JP5397773B2 - Light source device - Google Patents

Description

  The present invention relates to a light source device in which laser light emitted from a plurality of laser output units is wavelength-converted by a wavelength conversion unit, and more specifically, the optical path of laser light emitted from the wavelength conversion unit is adjusted at high speed. The present invention relates to a possible light source device.

  As a light source device in which laser light emitted from a plurality of laser output units is wavelength-converted by a wavelength conversion unit and emitted, laser light (seed light) in the infrared to visible region generated by a semiconductor laser is used as a fiber optical amplifier, etc. There is an all-solid-state light source device that outputs a pulsed light in the ultraviolet region by amplifying it by a wavelength converting unit comprising a plurality of wavelength converting optical elements. 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. (For example, Patent Document 1).

  In general, beam pointing of laser light emitted from a light source device varies with time. This is considered to be due to airflow, thermal stability of members constituting the light source device, resonance, and the like. In some applications such as microfabrication and optical inspection, it is required to stabilize the pointing of laser light. Conventionally, there has been used a method of adjusting the outgoing optical path of the incident light that fluctuates by controlling a mirror provided on the optical path with a galvanometer or the like, thereby stabilizing the pointing of the laser light emitted from the light source device. .

JP 2004-86193 A

  However, in the configuration in which the mirror is controlled as described above, there are problems such as wear of mechanical parts and problems of dust generation, and mirror damage in a short wavelength region. Further, the response speed of the mirror is limited, and the response speed that can be practically used is on the order of kHz in terms of frequency. Therefore, when the beam pointing of the laser light incident on the mirror fluctuates at a high speed on the order of msec or less, it is difficult to adjust the outgoing optical path in response to this and stabilize the beam pointing. There was also.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a new light source device that can solve these problems and can control the emission optical path of laser light.

  According to the embodiment illustrating the present invention, the first laser output unit and the second laser output unit that emit laser beams, respectively, and the first nonlinear optical crystal (for example, the wavelength conversion optical element 35 in the embodiment) are the first ones. At least one of the laser beam emitted from the first laser output unit and the laser beam emitted from the second laser output unit is used for angular phase matching in an arrangement that causes walk-off in the angular direction. A first wavelength conversion unit (for example, the wavelength conversion unit 30 in the embodiment) that is incident and wavelength-converted and a second nonlinear optical crystal (for example, the wavelength conversion optical element 36 in the embodiment) are arranged in the first angular direction. Used in angular phase matching with an arrangement that causes a walk-off in an orthogonal angular direction, the laser beam emitted from the first wavelength converter and the other laser beam (emitted from the first laser output unit) When both the laser beam and the laser beam emitted from the second laser output unit are incident on the first wavelength conversion unit, the laser beam emitted from the first wavelength conversion unit) is incident and wavelength converted. Change at least one of a phase matching state in the conversion unit (for example, the wavelength conversion unit 30 in the embodiment) and the first nonlinear optical crystal and a phase matching state in the second nonlinear optical crystal, and depending on the amount of phase mismatch The light source device is configured to include a beam control device that changes the emission optical path of the laser light emitted from the second wavelength conversion unit by changing the beam pointing.

  The beam control device may change at least one of the wavelength of the laser beam emitted from the first laser output unit and the wavelength of the laser beam emitted from the second laser output unit, thereby changing the first laser output unit. The phase mismatch amount in the second nonlinear optical crystal can be changed.

  In this case, at least one of the first and second laser output units includes a pulsed laser light source, an optical modulator that cuts out and emits a part of the pulsed laser light generated by the laser light source, and It is one preferable aspect that the beam control device is configured to change the wavelength of the emitted laser light by changing the extraction timing by the optical modulator.

In addition, while further comprising a third laser output unit that emits laser light, at least one of the laser beams emitted from the first, second, and third laser output units is incident on the first wavelength conversion unit, At least one of the laser light emitted from the first wavelength conversion unit and the laser light emitted from the first, second, and third laser output units is incident on the second wavelength conversion unit (first to third). When all of the laser light emitted from the laser output unit is incident on the first wavelength conversion unit, the beam control device includes the first, second, and third lasers. By changing at least any two of the wavelengths of the laser light emitted from the output unit, the amount of phase mismatch in the first and second nonlinear optical crystals is changed and emitted from the second wavelength conversion unit. Laser light emission It is also preferable to adjustably configured in any direction perpendicular to the road to the optical axis.

In the present invention described above, the laser beam detector includes a beam position detector that detects the position of the laser beam emitted from the second wavelength conversion unit in the direction orthogonal to the optical axis, and the beam controller detects the laser beam detected by the beam position detector. It is a preferable aspect that the configuration is such that the emission optical path of the laser light is adjusted based on the position perpendicular to the optical axis of the light.

