to the optical axis of the pulsed light. It is connected to the drive.

  2A, 2B, and 2C, the frequency characteristics of the pulsed light propagating through each part of the laser light source device 1 are shown on the left side, and the time axis characteristics of the pulsed light are shown on the right side. . Symbols Sn (n is an integer) shown in these figures correspond to the optical signals Sn (n = 1, 2,...) At the output nodes of the respective parts of the laser light source device 1 shown in FIG.

  In response to the trigger signal output from the control unit 100, a narrow-band laser pulse light having a center wavelength of 1064 nm is output at a predetermined period from the DFB laser that is the seed light source 10 (see FIG. 2A). In the process in which the pulsed light output from the seed light source 10 is guided to the fiber amplifier 20 and amplified, the spectrum width is unnecessarily widened by self-phase modulation, Raman scattering, etc., and further, ASE noise is generated and S of the optical pulse is generated. The / N ratio decreases (see FIG. 2B). In the process where such pulsed light is guided to the subsequent fiber amplifier 30 and amplified, the bandwidth is further increased, and the ASE noise level increases (see FIG. 2C).

  In order to obtain deep ultraviolet pulsed light having a desired intensity, it is necessary to amplify the pulsed light amplified by the fiber amplifiers 20 and 30 to a larger peak power by the solid-state amplifier 50 at the subsequent stage. However, since the wavelength range that can be converted by the wavelength converting unit 1D is limited by the characteristics of the nonlinear optical elements 60 and 70, the energy required for amplification does not contribute to wavelength conversion efficiently. That is, the wavelength conversion efficiency is lowered.

  As a result of the wasteful consumption of the excitation energy of the solid-state amplifier 50 by ASE noise amplification and broadband pulse light, there is a problem that energy efficiency is greatly reduced. For this reason, if the excitation energy is increased, damage to the element due to heat generation is avoided. Therefore, a large cooling device is required, and there is a problem that the laser light source device 1 is expensive. If the frequency of the pulsed light is larger than the order of megahertz, the ASE noise is negligible, so that there is no problem. However, in the region where the oscillation frequency of the pulsed light is lower than 1 megahertz, the influence of the ASE noise becomes significant.

  On the other hand, when pulse light having a wavelength in the deep ultraviolet region output from the laser light source device 1 is used for various laser processing, there are many cases where it is desired to temporarily stop the light. In such a case, when the oscillation of the seed light source 10 is stopped or the propagation of the pulsed light to the optical amplifiers 20, 30, 50 is stopped, the excitation laser light source provided in the optical amplifiers 20, 30, 50 is also used in the meantime. Each laser active region continues to be excited and reaches an excessive population inversion state.

  As a result, the next time the seed light source is oscillated or the propagation of the pulsed light to the optical amplifier 50 is allowed, a giant pulse is output, causing damage to the solid-state amplifier 50, the subsequent nonlinear optical element, or the like. There is also a problem.

  In addition, when the output is resumed after temporarily stopping the output of the pulsed light, if excessive energy is accumulated in the solid-state laser medium constituting the solid-state amplifier, the solid-state laser medium generates excessive heat and the temperature is increased. As a result, the beam propagation characteristics are deteriorated, which may adversely affect the quality of the processing target using the laser pulse light.

  Therefore, the present embodiment includes the optical switch element 40 that functions as a noise filter that removes ASE noise and the like in the time domain, and the reflective VBG 90 that functions as a noise filter that removes ASE noise and the like in the frequency domain. .

  First, the optical switch element 40 will be described. The control unit 100 allows the optical switch element 40 to allow light propagation during the output period of the pulsed light from the seed light source 10 and to prevent light propagation during a period different from the output period of the pulsed light from the seed light source 10. By controlling, it is configured to generate an output permission state that allows the output of pulsed light from the nonlinear optical elements 60 and 70.

  Further, the control unit 100 prevents the light from propagating during the output period of the pulsed light from the seed light source 10 and allows the light to propagate during a period different from the output period of the pulsed light from the seed light source 10. 40 is configured to generate an output stop state in which the output of the pulsed light from the nonlinear optical elements 60 and 70 is stopped.

