JP2011053314A - Light source device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light source device capable of outputting high-speed and high-stability harmonic wave pulses. <P>SOLUTION: The light source device 1 includes a laser beam generating section 10; a light-amplifying section 20; and a wavelength-converting section 30 including non-linear optical crystals 33 that cause walk-offs. A control section exerts on/off control for beam output, by changing the phase matching condition in the non-linear optical crystals 33 in a predetermined range, and changes beam pointing according to an amount of phase mismatch, and thereby switching between an output optical path Lon through which harmonic wave output is emitted from a window 35, and a non-output optical path Loff which is to be blocked by a blocking member 38. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a light source device including a laser light generation unit, an optical amplification unit, and a wavelength conversion unit.

  As a light source device as described above, infrared to visible pulse light (seed light) generated by a semiconductor laser is amplified by an optical amplifying unit such as a fiber optical amplifier, and is composed of a plurality of wavelength conversion optical elements. There is an all-solid-state light source device that performs wavelength conversion by a wavelength conversion unit and outputs pulsed light in the ultraviolet region. Such a light source device has been used as a suitable light source in fields such as a laser microscope for observing a fine structure, various optical inspection devices, an exposure device for transferring a fine pattern of a reticle, and a medical device used for ophthalmic treatment. ing.

  The on / off of the output light from the light source device is generally performed in a laser light generation unit. For example, the seed light is turned on / off by controlling the waveform of the driving current of the semiconductor laser, or the semiconductor The seed light output from the laser is switched by an optical switch such as an electro-optic modulator (EOM), and the output from the laser light generation unit is controlled on / off (for example, Patent Document 1).

JP 2004-86193 A

  However, in the conventional light source device, even if the seed light is injected into the optical amplifying unit previously held in the pumped state, the gain inversion distribution and thermal stability in the fiber optical amplifier change and are emitted from the optical amplifying unit. There has been a problem that it is difficult to obtain a stable light output at the time of rising of the amplified light, and hence the harmonics output from the wavelength conversion unit.

  For such a problem, a configuration in which a mechanical shutter is provided at the exit of the optical amplifying unit to block the amplified light of the fundamental wave emitted from the optical amplifying unit is conceivable. However, the mechanical shutter takes about tens to hundreds of milliseconds for opening and closing, and high-speed on / off control in units of several milliseconds is difficult. In addition, since the wavelength conversion optical element constituting the wavelength conversion unit absorbs the beam slightly and the element temperature changes, the phase matching is adjusted in the harmonic output state where the wavelength conversion optical element is thermally stable. The Therefore, when the time to stop the generation of harmonics by blocking the amplified light by the mechanical shutter is a predetermined time or more (for example, several seconds or more), even if the amplified light incident on the wavelength conversion unit is stable from the time the shutter is opened, The conversion efficiency is low until the wavelength conversion optical element is thermally stabilized, and it is necessary to compensate for this. Such a thermal problem of the wavelength conversion optical element is considered to be an important problem for a light source device that generates high-power ultraviolet light.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a light source device capable of outputting a stable harmonic beam from the rising edge.

  According to the first aspect illustrating the present invention, a laser light generating unit that generates pulsed light, an optical amplifying unit that amplifies pulsed light generated by the laser light generating unit, and a walk-off are generated. A non-linear optical crystal includes a wavelength conversion stage that is used for angle phase matching, and includes a wavelength conversion unit that converts the wavelength of the pulsed light amplified by the optical amplification unit and outputs the light. By changing the phase matching state within a predetermined range and changing the beam pointing according to the amount of phase mismatch, the emission path of the harmonics emitted from the nonlinear optical crystal is changed to the output optical path and the non-output optical path. A beam control device that performs switching setting and a shielding member that is disposed on the optical path of the non-output optical path and blocks output from the non-output optical path are configured.

  The beam control device can be configured to change the phase mismatch amount in the nonlinear optical crystal within a predetermined range by changing the wavelength of the pulsed light incident on the wavelength converter. In this case, the laser light generation unit includes a laser light source that oscillates in pulses, and an optical modulator that cuts out and emits a part of the pulsed light generated by the laser light source, and the beam control device is an optical modulator. It is one preferable aspect that the configuration is such that the wavelength of the pulsed light incident on the wavelength conversion unit is changed by changing the cut-out timing. The laser light generator includes a first laser light source that oscillates pulsed light of a first wavelength and a second laser light source that oscillates pulsed light of a second wavelength, and the beam control device includes the laser light generator. It is another preferable aspect that the wavelength of the pulsed light incident on the wavelength conversion unit is changed by selectively switching the pulsed light emitted from the first wavelength pulsed light or the second wavelength.