  According to the light source device of the present invention, the beam pointing is changed by giving a phase mismatch amount to at least one of the first and second nonlinear optical crystals arranged in the direction in which the walk-off angle is orthogonal. 2 The emission path of the laser beam emitted from the nonlinear optical crystal is controlled. That is, by giving a phase mismatch amount to the first nonlinear optical crystal, the beam pointing is changed in the first angular direction (for example, the X-axis direction), and by giving a phase mismatch amount to the second nonlinear optical crystal, the first nonlinear optical crystal is given. The beam pointing is changed in an angle direction (for example, the Y-axis direction) orthogonal to the angle direction of the laser beam, thereby changing the emission optical path of the laser light emitted from the second nonlinear optical crystal in an arbitrary direction in the XY plane. be able to. For this reason, it is possible to provide a light source device capable of controlling the emission optical path of laser light with a novel configuration that does not use a mirror control system. Even when one of the laser beams emitted from the first and second laser output units is incident on the first nonlinear optical crystal and the other is incident on the second nonlinear optical crystal, the first nonlinear optical crystal and the first nonlinear optical crystal By arranging the two nonlinear optical crystals close to each other, it is possible to maintain the beam overlap in the second nonlinear optical crystal. Further, by arranging a lens between the first nonlinear optical crystal and the second nonlinear optical crystal and arranging the second nonlinear optical crystal at the focal position of the lens, the laser beam emitted from the first nonlinear optical crystal Good beam superposition can be ensured regardless of pointing changes.

  The beam control device changes at least one of the wavelength of the laser beam emitted from the first laser output unit and the wavelength of the laser beam emitted from the second laser output unit, whereby the first and second nonlinearities are changed. According to the configuration in which the amount of phase mismatch in the optical crystal is changed, it is possible to provide a light source device having the above effects with a relatively simple configuration using a wavelength region that is easy to handle. In this case, an optical modulator that cuts out and emits a part of the pulsed laser beam generated by the laser light source is provided, and the wavelength of the emitted laser beam is changed by changing the extraction timing by the optical modulator. According to such a configuration, it is possible to provide a light source device capable of controlling the emission light path of the laser light in units of one pulse of the pulsed light (nanosecond to millisecond).

Furthermore, a beam position detector that detects the position of the laser beam emitted from the second wavelength conversion unit in the direction orthogonal to the optical axis is provided, and the beam control device detects the position of the laser beam detected by the beam position detector in the direction orthogonal to the optical axis. According to the configuration in which the laser beam emission path is adjusted based on the position, a light source device with high beam pointing stability can be provided.

It is a schematic block diagram of the light source device which illustrates this invention. It is a schematic block diagram which shows the structural example of a wavelength converter. It is the graph which showed the dependence with respect to the phase mismatch of a harmonic output and beam pointing about the nonlinear optical crystal for 7th harmonic generation. It is the graph which showed the dependence with respect to the phase mismatch of a harmonic output and beam pointing about the nonlinear optical crystal for 8th harmonic generation. 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.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to FIG. 1 illustrating 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.

  Broadly speaking, the light source device 1 is amplified by a laser light generation unit 10 that generates laser light, an optical amplification unit 20 that amplifies the laser light generated by the laser light generation unit 10, and an optical amplification unit 20. The wavelength conversion unit 30 that converts the wavelength of the laser light that is output and the control device 8 that controls the operation of each unit of the light source device 1 are configured. In the embodiment, a configuration example in which the laser light generation unit 10 and the optical amplification unit 20 include three parallel systems is shown. For convenience of explanation, they are referred to as a first series, a second series, and a third series from above in FIG. I will explain. In addition, the area | region enclosed with a dashed-dotted line in FIG. 1 is equivalent to the 1st-3rd laser output part in a claim, and in embodiment described below, in 1st laser output part II and 2nd laser output part III, the third laser output unit I.

  The laser light generator 10 is provided in each of the first, second, and third series, and emits pulsed laser light having a predetermined wavelength in the infrared to visible regions (hereinafter referred to as “seed light” Ls for convenience). Light modulation for generating laser light sources 11, 12, 13 to be generated and a part of the seed light generated by each laser light source to emit a short pulse seed light (hereinafter referred to as “pulse seed light” Lp for convenience) And 15, 16, and 17.

As the laser light sources 11, 12, and 13, those having an appropriate oscillation wavelength and oscillation form can be used according to the output wavelength of the light source device 1 and the configuration of the wavelength conversion unit 30. In this embodiment, the laser light source is used. By using a DFB semiconductor laser having an oscillation wavelength of 1.5 [μm] band as 11 to 13 and oscillating in a state where the temperature is controlled by a temperature regulator using a Peltier element or the like, the wavelength λ = 1.544 [μm]. ] Shows a configuration for generating seed light having a single wavelength. The DFB semiconductor laser can be oscillated or pulsed at an arbitrary intensity by controlling the waveform of the excitation current. In the light source device 1, the control device 8 controls the operation of the laser light sources 11 to 13, and the repetition frequency from each laser light source is about several hundreds [kHz] to several [MHz] and the pulse width is about 1 to 20 [nsec]. A single wavelength seed light Ls (Ls ₁ , Ls ₂ , Ls ₃ ) is generated. Hereinafter, the laser light sources 11 to 13 are also referred to as “DFB semiconductor laser” as appropriate.