  If the optical switch element 40 is turned off by the control unit 100 in a period different from the output period of the pulsed light from the seed light source 10 in the permissible output state, ASE noise is prevented from propagating to the solid-state amplifier 50 in the subsequent stage. As a result, it is avoided that the energy in the active region of the solid-state amplifier 50 is wasted (see section Toff in FIG. 3D).

  Then, when the optical switch element 40 is turned on by the control unit 100 during the period in which the pulse light is output from the seed light source 10, the pulse light propagates from the fiber amplifier 30 to the solid-state amplifier 50 (section in FIG. 3D). Ton), the pulse light is amplified with energy efficiency (see FIG. 3 (f)), and the pulse light with a large peak power is output from the nonlinear optical element. That is, the optical switch element 40 is caused to function as a filter for removing ASE noise in the time domain.

  Further, when the control unit 100 turns off the optical switch element 40 during the output period of the pulsed light from the seed light source 10, the propagation of the pulsed light from the fiber amplifier 30 to the solid-state amplifier 50 is blocked, and the seed light source 10 is stopped. Even if not, an output stop state in which the output of pulsed light from the nonlinear optical elements 60 and 70 stops can be easily realized.

  When the optical switch element 40 is turned on by the control unit 100 in a period different from the output period of the pulsed light from the seed light source 10 in the output stop state, the ASE noise generated in the front-stage fiber amplifier 30 is transferred to the subsequent-stage solid-state amplifier. Propagating (see FIG. 3E), the energy of the active region of the solid state amplifier 50 in the excited state is released by the excitation light source 51.

  As a result, the output shift state is entered after the output stop state, and the optical switch element 40 is turned on by the control unit 100 during the output period of the pulsed light from the seed light source 10, and the pulsed light is emitted from the wavelength converters 60 and 70. Even in the case of output, no giant pulse is generated and the solid-state amplifier 50 and the nonlinear optical elements 60 and 70 are not damaged.

  Furthermore, since excessive heat generation of the solid-state laser medium is suppressed, the beam propagation characteristics immediately after the restart of output is not deteriorated, and the quality of the processing target using the laser pulse light is not adversely affected.

  Moreover, even if the ASE noise amplified by the solid-state amplifier 50 is incident on the nonlinear optical elements 60 and 70 during a period different from the output period of the pulsed light from the seed light source 10, the nonlinear optical elements 60, ASE noise in a wider wavelength band than the wavelength conversion characteristic of 70 is not output as light having a large peak power. In addition, since the output light from the fiber amplifier 30 is not amplified to a light having such a large peak power, peripheral optical components including the optical switch element 40 are heated and the like even if blocked by the optical switch element 40. Will not be damaged by.

  “The output period of the pulsed light from the seed light source” in which the optical switch element 40 is on-controlled by the control unit 100 in the output-permitted state does not mean only the entire period in which the pulsed light is output from the seed light source. If the peak power of the pulsed light converted by the nonlinear optical element shows an appropriate value, it may be a partial period, or slightly before and after the period when the pulsed light is output from the seed light source. It is a concept that includes various periods.

  The “period different from the output period of the pulsed light from the seed light source” in which the optical switch element 40 is controlled to be off by the control unit 100 in the output allowable state is the entire period between the output periods of the plurality of pulsed light, that is, It does not mean only the whole period in which no pulsed light exists, but if it is within a range where it is possible to reduce the wasteful consumption of energy in the active region of the solid-state amplifier excited by the excitation light source due to ASE noise, a part thereof It is a concept that includes a period.

  The “pulse light output period from the seed light source” in which the optical switch element 40 is off-controlled by the control unit 100 in the output stop state does not mean only the entire period in which the pulse light is output from the seed light source. If the pulse light whose wavelength is converted by the non-linear optical element is weak, it may be a partial period, and also includes a short period before and after the period when the pulse light is output from the seed light source. It is.

