Pulsed light generation device, pulsed light generation method, and processing equipment

Abstract

To provide a pulsed light generation device capable of reducing variations in pulse front tilt and pointing occurring during wavelength conversion.SOLUTION: A pulsed light generation device 10 is provided, comprising: a nonlinear optical crystal 20 configured to receive (first) pulsed light and output second pulsed light obtained by wavelength-converting the first pulsed light; and a diffraction grating 30 provided in a travel path of the second pulsed light output from the nonlinear optical crystal and configured to output third pulsed light obtained by subtracting a proportion of a variation in output angle from the nonlinear optical crystal for each frequency component of the pulsed light to a variation in frequency included in a frequency band of incident pulsed light.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a pulsed light generating device, a pulsed light generating method, and a processing device. This application claims priority based on Japanese Patent Application No. 2021-194049, filed on November 30, 2021, the contents of which are incorporated herein by reference. [Background technology]

[0002] Conventionally, a method has been known in which a workpiece is irradiated with a first ultrashort laser pulse light having a near-infrared wavelength and a second ultrashort laser pulse light having an ultraviolet wavelength and generated by wavelength conversion of the first ultrashort laser pulse light using a nonlinear optical crystal unit, thereby efficiently processing the workpiece with two types of ultrashort laser pulse light (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-272794 Summary of the Invention

[0004] One aspect of the present invention is a pulsed light generating device including: a nonlinear optical crystal that receives a first pulsed light emitted from a pulsed light source and emits a second pulsed light obtained by wavelength-converting the first pulsed light; and a diffraction grating that is disposed on a path of the second pulsed light emitted from the nonlinear optical crystal and that emits a third pulsed light obtained by reducing the ratio of a pointing change amount to a frequency change amount of the incident pulsed light.

[0005] One aspect of the present invention is a pulsed light generation method including the steps of: emitting, from a nonlinear optical crystal toward a diffraction grating, a second pulsed light obtained by wavelength-converting a first pulsed light incident from a pulsed light source; and emitting, on a path of the second pulsed light emitted from the nonlinear optical crystal, a third pulsed light obtained by reducing a ratio of a pointing change amount to a frequency change amount of the pulsed light incident on the diffraction grating.

[0006] One aspect of the present invention is a processing device including: a pulsed light source that emits a first pulsed light; a nonlinear optical crystal that emits a second pulsed light obtained by wavelength-converting the first pulsed light emitted from the pulsed light source; a diffraction grating that is arranged on a path of the second pulsed light emitted from the nonlinear optical crystal and emits a third pulsed light in which the ratio of a change in pointing to a change in frequency of the incident pulsed light is reduced; and a processing unit that irradiates a workpiece with the third pulsed light emitted from the diffraction grating and processes the workpiece. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a diagram illustrating a configuration of a pulsed light generating device according to an embodiment of the present invention. [Figure 2] 2 is a diagram illustrating second harmonic generation in a nonlinear optical crystal of the pulsed light generating device shown in FIG. 1. FIG. [Figure 3] 2 is a diagram for explaining the tilt amount of pulsed light generated by a diffraction grating of the pulsed light generating device shown in FIG. 1. FIG. [Figure 4] 2 is a diagram showing the relationship between the angle and the refractive index of the nonlinear optical crystal of the pulsed light generating device shown in FIG. [Figure 5] 1. FIG. 4 is a diagram showing the relationship between the pulse plane of the second harmonic wave emitted from the nonlinear optical crystal of the pulsed light generating device shown in FIG. 1 and chromatic dispersion depending on the angle of the second pulsed light. [Figure 6] 10A and 10B are diagrams illustrating correction of a pulse surface and correction of chromatic dispersion of pulsed light by a diffraction grating. [Figure 7] FIG. 10 is another diagram illustrating correction of the pulse surface and correction of chromatic dispersion of pulsed light by a diffraction grating. [Figure 8] 1 is a flowchart of a pulsed light generating method according to the present embodiment. [Figure 9] 1 is a diagram showing a configuration of a processing apparatus according to an embodiment of the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0008] The present embodiments will now be described with reference to the drawings. The following detailed description of the present embodiments is by way of example only and not by way of limitation. The same or similar reference numerals are used throughout the drawings and the following detailed description.

[0009] [Pulse light generating device] Fig. 1 is a diagram showing the configuration of a pulsed light generating device 10 according to the present embodiment. The pulsed light generating device 10 is a device that uses a diffraction grating to improve the beam quality of pulsed light that has been wavelength-converted by a nonlinear optical crystal. As shown in Fig. 1, the pulsed light generating device 10 includes at least a nonlinear optical crystal 20 and a diffraction grating 30, and further includes a magnification / reduction optical system (optical system) 40.

[0010] The nonlinear optical crystal 20 is a crystal that converts the wavelength of a first pulsed light LP1 emitted from a pulsed light source (not shown) and emits a second pulsed light LP2 having a wavelength band different from that of the first pulsed light LP1. The wavelength band of the second pulsed light LP2 is a region determined depending on the application of the pulsed light generating device 10, and is, for example, the ultraviolet (UV) region or the visible region. The wavelength band of the first pulsed light LP1 is determined depending on the wavelength band of the second pulsed light LP2 and the material of the nonlinear optical crystal 20, and is, for example, the near-infrared (IR) region or the visible region.