  According to the light source device of the present invention, by changing the beam pointing by giving a phase mismatch amount to the nonlinear optical crystal, the harmonic emission optical path is switched between the output optical path and the non-output optical path, and set as the non-output optical path. In this state, the harmonic output is blocked by the shielding member. For this reason, the light source device including not only the laser light generation unit and the optical amplification unit but also the nonlinear optical crystal can be held in a thermally stable state, and the beam control device switches the output optical path to the output optical path. Thus, it is possible to provide a light source device capable of outputting a stable harmonic beam from the rising edge.

  According to the configuration in which the beam control device changes the phase mismatch amount in the nonlinear optical crystal by changing the wavelength of the pulsed light incident on the wavelength converter, the wavelength region of the fundamental wave that is easy to handle Can be used to provide a light source device having the above effects with a relatively simple configuration. In this case, an optical modulator that cuts out part of the pulsed light generated by the laser light source is provided, and a configuration that changes the wavelength of the pulsed light by changing the cutout timing of the pulsed light, the first and second According to the configuration in which the pulsed light generated by the laser light source is selectively switched to change the wavelength of the pulsed light, on / off control can be performed in units of one pulse (nanosecond to millisecond) of the pulsed light. Therefore, it is possible to provide a light source device capable of high-speed and highly stable output control.

The change of the beam emitted from the nonlinear optical crystal when the beam pointing is changed is schematically shown by a straight line and a dotted line. It is a schematic block diagram of the light source device shown as an example of application of this invention. It is a schematic block diagram which shows the structural example of a wavelength converter. It is a graph which shows the dependence with respect to the phase mismatch of a harmonic output and beam pointing at the time of using the nonlinear optical crystal which produces a walk-off by angle phase matching. It is a schematic block diagram of the laser beam generation part of a 1st structure form. It is explanatory drawing which shows the relationship between the pulsed light which a laser beam generation part generate | occur | produces, and the transmittance | permeability of an optical modulator. It is a schematic block diagram of the laser beam generation part of a 2nd structure form.

  Hereinafter, an embodiment for carrying out the present invention will be described with reference to FIG. 2 showing a schematic configuration of a light source device 1 to which the present invention is applied. In the present embodiment, a light source device suitably used for an optical inspection apparatus such as a laser microscope or a shape measuring instrument will be described as an example.

  The light source device 1 is broadly divided into a laser light generation unit 10 (10A, 10B) that generates pulsed light, an optical amplification unit 20 that amplifies the pulsed light generated by the laser light generation unit 10, and an optical amplification. The wavelength conversion unit 30 that converts the wavelength of the fundamental pulse light amplified by the unit 20 and outputs it, and the control device 8 that controls the operation of each unit of the light source device 1 are configured.

  The laser light generation unit 10 is provided with a laser light source 11 that generates pulsed light (seed light) having a predetermined wavelength in the infrared to visible region. The laser light source 11 can have an appropriate oscillation wavelength and oscillation form depending on the application and function of the light source device. For example, distributed feedback of InGaAsAs with an oscillation wavelength of 1.51-1.59 [μm]. A type semiconductor laser (DFB semiconductor laser) is used. The DFB semiconductor laser can be pulse-oscillated with an arbitrary repetition frequency and intensity pattern by controlling the waveform of the drive current. The DFB semiconductor laser 11 is attached to a heat sink provided with a temperature regulator using a Peltier element or the like, and is temperature-controlled by the control device 8, whereby the wavelength λ = 1.544 [μm from the DFB semiconductor laser 11. ] Is used as a reference, and is incident on the optical amplifying unit 20.

  The optical amplifying unit 20 converts the pulsed light generated by the laser light generating unit 10 by using a fiber optical amplifier 21 having a single stage or a plurality of stages, depending on the configuration of the wavelength converter 30 and the required harmonic output. The amplified fundamental wave pulse light is output to the wavelength converter 30. The fiber optical amplifier 21 uses a semiconductor laser pumped erbium (Er) -doped fiber optical amplifier (EDFA) or a Raman laser pumped EDFA, and amplifies with a predetermined gain of, for example, about 30 [dB]. The pulsed light La amplified by the optical amplification unit 20 enters the wavelength conversion unit 30.