  The “period different from the output period of the pulsed light from the seed light source” in which the optical switch element 40 is on-controlled by the control unit 100 in the output stopped state is the entire period between the output periods of the plurality of pulsed light, that is, It does not mean only the whole period in which no pulsed light exists, but it is a concept that includes a part of the period as long as the excessive excitation state of the solid-state amplifier is eliminated by ASE noise. It is a concept that includes not only every period between light output periods but also a period once in a plurality of times.

  FIG. 4 illustrates a control timing chart for the seed light source 10 and the optical switch element 40 executed by the control unit 100.

  In the output allowable state, a gate signal is output to the RF driver D2 of the optical switch element 40 at a reference time t0, and a trigger signal for the driver D1 of the seed light source 10 is turned on at a time t3 after a predetermined delay time. To do. By turning off the trigger signal at a predetermined time t5 after the relaxation oscillation occurs at the time t4, the pulsed light S1 having a predetermined pulse width is obtained, and the pulsed light S3 amplified by the fiber amplifiers 20 and 30 is obtained. The pulsed light S3 has a broad band and is further superimposed with ASE noise.

  The controller 100 does not stop the laser oscillation by turning off the trigger signal at time t5, but the driver D1 stops the laser oscillation of the seed light source 10 at the predetermined time t5 for the seed light source 10 in which the relaxation oscillation has occurred. You may be comprised so that it may make. In this case, the trigger signal OFF timing may be set arbitrarily.

  The optical switch element 40 is turned on at time t2 by the gate signal turned on at time t0, and the optical switch element 40 is turned off at time t6 by the gate signal turned off at time t1. Between time t2 and time t6 when the optical switch element 40 is turned on, the output light S4 that has been amplified by the fiber amplifier 30 and passed through the optical switch element 40 propagates to the solid-state amplifier 50 via the VBG 90.

  Therefore, the output light S4 amplified by the fiber amplifier 30 and passed through the optical switch element 40, that is, the pulsed light S4 output from the seed light source 10, is transmitted to the solid-state amplifier 50 between the time t2 and t6 when the optical switch element 40 is turned on. Propagate. Then, during the time t6 to t9 when the optical switch element 40 is turned off, the propagation of the ASE noise to the solid-state amplifier 50 is prevented, so that the excitation energy accumulated in the active region of the solid-state amplifier 50 is wasted. Will be avoided.

  In the output stop state, a gate signal is output to the RF driver D2 of the optical switch element 40 at a reference time t1, and after a predetermined delay time, a trigger signal for the driver D1 of the seed light source 10 is turned on at a time t3. To do. By turning off the trigger signal at a predetermined time t5 after the relaxation oscillation occurs at the time t4, the pulsed light S1 having a predetermined pulse width is obtained, and the pulsed light S3 amplified by the fiber amplifiers 20 and 30 is obtained. The pulsed light S3 has a broad band and is further superimposed with ASE noise.

  The optical switch element 40 is turned on at time t6 by the gate signal turned on at time t1, and the optical switch element 40 is turned off at time t9 by the gate signal turned off at time t7. Between time t6 and time t9 when the optical switch element 40 is turned on, the output light S4 ′ amplified by the fiber amplifier 30 and passed through the optical switch element 40 propagates to the solid-state amplifier 50.

  At this time, pulse light is not input to the solid-state amplifier 50, and only ASE noise is input. The excitation energy accumulated in the active region of the solid-state amplifier 50 is released by this ASE noise, and the occurrence of a giant pulse is avoided even when the output is allowed next.

  In the example described with reference to FIG. 4, the phase of the gate signal for the optical switch element 40 in the output-permitted state is 180 degrees reversed from that of the gate signal in the output-stopped state. The OFF state is basically reversed.

  In FIG. 4, a diffraction grating is formed in the optical switch element 40 when an RF signal is input, and the state in which the diffracted light propagates to the solid-state amplifier 50 is expressed as ON, and the diffraction grating is formed in the optical switch element 40. The state in which the zero-order light is attenuated by the damper without propagating the light to the solid-state amplifier 50 is expressed as OFF. The logic of the control signal output to the optical switch element 40 may be either positive logic or negative logic.