[0011] The type of nonlinear optical crystal 20 is a material capable of wavelength-converting the first pulsed light LP1 emitted from the pulse light source into the second pulsed light LP2 having the wavelength band determined as described above, and is appropriately selected in consideration of the wavelength band of the first pulsed light LP1, the wavelength band of the second pulsed light LP2, the power required for the second pulsed light LP2, etc. For example, when the wavelength band of the first pulsed light LP1 is the visible region with a peak wavelength (center wavelength) of 532 nm and the wavelength band of the second pulsed light LP2 is the UV region with a peak wavelength (center wavelength) of 266 nm, examples of the nonlinear optical crystal 20 include CsLiB6O10 (CLBO) crystal and β-BaB2O4 (BBO) crystal.

[0012] The nonlinear optical crystal 20 of this embodiment converts the wavelength of the incident first pulse light LP1 (fundamental wave, center frequency ω1) into the second pulse light LP2 (second harmonic, center frequency ω2). Hereinafter, the "center frequency" may be simply referred to as the "frequency." Here, second harmonic generation (SHG) is assumed to be type I phase matching. That is, the polarization of the first pulse light LP1 is an ordinary ray (o), and the polarization of the second pulse light LP2 is an extraordinary ray (e).

[0013] In this specification and each drawing, the Z direction is the traveling direction of the first pulsed light LP1 incident on the nonlinear optical crystal 20. The optical axis AX of the first pulsed light LP1 is parallel to the Z direction. The YZ plane is parallel to the paper surface of FIG.

[0014] The diffraction grating 30 is disposed on the optical axis AX in the +Z direction relative to the nonlinear optical crystal 20. The diffraction grating 30 has a grating surface 32 on which a plurality of gratings are formed at equal intervals. The gratings are parallel to the X axis. The angle between the normal to the grating surface and the optical axis AX is the angle of incidence θi. The diffraction grating 30 outputs a third pulse light LP3 from a fourth pulse light (pulse light) LP4 incident on the grating surface 32. In the third pulse light LP3, the ratio of the amount of change in pointing to the amount of change in frequency is reduced compared to the fourth pulse light LP4 incident on the grating surface 32.

[0015] The magnification / reduction optical system 40 is disposed on the optical axis AX between the nonlinear optical crystal 20 and the diffraction grating 30, and has a first lens 41 and a second lens 42. The first lens 41 is disposed on the optical axis AX between the nonlinear optical crystal 20 and the diffraction grating 30. The second lens 42 is disposed on the optical axis AX between the first lens 41 and the diffraction grating 30.

[0016] The exit surface 22 of the nonlinear optical crystal 20 and the grating surface 32 of the diffraction grating 30 are arranged at positions conjugate to each other. In addition, the focal length f1 of the first lens 41 is shorter than the focal length f2 of the second lens 42. The first lens 41 is arranged at a position away from the exit surface 22 in the +Z direction by the focal length f1. The second lens 42 is arranged at a position away from the first lens 41 in the +Z direction by (f1+f2), and at a position away from the grating surface 32 in the -Z direction by the focal length f2. In other words, the distance between the first lens 41 and the second lens 42 is (f1+f2).

[0017] In the pulsed light generating device 10 having the above-described configuration and in which the respective components are relatively arranged, the nonlinear optical crystal 20 is phase-matched at the center frequency ω1 of the first pulsed light LP1, and generates the second pulsed light LP2. In the following description, frequency may be used instead of wavelength. The amount of phase mismatch in SHG is expressed by equation (1).

[0018]

number

[0019] k1 represents the wave number of the first pulse light LP1. k2 represents the wave number of the second pulse light LP2. The change in the amount of phase mismatch when the frequency ω1 is shifted by the frequency δω1 is expressed by equation (2).

[0020]

number

[0021] As shown in equation (3), σ represents the difference between the reciprocal of the group velocity v1 of the first pulse light LP1 and the reciprocal of the group velocity v2 of the second pulse light LP2.

[0022]

number

[0023] On the other hand, the change δ(Δk) in the amount of phase mismatch that occurs when the pointing (direction of k2) of the second harmonic is tilted by δθ is expressed by equation (4).

[0024]

number

[0025] n represents the refractive index of the nonlinear optical crystal 20. ρ represents the walkoff angle of the nonlinear optical crystal 20. Consider the change in pointing of the second harmonic when the fundamental frequency is changed by δω1 (therefore, the second harmonic frequency is changed by δω2 = 2 x δω1). It is considered that the pointing change occurs to compensate for the phase mismatch caused by the frequency change. By equating equations (2) and (4), the ratio of the pointing change to the frequency change can be calculated as shown in equation (5).

[0026]

number

[0027] In equation (5), the change in pointing is converted into the angle that the second pulsed light LP2 makes with respect to the optical axis AX observed outside the nonlinear optical crystal 20. If the refractive index of the nonlinear optical crystal 20 is n, the angle observed outside is approximately n times the angle inside the nonlinear optical crystal 20.

