Laser apparatus and method of producing electronic device

Abstract

This laser apparatus comprises: a laser oscillator that includes an optical resonator and a pair of electrodes for applying a voltage to laser gas to generate a discharge, and outputs a first pulse laser light; a first optical pulse stretcher that allows a part of the first pulse laser light to pass through and causes another part to circulate once to output a first transmitted light and a first single circulated light that have a first deviation amount and are spatially partly overlapped, thereby outputting a second pulse laser light obtained by expanding the pulse time width of the first pulse laser light; and a second optical pulse stretcher that outputs a second transmitted light and a second single circulated light that have a second deviation amount different from the first deviation amount and are spatially partly overlapped, thereby outputting a third pulse laser light obtained by expanding the pulse time width of the second pulse laser light.

Description

Laser device and method for manufacturing electronic device

[0001] The present disclosure relates to a laser apparatus and a method for manufacturing an electronic device.

[0002] In recent years, semiconductor exposure apparatuses have been required to improve their resolution in response to the miniaturization and high integration of semiconductor integrated circuits. To this end, the wavelength of light emitted from exposure light sources has been shortened. For example, KrF excimer laser devices that output laser light with a wavelength of approximately 248 nm and ArF excimer laser devices that output laser light with a wavelength of approximately 193 nm are used as gas laser devices for exposure.

[0003] The spectral linewidth of the spontaneously oscillating light from KrF excimer laser devices and ArF excimer laser devices is as wide as 350 to 400 pm. Therefore, if a projection lens is constructed using a material that transmits ultraviolet light, such as KrF and ArF laser light, chromatic aberration may occur. As a result, resolution may be reduced. Therefore, it is necessary to narrow the spectral linewidth of the laser light output from the gas laser device to a level where chromatic aberration is negligible. Therefore, a line narrowing module (LNM) containing a line narrowing element (e.g., an etalon or grating) may be installed within the laser resonator of the gas laser device to narrow the spectral linewidth. A gas laser device with a narrowed spectral linewidth is called a line narrowing gas laser device.

[0004] US Patent Application Publication No. 2008 / 0144671 overview

[0005] A laser device according to one aspect of the present disclosure includes: a laser oscillator including an optical resonator and a pair of electrodes that apply a voltage to a laser gas to generate a discharge, and that outputs a first pulsed laser beam; and a first optical pulse stretcher that is disposed in an optical path of the first pulsed laser beam and transmits a part of the first pulsed laser beam and causes another part of the first pulsed laser beam to circulate once, thereby outputting a first transmitted light and a first one-circulation light, thereby outputting a second pulsed laser beam in which the pulse time width of the first pulsed laser beam is stretched, wherein the optical path of the first transmitted light and the optical path of the first one-circulation light have a first deviation in a first direction, and the second optical pulse stretcher is spaced apart. and a second optical pulse stretcher arranged in an optical path of the second pulsed laser beam, which transmits a part of the second pulsed laser beam and causes another part of the second pulsed laser beam to circulate once, thereby outputting a second transmitted light and a second one-circulation light, thereby outputting a third pulsed laser beam having an extended pulse time width of the second pulsed laser beam, wherein the optical path of the second transmitted light and the optical path of the second one-circulation light are configured to spatially overlap with each other by a second shift amount different from the first shift amount in a first direction.

[0006] A method for manufacturing an electronic device according to one aspect of the present disclosure includes: a laser oscillator including an optical resonator and a pair of electrodes that apply a voltage to a laser gas to generate a discharge, and that outputs a first pulsed laser beam; a first optical pulse stretcher that is disposed in an optical path of the first pulsed laser beam and transmits a part of the first pulsed laser beam and causes another part of the first pulsed laser beam to circulate once to output a first transmitted light and a first one-circulation light, thereby outputting a second pulsed laser beam obtained by stretching the pulse time width of the first pulsed laser beam, wherein the optical path of the first transmitted light and the optical path of the first one-circulation light are configured to spatially partially overlap with each other by a first amount of deviation in a first direction; a second optical pulse stretcher that is arranged in an optical path of a second pulsed laser beam and transmits a part of the second pulsed laser beam while causing another part to circulate once, thereby outputting a second transmitted light and a second one-circulation light, thereby outputting a third pulsed laser beam having a stretched pulse time width of the second pulsed laser beam, wherein the second optical pulse stretcher is configured so that the optical path of the second transmitted light and the optical path of the second one-circulation light are spatially shifted in a first direction by a second shift amount different from the first shift amount and are partially overlapped in space,

[0007] Some embodiments of the present disclosure are described below, by way of example only, with reference to the accompanying drawings. FIG. 1 schematically illustrates the configuration of an exposure system in a comparative example. FIG. 2 schematically illustrates the configuration of an exposure system in a comparative example. FIG. 3 schematically illustrates an example of an optical pulse stretcher that shifts the traveling direction of circulated light in the V direction. FIG. 4 illustrates the pulse time waveform of a fourth pulsed laser beam incident on the optical pulse stretcher shown in FIG. 3. FIG. 5 illustrates the pulse time waveform of a fifth pulsed laser beam output from the optical pulse stretcher shown in FIG. 3. FIG. 6 schematically illustrates an example of an optical pulse stretcher that shifts the traveling direction of circulated light in the H direction. FIG. 7 illustrates the beam cross-sectional shape of a second pulsed laser beam output from the optical pulse stretcher shown in FIG. 6. FIG. 8 illustrates an example of optical path shift caused by first and second optical pulse stretchers. FIG. 9 illustrates another example of optical path shift caused by first and second optical pulse stretchers. FIG. 10 shows a first example of optical path deviation caused by the first and second optical pulse stretchers in the first embodiment. FIG. 11 shows a second example of optical path deviation caused by the first and second optical pulse stretchers in the first embodiment. FIG. 12 shows examples of optical path deviation caused by the first to third optical pulse stretchers in the first embodiment. FIG. 13 shows examples of optical path deviation caused by the first to fourth optical pulse stretchers in the first embodiment. FIG. 14 is a graph showing the results of a simulation of the relationship between the amount of optical path deviation caused by one circulation in the optical pulse stretcher and the correlation between the speckle patterns of transmitted light and light that has circulated once. FIG. 15 shows examples of optical path deviation caused by the first to fourth optical pulse stretchers in the second embodiment. FIG. 16 schematically shows an example of an optical pulse stretcher included in the third embodiment. FIG. 17 shows examples of optical path deviation caused by the first to fourth optical pulse stretchers in the third embodiment. Fig. 18 is a graph showing the results of simulating the relationship between the amount of deviation of the optical path due to one revolution in the optical pulse stretcher and the correlation between the speckle patterns of the transmitted light and the light that has made one revolution. Fig. 19 is a schematic diagram of a first modified example of the optical pulse stretcher. Fig. 20 is a schematic diagram of a second modified example of the optical pulse stretcher. Embodiment

[0008] <Contents> 1. Comparative Examples 1.1 Exposure System 1.2 Exposure Apparatus 200 1.2.1 Configuration 1.2.2 Operation 1.3 Laser Apparatus 100 1.3.1 Configuration 1.3.2 Operation 1.4 Speckle 1.5 Examples of Optical Pulse Stretcher 1.5.1 Optical Pulse Stretcher that Shifts the Propagation Direction of Circulating Light in the V Direction 1.5.2 Optical Pulse Stretcher that Shifts the Propagation Direction of Circulating Light in the H Direction 1.6 Issues with the Comparative Examples 2. Multiple Optical Pulse Stretchers with Different Absolute Values ​​of Optical Path Shift Amount 2.1 Principle 2.2 First Example 2.3 Second Example 2.4 Third Example 2.5 Fourth Example 2.6 Relationship between the Correlation between the Optical Path Shift Amount and the Speckle Pattern 2.7 Action 3. 3. Optical pulse stretcher that shifts the optical path in the V direction 3.1 Configuration 3.2 Operation 4. Optical pulse stretcher in which the shift in the optical path includes the shift in the light emission position 4.1 Configuration 4.2 Operation 5. Other 5.1 Modified example of the optical pulse stretcher 5.2 Supplementary information

[0009] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The embodiments described below show some examples of the present disclosure and do not limit the content of the present disclosure. Furthermore, not all of the configurations and operations described in each embodiment are necessarily essential as the configurations and operations of the present disclosure. Note that the same components are given the same reference symbols, and redundant explanations will be omitted.