  In the above-described example, the mode in which the optical switch element 40 is turned on in the entire period between the output periods of the plurality of pulse lights repeatedly output from the seed light source 10 in the output stopped state has been described. If the excitation energy accumulated in the active region is sufficiently released by the ASE noise, the optical switch only during a part of the period between the output periods of the plurality of pulse lights repeatedly output from the seed light source 10 The element 40 may be turned on.

  Further, the optical switch element 40 may be controlled so as to be repeatedly turned on and off in the period between the output periods of the plurality of pulse lights repeatedly output from the seed light source 10. By controlling in this way, the heat generation of the AOM that constitutes the optical switch element 40 can be reduced.

  Since it is desirable to remove ASE noise as much as possible, the ON time of the optical switch element 40 in the output allowable state is set to a range of 1.5 to 10 times the pulse width of the pulsed light output from the seed light source 10. It is preferable that it is set in the range of 1.5 to 3 times. For example, if the pulse width of the pulsed light output from the seed light source 10 is 50 picoseconds, it may be set from 75 picoseconds to 500 picoseconds. However, the range may be limited by the control period of the control unit 100.

  The off-time of the optical switch element 40 in the output stop state is preferably sufficiently short as compared with the pulse period so that the propagation of the pulsed light output from the seed light source 10 can be almost certainly prevented. Therefore, the off time of the switch element 40 at this time may be set in a range of 2 to 10 times the pulse width of the pulsed light, and is further set in a range of 2 to 5 times. preferable.

  That is, it is preferable that the ON time of the optical switch element in the output allowable state is set to be shorter than the OFF time of the optical switch element 40 in the output stop state.

  In the example described with reference to FIG. 4, the control unit 100 is configured to output a trigger signal that controls the seed light source 10 based on a control signal (gate signal) for the optical switch element 40. With this configuration, even if the response of the optical switch element 40 is slower than the response of the pulsed light output from the seed light source 10, the seed light source 10 is controlled based on the control signal for the optical switch element 40. By generating a control signal to be controlled, the optical switch element 40 can be appropriately driven.

  When the response of the optical switch element 40 is sufficiently faster than the response of the pulsed light output from the seed light source 10, the optical switch element 40 is naturally controlled based on the control signal for the seed light source 10. It is also possible to do.

  That is, when stopping the output of the pulsed light from the nonlinear optical elements 60 and 70 by the control unit 100 described above, the optical switching element 40 disposed between the fiber amplifier 30 and the solid-state amplifier 50 is controlled, A laser pulse light generation method is executed in which light propagation is prevented during the pulse light output period from the seed light source 10 and light propagation is allowed during a period different from the output period.

  Similarly, when output of pulsed light from the nonlinear optical elements 60 and 70 is allowed by the control unit 100 described above, the optical switch element 40 is controlled to output the pulsed light from the seed light source 10 during the output period. A laser pulse light generation method that allows light propagation and prevents light propagation in a period different from the output period is executed.

  FIG. 5A shows the wavelengths when the optical switch element that removes ASE noise is used and the optical switch element is not used in a state where the power of the excitation light sources 21, 31, 51 is kept constant. The converted pulse energy characteristics are shown, and FIG. 5B shows the average power characteristics after wavelength conversion when the optical switch element for removing ASE noise is used and when the optical switch element is not used. ing. In both figures, the characteristics plotted with black circles are characteristics when an optical switch element is used, and the characteristics plotted with black squares are characteristics when no optical switch element is used.

  According to FIGS. 5A and 5B, the pulse energy and the average power are effectively increased in the frequency range from several tens of kilohertz to several megahertz by removing the ASE noise using the optical switch element. I understand that.

  Next, the VBG 90 will be described. When the pulsed light that has been broadened by the fiber amplifiers 20 and 30 enters the VBG 90 via the optical switch element 40, the pulsed light is diffracted by the VBG 90 and narrowed to a specific wavelength range. That is, the wavelength components deviating from the wavelength range that can be converted by the nonlinear optical elements 60 and 70 are removed. The reflection type VBG 90 reflects only the diffracted light in the desired wavelength range, so that a filter mechanism for selecting the diffracted light in the desired wavelength range becomes unnecessary.