The optical modulators 15, 16, and 17 respectively cut out a part of the seed light Ls generated by the first, second, and third series laser light sources and emit it. For example, electro-optic modulators (EOM) are used as the optical modulators 15 to 17. The optical modulators 15 to 17 are synchronously controlled with the laser light sources 11 to 13 by the control device 8, and the pulse widths 0.3 to 1 [nsec] from the seed light Ls having the pulse widths 1 to 20 [nsec] generated by the laser light sources. ], And the extracted pulse seed light Lp (Lp ₁ , Lp ₂ , Lp ₃ ) is emitted from the laser light generator 10.

The optical amplifying unit 20 is mainly composed of fiber optical amplifiers 21, 22 and 23 provided for each series, and receives pulse seed light Lp (Lp ₁ , Lp ₂ , Lp ₃ ) emitted from the laser light generating unit 10. Amplification is performed by each fiber optical amplifier in accordance with the configuration of the wavelength converter 30 and the required harmonic output. Examples of fiber optical amplifiers 21 to 23 that amplify infrared light having a wavelength of 1.5 [μm] band include erbium (Er) -doped fiber optical amplifier (EDFA) pumped by semiconductor laser and EDFA pumped by Raman laser. Used. Light (hereinafter referred to as “pulse light” for convenience) La (La ₁ , La ₂ , La ₃ ) amplified by the fiber optical amplifiers 21 to 23 is emitted from the optical amplification unit 20 and is incident on the wavelength conversion unit 30. The

The wavelength conversion unit 30 converts the pulsed light La incident from the optical amplification unit 20 into a wavelength corresponding to the specification of the light source device 1 and outputs the converted wavelength. Here, the light source device 1 of the present invention only needs to include a configuration in which two nonlinear optical crystals that cause a walk-off in the orthogonal direction are arranged in series in the wavelength conversion unit 30, and enter the wavelength conversion unit 30. The wavelength of the pulsed light La (La ₁ , La ₂ , La ₃ ) to be output, the wavelength of the output light emitted from the wavelength conversion unit 30, and the specific configuration of the wavelength conversion unit 30 for converting into the wavelength (wavelength conversion optics) The combination and arrangement of the elements can be applied to various known forms.

  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 = 193 [nm] corresponding to an eighth harmonic is illustrated in FIG. 2 as a representative example. The configuration will be described. In FIG. 2, the ellipse on the optical path is a collimator lens or a condensing lens, and the description thereof is omitted. Further, 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, and an n-fold wave thereof is indicated by nω.

The wavelength conversion unit 30 is mainly composed of six wavelength conversion optical elements 31 to 36. The pulsed light La ₁ having the frequency ω (fundamental wave) that has been amplified by the first series of fiber optical amplifiers 21 and entered the wavelength conversion section 30 is changed to ω → 2ω → 3ω → 5ω by the wavelength conversion optical element provided in this series. Wavelength conversion is performed in order. The pulsed light La ₂ having the frequency ω that is amplified by the second-series fiber optical amplifier 22 and incident on the wavelength conversion unit 30 is wavelength-converted from ω → 2ω by the wavelength conversion optical element provided in this series. Then, a 7th harmonic wave 7ω is generated by the sum frequency generation of the 5th harmonic wave of the 1st series and the 2nd harmonic wave of the 2nd series, and the 7th harmonic wave and the frequency ω amplified by the fiber optical amplifier 23 of the 3rd series are generated. The eighth harmonic wave 8ω is generated by the sum frequency generation of the pulsed light La ₃ .

In the first series, a P-polarized fundamental wave (pulsed light) La ₁ emitted from the fiber optical amplifier 21 is condensed and incident on the wavelength conversion optical element 31, and a P-polarized double wave (2ω) is generated. 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 harmonic wave (3ω) of S-polarized light is generated by sum frequency generation. Examples of the wavelength conversion optical element 31 for generating the second harmonic wave include a PPLN crystal and an LBO crystal as the wavelength conversion optical element 32 for generating the third harmonic wave. The wavelength conversion optical element 31 includes a PPKTP crystal, a PPSLT crystal, and an LBO crystal. Etc. can also be used.

  The S-polarized third harmonic wave generated by the wavelength conversion optical element 32 and the P-polarized fundamental wave and the second harmonic wave 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. The second harmonic and the third harmonic, both of which are S-polarized light, are collected 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 converting optical element 33 for generating the fifth harmonic wave, for example, an LBO crystal is used, but a BBO crystal or a CBO crystal can also be used. The fifth harmonic wave emitted from the wavelength conversion optical element 33 is shaped by the cylindrical lenses 42v and 42h and is incident on the dichroic mirror 43.