  The wavelength conversion unit 30 converts the fundamental pulsed light La having a wavelength λ = 1.544 [μm] incident from the optical amplification unit 20 into a wavelength according to the specifications of the light source device 1 and outputs the converted light. Here, the light source device 1 of the present invention only needs to include a wavelength conversion stage in which a nonlinear optical crystal that causes a walk-off in the wavelength conversion optical unit 30 is used for angle phase matching. The wavelength of the (fundamental wave), the wavelength of the output light output from the wavelength conversion unit, and the specific configuration (combination and arrangement of wavelength conversion optical elements) of the wavelength conversion unit 30 for conversion to the wavelength are already known. The present invention can be applied to various forms.

  Therefore, in this embodiment, a configuration for converting a fundamental wave having a wavelength λ = 1.544 [μm] into an ultraviolet wave having a wavelength λ = 309 [nm] corresponding to a fifth harmonic is illustrated in FIG. 3 as a representative example. This configuration will be briefly described. Note that in FIG. 3, the figure indicated by an ellipse on the optical path is a collimator lens or a condensing lens, and each description is omitted. In addition, P-polarized light is indicated by an arrow, S-polarized light is indicated by a dot in the circle, a fundamental wave is indicated by ω, a second harmonic is indicated by 2ω, and a third harmonic is indicated by 3ω.

  The wavelength conversion unit 30 includes three wavelength conversion stages connected in series with the wavelength conversion optical elements 31, 32, and 33 as main components, and the fundamental wave pulse light La having a frequency ω incident on the wavelength conversion unit 30 is generated. , Ω → 2ω → 3ω → 5ω in this order.

  The P-polarized fundamental pulse light La incident on the wavelength conversion unit 30 is condensed and incident on the wavelength conversion optical element 31 to generate a P-polarized double wave (2ω). The generated second harmonic wave and the fundamental wave transmitted through the wavelength conversion optical element 31 are condensed and incident on the wavelength conversion optical element 32, and a third frequency (3ω) of S-polarized light is generated by sum frequency generation. As the wavelength conversion optical elements 31 and 32, for example, a PPLN crystal is used as the wavelength conversion optical element 31 for generating the second harmonic wave, and an LBO crystal is used as the wavelength conversion optical element 32 for generating the third harmonic wave. As the wavelength conversion optical element 31, a PPKTP crystal, a PPSLT crystal, an LBO crystal, or the like can be used.

  The third harmonic wave of the S-polarized light generated by the wavelength conversion optical element 32 and the fundamental wave and the second harmonic wave of the P-polarized light transmitted through the wavelength conversion optical element 32 are transmitted through the two-wavelength wavelength plate 41 and only the second harmonic wave is transmitted. Convert to S-polarized light. As the two-wavelength wave plate 41, for example, a wave plate made of a uniaxial crystal flat plate cut in parallel with the optical axis of the crystal is used. This wave plate rotates the polarization with respect to light of one wavelength (second harmonic), and reduces the thickness of the wave plate (crystal) to prevent the polarization of light of the other wavelength from rotating. It is configured by cutting so as to be an integral multiple of λ / 2 with respect to light of the wavelength of λ and an integral multiple of λ with respect to light of the other wavelength.

The second and third harmonics, both of which are S-polarized light, are condensed and incident on the wavelength conversion optical element 33, and the fifth harmonic (5ω) of the P-polarized light is generated by sum frequency generation. As the wavelength conversion optical element 33, a nonlinear optical crystal having a large walk-off angle ρ with respect to the fifth harmonic of the wavelength λ = 309 [nm] is used. For example, a BBO crystal (β-BaB ₂ O ₄ crystal) is of type I. Used for angular phase matching (CPM). The fifth harmonic generated by the wavelength conversion optical element 33 is output to the output terminal of the wavelength conversion unit 30 in a state where the beam output from the light source device is turned on in the beam control device 80 (80A, 80B) described below. Through the provided window 35, pulsed light (referred to as “ultraviolet pulsed light”) Lv having a wavelength of 309 [nm] is output from the light source device 1.