  In FIG. 2 (d), the spectrum of the pulsed light that has been broadened by the fiber amplifier (shown by a broken line in the figure) and the spectrum of the pulsed light that has been narrowed by the VBG 90 (in the figure, by the solid line). Are shown for comparison.

  The center wavelength of the diffracted light can be adjusted by adjusting the incident angle of the pulsed light to the VBG 90, and the optical axis of the diffracted light after the adjustment can be adjusted by the reflection mirror MR1 that is an optical mirror. In this embodiment, the spectral width of the pulsed light having the center wavelength of 1064 nm ± 0.05 nm is expanded to about ± 0.15 nm by passing through the fiber amplifiers 20 and 30, and is narrowed to about ± 0.10 nm by the VBG90. The degree of band narrowing is set based on the allowable wavelength-convertible width that is a characteristic of the nonlinear optical elements 60 and 70, and the band can be narrowed to, for example, about ± 0.05 nm depending on the characteristics of the VBG 90 used. Become.

  In FIG. 1, the reflection mirror MR1 is arranged so as to guide the diffracted light from the VBG 90 to the solid-state amplifier 50, but the VBG 90 and the reflection mirror MR1 may be arranged in reverse. That is, the output light of the fiber amplifier 30 may be reflected by the reflection mirror MR1 and incident on the VBG 90, and the diffracted light of the VBG 90 may be guided to the solid-state amplifier 50.

  That is, the VBG 90 is disposed between the fiber amplifier 30 and the solid-state amplifier 50 and diffracts light in a specific wavelength range from the pulsed light output from the fiber amplifier 30, and the pulsed light output from the fiber amplifier 30 is directed to the VBG 90. It suffices to include an optical mirror MR1 that reflects light in a specific wavelength range reflected or diffracted by the VBG 90 toward the solid-state amplifier 50.

  The pulsed light incident on and diffracted into the VBG 90 is reduced in ASE noise and narrowed to be propagated to the solid-state amplifier 50 (see FIG. 2D). Pulse light having a large peak power is output from the optical elements 60 and 70.

  FIG. 6A shows the output characteristics of the case where the VBG is used and the case where it is not used for the pulsed light having a wavelength of 1064 nm amplified by the fiber amplifier. FIG. A spectral characteristic comparing the case where VBG is used with respect to pulsed light and the case where VBG is not used is shown.

  FIG. 6 (c) shows the conversion efficiency of harmonics comparing the case where VBG is used and the case where it is not used for the same pulse light, and FIG. 6 (d) shows the same pulse light. On the other hand, the output characteristics of the harmonics are shown comparing the case where the VBG is used and the case where the VBG is not used. In both figures, the characteristic indicated by a solid line is a characteristic when VBG is used, and the characteristic indicated by a broken line is a characteristic when VBG is not used.

  According to FIGS. 6A and 6B, the output of the 1064 nm wavelength light amplified by the solid-state amplifier is slightly reduced when VBG is used, compared to the case where VBG is not used. It can be seen that the spectral width (FWHM) of light is equal to 0.11 nm, and that when VBG is used, the rise in the bottom region of the spectrum becomes steep and narrowed.

  As can be seen from FIGS. 6C and 6D, when the VBG is used, the conversion efficiency at the time of wavelength conversion to the wavelength of 532 nm is higher by about 8% than when the VBG is not used. As a result, it was found that the effect of removing ASE noise can be obtained by using VBG.

  FIG. 7A shows the pulse energy characteristics after wavelength conversion when the VBG is used with the power of the excitation light sources 21, 31, 51 kept constant and when the VBG is not used. 7 (b) shows the average power characteristics after wavelength conversion when VBG is used and when VBG is not used. In both figures, the characteristic indicated by a solid line is a characteristic when VBG is used, and the characteristic indicated by a broken line is a characteristic when VBG is not used.