In the second series, the P-polarized fundamental wave (pulse light) La ₂ emitted from the fiber optical amplifier 22 is condensed and incident on the wavelength conversion optical element 34 to generate a P-polarized double wave (2ω). The second harmonic generated by the wavelength conversion optical element 34 is incident on the dichroic mirror 44. The wavelength conversion optical element 34 for generating the second harmonic wave uses the same crystal as the wavelength conversion optical element 31.

In the third series, the fundamental wave (pulse light) La ₃ emitted from the fiber optical amplifier 23 is incident on the wavelength conversion unit 30 as S-polarized light, and is incident on the dichroic mirror 44 without wavelength conversion.

  The dichroic mirror 44 is configured to transmit light in the fundamental wavelength band and reflect light in the second harmonic wavelength band. The S-polarized fundamental wave transmitted through the dichroic mirror 44 and the dichroic mirror 44. The second harmonic wave of the P-polarized light reflected by the laser beam is superimposed on the same axis and enters the dichroic mirror 43. The dichroic mirror 43 is configured to transmit light in the fundamental and second harmonic wavelength bands and reflect light in the fifth harmonic wavelength band. The dichroic mirror 43 transmits the fundamental wave of S-polarized light transmitted through the dichroic mirror 43 and The P-polarized second harmonic wave and the P-polarized fifth harmonic wave reflected by the dichroic mirror 43 are coaxially superimposed and incident on the wavelength conversion optical element 35.

In the wavelength conversion optical element 35, sum frequency generation is performed by P-polarized second harmonic (2ω) and P-polarized fifth harmonic (5ω), and seventh harmonic (7ω) is generated. For example, a CLBO crystal (CsLiB ₆ O ₁₀ crystal) is used for type I angular phase matching (CPM) as the wavelength conversion optical element 35 for generating the seventh harmonic wave.

  The 7th harmonic wave (7ω) of the S-polarized light generated by the wavelength conversion optical element 35 and the fundamental wave (ω) of the S-polarized light transmitted through the wavelength conversion optical element 35 are incident on the wavelength conversion optical element 36 disposed in proximity. The 8th harmonic wave (8ω) of the P-polarized light is generated by the sum frequency generation. As the wavelength conversion optical element 36 for generating the eighth harmonic wave, for example, a CLBO crystal is used in the type I angular phase matching as described above.

  In this manner, the fundamental laser beam having a wavelength of 1.544 [μm] output from the optical amplifier 20 is sequentially wavelength-converted by the wavelength converter 30, and the ultraviolet light Lv having a wavelength of 193 [nm] is output from the wavelength converter 30. Is emitted.

  In the light source device 1 configured as described above, the control device 8 is caused to change at least one of the phase matching state in the wavelength conversion optical element 35 and the phase matching state in the wavelength conversion optical element 36 to thereby achieve phase mismatch. A beam control device 80 is provided that changes the beam path of the ultraviolet light Lv emitted from the wavelength conversion unit 30 by changing the beam pointing according to the amount. Hereinafter, the principle for realizing the above-described operation will be described first.

Now, when the frequency of the fundamental wave incident on the wavelength conversion unit 30 is changed, the change Δk _{7 in} the amount of phase mismatch in the nonlinear optical crystal (wavelength conversion optical element) 35 for generating the _seventh harmonic wave, and the eighth harmonic wave generation. The change Δk ₈ in the amount of phase mismatch in the non-linear optical crystal (wavelength conversion optical element) 36 is given by the following equation (1). Note that the directions of the walk-off of the nonlinear optical crystals 35 and 36 are respectively perpendicular and horizontal to the paper surface.

Here, the change in the amount of phase mismatch is inherently expressed as d (Δk _i ), but in this specification, it is expressed as Δk _i for the purpose of simplifying the description. In the equation (1), α _i and β _i are determined from the dispersion of the crystal material. For example, α ₂ is obtained as follows using the refractive index n of the crystal.

df _i is the frequency shift of the i-th harmonic (i-th harmonic), and the seventh and eighth harmonics have the following relationship.

From the above formulas (1) and (3),

The change Δθ in beam pointing and the change Δk in the amount of phase mismatch are generally in a proportional relationship, as can be seen from the results of numerical calculations shown below.

From the equation (5), by changing the phase mismatch amount by Δk ₇ , the beam pointing of the seventh harmonic wave emitted from the nonlinear optical crystal 35 can be changed by Δθ ₇ in the vertical direction, and the phase mismatch amount can be changed by Δk _8. It can be seen that the beam pointing of the eighth harmonic wave emitted from the nonlinear optical crystal 36 can be changed by Δθ ₈ in the horizontal direction by changing. Further, from equation (4), as a means for changing the phase mismatch amount by Δk ₇ , it is only necessary to change the frequency (wavelength) for at least one of the second harmonic and the fifth harmonic, and the phase mismatch amount is changed by Δk _8. It can be seen that it is only necessary to change the frequency (wavelength) of at least one of the fundamental wave, the second harmonic wave, and the fifth harmonic wave as a means for performing this.