[0028] As an example of broadband pulsed light, consider first pulsed light LP1 and second pulsed light LP2 whose spectral widths have been expanded by self-phase modulation (SPM) occurring in an optical fiber (not shown). Specifically, a pulsed light source (not shown) and a nonlinear optical crystal 20 are connected by an optical fiber, and pulsed light emitted from the pulsed light source propagates through the core of the optical fiber and enters the nonlinear optical crystal 20 as the first pulsed light LP1. The change in frequency of the pulsed light, i.e., chirp, is given by the time derivative of the amount of phase modulation. The frequency change of the second pulsed light LP2 is approximately twice the frequency change of the first pulsed light LP1. The value obtained by multiplying the change in frequency of the second pulsed light LP2 by αc in equation (5) represents the change in pointing of the second pulsed light LP2. In other words, the pointing of the second pulsed light LP2 changes over time.

[0029] When determining the beam quality of pulsed light, the divergence angle of the entire pulsed light (corresponding to integration over time) is usually measured. The divergence angle obtained by integrating the pointing of the second pulsed light LP2 over time is larger than the divergence angle of narrowband pulsed light without frequency change and therefore without time change in pointing. In other words, the M2 factor of the second pulsed light LP2 whose spectral width has been expanded by SPM is larger than the M2 factor of narrowband pulsed light whose spectral width has not been expanded (in this case, the M2 factor is roughly proportional to the divergence angle). Here, considering that the change in pointing of the second pulsed light LP2 is proportional to the change in frequency, the diffraction grating 30, which is positioned in the +Z direction relative to the nonlinear optical crystal 20, can reduce or compensate for the change in pointing of the second pulsed light LP2, thereby suppressing deterioration of the beam quality of the second pulsed light LP2.

[0030] If the relationship between the pointing of the diffraction grating 30 and the wavelength is expressed as equation (6), then in the pulsed light generating device 10, at least equation (7) holds, and the change in pointing of the second pulsed light LP2 is reduced, thereby suppressing deterioration of the beam quality.

[0031]

number

[0032]

number

[0033] In the pulsed light generating device 10, by arranging the diffraction grating 30 in the +Z direction relative to the nonlinear optical crystal 20, the pointing change (αc) due to the nonlinear optical crystal 20 is subtracted by the pointing change (αg) due to the diffraction grating 30, and finally, the third pulsed light LP3 having a smaller pointing change (αe) in the +Z direction relative to the diffraction grating 30 is emitted. αe is expressed as in equation (8). αe is synonymous with "the ratio of the amount of pointing change to the amount of change in frequency of the third pulsed light LP3."

[0034]

number

[0035] As can be seen from equation (8), when equation (9) holds, αe approaches zero.

[0036]

number

[0037] The diffraction condition of the first-order light of the diffraction grating 30 is expressed by equation (10).

[0038]

number

[0039] d represents the pitch of the plurality of gratings formed on the grating surface 32. θi represents the angle of incidence of the fourth pulse light LP4 on the grating surface 32. θo represents the angle of emission of the third pulse light LP3 from the grating surface 32. λ in the formula represents the central wavelength of the fourth pulse light LP4, i.e., the central wavelength of the second pulse light LP2. From formula (10), the amount of change in the emission angle θo of the third pulse light LP3 with respect to the amount of change in wavelength is expressed by formula (11).

[0040]

number

[0041] When the wavelength λ is converted into the frequency ω, αg is expressed by equation (12).

[0042]

number

[0043] where c represents the speed of light. From equation (12), it can be seen that αg increases as the pitch d of the grating surfaces 32 of the diffraction grating 30 decreases. However, even if the pitch d is made small enough to be practical and within the limits of fabrication, if αg is significantly smaller than αc, the effect of reducing αc becomes excessively weak. In other words, there may be a situation where the pitch d required to achieve a certain degree of the effect of reducing αc is too small, making it difficult to fabricate the diffraction grating 30. Therefore, in the pulsed light generation device 10, the magnification / reduction optical system 40 is disposed between the nonlinear optical crystal 20 and the diffraction grating 30 in the Z direction, as described above. The magnification / reduction optical system 40 appropriately magnifies or reduces the pointing change of the beam of the incident second pulsed light LP2.

[0044] In this embodiment, the scaling optical system 40 uses a first lens 41 having a focal length f1 and a second lens 42 having a focal length f2 to expand or contract the pointing change of the beam of the second pulsed light LP2 and convert it into a fourth pulsed light LP4. The first lens 41 and the second lens 42 form a so-called telescope. Each pulse component of the second pulsed light LP2 that enters the scaling optical system 40 in a collimated state is emitted from the scaling optical system 40 while maintaining its collimated state. Note that, of the pulse components included in the second pulsed light LP2, only the pulse component p1 having the lowest frequency and the pulse component p2 having the highest frequency are shown in FIG. 1 .

[0045] As described above, the exit surface 22 of the nonlinear optical crystal 20 and the grating surface 32 of the diffraction grating 30 are arranged at conjugate positions. The distance in the Z direction between the exit surface 22 and the first lens 41 is equal to the focal length f1. The distance in the Z direction between the first lens 41 and the second lens 42 is equal to (f1 + f2). The distance in the Z direction between the second lens 42 and the grating surface 32 is equal to the focal length f2. In this case, considering that the magnification rate of the pointing change of the magnification / reduction optical system 40 is f1 / f2, equation (9) can be expressed as equation (13).