  In the light source device 1 schematically configured as described above, when the light source device 1 is activated and in a predetermined output standby state, the laser light generation unit 10, the optical amplification unit 20, and the wavelength conversion unit 30 are all The state is set to a steady operation state, and the light source device 1 is held in a state where the ultraviolet pulse light Lv is generated. Turning on / off the beam output from the light source device 1 (outputting / stopping ultraviolet pulsed light) includes an output optical path for outputting the optical path of the ultraviolet pulsed light Lv emitted from the wavelength conversion optical element 33 to the outside through the window 35, and shielding. This is done by switching to a non-output optical path that blocks output to the outside by a member.

The principle for realizing the above operation will be described in detail with reference to FIG. FIG. 4 shows the dependence of the harmonic output and beam pointing on the phase mismatch Δk when a nonlinear optical crystal that generates a walk-off is used for angular phase matching to generate a harmonic wave. A BBO crystal used as the element 33 is shown. In this calculation, BBO crystal length: 15 [mm], walk-off angle: 80 [mrad], double wave incident beam diameter: 70 [μm] (1 / e ² , full width), peak power: 1 [kW] Third harmonic incident beam diameter: 58 [μm] (1 / e ² , full width), peak power: 1.5 [kW]. Here, the horizontal axis in the figure is the phase mismatch Δk [rad / cm = cm ⁻¹ ], and the vertical axis is the normalized output normalized with the harmonic output when the phase mismatch Δk = 0 on the left as 1. : Normalized efficiency, right side is beam pointing: Pointing [mrad].

  As shown in the figure, when the phase mismatch Δk is given, the normalized output of the harmonic (5th harmonic) changes, and the beam pointing also changes. The change between the two results in the normalized output gradually decreasing in both positive and negative directions with Δk = 0 as the maximum, whereas the beam pointing linearly changes linearly as Δk changes.

If the phase mismatch Δk is changed from −15 [cm ⁻¹ ] to +15 [cm ⁻¹ ], the harmonic output can ensure 90% or more with respect to the optimal phase matching state of Δk = 0. In addition, substantially the same output can be obtained when the phase mismatch Δk is −15 [cm ⁻¹ ] and 15 [cm ⁻¹ ]. On the other hand, when the phase mismatch Δk is changed from −15 [cm ⁻¹ ] to 15 [cm ⁻¹ ], the beam pointing changes by about 2 [mrad]. In contrast, the beam divergence angle of the fifth harmonic wave emitted from the wavelength conversion optical element 33 is about 1 [mrad] in all angles. Therefore, by appropriately installing a shielding member such as an aperture, one can be passed and the other can be blocked.

  FIG. 1 schematically shows a change of the beam emitted from the wavelength conversion optical element 33 when the beam pointing is changed as described above by a straight line and a dotted line. One of the outgoing optical paths of the beam thus changing (optical path indicated by a solid line in FIG. 1) is an output optical path Lon that is output from the window 35 of the wavelength converter 30, and the other (optical path indicated by a dotted line) is a non-output optical path Loff. If a shielding member 38 such as an aperture or a shielding plate that blocks the beam passing through the non-output optical path is arranged at a position where the beams of both optical paths can be separated, the light source device 1 can be changed by changing the phase mismatch Δk. It is possible to switch the beam output of the ultraviolet pulse light between the on state and the off state.

For example, when the phase mismatch Δk = −15 [cm ⁻¹ ] is given, the optical path of the ultraviolet pulsed light emitted from the wavelength conversion optical element 33 is the output optical path Lon, and the phase mismatch Δk = 15 [cm ^−1]. ] Is set as a non-output optical path Loff, and a shielding member 38 that blocks and absorbs ultraviolet light having a wavelength λ = 309 [nm] is disposed on the optical path of the non-output optical path Loff. By changing the phase mismatch Δk between −15 [cm ⁻¹ ] and 15 [cm ⁻¹ ], the beam output of the ultraviolet pulsed light Lv from the light source device 1 can be switched on / off.

  According to such a method, the laser light generation unit 10, the optical amplification unit 20, and the wavelength conversion unit 30 are all set in a steady operation state, and the ultraviolet pulse light Lv is generated inside the light source device 1. Thus, the beam output is turned on / off depending on whether the generated ultraviolet pulse light Lv is output to the outside from the wavelength conversion unit 30 or cut off. Therefore, including not only the laser light generation unit 10 and the optical amplification unit 20 but also the wavelength conversion optical elements 31, 32, and 33 constituting the wavelength conversion unit 30, regardless of the on / off state of the beam output, It can be held in a thermally stable state, and stable ultraviolet pulse light can be output from the rising edge.