Here, for simplicity, the wavelength of the fundamental wave emitted from the first series of laser light sources 11 is constant, and the wavelength of the fifth harmonic wave incident on the nonlinear optical crystal 35 for generating the seventh harmonic wave is constant (df ₅ = 0). ).

In this case, for example, when it is desired to generate only a pointing change of Δθ _{7 in} the vertical direction, df ₂ is given to the second harmonic of the second series from equation (4) so that dk ₈ = 0 in the horizontal direction. What is necessary is just to adjust df ₁ with the fundamental wave of the 3rd series. On the other hand, when it is desired to generate only a pointing change of Δθ _{8 in} the horizontal direction, df ₁ may be given to the third series of fundamental waves. From the above, it is possible to generate an arbitrary combination of Δθ ₇ and Δθ ₈ by appropriately giving the third series df ₁ and the second series df ₂ , and the light is emitted from the wavelength conversion unit 30. The outgoing optical path of the ultraviolet light Lv can be changed in an arbitrary direction within a plane orthogonal to the optical axis of the outgoing light.

  Here, three laser light sources 11, 12, and 13 are used, but as is apparent from the equation (4), the fundamental of the laser light source 11 is the fifth harmonic and the second harmonic used for the seventh harmonic generation. The laser light source 13 may generate a fundamental wave that is generated from a wave and is used to generate an eighth harmonic wave. According to such a configuration, the number of laser light sources that generate the fundamental wave (seed light) may be two, and the configuration of the light source device 1 can be simplified.

  Next, the relationship between beam pointing and phase mismatch will be specifically described. 3 and 4 show the results of numerical calculation representing the relationship between the pointing shift Δθ of harmonics (abnormal light) and the phase mismatch amount Δk. This calculation is general, including beam diffraction effects, walk-off, incident fundamental depletion, and the like. For details of the calculation method, see, for example, [Smith and Bowers, Phase distortions in sum- and difference-frequency mixing in crystals, JOSA B, Vol.12, No.1, p.49-, (1995)]. It is disclosed.

  FIG. 3 shows the dependence of the harmonic output and beam pointing on the phase mismatch when a CLBO crystal is used as the wavelength conversion optical element 35 and the seventh harmonic is generated by the sum frequency generation of the second harmonic and the fifth harmonic. FIG. 4 shows the dependence of the harmonic output and beam pointing on the phase mismatch when a CLBO crystal is used as the wavelength conversion optical element 36 and an eighth harmonic is generated by the sum frequency generation of the fundamental wave and the seventh harmonic. It is the graph which showed.

In both figures, the horizontal axis is the phase mismatch amount Δk [rad / cm = cm ⁻¹ ], and the vertical axis is the normalized output that is normalized with the harmonic output when the phase mismatch amount Δk = 0 as 1. Efficiency and beam pointing: Pointing [mrad]. In the calculation, the beam diameter of the incident wave is about 200 [μm], the crystal length is 10 [mm], and the CLBO crystal for 7th harmonic generation has a walk-off angle of about 10 [mrad] for 8th harmonic generation. The walk-off angle of the CLBO crystal was about 38 [mrad].

  As shown in the figure, when the phase mismatch Δk is given, the normalized output of the harmonics (seventh harmonic and eighth harmonic) changes, and the beam pointing also changes. These changes are such that the normalized output gradually decreases in both positive and negative directions with Δk = 0 as the maximum, whereas beam pointing changes linearly linearly as Δk changes.

As shown in FIG. 3, this change indicates that the relationship between pointing and phase mismatch is Δθ ₇ / Δk ₇ ≈0.12 [mrad · cm] in the seventh harmonic generation by the CLBO crystal. . As can be seen from FIG. 4, in the generation of the eighth harmonic wave by the CLBO crystal, the relationship between the pointing and the phase mismatch is Δθ ₈ / Δk ₈ ≈0.07 [mrad · cm].

On the other hand, regarding the wavelength shift necessary to generate Δk = 1 [cm ⁻¹ ], in the process of the 7th harmonic generation (2ω + 5ω → 7ω) using the CLBO crystal, the wavelength change Δλ of the 2nd harmonic (2ω). ₂ = 0.041 [nm] corresponds to Δk ₇ = 1 [cm ⁻¹ ]. When this is converted into the wavelength change of the fundamental wave that is the basis of the second harmonic wave, the wavelength change Δλ ₁ = 0.082 [nm] at the fundamental wave (ω). In addition, in the process of the eighth harmonic generation (ω + 7ω → 8ω) using the CLBO crystal, the wavelength change Δλ ₁ = 0.086 [nm] of the fundamental wave (ω) corresponds to Δk ₈ = 1 [cm ⁻¹ ]. To do.