  According to FIGS. 7A and 7B, the pulse energy and the average power are effectively increased in the frequency range from several tens of KHz to several hundreds of MHz by narrowing the band using VBG and reducing ASE noise. You can see that

  When the frequency of the pulsed light output from the seed light source 10 is several megahertz or less, particularly when it is 1 megahertz or less, the ASE noise removal effect by the optical switch element 40 and the VBG 90 is remarkable. Note that when the frequency of the pulsed light is several hundred kilohertz or less, the ASE noise removal effect by the optical switch element 40 becomes more prominent than the VBG 90.

  The present invention relates to a laser light source device including a seed light source configured to drive a semiconductor laser including a DFB laser at a frequency of several hundred MHz or less and a pulse width of several hundred picoseconds or less. Widely applicable to.

Hereinafter, another embodiment of the present invention will be described.
In the above-described embodiment, an example in which the reflective VBG 90 is employed has been described. However, a transmissive VBG 90 can also be employed. Furthermore, instead of the VBG 90, a general-purpose diffraction grating in which striped irregularities are formed on the surface of the optical glass may be incorporated.

  In the above-described embodiment, the example in which the VBG 90 is disposed at the subsequent stage of the optical switch element 40 has been described. However, the optical switch element 40 may be disposed at the subsequent stage of the VBG 90.

  In addition to the above-described embodiment, a band pass filter that narrows the band of pulse light that has been widened by self-phase modulation, Raman scattering, or the like in the optical fiber may be provided after the fiber amplifiers 20 and 30.

  In FIG. 2 (e), the spectrum of the pulsed light that is broadened by the fiber amplifier (indicated by a broken line in the figure) and the spectrum of the pulsed light that is narrowed by the bandpass filter (in the figure, It is shown as a solid line). Although the degree of band narrowing by the VBG 90 shown in FIG. 2D is different by about an order of magnitude, a band narrowing of about ± several nm can be achieved.

  FIG. 8 shows an example in which a bandpass filter BPF1 is provided at the subsequent stage of the fiber amplifier 20. The pulse light that has been broadened in the process of being amplified by the fiber amplifier 20 and on which the ASE noise is superimposed is filtered by the bandpass filter BPF1 to become a pulse light that has been narrowed to some extent and from which the ASE noise has been removed. Then, it is input to the fiber amplifier 30 at the subsequent stage.

  A band pass filter may be provided between the seed light source 10, the optical isolator ISL1, and the fiber amplifier 20, so that reflection of ASE noise to the seed light source may be avoided.

  In the above-described embodiment, an example in which an acousto-optic device that turns on or off the first-order diffracted light by turning on or off the ultrasonic transducer has been described as the optical switch device 40. It is also possible to use an electro-optic element that turns on and off light by using an electric field.

  Further, whether or not the output of the fiber amplifier 30 is propagated to the solid-state amplifier 50 by using a micro peristaltic mirror (mirror composed of MEMS (Micro Electro Mechanical Systems)) manufactured by micromachining technology as the optical switch element 40. May be configured to be switched according to a slight swing angle of the swing mirror. Alternatively, a polarization device capable of dynamically switching the polarization state and controlling transmission and blocking of light may be used. In other words, the optical switch element only needs to be composed of a dynamic optical element.

  In the above-described embodiment, the aspect in which the gate signal for the optical switch element 40 controlled by the control unit 100 is configured so that the phase is inverted by 180 degrees between the output allowable state and the output stop state has been described. It is not limited to the embodiment, and at least in the output stop state where the output of the pulsed light from the nonlinear optical elements 60 and 70 is stopped, the propagation of the light is blocked at the output timing of the pulsed light from the seed light source 10, It suffices if the gate signal is output so that light propagation is allowed at a timing different from the output timing.

  For example, as shown in FIG. 9A, the propagation of light is allowed during a period Pb between the output periods Pa of the plurality of pulse lights repeatedly output from the seed light source 10, that is, a period in which no pulse light exists. The control unit 100 may be configured to shift from the output stop state to the output permissible state by shifting the output timing Ts of the control signal Cs for controlling the optical switch element 40 stepwise or continuously. . For example, the output time may be shifted stepwise or continuously based on the previous output time, or may be shifted stepwise or continuously based on the output time several times before.