[0010] 1 and 2 show schematic diagrams of the configuration of an exposure system in a comparative example. The comparative example in the present disclosure is a configuration that the applicant recognizes as being known only by the applicant, and is not a publicly known example that the applicant acknowledges.

[0011] The exposure system includes a laser apparatus 100 and an exposure apparatus 200. The laser apparatus 100 is shown in a simplified form in Fig. 1. The exposure apparatus 200 is shown in a simplified form in Fig. 2.

[0012] The laser device 100 includes a laser control processor 130. The laser device 100 is configured to output laser light toward the exposure device 200.

[0013] 1.2 Exposure Apparatus 200 1.2.1 Configuration As shown in FIG. 1, the exposure apparatus 200 includes an illumination optical system 201 , a projection optical system 202 , and an exposure control processor 210 .

[0014] The illumination optical system 201 illuminates a reticle pattern of a reticle (not shown) arranged on a reticle stage RT with laser light incident from the laser device 100 .

[0015] The projection optical system 202 reduces and projects the laser light that has passed through the reticle, forming an image on a workpiece (not shown) placed on a workpiece table WT. The workpiece is a photosensitive substrate such as a semiconductor wafer coated with a resist film.

[0016] The exposure control processor 210 is a processing device that includes a memory 212 in which a control program is stored, and a CPU (central processing unit) 211 that executes the control program. The exposure control processor 210 is specially configured or programmed to execute various processes included in the present disclosure. The exposure control processor 210 manages the overall control of the exposure apparatus 200, and transmits and receives various data and signals to and from the laser control processor 130.

[0017] 1.2.2 Operation The exposure control processor 210 sets various parameters related to exposure conditions and controls the illumination optical system 201 and the projection optical system 202 .

[0018] The exposure control processor 210 transmits data on the target wavelength value and a trigger signal to the laser control processor 130. The laser control processor 130 controls the laser device 100 in accordance with this data and signal.

[0019] The exposure control processor 210 synchronizes the reticle stage RT and the workpiece table WT and translates them in opposite directions, thereby exposing the workpiece to laser light that reflects the reticle pattern.

[0020] The reticle pattern is transferred onto the semiconductor wafer through this exposure process, after which electronic devices can be manufactured through multiple processes.

[0021] 2, the laser apparatus 100 includes, in addition to the laser control processor 130, a laser oscillator MO, first to fourth optical pulse stretchers OPS1 to OPS4, and a monitor module 17. The laser oscillator MO includes a laser chamber 10, a pulse power module (PPM) 12, a line narrowing module 14, and an output coupling mirror 15. The line narrowing module 14 and the output coupling mirror 15 form an optical resonator.

[0022] The laser chamber 10 is disposed in the optical path of the optical resonator and is provided with windows 10a and 10b.

[0023] The laser chamber 10 has a pair of electrodes 11a and 11b therein and further contains a laser gas containing components of a laser medium. ２ , ArF, KrF, XeCl, or XeF.

[0024] The direction of the optical path axis of the optical resonator is defined as the Z direction or the −Z direction. The direction of discharge between electrodes 11a and 11b is defined as the V direction or the −V direction. The Z direction and the V direction are perpendicular to each other, and the direction perpendicular to both of these directions is defined as the H direction or the −H direction.

[0025] The pulse power module 12 includes a switch (not shown) and is connected to a charger (not shown).

[0026] The line narrowing module 14 includes a plurality of prisms and a grating, not shown. Light emitted from the window 10a of the laser chamber 10 passes through the prisms and enters the grating. The grating is in a Littrow configuration so that the angle of incidence of light entering the grating from the prism matches the angle of diffraction of diffracted light of the desired wavelength. The diffracted light of the desired wavelength passes through the prism again and enters the laser chamber 10 via the window 10a. Changing the orientation of at least one prism changes the angle of incidence of the light entering the grating, thereby changing the wavelength selected by the line narrowing module 14.

[0027] The output coupling mirror 15 is composed of a partial reflection mirror. A first optical pulse stretcher OPS1 is disposed in the optical path of the first pulse laser beam B1 output from the output coupling mirror 15. A second optical pulse stretcher OPS2 is disposed in the optical path of the second pulse laser beam B2 output from the first optical pulse stretcher OPS1. A third optical pulse stretcher OPS3 is disposed in the optical path of the third pulse laser beam B3 output from the second optical pulse stretcher OPS2. A fourth optical pulse stretcher OPS4 is disposed in the optical path of the fourth pulse laser beam B4 output from the third optical pulse stretcher OPS3.

[0028] A beam splitter 16 is disposed in the optical path of the fifth pulsed laser beam B5 output from the fourth optical pulse stretcher OPS4. The beam splitter 16 transmits a portion of the fifth pulsed laser beam B5 with high transmittance and reflects the other portion. The fifth pulsed laser beam B5 transmitted through the beam splitter 16 enters the exposure device 200 as a laser beam, and the fifth pulsed laser beam B5 reflected by the beam splitter 16 enters the monitor module 17.

[0029] The laser control processor 130 is a processing device that includes a memory 132 that stores a control program and a CPU 131 that executes the control program. The laser control processor 130 is specially configured or programmed to perform the various processes included in this disclosure.

[0030] 1.3.2 Operation The laser control processor 130 acquires data on the wavelength target value from the exposure control processor 210. The laser control processor 130 transmits an initial setting signal to the line narrowing module 14 based on the wavelength target value. After the output of the laser light starts, the laser control processor 130 receives wavelength measurement data from the monitor module 17 and transmits a feedback control signal to the line narrowing module 14 based on the wavelength target value and the wavelength measurement data.

[0031] The laser control processor 130 receives a trigger signal from the exposure control processor 210. The laser control processor 130 transmits an oscillation trigger signal based on the trigger signal to the switch of the pulse power module 12.

[0032] The switch is turned on when it receives an oscillation trigger signal from the laser control processor 130. When the switch is turned on, the pulse power module 12 generates a pulsed high voltage from the electrical energy stored in the charger. The pulse power module 12 applies this high voltage to the electrode 11a.

[0033] When a high voltage is applied to the electrode 11a, a discharge occurs between the electrodes 11a and 11b. The energy of this discharge excites the laser gas in the laser chamber 10 and causes it to transition to a higher energy level. When the excited laser gas subsequently transitions to a lower energy level, it emits light with a wavelength corresponding to the difference in energy levels.

[0034] Light generated within the laser chamber 10 is emitted to the outside of the laser chamber 10 through windows 10a and 10b. The light emitted from the window 10a is incident on the line narrowing module 14. Of the light incident on the line narrowing module 14, light having a wavelength near the desired wavelength is reflected by the line narrowing module 14 and returned to the laser chamber 10.

[0035] The output coupling mirror 15 transmits and outputs a portion of the light emitted from the window 10 b , and reflects the other portion back into the laser chamber 10 .

[0036] In this way, the light emitted from the laser chamber 10 travels back and forth between the line-narrowing module 14 and the output-coupling mirror 15. This light is amplified each time it passes through the discharge space between the electrodes 11a and 11b. The light thus laser-oscillated and line-narrowed is output from the output-coupling mirror 15 as a first pulsed laser beam B1. The first to fourth optical pulse stretchers OPS1 to OPS4 extend the pulse time widths of the first to fourth pulsed laser beams B1 to B4, respectively, and emit them as second to fifth pulsed laser beams B2 to B5. The fifth pulsed laser beam B5 enters the exposure apparatus 200 as a laser beam via the beam splitter 16.

[0037] 1.4 Speckle Speckle is a speckle of light and dark that occurs when laser light is scattered in a random medium and the scattered light interferes with each other. An image of these speckles is called a speckle image. The speckle contrast SC, expressed by the following formula, is used as an index for evaluating speckle: SC = σ(I) / Avg(I)

[0038] σ(I) is the standard deviation of the intensity I in the speckle image, and Avg(I) is the average value of the intensity I in the speckle image.

[0039] Speckles become noise in the exposure apparatus 200, and high speckle contrast can deteriorate exposure performance. In order to reduce the speckle contrast, it is necessary to reduce both the temporal overlap and the spatial overlap of the pulsed laser beams. A method using an optical pulse stretcher is known to reduce both the temporal overlap and the spatial overlap of the pulsed laser beams.