In summary, by giving Δk = 1 [cm ⁻¹ ] for both the 7th and 8th harmonics, a pointing shift of about 100 [μrad] can be generated, and Δk = 1 [cm ⁻¹ ] is generated. It can be seen that the wavelength λ ₁ of the fundamental wave may be changed by about 0.08 [nm].

  When the drive current I is changed, the oscillation wavelength of the DFB semiconductor laser used as the laser light sources 11 to 13 slightly changes. The degree of change of the oscillation wavelength λ with respect to the change of the drive current I varies depending on the model of the DFB semiconductor laser, but is generally about Δλ / ΔI = 0.015 [nm / mA]. Therefore, in order to generate a wavelength shift of about 0.08 [nm], the drive currents of the laser light sources 12 and 13 may be changed by about 5 [mA]. Note that the drive current I of the DFB semiconductor laser when the seed light is generated is normally about I = 100 [mA], and such a change in the drive current can be controlled sufficiently and at high speed.

3 and 4, even if the phase mismatch amount Δk is changed from ^{−1 to} +1 [cm ⁻¹ ] and thereby a pointing shift is generated in the range of −100 to +100 [μrad], the harmonics are increased. The wave output can ensure 90% or more with respect to the optimal phase matching state of Δk = 0, and when the phase mismatch Δk is −1 [cm ⁻¹ ] and 1 [cm ⁻¹ ], Almost the same output can be obtained. Therefore, by controlling the drive current of the laser light sources 12 and 13 and controlling the wavelength of the fundamental wave incident on the wavelength conversion unit 30, the emission path of the ultraviolet light Lv emitted from the wavelength conversion unit 30 can be arbitrarily set at high speed. It is understood that the direction is adjustable.

  Thus, 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. A light source device having the above effects can be provided with a simple configuration.

  Next, a specific method for changing the wavelength of the fundamental wave incident on the wavelength conversion unit 30 will be described. In this configuration mode, two configuration modes are illustrated in which the wavelength of the pulsed light La incident on the wavelength conversion unit 30 is changed by changing the wavelength of the pulse seed light Lp emitted from the laser beam generation unit 10. A schematic configuration of the laser beam generator 10 of the first configuration mode is shown in FIG. In FIG. 5, only the third system is shown as a representative example of the three laser beam generation units 10.

The laser beam generator 10 is a DFB semiconductor laser and generates a pulsed seed beam Ls (Ls ₃ ), and a light modulation that cuts out and emits a part of the seed beam Ls generated by the laser beam source 13. The beam control device 80 provided in the control device 8 changes the timing of extraction of the optical pulse by the optical modulator 15 to change the pulse seed light Lp (Lp ₃₎ emitted from the laser light generator 10. ) To change the wavelength. Therefore, the optical modulator 15 is an optical element that can be turned on / off faster than the oscillation frequency of the DFB semiconductor laser 13, and for example, an electro-optic modulator (EOM) is used. The optical modulator 15 is synchronously controlled with the laser light source (DFB semiconductor laser) 13 by a beam control device 80 provided in the control device 8.

  The beam controller 80 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 A trigger pulse delay that delays a trigger pulse input from a trigger pulse generator 82 within a predetermined range based on the pulse, a laser drive signal generator 83 that generates a laser drive signal S13 that drives a DFB semiconductor laser (laser light source) 13 Unit 84, a pulse modulation signal generation unit 85 that generates a pulse modulation signal S15 that drives the optical modulator 15 based on the trigger pulse input via the trigger pulse delay unit 84, and the like.

  The laser drive signal generator 83 generates a laser drive signal S13 for driving the DFB semiconductor laser 13 in response to the trigger pulse input from the trigger pulse generator 82, and outputs the laser drive signal S13 to the DFB semiconductor laser 13 for pulse oscillation. The laser drive signal S13 is a pulse signal having a repetition frequency of about several hundred [kHz] to several [MHz] and a pulse width of about 1 to 20 [nsec]. The pulse modulation signal generator 85 generates a pulse modulation signal S15 for driving the optical modulator 15 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 15. Output to. The pulse modulation signal S15 has a pulse width narrower than that of the laser drive signal S13 and is output with a rising time delayed by a predetermined time from the laser drive signal.

  FIG. 6 illustrates the relationship between the optical pulse of the seed light Ls generated by the laser drive signal S13 and the transmittance T of the optical modulator 15 by the pulse modulation signal S15. In this embodiment, an intensity-modulated laser drive signal S13 is output to the DFB semiconductor laser 13 at a repetition frequency of 1 [MHz] and a pulse width of 10 [nsec], and a pulse proportional to the laser drive signal as shown in the figure. A waveform seed light Ls is generated, a pulse modulation signal S15 having a pulse width of about 1 [nsec] is output to the optical modulator 15, and a part of the seed light Ls is cut out by changing the transmittance T as shown in the figure. The case is illustrated. The vertical axis in FIG. 6 indicates the light intensity with respect to the seed light Ls and the transmittance with respect to the optical modulator 15, and indicates each waveform for one optical pulse of the seed light Ls that is pulse-oscillated.