[0046]

number

[0047] Diffraction of pulsed light at the diffraction grating 30 causes tilt of the pulse front (defined based on intensity). When the pulse time width is short, the effect of the tilt of the pulse front cannot be ignored. In the pulsed light generating device 10, when equation (9) or equation (13) holds, the tilt of the pulse front of the fourth pulsed light generated by the diffraction grating 30 and the tilt of the pulse front of the second pulsed light generated by the nonlinear optical crystal 20 cancel each other out.

[0048] In the following, the tilt amount of the pulse surface is expressed in terms of time. FIG. 2 shows the process of SHG in a nonlinear optical crystal 20 having a walk-off effect. It corresponds to a snapshot when the first pulse light LP1 (fundamental wave, center frequency ω1) arrives at the exit surface 22 of the nonlinear optical crystal 20. The second harmonic (center frequency ω2) generated near the entrance surface 21 of the nonlinear optical crystal 20 spatially moves away from the path of the first pulse light LP1 in the ZY plane due to the walk-off effect, and is delayed in time from the first pulse light LP1 due to the difference in group velocity between the fundamental wave and the second harmonic. As a result, the pulse surface of the second harmonic emitted from the exit surface 22 of the nonlinear optical crystal 20, i.e., the pulse surface of the second pulse light LP2, is tilted with respect to the optical axis AX. The circular area depicted by the dot pattern in FIG. 2 is a schematic representation of the pulse surface of the first pulse light LP1. The elliptical area depicted by the diagonal lines in FIG. 2 is a schematic representation of the pulse surface of the second pulse light LP2.

[0049] As expressed by equation (3), the aforementioned σ is the difference in the reciprocal of the group velocities of the fundamental wave and the second harmonic wave, so the tilt amount Δτc generated in nonlinear optical crystal 20 is expressed by equation (14).

[0050]

number

[0051] L represents the length of the nonlinear optical crystal 20 in the Z direction. FIG. 3 is a diagram for explaining the tilt amount of the pulsed light generated by the diffraction grating 30. The elliptical area drawn with diagonal lines in FIG. 3 schematically represents the pulse surface of the fourth pulsed light LP4 incident on the diffraction grating 30. (For the sake of explanation, it is assumed here that the pulse surface of the fourth pulsed light LP4 is not tilted.) The elliptical area drawn with cross-hatched lines in FIG. 3 schematically represents the pulse surface of the third pulsed light LP3. As shown in FIG. 3, the tilt amount Δτg generated by the diffraction grating 30 is expressed by equation (15).

[0052]

number

[0053] Dg represents the beam diameter of the fourth pulse light LP4 in the X and Y directions. θi represents the angle of incidence of the fourth pulse light LP4 on the grating surface 32. Here, when deriving equation (15), it is assumed that the angle of incidence θi of the fourth pulse light LP4 on the grating surface 32 and the angle of emergence θo of the third pulse light LP3 from the grating surface 32 are equal to each other, that is, equation (16) is established.

[0054]

number

[0055] In the pulsed light generation device 10, at least Δτg≦Δτc, and preferably Δτg=Δτc, is satisfied in order to suppress deterioration of the beam quality of the third pulsed light LP3 emitted from the diffraction grating 30. The beam diameter Dc of the second pulsed light LP2 at the emission surface 22 of the nonlinear optical crystal 20 is given by equation (17).

[0056]

number

[0057] As described above, since the magnification / reduction optical system 40 having the lateral magnification (f2 / f1) is arranged between the exit surface 22 of the nonlinear optical crystal 20 and the grating surface 32 of the diffraction grating 30 in the Z direction, equation (18) is obtained.

[0058]

number

[0059] Therefore, if equation (13) holds, equation (19) is obtained.

number

[0060] Therefore, by using equations (5), (12), (14), (17), and (19) in equation (15), equation (20) is obtained.

[0061]

number

[0062] As described above, since it is assumed that the incident angle θi and the exit angle θo are equal as shown in equation (16), the diffraction condition of equation (10) can be expressed as equation (21).

[0063]

number

[0064] According to equations (20) and (21), it can be seen that Δτc = Δτg holds. That is, if the diffraction grating 30 is arranged so as to cancel out the angular dispersion occurring in the nonlinear optical crystal 20 (equation (13)), the tilt of the pulse plane of the fourth pulse light LP4 is also canceled out, and it can be seen that the third pulse light LP3 with a smaller tilt of the pulse plane (ideally no tilt) can be obtained. Δτc = Δτg represents the most preferable state. In general, if the diffraction grating 30 is arranged so as to reduce the angular dispersion occurring in the nonlinear optical crystal 20, the tilt of the pulse plane of the fourth pulse light LP4 also decreases (Δτc ≧ Δτg > 0).

[0065] In the above explanation, for example, when UV light is generated from visible light (pulsed light) by SHG, σ > 0, so δ(Δk) > 0 for δω2 > 0 (Equation (2)). To compensate for and reduce the change in phase mismatch δ(Δk), the change in phase mismatch δ(Δk) due to a change in pointing must be negative, and the wavenumber k2 must be reduced. In other words, the refractive index n2 must be reduced. Figure 4 shows that the direction of wavenumber k2 must change in the same direction as the walk-off direction. Figure 4 shows the refractive index of a positive uniaxial crystal as an example, as a function of the angle from the optic axis (the vertical axis of the figure). The solid line indicates the refractive index of the second harmonic, and the dotted line indicates the refractive index of the fundamental. The vector connecting the origin and the intersection of the solid and dotted lines indicates the direction of the wavenumbers k1 and k2 during phase matching. The direction indicated by ρ is the walk-off direction.