[0040] 1.5 Examples of Optical Pulse Stretcher 1.5.1 Optical Pulse Stretcher that Shifts the Propagation Direction of Circulating Light in the V Direction Figure 3 shows a schematic diagram of an example of an optical pulse stretcher that shifts the propagation direction of circulating light in the V direction. The fourth optical pulse stretcher OPS4 shown in Figure 3 includes a beam splitter 184a, concave mirrors 184b to 184e, and an actuator 184f. Note that Figure 3 is just one example, and the fourth optical pulse stretcher OPS4 described with reference to Figure 2 does not necessarily have to be exactly as shown in Figure 3, or any of the first to third optical pulse stretchers OPS1 to OPS3 may be the same as that shown in Figure 3.

[0041] The beam splitter 184a is disposed in the optical path of the fourth pulsed laser beam B4. The reflectivity of the beam splitter 184a is, for example, 60%. The fourth pulsed laser beam B4 is incident on a first surface of the beam splitter 184a, and the beam splitter 184a transmits a portion of the fourth pulsed laser beam B4 as transmitted light B50 and reflects the other portion as light B41. The transmitted light B50 corresponds to the fourth transmitted light described below. The concave mirrors 184b, 184c, 184d, and 184e are spherical mirrors and are disposed in this order in the optical path of the light B41 reflected by the beam splitter 184a. The concave mirrors 184b to 184e form a loop-shaped delay optical path. The concave mirrors 184b to 184e sequentially reflect the light B41 and cause it to be incident on the second surface of the beam splitter 184a.

[0042] The beam splitter 184a reflects a portion of the light B41 as a first-circuit light B51 and transmits the other portion as light B42. The first-circuit light B51 corresponds to a fourth first-circuit light described below. The concave mirrors 184b to 184e sequentially reflect the light B42 and cause it to be incident on the second surface of the beam splitter 184a.

[0043] The beam splitter 184a reflects a portion of the light B42 as a twice-circulating light B52.

[0044] In this way, the transmitted light B50, the first-circulation light B51, and the second-circulation light B52 are output from the fourth optical pulse stretcher OPS4. At this time, the concave mirrors 184b to 184e are arranged so that the transmitted light B50, the first-circulation light B51, and the second-circulation light B52 branch off as beams whose optical path axes are shifted from one another in the V direction. The actuator 184f may be configured to change the position or attitude of the concave mirror 184e, thereby finely adjusting the amount of shift in the V direction of the first-circulation light B51 and the second-circulation light B52 relative to the transmitted light B50.

[0045] Fig. 4 shows the pulse time waveform of a fourth pulsed laser beam B4 incident on the optical pulse stretcher shown in Fig. 3, and Fig. 5 shows the pulse time waveform of a fifth pulsed laser beam B5 emitted from the optical pulse stretcher shown in Fig. 3. The horizontal axes of Figs. 4 and 5 represent time t. The pulse time waveform of the fifth pulsed laser beam B5 is given as a composite waveform of the pulse time waveforms of the transmitted beam B50, the once-circumnavigation beam B51, and the twice-circumnavigation beam B52.

[0046] The transmitted light B50 and the first-circulation light B51 have lower peak intensities and smaller pulse energies than the fourth pulsed laser light B4. The second-circulation light B52 has lower peak intensities and smaller pulse energies than both the transmitted light B50 and the first-circulation light B51. Another portion of the light B42 passes through the beam splitter 184a and may become a third-circulation light (not shown) via the concave mirrors 184b to 184e and the beam splitter 184a, but this light has lower peak intensity and smaller pulse energy than the second-circulation light B52.

[0047] The branched transmitted light B50, the first-circuit light B51, and the second-circuit light B52 are superimposed at different timings, thereby reducing temporal overlap of the pulsed laser beams. Also, the fifth pulsed laser beam B5 has a pulse duration extended more than that of the fourth pulsed laser beam B4.

[0048] 1.5.2 Optical Pulse Stretcher that Shifts the Propagation Direction of Circulating Light in the H Direction Figure 6 shows a schematic diagram of an example of an optical pulse stretcher that shifts the propagation direction of circulating light in the H direction. The first optical pulse stretcher OPS1 shown in Figure 6 includes a beam splitter 181a, concave mirrors 181b to 181e, and an actuator 181f. Note that Figure 6 is just one example, and the first optical pulse stretcher OPS1 described with reference to Figure 2 does not necessarily have to be exactly as shown in Figure 6, or any of the second to fourth optical pulse stretchers OPS2 to OPS4 may be similar to that shown in Figure 6.

[0049] The beam splitter 181a, concave mirrors 181b to 181e, and actuator 181f have the same configuration as the beam splitter 184a, concave mirrors 184b to 184e, and actuator 184f described with reference to FIG.

[0050] The first pulsed laser beam B1 is incident on a first surface of the beam splitter 181a, which transmits a portion of the first pulsed laser beam B1 as transmitted light B20 and reflects another portion as light B11. The transmitted light B20 corresponds to the first transmitted light described below. The concave mirrors 181b to 181e sequentially reflect the light B11 and cause it to be incident on a second surface of the beam splitter 181a.

[0051] The beam splitter 181a reflects a portion of the light B11 as a first circular light B21 and transmits the other portion as light B12. The first circular light B21 corresponds to a first first circular light described below. The concave mirrors 181b to 181e sequentially reflect the light B12 and cause it to be incident on a second surface of the beam splitter 181a.

[0052] The beam splitter 181a reflects a part of the light B12 as a twice-circulating light B22.

[0053] In this way, the transmitted light B20, the first-circulation light B21, and the second-circulation light B22 are output from the first optical pulse stretcher OPS1 as the second pulse laser light B2. At this time, the concave mirrors 181b to 181e are arranged so that the transmitted light B20, the first-circulation light B21, and the second-circulation light B22 branch off as beams whose optical path axes are shifted from one another in the H direction. The actuator 181f may be configured to change the position or attitude of the concave mirror 181e, thereby finely adjusting the amount of shift in the H direction of the first-circulation light B21 and the second-circulation light B22 relative to the transmitted light B20.

[0054] FIG. 7 shows the beam cross-sectional shape of the second pulsed laser beam B2 emitted from the optical pulse stretcher shown in FIG. 6 . The beam cross-sectional shape of the transmitted beam B20 is a rectangle elongated in the V direction, corresponding to the shape of the discharge space between the electrodes 11a and 11b. The concave mirrors 181b to 181e are designed so that the once-circumnavigated beam B21 and the twice-circumnavigated beam B22 also have similar cross-sectional shapes. In the second pulsed laser beam B2, the beam cross-sections of the transmitted beam B20, the once-circumnavigated beam B21, and the twice-circumnavigated beam B22 are shifted in the H direction so that they partially overlap spatially with one another, thereby reducing spatial overlap of the pulsed laser beams. Methods for reducing spatial overlap include shifting the traveling direction of the circulating beam as shown in FIG. 6 and shifting the emission position of the circulating beam as will be described later with reference to FIG. 16 .

[0055] The pulse time waveform of the first pulsed laser beam B1 and the pulse time waveform of the second pulsed laser beam B2 are not shown in the drawings. By overlapping the branched transmitted beam B20, the first circulation beam B21, and the second circulation beam B22 with shifted timings, the temporal overlap of the pulsed laser beams is reduced, as in the case described with reference to FIGS.

[0056] In addition, in the fourth optical pulse stretcher OPS4 shown in FIG. 3, the beam cross sections of the transmitted light B50, the first-circumvention light B51, and the second-circumvention light B52 are shifted so that they partially overlap spatially with one another, thereby reducing spatial overlap of the pulsed laser beams, as in the case described with reference to FIG. 7, but differing from FIG. 3 in that the beam cross sections are shifted in the V direction.

[0057] 1.6 Issues with the Comparative Example As described above, speckle contrast can be reduced by using an optical pulse stretcher to reduce both the temporal overlap and the spatial overlap of pulsed laser beams. However, when multiple optical pulse stretchers are arranged in the optical path of pulsed laser beams, it is not known how to shift the transmitted light and the circulating light in each optical pulse stretcher to efficiently reduce speckle contrast. The embodiments described in the present disclosure relate to efficiently reducing speckle contrast using multiple optical pulse stretchers.