  In the output stop state, control signals Cs (1) and Cs (2) for controlling the optical switch element 40 so as to allow light propagation during a period Pb different from the output period Pa of the pulsed light output from the seed light source 10. ), Cs (3)... Output timing Ts (1), Ts (2), Ts (3)... The output allowable state is reached by overlapping with the output period Pa of the pulsed light output from the seed light source 10. In FIG. 9, changes in the control signals Cs (1), Cs (2), and Cs (3) are easily observed with the output timings Ts (1), Ts (2), and Ts (3). In addition, a broken line having a rough pitch, a dense broken line, and a solid line are shown.

  As shown in FIG. 9B, in the transition state where the output stop state shifts to the output permissible state, the output period Pa of the pulsed light output from the seed light source 10 is shifted to the ON state of the optical switch element 40. For the transitional time to shift to an appropriate ON state. Therefore, for example, when the acousto-optic modulator AOM is used as the optical switch element 40, the energy of the pulsed light propagating through the optical switch element 40 to the solid-state amplifier 50 is very small at an early stage when the diffraction efficiency is low, and then the diffraction is performed. Since the efficiency gradually increases as the efficiency increases, even if the active region of the solid-state amplifier 50 is in an excessive inversion distribution state, the energy in the active region is consumed by amplification of the pulse light with very small initial energy, and the giant pulse Will not occur.

  In FIG. 9B, after the ON signal is input to the optical switch element 40, the diffraction efficiency gradually rises and rises until it is saturated, and then after the OFF signal is input to the optical switch element 40. The trapezoidal shape is expressed in consideration of the falling transient state in which the diffraction efficiency gradually decreases. That is, even when the output period Pa of the pulse light initially overlaps with the rise of the optical switch element 40 (corresponding to Cs (2) in FIG. 9B), the diffraction efficiency of the optical switch element 40 is low. The energy of the pulsed light incident on the solid-state amplifier 50 is limited, but the input timing of the ON signal to the optical switch element 40 is advanced with respect to the next pulsed light and is superimposed on the saturation of the optical switch element 40 (FIG. 9 (b), corresponding to Cs (3)), the diffraction efficiency of the optical switch element 40 is stable at a high value, and the energy of the pulsed light incident on the solid-state amplifier 50 is not greatly attenuated. .

  Further, when the response speed of the optical switch element 40 is sufficiently high, the pulse width of the optical pulse propagating through the optical switch element 40 to the solid-state amplifier 50 is very short at first, and then gradually increases. Even if the active region of the solid-state amplifier 50 is in an excessive inversion distribution state, the energy in the active region is consumed by amplification of an optical pulse with a very short initial pulse width, and a giant pulse is not generated. .

  In the embodiment described above, an example in which the excitation light source of each of the optical amplifiers 20, 30, 50 is always driven has been described. However, the fiber amplifier 20 is input by the control unit 100 before at least the pulsed light output from the seed light source 10. , 30 and / or the solid-state amplifier 50 are configured to control the pumping light sources 21, 31, 51 of the fiber amplifier 20, 30, and / or the solid-state amplifier 50 periodically or intermittently so that the inverted distribution state of the solid-state amplifier 50 is obtained. May be.

  By controlling the excitation light sources 21, 31, 51 in this way, the fiber amplifiers 20, 30 and / or the solid-state amplifier 50 are in an inverted distribution state before the pulsed light output from the seed light source 10 is input. Since the excitation light is driven periodically or intermittently, it is possible to reduce wasteful energy consumption and heat generation that do not contribute to the amplification of the pulsed light.

  For example, periodic on / off control or intensity modulation control may be performed so that the optical amplifier is in an inverted distribution state at the input timing of the pulsed light output from the seed light source 10. It is preferable that the excitation light sources 21, 31, 51 are driven at a timing that is three times later than the fluorescence lifetime τ of the optical amplifier from the trigger signal that drives the seed light source 10. Furthermore, the optical amplifier may be in an inverted distribution state by intermittently driving the excitation light source during this period.