Here, the temperature of the DFB semiconductor laser 13 is controlled, and in this embodiment, the oscillation wavelength is light with a narrow band based on λ ₁ = 1.544 [μm]. On the other hand, as described above, the oscillation wavelength of the DFB semiconductor laser 13 slightly changes when the drive current changes, and the rate is about Δλ / ΔI = 0.015 [nm / mA]. Therefore, if the drive current of the DFB semiconductor laser 13 is changed by about 5 [mA], the oscillation wavelength λ ₁ can be shifted by about 0.08 [nm]. ₈ = 1 [cm ⁻¹ ] can be given.

  In the laser beam generator of the first configuration, the DFB semiconductor laser 13 is pulse-oscillated by a laser drive signal S13 that is intensity-modulated in a range of about ± 10% with respect to the drive current I = 100 [mA], for example. The pulse delay unit 84 changes the wavelength of the pulse seed light Lp emitted from the laser beam generation unit 10 by changing the delay time of the pulse modulation signal S15 with respect to the laser drive signal S13, that is, the extraction timing of the optical pulse.

Specifically, the temperature of the DFB semiconductor laser 13 is adjusted so that the drive current I = 100 [mA] and the oscillation wavelength is 1.544 [μm] (Δk ₈ = 0). The DFB semiconductor laser 13 is driven by a laser drive signal S13 having an inclined pulse shape that decreases from 90 to 90 [mA]. Then, the trigger pulse delay unit 84 changes the cut-out timing of the optical pulse, for example, cuts out the optical pulse in the portion of the drive current I = 95 [mA], and sets the wavelength of the pulse seed light Lp emitted from the laser beam generator 10. Change.

In the laser beam generator of the second configuration form, the drive current is directly controlled with respect to the central drive current I = 100 [mA]. That is, the temperature of the DFB semiconductor laser 13 is adjusted so that the oscillation current is 1.544 [μm] (Δk ₈ = 0) at the drive current I = 100 [mA], and the drive current at the time of ON is constant ( The DFB semiconductor laser 13 is driven by a laser drive signal S13 having a flat top rectangular pulse shape. Then, the wavelength of the pulse seed light Lp emitted from the laser light generation unit 10 is changed by directly controlling the driving current I at the time of on, for example, in the range of 90 to 110 [mA].

  In the above, the configuration in which the drive current (excitation intensity) of the DFB semiconductor laser is changed and the oscillation wavelength is changed by this is described. However, the oscillation wavelength of the DFB semiconductor laser may be directly changed. For example, as the laser light sources 12 and 13, DFB semiconductor lasers that can be tuned at high speed in the order of [μsec] to [nsec] are used, and the beam control device 80 is configured to directly control the oscillation wavelength of the DFB semiconductor lasers. be able to.

  As such a high-speed wavelength-tunable DFB semiconductor laser, it has two DFB sections and a phase shift section provided between them, and the oscillation wavelength can be adjusted by controlling the current injected into the phase shift section. The current control wavelength tunable DFB semiconductor laser is exemplified. According to such a configuration (third configuration form), the oscillation wavelength of the DFB semiconductor laser can be directly controlled at high speed by controlling the injection current to the phase shift unit.

  According to the configuration described above, the light source is in units of one pulse of a DFB semiconductor laser (laser light source) that oscillates at several hundred [kHz] to several [MHz], that is, in the order of [μsec] to [nsec]. The emission optical path of the ultraviolet light Lv emitted from the apparatus 1 can be changed.

Next, the configuration of the light source device that makes the beam pointing of the ultraviolet light emitted from the wavelength conversion unit 30 constant will be described with reference to FIG. The light source device 1 is provided on the output optical axis of the wavelength conversion unit 30, an optical element 51 that extracts a part of the ultraviolet light Lv emitted from the wavelength conversion optical element 36, and the optical axis of the extracted ultraviolet light Lv. A pointing detection unit 50 including a beam position detector 55 for detecting a position in the orthogonal direction is further provided, and the beam control device 80 is arranged in the direction orthogonal to the optical axis of the ultraviolet light Lv detected by the beam position detector 55. Depending on the position, the wavelength of the pulse seed light Lp (Lp ₂ , Lp ₃ in the above-described embodiment) emitted from the laser light generator 10 is changed, and the emission optical path of the ultraviolet light emitted from the wavelength converter 30 Is made constant.

  For example, a partial reflection mirror is used as the optical element 51, and reflects about 0.1 to 1% of the ultraviolet light Lv emitted from the wavelength conversion optical element 36 so as to enter the beam position detector 55. The beam position detector 55 detects the horizontal and vertical positions of the incident ultraviolet light beam and outputs horizontal and vertical detection signals (referred to as beam position detection signals) to the beam controller 80. There are various types of position detectors that detect the beam position of the laser light with high speed and high accuracy. For example, a position detector composed of four divided photodiodes is exemplified.