[0058] Fig. 8 shows an example of the deviation of the optical path caused by the first and second optical pulse stretchers OPS1 and OPS2. In Fig. 8, the first deviation amount in the H direction caused by one revolution of the first optical pulse stretcher OPS1 and the second deviation amount in the H direction caused by one revolution of the second optical pulse stretcher OPS2 are both 0.03 mrad.

[0059] In the following description, light contained in the third pulsed laser beam B3 will be represented by P ab in accordance with the following (a) and (b) depending on whether the light has passed through or circulated once in each of the first and second optical pulse stretchers OPS1 and OPS2.

[0060] (a) For the first transmitted light that has passed through the first optical pulse stretcher OPS1, a=0, and for the first single-circulation light that has circulated once in the first optical pulse stretcher OPS1, a=1.

[0061] (b) For the second transmitted light that has passed through the second optical pulse stretcher OPS2, b=0, and for the second single-circulation light that has circulated once in the second optical pulse stretcher OPS2, b=1.

[0062] Light that has circulated two or more times in at least one optical pulse stretcher is not considered because its energy is small.

[0063] The total deviation amount of light P00 is set to 0.00 mrad. The total deviation amount of light P10 is 0.03 mrad, which is larger than that of light P00 by one revolution in the first optical pulse stretcher OPS1. The total deviation amount of light P01 is 0.03 mrad, which is larger than that of light P00 by one revolution in the second optical pulse stretcher OPS2. The total deviation amount of light P11 is 0.06 mrad, which is larger than that of light P00 by one revolution each in the first and second optical pulse stretchers OPS1 and OPS2. In this case, light P10 and light P01 have the same total deviation amount of 0.03 mrad and are spatially consistent. In this case, it may not be possible to efficiently reduce the speckle contrast.

[0064] Fig. 9 shows another example of the optical path deviation caused by the first and second optical pulse stretchers OPS1 and OPS2. In Fig. 9, the first deviation amount in the H direction caused by one revolution of the first optical pulse stretcher OPS1 is 0.03 mrad, and the second deviation amount in the H direction caused by one revolution of the second optical pulse stretcher OPS2 is -0.03 mrad, and the absolute values ​​of the first and second deviation amounts are the same but are deviations in opposite directions.

[0065] The total deviation amount of light P00 is 0.00 mrad, while the total deviation amount of light P10 is 0.03 mrad, the total deviation amount of light P01 is -0.03 mrad, and the total deviation amount of light P11 is 0.00 mrad. In this case, the total deviation amounts of light P00 and light P11 are the same at 0.00 mrad and are spatially consistent. In this case, it may not be possible to efficiently reduce the speckle contrast.

[0066] 2. Multiple optical pulse stretchers with different absolute values ​​of optical path deviation 2.1 Principle In order to reduce speckle contrast, it is necessary for the light split and joined by the optical pulse stretcher to have speckle patterns that are independent of each other. A speckle pattern is an intensity distribution obtained by squaring the amplitude distribution of an electric field. Two speckle patterns being independent means that the amplitude distributions of the electric field are orthogonal, that is, the inner product or correlation is 0. When the light split and joined by the optical pulse stretcher has N independent speckle patterns, and the light intensity of the light having these speckle patterns is expressed as i １ , i ２ , ..., i Ｎ When the speckle contrast of the light incident on the optical pulse stretcher is ＩＮ The speckle contrast SC of the light emitted from the optical pulse stretcher ＯＵＴ is reduced to the following value: SC ＯＵＴ =SC ＩＮ × (i １ ２ +i ２ ２ +...+i Ｎ ２ ) １／２ / (i １ +i ２ +...+i Ｎ )

[0067] Light intensity i １ , i ２ , ..., i Ｎ When these are equal to each other, the speckle contrast SC ＯＵＴ SC ＩＮ / (N １／２ ) is reduced to

[0068] For the speckle patterns of optical pulses to be independent of each other, the optical pulses must not overlap in time. If the optical pulses overlap in time, they will simply change into different speckle patterns due to the superposition of electric fields, and this will not lead to a decrease in speckle contrast. This is why the optical pulse stretcher delays part of the light.

[0069] When the light beams branched by the optical pulse stretchers and recombined with a time difference are perfectly coincident in space, the speckle patterns will be exactly the same, and the speckle contrast will not be reduced. When multiple optical pulse stretchers are connected in series, not only is it necessary to spatially shift the transmitted light and circulating light in each optical pulse stretcher, but it is also necessary to take care to spatially shift, for example, the light P01 that has passed through the first optical pulse stretcher OPS1 and circulated in the second optical pulse stretcher OPS2 from the light P10 that has circulated in the first optical pulse stretcher OPS1 and passed through the second optical pulse stretcher OPS2.

[0070] 2.2 First Example Fig. 10 shows a first example of the deviation of the optical path caused by the first and second optical pulse stretchers OPS1 and OPS2 in Embodiment 1. In Fig. 10, the first deviation amount in the H direction caused by one revolution of the first optical pulse stretcher OPS1 is 0.03 mrad, and the second deviation amount in the H direction caused by one revolution of the second optical pulse stretcher OPS2 is 0.06 mrad.

[0071] With respect to the total deviation amount of light P00 being 0.00 mrad, the total deviation amount of light P10 is 0.03 mrad, the total deviation amount of light P01 is 0.06 mrad, and the total deviation amount of light P11 is 0.09 mrad. In this way, by making the second deviation amount different from the first deviation amount, the total deviation amounts of light P00, P10, P01, and P11 become different values, and four mutually shifted optical paths are formed. As a result, light P00, P10, P01, and P11 become light having speckle patterns that are independent of one another. When the light intensities of light P00, P10, P01, and P11 are equal to one another, the speckle contrast is 0.5 times as shown in the following formula, and the speckle contrast can be efficiently reduced. SC ＯＵＴ =SC ＩＮ × (1 ２ +1 ２ +1 ２ +1 ２ ) １／２ / (1+1+1+1) =SC ＩＮ ×0.5

[0072] In contrast to this, in the example described with reference to Figure 8, light P10 and light P01 have the same total deviation amount and do not have independent speckle patterns. There are three independent speckle patterns: light P00, light obtained by superimposing light P10 and P01, and light P11. In this case, the speckle contrast is 0.61 times as calculated from the following formula, and the effect of reducing the speckle contrast may be insufficient. SC ＯＵＴ =SC ＩＮ × (1 ２ +2 ２ +1 ２ ) １／２ / (1+2+1) =SC ＩＮ ×0.61

[0073] In the example described with reference to FIG. 9, the total amount of deviation between the light P00 and the light P11 is the same, so the effect of reducing the speckle contrast may be insufficient.

[0074] 2.3 Second Example Fig. 11 shows a second example of the deviation of the optical path caused by the first and second optical pulse stretchers OPS1 and OPS2 in Embodiment 1. In Fig. 11, the first deviation amount in the H direction caused by one revolution of the first optical pulse stretcher OPS1 is 0.03 mrad, and the second deviation amount in the H direction caused by one revolution of the second optical pulse stretcher OPS2 is -0.06 mrad.

[0075] The total deviation amount of light P00 is 0.00 mrad, while the total deviation amount of light P10 is 0.03 mrad, the total deviation amount of light P01 is −0.06 mrad, and the total deviation amount of light P11 is −0.03 mrad, so that four mutually shifted optical paths are formed. In this way, by making the second deviation amount different from the first deviation amount, the total deviation amounts of light P00, P10, P01, and P11 are different from one another, and speckle contrast can be efficiently reduced.

[0076] As can be seen from the explanations of FIGS. 8 to 11, the first and second deviation amounts only need to have different absolute values, and the signs of the deviation amounts may be either positive or negative.

[0077] The second deviation amount is preferably larger than the first deviation amount. Furthermore, the second deviation amount is preferably at least twice the first deviation amount. However, in the present disclosure, "at least twice" does not mean the strict numerical value of 2.0 times or more, but includes, for example, 1.9 times or more.