[0066] Figure 5 shows the pulse plane of the second pulse light LP2 emitted from the nonlinear optical crystal 20 and the change in pointing with frequency. As mentioned above, high-frequency components (shorter wavelength components) are emitted in the walk-off direction, i.e., in the direction of pulse component p2. Low-frequency components (longer wavelength components) are emitted in the opposite direction to the walk-off, in the direction of pulse component p1. Figure 6 shows the correction of the pulse plane by a diffraction grating and the correction of pointing change with frequency. The diffraction angle of the low-frequency pulse component p1 is larger than the diffraction angle of the high-frequency pulse component p2. Figure 6 shows that both the pulse plane tilt and the pointing change associated with frequency change are corrected. In other words, the pulse plane tilt and pointing change that occur during wavelength conversion are reduced, not increased. If the direction of diffraction by the diffraction grating in Figure 6 were reversed (Figure 7), the pointing change and pulse plane tilt would be exaggerated. That is, to obtain high beam quality, it is necessary to select the direction of diffraction by the diffraction grating correctly relative to the direction of walk-off of the nonlinear optical crystal.

[0067] It should be noted that a dispersion prism also produces a pointing change in response to a change in frequency, so that a dispersion prism can be used instead of a diffraction grating.

[0068] [Numerical example] A numerical example of pulsed light generation using the above-described pulsed light generating device 10 will be described. For example, a CLBO crystal is used as the nonlinear optical crystal 20, and SHG of the first pulsed light LP1 with a peak wavelength (center wavelength) of 532 nm is assumed. In this case, the walk-off angle ρ is ρ=0.032 [rad]. The group refractive index difference Δng between the fundamental wave and the second harmonic wave is Δng=0.098.

[0069] From equation (5), the relationship between the change in wavelength and the change in pointing during the SHG process in the nonlinear optical crystal 20 is calculated as in equation (22).

[0070]

number

[0071] When the pitch d of the diffraction grating 30 is d=333 nm, the number of lines / mm is 3000, and the incident angle θi and the outgoing angle θo are θi≈θo≈23.5 [deg.], the formula (23) is obtained from the formula (11).

[0072]

number

[0073] Therefore, by setting (f1 / f2) ≈ 0.29 based on equation (13), it is possible to generate the fourth pulsed light LP4 by subtracting αc from the second pulsed light LP2 emitted from the CLBO crystal, and to obtain the third pulsed light LP3 with reduced degradation in beam quality by reducing the amount of change in pointing of the fourth pulsed light LP4 using the diffraction grating 30. To achieve (f1 / f2) ≈ 0.29, for example, the focal length f1 of the first lens 41 may be set to f1 ≈ 50 mm, and the focal length f2 of the second lens 42 may be set to f2 ≈ 170 mm.

[0074] [Pulse light generation method] The pulsed light generation method of this embodiment is a method for generating pulsed light while suppressing deterioration of beam quality using the above-described pulsed light generation device 10. FIG. 8 is a flowchart of the pulsed light generation method of this embodiment. In the pulsed light generation method of this embodiment, in the pulsed light generation device 10, first pulsed light LP1 emitted from a pulsed light source (not shown) is made incident on the incidence surface 21 of the nonlinear optical crystal 20 (step S11). The first pulsed light LP1 is wavelength-converted to second pulsed light LP2 by the nonlinear optical crystal 20.

[0075] Next, the second pulsed light LP2 obtained by wavelength-converting the incident first pulsed light LP1 is output from the nonlinear optical crystal 20 via the scaling optical system 40 in the +Z direction toward the diffraction grating 30 (step S12). Specifically, in step S12, the second pulsed light LP2 is first output from the output surface 22 of the nonlinear optical crystal 20 in the +Z direction toward the scaling optical system 40 (step S15). Subsequently, the fourth pulsed light LP4, which has been obtained by reducing or increasing the amount of change in the output angle due to the change in frequency of the second pulsed light LP2, is output from the scaling optical system 40 toward the diffraction grating 30 in the +Z direction (step S16).

[0076] Next, the third pulse light LP3, which is obtained by reducing the proportion of the pointing change amount due to the frequency change of the fourth pulse light LP4 that is emitted from the magnification / reduction optical system 40 and incident on the diffraction grating 30, is emitted from the grating surface 32 of the diffraction grating 30 (step S21).

[0077] By performing the above steps S11, S15, S16, and S21, it is possible to generate the third pulse light LP3 obtained by subtracting the proportion αc of the second pulse light LP2 from the second pulse light LP2 emitted from the emission surface 22 of the nonlinear optical crystal 20, and emit the third pulse light LP3 from the diffraction grating 30. Furthermore, by performing the above steps S11, S15, S16, and S21, it is possible to suppress deterioration in the beam quality of the second pulse light LP2.

[0078] [Processing equipment] The processing apparatus 50 of this embodiment includes a pulsed light source 15, a nonlinear optical crystal 20, a diffraction grating 30, and a processing unit 60. Note that, with regard to the components and functions of the processing apparatus 50, those components that are common to the components of the pulsed light generation apparatus 10 described above are denoted by the same reference numerals as the corresponding components of the pulsed light generation apparatus 10, and a detailed description of their functions will be omitted. FIG. 9 is a diagram showing the configuration of the processing apparatus 50. In addition to the components of the pulsed light generation apparatus 10, the processing apparatus 50 includes a pulsed light source 15 and a processing unit 60.