The harmonic output is almost the same when the beam output is on (when phase mismatch Δk = −15 [cm ⁻¹ ]) and when it is off (when Δk = 15 [cm ⁻¹ ]). Therefore, even if the nonlinear optical crystal 33 that changes the phase mismatch is viewed alone, the thermal load hardly changes when the beam output is switched on / off, and neither the output level nor the beam quality changes. Highly stable ultraviolet pulse light can be output.

  As a method of changing the phase mismatch Δk in the wavelength conversion optical element 33, a mode of changing the wavelength of the pulsed light (fundamental wave) incident on the wavelength conversion unit 30 is proposed. When the wavelength of the fundamental wave incident on the wavelength conversion unit 30 is changed, the refractive index n in the crystal of the wavelength conversion optical element 33 changes. That is, a phase mismatch Δk occurs in the wavelength conversion optical element 33. For this reason, the beam pointing can be changed by changing the wavelength of the fundamental wave incident on the wavelength conversion unit 30, and the beam output of the ultraviolet pulsed light Lv from the light source device 1 can be switched on / off.

  As described above, according to the method of changing the phase mismatch Δk by changing the wavelength of the fundamental wave incident on the wavelength conversion unit 30, the fundamental wave region that is easy to handle is compared with the harmonic region of the short wavelength. It becomes possible to provide a light source device having the above effects with a simple configuration. Hereinafter, a configuration for changing the wavelength of the pulsed light incident on the wavelength conversion unit 30 will be described. In the present embodiment, two configuration forms in which the wavelength of the pulsed light incident on the length converting unit 30 is changed by changing the wavelength of the pulsed light (seed light) emitted from the laser light generating unit 10 will be exemplified. FIG. 5 shows a schematic configuration of the laser beam generator 10A of the first configuration form.

  The laser light generation unit 10A includes the DFB semiconductor laser (laser light source) 11 described above and an optical modulator 12 that cuts out and emits a part of the pulsed light generated by the DFB semiconductor laser 11, and is provided in the control device 8. The provided beam control device 80A is configured to change the wavelength of the pulsed light (seed light) emitted from the laser light generating unit 10A by changing the timing of extraction of the optical pulse by the optical modulator 12.

  The optical modulator 12 switches the internal optical path of the optical modulator 12 between a transmission state and a cutoff state, and cuts out part of the optical pulse of the pulsed light (seed light) generated by the DFB semiconductor laser 11 in time, The extracted short pulse seed light (hereinafter referred to as “short pulse seed light”) Ls is emitted to the optical amplifying unit 20. The optical modulator 12 is an optical element that can be turned on / off at a higher speed than the oscillation frequency of the DFB semiconductor laser 11. For example, an electro-optic modulator (EOM) is used. The optical modulator 12 is synchronously controlled with the DFB semiconductor laser 11 by a beam control device 80A provided in the control device 8.

  The beam control device 80A includes a clock 81 serving as a reference for synchronously controlling the operation of each unit, a trigger pulse generator 82 that generates a trigger pulse at a predetermined interval based on the clock 81, and a trigger input from the trigger pulse generator 82 Based on the pulse, a laser drive signal generator 83 for generating a laser drive signal S11 for driving the DFB semiconductor laser 11, a trigger pulse delay unit 84 for delaying a trigger pulse input from the trigger pulse generator 82 within a predetermined range, a trigger A pulse modulation signal generation unit 85 for generating a pulse modulation signal S12 for driving the optical modulator 12 based on a trigger pulse input via the pulse delay unit 84 is provided.

  The laser drive signal generator 83 generates a laser drive signal S11 for driving the DFB semiconductor laser 11 in response to the trigger pulse input from the trigger pulse generator 82, and outputs the laser drive signal S11 to the DFB semiconductor laser 11 for pulse oscillation. The laser drive signal S11 is set in a range where the repetition frequency is about several hundreds [kHz] to several [MHz] and the pulse width is about 1 to 20 [nsec]. The pulse modulation signal generation unit 85 generates a pulse modulation signal S12 for driving the optical modulator 12 in response to the trigger pulse input from the trigger pulse generator 82 via the trigger pulse delay unit 84 to generate the optical modulator 12. Output to. The pulse modulation signal S12 has a pulse width narrower than that of the laser drive signal S11 and is output with a rising time delayed by a predetermined time from the laser drive signal.