[0078] Since it is necessary to shift the light P00, P10, P01, and P11 not only spatially but also temporally, it is desirable that the optical path lengths of the delay optical paths of the first and second optical pulse stretchers OPS1 and OPS2 are different from each other. Furthermore, when the optical path is shifted by shifting the traveling direction of the circulating light, the longer the optical path length of the delay optical path, the greater the optical path position shift may become. Furthermore, increasing the optical path shift amount in the upstream optical pulse stretcher may increase the optical path position shift in the downstream optical pulse stretcher. Therefore, it is desirable that the optical path shift amount of the first optical pulse stretcher OPS1 located in the upstream stage is smaller than that of the second optical pulse stretcher OPS2 located in the downstream stage.

[0079] 2.4 Third Example Fig. 12 shows an example of optical path deviations caused by the first to third optical pulse stretchers OPS1 to OPS3 in Embodiment 1. In Fig. 12, the first deviation amount in the H direction caused by one revolution of the first optical pulse stretcher OPS1 is 0.03 mrad, the second deviation amount in the H direction caused by one revolution of the second optical pulse stretcher OPS2 is 0.06 mrad, and the third deviation amount in the H direction caused by one revolution of the third optical pulse stretcher OPS3 is 0.12 mrad.

[0080] The light contained in the fourth pulsed laser beam B4 is represented by Pabc depending on whether it has passed through or circulated once in each of the first to third optical pulse stretchers OPS1 to OPS3.

[0081] a and b are as described above in (a) and (b).

[0082] (c) For the third transmitted light that has passed through the third optical pulse stretcher OPS3, c=0, and for the third single-circulation light that has circulated once in the third optical pulse stretcher OPS3, c=1.

[0083] The total shift amount of light P100, P010, P110, P001, P101, P011, and P111 increases by 0.03 mrad in this order relative to the total shift amount of light P000, which is 0.00 mrad, and eight mutually shifted optical paths are formed. In this way, by making the first to third shift amounts due to each one revolution in the first to third optical pulse stretchers OPS1 to OPS3 different from one another, it is possible to efficiently reduce speckle contrast.

[0084] The third deviation amount is preferably larger than the second deviation amount. Also, the third deviation amount is preferably at least twice the second deviation amount. In particular, by doubling the second and third deviation amounts, the difference between the total deviation amounts can be made approximately equal.

[0085] Since it is necessary to shift the light P100, P010, P110, P001, P101, P011, and P111 not only spatially but also temporally, it is desirable that the optical path lengths of the delay optical paths of the first to third optical pulse stretchers OPS1 to OPS3 are different from one another. Also, it is desirable that the amount of shift in the optical path of an optical pulse stretcher located in the earlier stage is smaller.

[0086] 2.5 Fourth Example Fig. 13 shows an example of optical path deviations caused by the first to fourth optical pulse stretchers OPS1 to OPS4 in Embodiment 1. In Fig. 13, the first deviation amount in the H direction caused by one revolution of the first optical pulse stretcher OPS1 is 0.03 mrad, the second deviation amount in the H direction caused by one revolution of the second optical pulse stretcher OPS2 is 0.06 mrad, the third deviation amount in the H direction caused by one revolution of the third optical pulse stretcher OPS3 is 0.12 mrad, and the fourth deviation amount in the H direction caused by one revolution of the fourth optical pulse stretcher OPS4 is 0.24 mrad.

[0087] The light contained in the fifth pulsed laser beam B5 is represented by Pabcd depending on whether it has passed through or circulated once in each of the first to fourth optical pulse stretchers OPS1 to OPS4.

[0088] Regarding a to c, the same applies as above (a) to (c).

[0089] (d) For the fourth transmitted light that has passed through the fourth optical pulse stretcher OPS4, d=0, and for the fourth single-circulation light that has circulated once in the fourth optical pulse stretcher OPS4, d=1.

[0090] With respect to the total shift amount of 0.00 mrad for light P0000, the total shift amounts of light P1000, P0100, P1100, P0010, P1010, P0110, P1110, P1001, P0101, P1101, P0011, P1011, P0111, and P1111 increase by 0.03 mrad in this order, forming 16 mutually shifted optical paths. In this way, by making the first to fourth shift amounts due to each one revolution in the first to fourth optical pulse stretchers OPS1 to OPS4 different from one another, speckle contrast can be efficiently reduced.

[0091] The fourth deviation amount is preferably larger than the third deviation amount. Also, the fourth deviation amount is preferably at least twice as large as the third deviation amount. In particular, by doubling the second, third, and fourth deviation amounts, the differences in the total deviation amounts can be made approximately equal.

[0092] Since it is necessary to shift the light P1000, P0100, P1100, P0010, P1010, P0110, P1110, P1001, P0101, P1101, P0011, P1011, P0111, and P1111 not only spatially but also temporally, it is desirable that the optical path lengths of the delay optical paths of the first to fourth optical pulse stretchers OPS1 to OPS4 are different from one another. Also, it is desirable that the amount of shift in the optical path is smaller for an optical pulse stretcher located in an earlier stage.

[0093] 14 is a graph showing the results of simulating the relationship between the amount of deviation of the optical path due to one revolution in the optical pulse stretcher and the correlation between the speckle patterns of the transmitted light and the light that has made one revolution. The amount of deviation of the optical path is represented on the horizontal axis as the angle between the optical path axes of the transmitted light and the light that has made one revolution.

[0094] To simulate a speckle pattern, first simulate the electric field of the laser light. As described in X. Xiao et al., Optics Express Vol. 14 No. 16, 6989 (2006), the electric field of multimode laser light can be calculated using Monte Carlo simulation. Next, the speckle pattern is calculated from the electric field. The speckle pattern can be calculated using the method described in Appendix G of J.W. Goodman, "Speckle phenomena in optics," Second edition.

[0095] The speckle patterns of the transmitted light and the single-circulation light are respectively represented by I １ and I ２ Then, the correlation of the speckle pattern ρ １，２ can be calculated using the following formula: １，２ = {Avg(I １ I ２ )-Avg(I １ ) Avg(I ２ )} / [Avg[{I １ -Avg(I １ ) ２ ]Avg[{I ２ -Avg(I ２ ) ２ ]] １／２

[0096] Correlation ρ １，２ If ρ is 1, the two speckle patterns are identical and the speckle contrast is not reduced at all. １，２ When is 0, there is no correlation and the speckle contrast reduction effect is the highest.

[0097] The conditions of the light incident on the optical pulse stretcher are as follows: Beam width in the H direction BPH = 6 mm Beam width in the V direction BPV = 12 mm Beam divergence in the H direction BDH = 0.4 mrad Beam divergence in the V direction BDV = 1.0 mrad ２ Value M ２ H=12.4 M in V direction ２ Value M ２V=62

[0098] As shown in FIG. 14 , when the deviation amount of the optical path increases from 0, the correlation of the speckle pattern drops sharply, and after the correlation of the speckle pattern reaches near 0, the correlation of the speckle pattern changes gently around 0 even if the deviation amount of the optical path increases further.

[0099] Considering the amount of deviation of the optical path in the H direction, the correlation of the speckle pattern first becomes close to 0 when the amount of deviation is set to 0.032 mrad. This value is ２ It is almost identical to H.

[0100] Considering the amount of deviation of the optical path in the V direction, the correlation of the speckle pattern first becomes close to 0 when the amount of deviation is set to 0.016 mrad. This value is ２ It is almost identical to V.

[0101] From the above, the guideline for the amount of deviation of the optical path in the H direction required to reduce the speckle contrast is BDH / M ２ H, and the deviation of the optical path in the V direction is BDV / M ２ The V direction will be further explained with reference to FIG.

[0102] 10 and 11, the amount of deviation of the optical path in each optical pulse stretcher is set so that the total amount of deviation of the lights P00, P10, P01, and P11 increases by 0.03 mrad when arranged from smallest to largest. This reduces the correlation of the speckle patterns, thereby efficiently reducing the speckle contrast.

[0103] 12, the total shift amount of the light beams P100, P010, P110, P001, P101, P011, and P111 increases by 0.03 mrad in this order. Also in FIG. 13, the total shift amount of the light beams P1000, P0100, P1100, P0010, P1010, P0110, P1110, P1001, P0101, P1101, P0011, P1011, P0111, and P1111 increases by 0.03 mrad in this order. In these cases as well, the speckle contrast can be reduced efficiently.