[0079] The pulsed light source 15 emits a first pulsed light LP1. The peak wavelength (center wavelength) and pulse width of the first pulsed light LP1 are not limited to specific values, but are appropriately selected in consideration of the values ​​and conditions under which the workpiece S exhibits absorption characteristics or the values ​​and conditions under which the workpiece S is sensitive, so as to enable desired processing of the workpiece S. More specifically, the peak wavelength (center wavelength) and pulse width of the first pulsed light LP1 are set so as to generate, by the wavelength conversion function of the nonlinear optical crystal 20, a second pulsed light LP2 having a wavelength band that enables desired processing of the workpiece S. The first pulsed light LP1 emitted from the pulsed light source 15 enters the nonlinear optical crystal 20 from the incident surface 21.

[0080] The processing unit 60 irradiates the workpiece S with the third pulsed light LP3 emitted from the diffraction grating 30, thereby processing the workpiece S. The processing unit 60 includes, for example, a condenser lens 62, a stage 64, and a control device 70. The condenser lens 62 forms an image of the third pulsed light LP3 emitted from the diffraction grating 30 on the optical axis BX (path) of the third pulsed light LP3. In order to maintain the beam quality of the third pulsed light LP3, it is preferable that the main surface of the condenser lens 62 be arranged parallel to the pulse plane of the third pulsed light LP3.

[0081] The stage 64 has a mounting surface 66 on which the workpiece S is placed, and is formed, for example, in a rectangular shape when viewed along the optical axis BX parallel to the Y direction, and has a predetermined thickness in the Y direction parallel to the optical axis BX. The stage 64 is disposed on the -Y side of the condenser lens 62 so that a focal point F of the third pulsed light LP3 focused by the condenser lens 62 is irradiated onto a predetermined position on the workpiece S placed on the mounting surface 66. In other words, the distance in the Y direction between the condenser lens 62 and the predetermined position on the workpiece S is equal to the focal length of the condenser lens 62. The condenser lens 62 focuses the third pulsed light LP3 at the focal point F, thereby irradiating the third pulsed light LP3 emitted from the diffraction grating 30 onto the workpiece S.

[0082] The control device 70 is configured to be able to move the stage 64 so that the focal point F moves to a desired processing area on the workpiece S. Note that if the desired processing area is a single point, there is no need to move the stage 64. That is, the control device 70 controls the position of the stage 64 in each of the X, Y, and Z directions. The control device 70 is connected to the stage 64 by wire or wirelessly using an electric cable 65 or the like. The control device 70 is configured to be able to switch on and off the emission of the first pulsed light LP1 from the pulsed light source 15 in conjunction with the positioning of the stage 64, and to control the emission power of the first pulsed light LP1, etc. The control device 70 is connected to the pulsed light source 15 by wire or wirelessly using an electric cable 68 or the like.

[0083] The processing unit 60 focuses the third pulsed light LP3 emitted from the diffraction grating 30 onto a focal point F in the desired processing area of ​​the workpiece S using a focusing lens 62, moves or stops the stage 64 using the control device 70 to relatively move the focal point F within the processing area of ​​the workpiece S, and controls the power of the first pulsed light LP1 from the pulsed light source 15, thereby processing the workpiece S in a desired pattern.

[0084] Since the processing device 50 includes the components of the pulsed light generating device 10, the workpiece S is irradiated with the third pulsed light LP3 with reduced deterioration in beam quality, and high processing accuracy is obtained.

[0085] As described above, the pulsed light generation device 10 of this embodiment includes a nonlinear optical crystal 20 and a diffraction grating 30. The nonlinear optical crystal 20 receives a first pulsed light LP1 emitted from a pulsed light source and emits a second pulsed light LP2 obtained by wavelength-converting the first pulsed light LP1. The diffraction grating 30 is disposed on the path of the second pulsed light LP2 emitted from the nonlinear optical crystal 20. The diffraction grating 30 emits a third pulsed light LP3 obtained by reducing the rate αc of pointing change relative to frequency change of the incident fourth pulsed light (pulsed light) LP4. According to the pulsed light generation device 10 of this embodiment, the spatial and temporal distortions of the pulsed light that occur during wavelength conversion in the nonlinear optical crystal 20 can be simply corrected by the diffraction grating 30, thereby obtaining a third pulsed light LP3 with good beam quality.

[0086] As described with reference to FIGS. 5 and 6, the pulsed light generating device 10 of this embodiment can efficiently correct both the tilt of the pulse front of the second pulsed light LP2 and the change in pointing due to a change in frequency using a simple optical system that uses the diffraction grating 30.

[0087] The pulsed light generation device 10 of this embodiment further includes a scaling optical system 40. The scaling optical system 40 is disposed between the nonlinear optical crystal 20 and the diffraction grating 30 on the path of the second pulsed light LP2 output from the nonlinear optical crystal 20. The scaling optical system 40 outputs a fourth pulsed light LP4 obtained by reducing the pointing change amount for each frequency component of the second pulsed light PL2 incident from the nonlinear optical crystal 20. In this configuration, the diffraction grating 30 outputs, as the third pulsed light LP3, pulsed light obtained by reducing the proportion of the pointing change amount of the fourth pulsed light LP4 incident from the scaling optical system 40. According to the pulsed light generation device 10 described above, even if the pitch d required to directly reduce the αc of the second pulsed light LP2 using the diffraction grating 30 is too small and therefore difficult to fabricate, the scaling optical system 40 can be used to previously reduce the αc of the second pulsed light LP2, thereby making it possible to achieve an appropriate reduction proportion of αc by the diffraction grating 30.