  FIG. 6 exemplifies the relationship between the optical pulse of the seed light L generated by the laser drive signal S11 and the transmittance T of the optical modulator 12 by the pulse modulation signal S12. In this embodiment, a laser drive signal S11 subjected to intensity modulation with a repetition frequency of 1 [MHz] and a pulse width of 10 [nsec] is output to the DFB semiconductor laser 11, and a pulse waveform proportional to the laser drive signal as shown in the figure. Is generated, and a pulse modulation signal S12 having a pulse width of about 1 [nsec] is output to the optical modulator 12, and a part of the seed light L is cut out by changing the transmittance T as shown in the figure. Is illustrated. The vertical axis in FIG. 6 indicates the light intensity with respect to the seed light L, the transmittance with respect to the optical modulator 12, and each waveform for one optical pulse of the seed light L that is pulse-oscillated.

Here, the temperature of the DFB semiconductor laser 11 is controlled, and in this embodiment, the oscillation wavelength is light with a narrow band with λ = 1.544 [μm] as a reference. On the other hand, when the drive current (excitation intensity) changes, the oscillation wavelength of the DFB semiconductor laser 11 slightly changes. The degree of change of the oscillation wavelength with respect to the drive current varies depending on the type of the DFB semiconductor laser, and is, for example, about 0.015 [nm / mA] in a DFB semiconductor laser with a rated current of 400 [mA]. In this case, when the drive current of the DFB semiconductor laser 11 is changed from 400 [mA] to 270 [mA], the center wavelength of the output light changes by 2 [nm]. This change amount Δλ = 2 [nm] of the center wavelength is sufficient to change the phase mismatch Δk in the range of −15 to 15 [cm ⁻¹ ] in the wavelength conversion optical element 33.

  For this reason, the DFB semiconductor laser 11 is driven and pulse-oscillated by the laser drive signal S11 that has been subjected to intensity modulation of about 30% with respect to the rated current, and the trigger pulse delay unit 84 applies the pulse modulation signal S12 to the laser drive signal S11. By changing the delay time, that is, the timing of cutting out the optical pulse, the wavelength of the short pulse seed light Ls emitted from the laser light generation unit 10A is changed, and the required phase mismatch Δk is generated in the wavelength conversion 3. it can.

In this case, the temperature of the DFB semiconductor laser 11 is adjusted so that the center wavelength λ is 1.544 [μm] (Δk = 0) at 80% of the rated current, and the wavelength conversion optics is centered on this 80%. The required delay time is set so that the phase mismatch Δk in the element 33 is −15 to 15 [cm ⁻¹ ]. At this time, the output value (power) of the short pulse seed light Ls emitted from the laser light generation unit 10A changes in accordance with the extraction timing of the optical pulse. If this becomes a problem, the output to the optical modulator 12 is performed. By adjusting the amplitude (transmittance) of the pulse modulation signal S12, the output value of the short pulse seed light Ls can be made constant at a response speed on the order of [nsec] to [μsec]. Note that the gain of the optical amplification unit 20 can be changed according to the change in the output value of the short pulse seed light Ls, and the power level of the pulsed light incident on the wavelength conversion unit 30 can be made constant. A response speed on the order of several hundred [μsec] to 1 [msec] can be obtained.

  In the laser light generation unit 10A described above, the laser drive signal S11 subjected to the intensity modulation as described above is output from the laser drive signal generation unit 83 to pulse-oscillate the DFB semiconductor laser 11, and from the trigger pulse delay unit 84 By driving the optical modulator 12 by outputting the pulse modulation signal S12 with a predetermined delay time, the beam output from the light source device can be turned on / off.

  According to such a configuration, in addition to the effects described above, one pulse unit of the optical pulse of the laser light source 11 pulsating at a frequency of about several hundred [kHz] to several [MHz], that is, [μsec] to [nsec]. The beam output can be controlled on / off on the order, and high-speed and highly stable output control can be realized.

  Next, the laser beam generator 10B of the second configuration form will be described with reference to FIG. 7 showing the schematic configuration of this laser beam generator. The laser light generator 10B includes a first laser light source 11a that oscillates pulsed light with a first wavelength λ1, and a second laser light source 11b that oscillates pulsed light with a second wavelength λ2, and the beam control device 80B performs laser light. By selectively switching the pulsed light emitted from the generating unit to the pulsed light of the first wavelength or the second wavelength, the wavelength of the pulsed light incident on the wavelength conversion unit 30 is changed.