[0104] It has been stated that the deviation of the optical path in the H direction is set to 0.03 mrad in order to make the correlation of the speckle pattern almost zero, but the deviation of the optical path may be set smaller than this as long as the correlation of the speckle pattern is a sufficiently low value. On the other hand, if the deviation of the optical path is too large, the beam quality will deteriorate. ２ Value M ２ Since H is in the range of 10 to 20, the amount of deviation of the optical path in the H direction of the optical pulse stretcher having the smallest amount of deviation among the multiple optical pulse stretchers may be between 1 / 20 and 1 / 10 of the beam divergence BDH in the H direction.

[0105] Of the plurality of optical pulse stretchers, the optical pulse stretcher having the largest amount of optical path deviation in the H direction preferably has an amount of deviation that is less than the beam divergence BDH in the H direction.

[0106] The difference between the total amount of deviation in the H direction of each of the light beams P100, P010, P110, P001, P101, P011, and P111 shown in Fig. 12 and the total amount of deviation in the H direction of the other light beams is preferably equal to or greater than one-twentieth of the beam divergence BDH in the H direction. The difference between the total amount of deviation in the H direction of each of the light beams P1000, P0100, P1100, P0010, P1010, P0110, P1110, P1001, P0101, P1101, P0011, P1011, P0111, and P1111 shown in Fig. 13 and the total amount of deviation in the H direction of the other light beams is preferably equal to or greater than one-twentieth of the beam divergence BDH in the H direction.

[0107] 2.7 Operation According to the first embodiment, the laser device 100 includes a laser oscillator MO, a first optical pulse stretcher OPS1, and a second optical pulse stretcher OPS2. The laser oscillator MO includes an optical resonator and a pair of electrodes 11a and 11b that apply a voltage to a laser gas to generate a discharge, and outputs a first pulsed laser beam B1. The first optical pulse stretcher OPS1 is disposed in the optical path of the first pulsed laser beam B1 and transmits a portion of the first pulsed laser beam B1 and causes the other portion to circulate once, thereby outputting a first transmitted beam and a first one-time circulating beam, thereby outputting a second pulsed laser beam B2 in which the pulse time width of the first pulsed laser beam B1 is stretched. The first optical pulse stretcher OPS1 is configured such that the optical paths of the first transmitted beam and the first one-time circulating beam spatially overlap with each other by a first amount of deviation in a first direction. The second optical pulse stretcher OPS2 is arranged in the optical path of the second pulsed laser beam B2, and transmits a part of the second pulsed laser beam B2 and causes the other part to circulate once, thereby outputting a second transmitted beam and a second one-time circulating beam, thereby outputting a third pulsed laser beam B3 having a stretched pulse time width of the second pulsed laser beam B2. The second optical pulse stretcher OPS2 is configured so that the optical paths of the second transmitted beam and the second one-time circulating beam spatially partially overlap with each other in a first direction, with a second shift amount different from the first shift amount.

[0108] Even if multiple optical pulse stretchers are connected in series and the optical path is shifted by each optical pulse stretcher, the optical path shifts may cancel each other out if the amount of shift in the optical path in the multiple optical pulse stretchers is the same. By making the shift amounts different, the possibility of the optical path shifts caused by the multiple optical pulse stretchers cancel each other out is reduced, and speckle is effectively reduced.

[0109] According to the first embodiment, the second deviation amount is greater than the first deviation amount.

[0110] According to this, by reducing the deviation of the optical path in the upstream optical pulse stretcher, it is possible to prevent the beam from expanding too much when it is output from the laser device 100.

[0111] According to the first embodiment, the second deviation amount is at least twice the first deviation amount.

[0112] According to this, by making the amount of optical path deviation in the optical pulse stretcher at the latter stage at least twice that of the former stage, it is possible to prevent the optical path deviations caused by multiple optical pulse stretchers from being canceled out, and to more effectively reduce speckle.

[0113] According to the first embodiment, the laser device 100 includes a third optical pulse stretcher OPS3 that is disposed in an optical path of a third pulsed laser beam B3, transmits a part of the third pulsed laser beam B3 and causes another part of the third pulsed laser beam B3 to circulate once, thereby outputting a third transmitted beam and a third one-time circulating beam, and thereby outputs a fourth pulsed laser beam B4 obtained by stretching the pulse time width of the third pulsed laser beam B3. The third optical pulse stretcher OPS3 is configured so that the optical paths of the third transmitted beam and the third one-time circulating beam spatially partially overlap with each other in a first direction, with a third shift amount different from both the first and second shift amounts.

[0114] According to this, by connecting three or more optical pulse stretchers in series, each having a different amount of deviation from the other in the optical path, speckles can be further reduced.

[0115] According to the first embodiment, when light contained in the fourth pulse laser beam B4 is represented by Pabc, the optical paths of the light P000, P100, P010, P110, P001, P101, P011, and P111 are shifted from one another depending on whether the light has been transmitted through or circulated once in the first, second, and third optical pulse stretchers OPS1, OPS2, and OPS3, respectively. Here, the first transmitted light is represented by a=0, the first once-circulated light is represented by a=1, the second transmitted light is represented by b=0, the second once-circulated light is represented by b=1, the third transmitted light is represented by c=0, and the third once-circulated light is represented by c=1.

[0116] According to this, the light contained in the fourth pulsed laser beam B4 has eight optical paths that are shifted from one another, so that speckles can be effectively reduced.

[0117] According to the first embodiment, the second deviation amount is at least twice the first deviation amount, and the third deviation amount is at least twice the second deviation amount.

[0118] According to this, by setting the third shift amount in the third optical pulse stretcher OPS3 to be at least twice the second shift amount in the second optical pulse stretcher OPS2, it is possible to prevent the shifts of the optical paths caused by the multiple optical pulse stretchers from being canceled out, and to more effectively reduce speckles.

[0119] According to the first embodiment, the laser device 100 includes a fourth optical pulse stretcher OPS4 disposed in the optical path of a fourth pulsed laser beam B4, which transmits a portion of the fourth pulsed laser beam B4 and causes another portion of the fourth pulsed laser beam B4 to circulate once, thereby outputting a fourth transmitted beam and a fourth once-circulated beam, thereby outputting a fifth pulsed laser beam B5 obtained by stretching the pulse time width of the fourth pulsed laser beam B4. The fourth optical pulse stretcher OPS4 is configured such that the optical paths of the fourth transmitted beam and the fourth once-circulated beam spatially overlap with each other by a fourth shift amount in the first direction. The fourth shift amount is at least twice the third shift amount.

[0120] According to this, by setting the fourth shift amount in the fourth optical pulse stretcher OPS4 to be at least twice the third shift amount in the third optical pulse stretcher OPS3, speckles can be reduced more effectively.

[0121] According to the first embodiment, the first direction is the H direction perpendicular to both the discharge direction and the direction of the optical path axis of the optical resonator.

[0122] The first pulsed laser beam B1 is directed in the H direction perpendicular to the discharge direction. ２ Value M ２ M in the V direction parallel to the discharge direction rather than H ２ Value M ２ The beam quality is low due to a large V. By shifting the optical path in the H direction and lowering the beam quality in the H direction, the anisotropy of the beam quality can be alleviated and the deterioration of the beam quality in the V direction can be suppressed.

[0123] According to the first embodiment, the deviation of the optical paths between the second transmitted light and the second one-time circular travel light and the deviation of the optical paths between the first transmitted light and the first one-time circular travel light each include a deviation in the traveling direction of the light, and further, the smaller of the second deviation amount and the first deviation amount is equal to or greater than one-twentieth and equal to or less than one-tenth of the beam divergence BDH of the first pulsed laser beam B1 in the first direction.

[0124] According to this, by setting the amount of deviation of the optical path so that the correlation of the speckle pattern becomes low, speckle can be effectively reduced.

[0125] According to the first embodiment, the larger of the second shift amount and the first shift amount is less than the beam divergence BDH of the first pulsed laser beam B1 in the first direction.

[0126] According to this, by overlapping parts of the beams, speckles can be reduced and excessive beam broadening and deterioration of beam quality can be suppressed.