[0088] In the pulsed light generating device 10 of the above-described embodiment, it is assumed that αg<αc, and the scaling optical system 40 reduces αc of the second pulsed light LP2. If αg>αc, it is preferable that the scaling optical system 40 increases αc of the second pulsed light LP2. In other words, whether the scaling optical system 40 reduces or enlarges αc of the second pulsed light LP2 depends on the magnitude relationship between αc and αg.

[0089] Although the pulsed light generation device 10 of this embodiment includes the magnification / reduction optical system 40, if αc of the second pulsed light LP2 and αg of the diffraction grating 30 are relatively close to each other and the desired effect can be obtained by directly subtracting αc using αg of the diffraction grating 30, the magnification / reduction optical system 40 may be omitted. In this case, the fourth pulsed light LP4 incident on the grating surface 32 of the diffraction grating 30 in the pulsed light generation device 10 of this embodiment may be replaced with the second pulsed light LP2.

[0090] Furthermore, in the pulsed light generation device 10 of this embodiment, the scaling optical system 40 has a first lens 41 and a second lens 42. The first lens 41 is disposed between the nonlinear optical crystal 20 and the diffraction grating 30. The second lens 42 is disposed between the first lens 41 and the diffraction grating 30. The exit surface 22 of the nonlinear optical crystal 20 and the grating surface 32 of the diffraction grating are disposed at positions conjugate to each other. Furthermore, when collimated light enters the scaling optical system 40, it is output as collimated light. That is, the first lens 41 and the second lens 42 constitute a so-called 4f optical system between the nonlinear optical crystal 20 and the diffraction grating 30. When the scaling optical system 40 reduces the pointing change αc of the second pulsed light LP2, the focal length f1 of the first lens 41 is set shorter than the focal length f2 of the second lens 42. According to the pulsed light generating device 10 of this embodiment, the magnification / reduction optical system 40 can be realized with a simple configuration consisting of a 4f optical system using the first lens 41 and the second lens 42. Furthermore, the focal lengths f1 and f2 can be determined independently of each other, and the magnification of the magnification / reduction optical system 40 can be adjusted freely and accurately.

[0091] In the pulsed light generating device 10 of the above embodiment, the magnification of the magnifying / reducing optical system 40 is determined by the magnitude relationship between αc and αg. If αg>αc as in the above modified example, the focal length f1 of the first lens 41 is made longer than the focal length f2 of the second lens 42, and αc is made larger.

[0092] The pulsed light generation method of this embodiment includes at least a first step and a second step. In the first step, second pulsed light LP2, which is obtained by wavelength-converting first pulsed light LP1 incident from a pulsed light source, is emitted from the nonlinear optical crystal 20 toward the diffraction grating 30 (steps S11 and S12). Next, in the second step, third pulsed light LP3, which is obtained by subtracting the Pointing change due to the frequency-varied component of the second pulsed light LP2, is emitted from the diffraction grating 30 (step S21). In the pulsed light generation method of this embodiment, the scaling optical system 40 is disposed between the nonlinear optical crystal 20 and the diffraction grating 30, and therefore the aforementioned "pulsed light incident on the grating surface 32 of the diffraction grating 30" refers to the fourth pulsed light LP4 emitted from the scaling optical system 40.

[0093] According to the pulsed light generation method of the present embodiment, the third pulsed light LP3 can be generated by subtracting αc from the second pulsed light LP2 emitted from the nonlinear optical crystal 20 via the magnifying / demagnifying optical system 40 and the diffraction grating 30, and the third pulsed light LP3 can be emitted from the diffraction grating 30. Furthermore, according to the pulsed light generation method of the present embodiment, deterioration of the beam quality of the second pulsed light LP2 can be efficiently suppressed.

[0094] As described above for the pulsed light generation device 10 of this embodiment, if αc and αg are close to each other, the magnification / reduction optical system 40 can be omitted. If the magnification / reduction optical system 40 is omitted, the above-mentioned step S16 is not performed, and the second pulsed light LP2 is directly emitted from the exit surface 22 of the nonlinear optical crystal 20 toward the diffraction grating 30 in step S15, and then step S21 is performed. In this case, the above-mentioned "pulsed light incident on the grating surface 32 of the diffraction grating 30" refers to the second pulsed light LP2 itself emitted from the nonlinear optical crystal 20.