  The beam controller 80 calculates a pointing change of the ultraviolet light Lv emitted from the wavelength conversion optical element 36 based on the beam position detection signal input from the beam position detector 55, and corrects the pulse seed so as to correct it. By changing the wavelength of the light Lp, the emission optical path of the ultraviolet light Lv emitted from the wavelength conversion unit 30 is made constant.

  For example, when it is determined by the position detection signal input from the beam position detector 55 that the pointing of the output beam has fluctuated by 100 [μrad] in the horizontal direction, the beam controller 80 determines the drive current of the DFB semiconductor laser 13. By changing about 5 [mA], a pointing shift of 100 [μrad] is generated in the opposite direction to the output beam, and the outgoing optical path of the ultraviolet light Lv emitted from the wavelength converter 30 is made constant. Similarly, when it is determined that the pointing of the output beam calculated from the position detection signal fluctuates by 50 [μrad] in the vertical direction, the beam control device 80 sets the drive current of the DFB semiconductor laser 12 to 2.5 [mA]. By changing the degree, a pointing shift of 50 [μrad] is generated in the reverse direction, and the emission optical path of the ultraviolet light Lv emitted from the wavelength converter 30 is made constant.

  According to such a configuration, the pointing fluctuation of the ultraviolet light emitted from the wavelength conversion optical element 36 is feedback-controlled at high speed, and the output light path of the output light is made constant, so that the light source device having high pointing stability Can be provided.

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 case where the wavelength of the fundamental wave emitted from the laser light generation unit is λ = 1.544 [μm] and ultraviolet light of λ = 193 [nm] that is an eighth harmonic is generated is illustrated. However, the present invention is not limited as long as the wavelength converter 30 includes a configuration in which two nonlinear optical crystals that cause a walk-off in the orthogonal direction are arranged in series. The wavelength of the pulsed light La incident on the wavelength converter Further, the wavelength of the output light emitted from the wavelength conversion unit 30, the specific configuration of the wavelength conversion unit 30 for converting to the wavelength, and the like can be appropriately configured to obtain the same effect.

I Third laser output section
II First laser output section
III Second laser output unit 1 Light source device 8 Control device 10 Laser light generation unit 11, 12, 13 Laser light source 15, 16, 17 Optical modulator 20 Optical amplification unit 21, 22, 23 Fiber optical amplifier 30 Wavelength conversion unit (first 1 wavelength conversion unit, 2nd wavelength conversion unit)
31-36 Wavelength conversion optical element (35: first nonlinear optical crystal, 36: second nonlinear optical crystal)
50 Pointing detector 51 Beam position detector 80 Beam control device

Claims (4)

A first laser output unit and a second laser output unit for emitting laser beams,
A laser beam emitted from the first laser output unit and a laser beam emitted from the second laser output unit are used for angular phase matching in which the first nonlinear optical crystal is arranged to cause a walk-off in the first angular direction. A first wavelength conversion unit that receives and converts at least one of the laser beams;
The second nonlinear optical crystal is used for angular phase matching in which a walk-off occurs in an angular direction orthogonal to the first angular direction, and the laser beam emitted from the first wavelength conversion unit and the other laser beam are incident A second wavelength conversion unit for wavelength conversion,
The phase in the first and second nonlinear optical crystals is changed by changing at least one of the wavelength of the laser beam emitted from the first laser output unit and the wavelength of the laser beam emitted from the second laser output unit. A beam control device that changes an emission optical path of the laser light emitted from the second wavelength conversion unit by changing the mismatch amount and changing the beam pointing according to the phase mismatch amount. A light source device. At least one of the first and second laser output units includes a pulsed laser light source, and an optical modulator that cuts out and emits a part of the pulsed laser light generated by the laser light source,
2. The light source device according to claim 1 , wherein the beam control device is configured to change a wavelength of emitted laser light by changing a cut-out timing by the optical modulator. 3. A third laser output unit that emits laser light is further provided, and at least one of the laser beams emitted from the first, second, and third laser output units is incident on the first wavelength conversion unit,
At least one of the laser light emitted from the first wavelength conversion unit and the laser light emitted from the first, second, and third laser output units is incident on the second wavelength conversion unit,
The beam control device changes the phase error in the first and second nonlinear optical crystals by changing at least two of the wavelengths of the laser beams emitted from the first, second, and third laser output units. 2. The light source device according to claim 1, wherein a matching amount is changed, and an emission optical path of laser light emitted from the second wavelength conversion unit is adjustable in an arbitrary direction orthogonal to the optical axis. A beam position detector for detecting the position of the laser beam emitted from the second wavelength conversion unit in the direction perpendicular to the optical axis;
The beam control device, of claims 1 to 3, characterized by being configured to adjust the emission light path of the laser beam on the basis of the direction perpendicular to the optical axis position of the laser light detected by the beam position detector The light source device according to any one of the above.

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