[0127] According to the first embodiment, the laser device 100 includes a third optical pulse stretcher OPS3 that is disposed in the optical path of a third pulsed laser beam B3, transmits a part of the third pulsed laser beam B3 and causes another part of the third pulsed laser beam B3 to circulate once, thereby outputting a third transmitted beam and a third one-time circulating beam, and thereby outputs a fourth pulsed laser beam B4 obtained by stretching the pulse time width of the third pulsed laser beam B3. The third optical pulse stretcher OPS3 is configured so that the optical paths of the third transmitted beam and the third one-time circulating beam spatially partially overlap each other. When light contained in the fourth pulse laser beam B4 is represented by Pabc depending on whether the light has passed through or circulated once in each of the first, second, and third optical pulse stretchers OPS1, OPS2, and OPS3, a difference between a total shift amount in the first direction of the optical paths of the light beams P000, P100, P010, P110, P001, P101, P011, and P111 and a total shift amount in the first direction of the other optical paths is equal to or greater than one-twentieth of a beam divergence BDH in the first direction of the first pulse laser beam B1. Here, the first transmitted light is represented by a=0, the first one-circuit circulating light is represented by a=1, the second transmitted light is represented by b=0, the second one-circuit circulating light is represented by b=1, the third transmitted light is represented by c=0, and the third one-circuit circulating light is represented by c=1.

[0128] This makes it possible to reduce the correlation between the eight types of speckle patterns of light.

[0129] In other respects, the first embodiment is similar to the comparative example.

[0130] 3. Optical pulse stretcher that shifts the optical path in the V direction 3.1 Configuration Fig. 15 shows an example of optical path shifts caused by the first to fourth optical pulse stretchers OPS1 to OPS4 in the second embodiment. Fig. 15 shows the first to fourth shift amounts and directions of shifts caused by each rotation in the first to fourth optical pulse stretchers OPS1 to OPS4. The difference is that in Fig. 13, the fourth optical pulse stretcher OPS4 shifts the optical path in the H direction, whereas in Fig. 15, the fourth optical pulse stretcher OPS4 shifts the optical path in the V direction.

[0131] 15 shows a case where the fourth optical pulse stretcher OPS4 shifts the optical path in the V direction, but the present disclosure is not limited to this. In Fig. 15, the fourth optical pulse stretcher OPS4 may be removed, and instead, an optical pulse stretcher (not shown) that shifts the optical path in the V direction may be disposed between the output coupling mirror 15 and the first optical pulse stretcher OPS1, or between the first optical pulse stretcher OPS1 and the second optical pulse stretcher OPS2, or between the second optical pulse stretcher OPS2 and the third optical pulse stretcher OPS3.

[0132] As explained with reference to FIG. 14, the deviation of the optical path in the V direction required to reduce the speckle contrast is estimated as BDV / M ２ V, which is approximately 0.016 mrad. Therefore, it is preferable to shift the optical path in the V direction by approximately 0.016 mrad, for example, 0.02 mrad. The shift amount of the optical pulse stretcher that shifts the optical path in the V direction may be smaller than the shift amount of any of the multiple optical pulse stretchers that shift the optical path in the H direction.

[0133] As shown in FIG. 14, in an excimer laser device, the M ２ Value M ２ M in V direction rather than H ２ Value M ２ In this case, V is large, and the beam quality in the V direction is lower than that in the H direction. If an optical path shift is imparted in the V direction by an optical pulse stretcher, the beam quality in the V direction will be further reduced. Therefore, it is desirable to reduce the number of optical pulse stretchers that impart optical path shifts in the V direction compared to the number of optical pulse stretchers that impart optical path shifts in the H direction. For example, when a total of four stages of optical pulse stretchers are used as shown in FIG. 15 , three stages of optical pulse stretchers impart different optical path shifts in the H direction, and one stage of optical pulse stretcher imparts an optical path shift in the V direction. Alternatively, when a total of three stages of optical pulse stretchers are used, two stages of optical pulse stretchers impart different optical path shifts in the H direction, and one stage of optical pulse stretcher imparts an optical path shift in the V direction.

[0134] It has been mentioned that the deviation of the optical path in the V direction is set to 0.02 mrad in order to make the correlation of the speckle pattern almost zero, but the deviation of the optical path may be set smaller than that as long as the correlation of the speckle pattern is a sufficiently low value. On the other hand, if the deviation of the optical path is too large, the beam quality will deteriorate. ２ Value M ２ Since V is in the range of 40 to 80, the deviation of the optical path in the V direction may be between 1 / 80 and 1 / 40 of the beam divergence BDV in the V direction.

[0135] 3.2 Operation According to the second embodiment, the laser device 100 includes a third optical pulse stretcher OPS3 that is disposed in the optical path of a third pulsed laser beam B3 and transmits a portion of the third pulsed laser beam B3 and causes another portion to circulate once, thereby outputting a third transmitted beam and a third one-time circulating beam, thereby outputting a fourth pulsed laser beam B4 obtained by stretching the pulse time width of the third pulsed laser beam B3. The third optical pulse stretcher OPS3 is configured so that the optical paths of the third transmitted beam and the third one-time circulating beam spatially overlap with each other by a third amount of deviation in a second direction. The first direction is an H direction perpendicular to both the direction of discharge and the direction of the optical path axis of the optical resonator, and the second direction is a V direction parallel to the direction of discharge.

[0136] According to this, by shifting and overlapping the beams not only in the H direction but also in the V direction, speckles can be reduced, and excessive beam spread in the H direction and degradation of beam quality can be suppressed. Furthermore, by using fewer optical pulse stretchers that shift the optical path in the V direction than optical pulse stretchers that shift the optical path in the H direction, degradation of beam quality in the V direction can be suppressed.

[0137] According to the second embodiment, the third deviation amount is smaller than both the first and second deviation amounts.

[0138] According to this, by reducing the deviation of the optical path in the V direction, it is possible to suppress the deterioration of the beam quality in the V direction.

[0139] According to the second embodiment, the deviation of the optical paths between the third transmitted light and the third one-time circular travel light, the deviation of the optical paths between the second transmitted light and the second one-time circular travel light, and the deviation of the optical paths between the first transmitted light and the first one-time circular travel light each include a deviation in the traveling direction of the light, and further, the amount of the third deviation is between 1 / 80 and 1 / 40 of the beam divergence BDV of the first pulsed laser beam B1 in the second direction.

[0140] According to this, by setting the amount of deviation in the V direction so that the correlation of the speckle patterns becomes low, speckles can be effectively reduced.

[0141] According to the second embodiment, the laser apparatus 100 includes: a third optical pulse stretcher OPS3 disposed in an optical path of a third pulsed laser beam B3, which transmits a part of the third pulsed laser beam B3 and causes another part of the third pulsed laser beam B3 to circulate once, thereby outputting a third transmitted light and a third once-circulated light, thereby outputting a fourth pulsed laser beam B4 having a stretched pulse time width of the third pulsed laser beam B3; and a fourth optical pulse stretcher OPS4 disposed in an optical path of the fourth pulsed laser beam B4, which transmits a part of the fourth pulsed laser beam B4 and causes the other part of the fourth pulsed laser beam B4 to circulate once, thereby outputting a fourth transmitted light and a fourth once-circulated light, thereby outputting a fifth pulsed laser beam B5 having a stretched pulse time width of the fourth pulsed laser beam B4. The third optical pulse stretcher OPS3 is configured so that the optical path of the third transmitted light and the optical path of the third one-time circulating light spatially partially overlap, and the fourth optical pulse stretcher OPS4 is configured so that the optical path of the fourth transmitted light and the optical path of the fourth one-time circulating light spatially partially overlap. Furthermore, one of the third and fourth optical pulse stretchers OPS3 and OPS4 is configured so that the optical path is shifted in a first direction by a single rotation by an amount different from either the first or second shift amount, and the other is configured so that the optical path is shifted in a second direction by a single rotation, the first direction being an H direction perpendicular to both the direction of discharge and the direction of the optical path axis of the optical resonator, and the second direction being a V direction parallel to the direction of discharge.

[0142] According to this, even when four optical pulse stretchers are used, by shifting and overlapping the beams not only in the H direction but also in the V direction, speckles can be reduced and excessive beam spread in the H direction and degradation of beam quality can be suppressed. Furthermore, by using fewer optical pulse stretchers that shift the optical path in the V direction than the number of optical pulse stretchers that shift the optical path in the H direction, degradation of beam quality in the V direction can be suppressed.

[0143] In other respects, the second embodiment is similar to the first embodiment.