  In the embodiment described above, when the output of pulsed light from the nonlinear optical element is allowed, the propagation of light is allowed at the output timing of the pulsed light from the seed light source 10, and the light is propagated at a timing different from the output timing. Although the example provided with the control part 100 which controls the optical switch element 10 to prevent was demonstrated, the control part 100 of the laser light source apparatus by this invention stops the output of the pulsed light from a nonlinear optical element at least In addition, it is only necessary that the optical switch element 10 is configured to prevent light propagation at the output timing of the pulsed light from the seed light source 10 and to allow light propagation at a timing different from the output timing. .

  In the embodiment described above, an example has been described in which a DFB laser is used as a seed light source and a gain switching method is applied to the DFB laser to generate pulsed light having a higher intensity than that in a steady state in a single longitudinal mode. The present invention only needs to use a semiconductor laser as a seed light source, and a general Fabry-Perot type semiconductor laser other than a DFB laser can also be used.

  The present invention is not limited to a seed light source with an oscillation wavelength of 1064 nm. For example, it is possible to select a seed light source with a different wavelength depending on the application, such as 1030 nm, 1550 nm, and 976 nm. Furthermore, it is possible to generate harmonics, sum frequencies, and difference frequencies having these wavelengths as fundamental waves through a nonlinear optical element. Nonlinear optical elements other than those described above can be used as the nonlinear optical element. For example, a BBO crystal, a KBBF crystal, an SBBO crystal, a KABO crystal, a BABO crystal, or the like can be used instead of the CLBO crystal.

  The plurality of embodiments described above are all descriptions of one embodiment of the present invention, and the scope of the present invention is not limited by the description. Needless to say, the specific circuit configuration of each part and the optical elements used in the circuit can be appropriately selected or modified as long as the effects of the present invention can be achieved.

1: Laser light source device 10: seed light source 20, 30: fiber amplifier 40: optical switch element 50: solid state amplifier 60, 70: nonlinear optical element 90: diffraction grating (VBG)

Claims (7)

A seed light source that outputs pulsed light by a gain switching method, a fiber amplifier that amplifies pulsed light output from the seed light source, a solid-state amplifier that amplifies pulsed light output from the fiber amplifier, and an output from the solid-state amplifier A non-linear optical element that converts the wavelength of the pulsed light to be output, and a laser light source device comprising:
An optical switching element that is disposed between the fiber amplifier and the solid-state amplifier and that allows or blocks the propagation of light from the fiber amplifier to the solid-state amplifier;
A diffraction grating disposed between the fiber amplifier and the solid-state amplifier and diffracting light in a specific wavelength range from pulsed light output from the fiber amplifier and guiding the light to the solid-state amplifier;
By controlling the optical switch element to allow light propagation during the output period of the pulsed light from the seed light source and to prevent light propagation during a period different from the output period of the pulsed light from the seed light source, A control unit configured to generate an output permission state that allows the output of pulsed light from the nonlinear optical element;
A laser light source device.   The control unit prevents the light propagation during an output period of the pulsed light from the seed light source, and allows the optical switch element to allow light propagation during a period different from the output period of the pulsed light from the seed light source. The laser light source device according to claim 1, wherein the laser light source device is configured to generate an output stop state that blocks output of pulsed light from the nonlinear optical element by controlling.   3. The laser light source device according to claim 1, wherein the diffraction grating is constituted by a volume Bragg grating.   A reflection mirror that reflects the pulsed light output from the fiber amplifier toward the volume Bragg grating or reflects light in a specific wavelength range diffracted by the volume Bragg grating toward the solid state amplifier; The laser light source device according to claim 3, further comprising:   5. The laser light source device according to claim 1, further comprising a band-pass filter that transmits light in a wavelength range including the specific wavelength range after the fiber amplifier.   6. The laser light source device according to claim 1, wherein the optical switch element is composed of a dynamic optical element including an acousto-optic element or an electro-optic element.   The seed light source is configured by a DFB laser, and the control unit is configured to drive the DFB laser at a frequency of several megahertz or less and a pulse width of several hundred picoseconds or less. The laser light source device according to any one of the above.

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