[0095] The machining apparatus 50 of this embodiment includes a pulsed light source 15, a nonlinear optical crystal 20, a diffraction grating 30, and a machining unit 60. The pulsed light source 15 emits a first pulsed light LP1. The nonlinear optical crystal 20 emits a second pulsed light LP2 obtained by wavelength-converting the first pulsed light LP1 emitted from the pulsed light source 15. The diffraction grating 30 is disposed on the path of the second pulsed light LP2 emitted from the nonlinear optical crystal 20, and emits a third pulsed light LP3 obtained by reducing the ratio of the pointing change amount to the frequency change amount of the incident fourth pulsed light LP4. The machining unit 60 irradiates the workpiece S with the third pulsed light LP3 emitted from the diffraction grating 30, thereby machining the workpiece S. According to the machining apparatus 50 of this embodiment, the first pulsed light LP1 emitted from the pulsed light source 15 is wavelength-converted by the nonlinear optical crystal 20 into the second pulsed light LP2 having a wavelength band suitable for machining the workpiece S, and the αc of the second pulsed light LP2 can be reduced using an arrangement similar to that of the above-mentioned pulsed light generating apparatus 10. Moreover, according to the machining apparatus 50 of this embodiment, the workpiece S can be machined using the third pulsed light LP3 with good beam quality emitted from the diffraction grating 30, and high machining accuracy can be obtained.

[0096] As explained in the pulsed light generation method of the present embodiment, when αc and αg are close to each other, the magnification / reduction optical system 40 in the processing device 50 can be omitted. In this case, the second pulsed light LP2 emitted from the nonlinear optical crystal 20 is directly incident on the grating surface 32 of the diffraction grating 30.

[0097] Although the present embodiment has been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and the present invention also includes designs within the scope of the gist of the present invention.

[0098] For example, the pulsed light generating device 10 may further include a pulsed light source 15 that emits a first pulsed light LP1. The first pulsed light LP1 is, for example, a short pulse, but the parameters and characteristics, such as the pulse widths, of the first pulsed light LP1 and the second pulsed light LP2 are not limited to specific values ​​and are set appropriately depending on the application of the pulsed light generating device 10. The diffraction grating 30 may be formed of an active element, such as a liquid crystal spatial modulator.

[0099] For example, in the processing device 50, the processing section 60 is not limited to one equipped with a focusing lens 62, a stage 64, and a control device 70, and is not particularly limited as long as it is configured to be able to irradiate the third pulse light LP3 emitted from the diffraction grating 30 onto the workpiece S and to be able to process the workpiece S.

[0100] Furthermore, the pulsed light generating device 10 and the pulsed light generating device of this embodiment including at least a nonlinear optical crystal and a diffraction grating may be applied to a pulse generating section in an exposure device or a measurement device in addition to a processing device. [Explanation of symbols]

[0101] 10...pulsed light generating device, 15...pulsed light source, 20...nonlinear optical crystal, 22...output surface, 30...diffraction grating, 32...grating surface, 40...magnification / reduction optical system, 41...first lens, 42...second lens, 50...processing device, 60...processing unit, f1, f2...focal length, LP1...first pulsed light, LP2...second pulsed light, LP3...third pulsed light, LP4...fourth pulsed light, S...workpiece

Claims

1. a nonlinear optical crystal that receives a first pulsed light emitted from a pulsed light source and that emits a second pulsed light obtained by wavelength-converting the first pulsed light; a diffraction grating that is disposed on a path of the second pulsed light output from the nonlinear optical crystal and that outputs a third pulsed light obtained by reducing a rate of change in pointing relative to a rate of change in frequency of the incident pulsed light; A pulsed light generating device comprising:

2. an optical system disposed between the nonlinear optical crystal and the diffraction grating on the path, for emitting a fourth pulsed beam in which a pointing change amount relative to a frequency change amount of the second pulsed beam incident from the nonlinear optical crystal is reduced or increased; the diffraction grating emits pulsed light obtained by reducing the rate of change of the fourth pulsed light incident thereon as the third pulsed light; The pulsed light generating device according to claim 1 .

3. The optical system comprises: a first lens disposed on the path between the nonlinear optical crystal and the diffraction grating; a second lens disposed on the path between the first lens and the diffraction grating; and an output surface of the nonlinear optical crystal and a grating surface of the diffraction grating are arranged at positions conjugate with each other; The pulsed light generating device according to claim 2 .

4. If the focal length of the first lens is represented as f1 and the focal length of the second lens is represented as f2, then The distance between the first lens and the second lens is (f1+f2). The pulsed light generating device according to claim 3 .

5. When the change in pointing due to the nonlinear optical crystal is represented as αc and the change in pointing due to the diffraction grating is represented as αg, the following equation (1) is established: The pulsed light generating device according to claim 4 . [Equation 1]

6. an incident angle of the pulsed light on a grating surface of the diffraction grating and an exit angle of the third pulsed light from the grating surface are substantially equal to each other; The pulsed light generating device according to claim 1 .

7. a step of emitting second pulsed light obtained by wavelength-converting first pulsed light incident from a pulsed light source from the nonlinear optical crystal toward a diffraction grating; emitting a third pulsed light obtained by reducing a ratio of a change in pointing to a change in frequency of the second pulsed light; A pulsed light generating method comprising:

8. a pulsed light source that emits a first pulsed light; a nonlinear optical crystal that emits second pulsed light obtained by wavelength-converting the first pulsed light emitted from the pulsed light source; a diffraction grating that is disposed on a path of the second pulsed light output from the nonlinear optical crystal and that outputs a third pulsed light obtained by reducing a rate of change in pointing relative to a rate of change in frequency of the incident pulsed light; a processing unit that irradiates a workpiece with the third pulsed light emitted from the diffraction grating and processes the workpiece, Processing equipment.

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