That is, with respect to λ = 1.544 [μm], which is the reference wavelength of the fundamental wave described so far, for example, a fundamental wave that causes phase mismatch Δk = −15 [cm ⁻¹ ] in the wavelength conversion optical element 33. The first laser light source 11a and the second laser light source 11b that oscillate at the respective wavelengths are defined as a first wavelength λ1 and a fundamental wavelength that generates a phase mismatch Δk = 15 [cm ⁻¹ ] as a second wavelength λ2. It is provided in advance in the laser light generation unit, and is configured to selectively select and emit the pulsed light emitted from the laser light generation unit 10B.

  The wavelength difference Δλ between the first wavelength λ1 and the second wavelength λ2 is very small with respect to the reference wavelength λ. Accordingly, the first laser light source 11a and the second laser light source 11b use the same DFB semiconductor laser (the DFB semiconductor laser 11 described above), and the temperature of each laser light source is controlled by a temperature regulator provided in each DFB semiconductor laser. The oscillation wavelength can be set to the first wavelength λ1 and the second wavelength λ2. In the case of this configuration, the laser drive signal for driving the DFB semiconductor laser may be a rectangular wave pulse having a flat top pulse waveform, and the control configuration of the laser driver can be simplified.

  As a specific configuration for switching the pulsed light emitted from the laser light generator 10B to the pulsed light of the first wavelength λ1 or the pulsed light of the second wavelength λ2, either the first laser light source 11a or the second laser light source 11b is used. The first configuration example to be oscillated, and the first laser light source 11a and the second laser light source 11b are both oscillated to emit either pulsed light of the first wavelength λ1 or pulsed light of the second wavelength λ2. There is a configuration example.

  In the first configuration example, the output end of the first laser light source 11a and the output end of the second laser light source 11b are connected to a multiplexer (2 × 1 coupler) 91 and coupled together, so that the laser light generator 10B Output. The beam control device 80B outputs a laser drive signal to either the first laser light source 11a or the second laser light source 11b to cause pulse oscillation, and emits pulsed light having the first wavelength or the second wavelength incident on the multiplexer 91. The light is emitted from the laser light generator 10B. The multiplexer 91 includes a 50:50 coupler, a WDM (Wavelength Division Multiplexer), and the like.

  In the second configuration example, the output end of the first laser light source 11a and the output end of the second laser light source 11b are connected to a high-speed optical path selection switch (for example, EOM2 × 2 switch) 92, and the output port of the optical path selection switch 92 (One output port in the case of the EOM2 × 2 switch) is set as the output of the laser beam generator 10B. The beam control device 80B oscillates both the first laser light source 11a and the second laser light source 11b, and emits either one of the pulsed light with the first wavelength λ1 or the pulsed light with the second wavelength λ2 incident on the optical path selection switch 92. The laser beam is emitted from the laser beam generator 10B. Note that an EOM optical switch for switching the light path between a light transmitting state and a light blocking state is provided at the output end of the first laser light source 11a and the output end of the second laser light source 11b, and the outputs of these EOM optical switches are combined. May be configured so that either one of the pulse lights is emitted from the laser light generator 10B.

  According to such a configuration, the beam output from the light source device can be turned on / off by controlling the laser drive signal or the control signal of the optical path selection switch. Accordingly, similarly to the above-described configuration, the beam output is output in units of one pulse of the optical pulse of the laser light source 11 that oscillates at a frequency of about several hundreds [kHz] to several [MHz], that is, on the order of [μsec] to [nsec]. On / off control can be performed, and high-speed and highly stable output control can be realized.

  Further, according to the light source device of the present configuration, the pulsed light emitted from the laser light generation unit is changed to the first wavelength pulsed light generated by the first laser light source or the second wavelength generated by the second laser light source. In addition to simplifying the control configuration of the laser light source driver and the beam control device, the laser drive current and the gain of the optical amplifying unit 20 can be made constant, and a highly efficient light source device with less noise can be achieved. Can be provided. Further, according to the first configuration example in the present configuration, it can be configured at a low cost with a very simple control configuration for switching the output destination of the laser drive signal. On the other hand, according to the second configuration example, the first laser light source 11a and the second laser light source 11b are constantly pulse-oscillated, and the output pulse is switched by an optical switch having a high-speed response to the pulse frequency. At the same time, pulse light having a highly stable pulse waveform can be obtained from the first light pulse.

  In the above, as a method for changing the wavelength of the pulsed light (seed light) emitted from the laser light generation unit 10, the optical modulator 12 is provided in the laser light generation unit 10, and the extraction timing of the pulsed light emitted from the laser light source 11 is obtained. And a configuration (second configuration mode) in which two laser light sources 11a and 11b having different oscillation wavelengths are provided in the laser light generation unit 10 to emit one of the pulse lights. Illustrated. However, as a method of changing the wavelength of the seed light emitted from the laser light generator 10, the oscillation wavelength itself of the laser light source 11 may be changed.

  For example, as the laser light source 11, a DFB semiconductor laser capable of high-speed wavelength tuning on the order of [μsec] to [nsec] is used, and the beam control device 80 is configured to switch the oscillation wavelength between the first wavelength and the second wavelength. can do. As such a DFB semiconductor laser, it has two DFB parts and a phase shift part provided between them, and the current control wavelength variable enables the oscillation wavelength to be changed by controlling the current injected into the phase shift part. A DFB semiconductor laser is exemplified. According to such a configuration (third configuration form), the oscillation wavelength of the seed light can be changed at high speed only by changing the injection current to the phase shift unit, and the configuration of the light source device can be simplified. it can.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to these embodiments. For example, in the embodiment, the wavelength of the fundamental wave emitted from the laser beam generator is λ = 1.544 [μm], and λ = 309, which is a fifth harmonic from the second and third harmonics of the fundamental wave. Although the case where ultraviolet light of [nm] is generated has been illustrated, the present invention includes a nonlinear optical crystal that causes a walk-off in the wavelength conversion unit, and if the nonlinear optical crystal is used for angular phase matching, the same applies. Apply and get similar effects. That is, the wavelength of the fundamental wave incident on the wavelength conversion unit, the wavelength of the light output from the wavelength conversion unit, the incident light incident on the nonlinear optical crystal and the wavelength of the output light after wavelength conversion, and nonlinear optics such as BBO and LBO The type of crystal, the mode of wavelength conversion such as whether it is second-harmonic generation or sum-frequency generation, and the type I and type II in the angle phase matching can be appropriately changed and applied.

DESCRIPTION OF SYMBOLS 1 Light source device 10 (10A, 10B) Laser light generation part 11 Laser light source (DFB semiconductor laser)
11a First laser light source 11b Second laser light source 12 Optical modulator 20 Optical amplifying unit 30 Wavelength converting unit 31, 32, 33 Wavelength converting optical element (33 Nonlinear optical crystal causing walk-off)
38 Shielding member 80 (80A, 80B) Beam control device Ls Pulse light (seed light, short pulse seed light)
La amplified pulsed light Lv ultraviolet pulsed light Lon output optical path Loff non-output optical path

Claims (4)

A laser beam generator for generating pulsed light;
An optical amplifying unit for amplifying the pulsed light generated by the laser light generating unit;
A non-linear optical crystal that generates a walk-off includes a wavelength conversion stage used in angle phase matching, and a light source device including a wavelength conversion unit that converts the wavelength of the pulsed light amplified by the optical amplification unit and outputs the converted light
By changing the phase matching state in the nonlinear optical crystal within a predetermined range and changing the beam pointing according to the phase mismatch amount, the output path of the harmonics emitted from the nonlinear optical crystal is set as the output optical path and the non-output path. A beam control device for switching to an optical path;
A light source device comprising: a shielding member that is disposed on an optical path of the non-output optical path and blocks output from the non-output optical path.   The beam control device is configured to change a phase mismatch amount in the nonlinear optical crystal within a predetermined range by changing a wavelength of pulsed light incident on the wavelength conversion unit. 2. The light source device according to 1. The laser light generation unit includes a laser light source that oscillates in pulses, and an optical modulator that cuts out and emits part of the pulse light generated by the laser light source,
The light source device according to claim 2, wherein the beam control device changes the wavelength of the pulsed light incident on the wavelength conversion unit by changing a cut-out timing by the optical modulator. The laser light generator includes a first laser light source that oscillates pulsed light of a first wavelength, and a second laser light source that oscillates pulsed light of a second wavelength,
The beam control device changes the wavelength of the pulsed light incident on the wavelength conversion unit by selectively switching the pulsed light emitted from the laser light generating unit to the pulsed light of the first wavelength or the second wavelength. The light source device according to claim 2.

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