[0144] 4. Optical Pulse Stretcher in Which the Deviation of the Optical Path Includes a Deviation of the Exit Position of Light 4.1 Configuration Fig. 16 schematically illustrates an example of an optical pulse stretcher included in the third embodiment. In the fourth optical pulse stretcher OPS4 described with reference to Fig. 3, the deviation of the optical path includes a deviation in the traveling direction of light, whereas in the fourth optical pulse stretcher OPS4 shown in Fig. 16, the deviation of the optical path includes a deviation in the exit position of light. A fifth pulse laser beam B5 emitted from the fourth optical pulse stretcher OPS4 shown in Fig. 16 may include transmitted light B50, one-time circulation light B51, and two-time circulation light B52, which are parallel to each other. Such deviation of the optical path is achieved by the arrangement of concave mirrors 184b to 184e.

[0145] Although FIG. 16 shows a case where the light emission position is shifted in the V direction, the light emission position may be shifted in the H direction.

[0146] For example, the shift in the optical path in each of the first and second optical pulse stretchers OPS1 and OPS2 may include a shift in the light emission position, and the first and second shift amounts in the first and second optical pulse stretchers OPS1 and OPS2 may be different from each other.

[0147] When the third optical pulse stretcher OPS3 is further provided, the deviation of the optical path in the third optical pulse stretcher OPS3 includes the deviation of the light emission position, and the direction of the deviation may be either the H direction or the V direction.

[0148] When a fourth optical pulse stretcher OPS4 is further provided, the shift of the optical path in each of the third and fourth optical pulse stretchers OPS3 and OPS4 may include a shift in the light emission position. Both the third and fourth optical pulse stretchers OPS3 and OPS4 may shift the optical path in the H direction, or one of them may shift the optical path in the H direction and the other may shift the optical path in the V direction.

[0149] Fig. 17 shows an example of optical path deviations caused by the first to fourth optical pulse stretchers OPS1 to OPS4 in the third embodiment, showing the first to fourth deviation amounts and deviation directions caused by one revolution in each of the first to fourth optical pulse stretchers OPS1 to OPS4.

[0150] In the example shown in FIG. 17 , the first optical pulse stretcher OPS1 shifts the optical path by 0.5 mm in the H direction, the second optical pulse stretcher OPS2 shifts the optical path by 1.0 mm in the H direction, the third optical pulse stretcher OPS3 shifts the optical path by 2.0 mm in the H direction, and the fourth optical pulse stretcher OPS4 shifts the optical path by 0.2 mm in the V direction.

[0151] 18 is a graph showing the results of a simulation of the relationship between the amount of deviation of the optical path due to one revolution in the optical pulse stretcher and the correlation between the speckle patterns of the transmitted light and the light that has made one revolution. The amount of deviation of the optical path is represented on the horizontal axis as the distance between the optical path axes of the transmitted light and the light that has made one revolution, which are parallel to each other. The simulation method and the conditions for the light incident on the optical pulse stretcher are the same as those described with reference to FIG. 14.

[0152] Considering the amount of deviation of the optical path in the H direction, the correlation of the speckle pattern first becomes close to 0 when the deviation is set to 0.48 mm. This value is ２ It is almost identical to H.

[0153] Considering the amount of deviation of the optical path in the V direction, the correlation of the speckle pattern first becomes close to 0 when the deviation is set to 0.18 mm. This value is ２ It is almost identical to V.

[0154] From the above, the guideline for the amount of deviation of the optical path in the H direction required to reduce the speckle contrast is BPH / M ２ H, and the deviation of the optical path in the V direction is BPV / M ２ It's V.

[0155] In Fig. 17, an example is shown in which the amount of deviation of the optical path in the H direction in the first optical pulse stretcher OPS1 is set to 0.5 mm in order to make the correlation of the speckle pattern almost zero, but the amount of deviation of the optical path may be set smaller than that as long as the correlation of the speckle pattern is a sufficiently low value. On the other hand, if the amount of deviation of the optical path is made too large, the beam quality will deteriorate. ２ Value M ２ Since H is in the range of 10 to 20, the amount of deviation of the optical path in the H direction of the optical pulse stretcher having the smallest amount of deviation among the multiple optical pulse stretchers may be between 1 / 20 and 1 / 10 of the beam width BPH in the H direction.

[0156] Of the plurality of optical pulse stretchers, the optical pulse stretcher having the largest optical path deviation in the H direction preferably has a deviation less than the beam width BPH in the H direction.

[0157] When the emission positions of the light beams are shifted in each of the first to third optical pulse stretchers OPS1 to OPS3 in FIG. 12, it is desirable that the difference between the total amount of shift in the H direction of each of the light beams P100, P010, P110, P001, P101, P011, and P111 and the total amount of shift in the H direction of the other light beams be equal to or greater than one-twentieth of the beam width BPH in the H direction. When the emission positions of the light beams are shifted in each of the first to fourth optical pulse stretchers OPS1 to OPS4 in FIG. 13, it is desirable that the difference between the total amount of shift in the H direction of each of the light beams P1000, P0100, P1100, P0010, P1010, P0110, P1110, P1001, P0101, P1101, P0011, P1011, P0111, and P1111 and the total amount of shift in the H direction of the other light beams is equal to or greater than one-twentieth of the beam width BPH in the H direction.

[0158] In Fig. 17, an example is shown in which the deviation amount of the optical path in the V direction in the fourth optical pulse stretcher OPS4 is set to 0.2 mm in order to make the correlation of the speckle pattern almost zero, but the deviation amount of the optical path may be set smaller than that as long as the correlation of the speckle pattern is a sufficiently low value. On the other hand, if the deviation amount of the optical path is made too large, the beam quality will deteriorate. ２ Value M ２ Since V is in the range of 40 to 80, the deviation of the optical path in the V direction may be between 1 / 80 and 1 / 40 of the beam width BPV in the V direction.

[0159] 17 has been described in which four optical pulse stretchers each shift the emission position of light, but some of the four optical pulse stretchers may shift the emission position of light and the remaining may shift the traveling direction of light. Also, one optical pulse stretcher may shift both the emission position and the traveling direction of light.

[0160] According to the third embodiment, the deviation of the optical paths of the second transmitted light and the second one-time circular travel light and the deviation of the optical paths of the first transmitted light and the first one-time circular travel light each include a deviation of the light emission positions. Furthermore, the smaller of the second deviation amount and the first deviation amount is equal to or greater than one-twentieth and equal to or less than one-tenth of the beam width BPH of the first pulsed laser beam B1 in the first direction.

[0161] According to this, by setting the amount of deviation of the optical path so that the correlation of the speckle pattern becomes low, speckle can be effectively reduced.

[0162] According to the third embodiment, the larger of the second shift amount and the first shift amount is less than the beam width BPH of the first pulsed laser beam B1 in the first direction.

[0163] According to this, by overlapping parts of the beams, speckles can be reduced and excessive beam broadening and deterioration of beam quality can be suppressed.

[0164] According to the third embodiment, the laser device 100 includes a third optical pulse stretcher OPS3 that is disposed in the optical path of a third pulsed laser beam B3, transmits a part of the third pulsed laser beam B3 and causes another part of the third pulsed laser beam B3 to circulate once, thereby outputting a third transmitted beam and a third one-time circulating beam, and thereby outputs a fourth pulsed laser beam B4 obtained by stretching the pulse time width of the third pulsed laser beam B3. The third optical pulse stretcher OPS3 is configured so that the optical paths of the third transmitted beam and the third one-time circulating beam spatially partially overlap each other. Furthermore, when light contained in the fourth pulse laser beam B4 is represented by Pabc depending on whether it has transmitted through or circulated once in each of the first, second, and third optical pulse stretchers OPS1, OPS2, and OPS3, a difference between a total shift amount in the first direction of the optical paths of each of the light beams P000, P100, P010, P110, P001, P101, P011, and P111 and a total shift amount in the first direction of the other optical paths is equal to or greater than one-twentieth of the beam width BPH of the first pulse laser beam B1 in the first direction. Here, the first transmitted light is represented by a=0, the first one-circuit circulating light is represented by a=1, the second transmitted light is represented by b=0, the second one-circuit circulating light is represented by b=1, the third transmitted light is represented by c=0, and the third one-circuit circulating light is represented by c=1.

[0165] This makes it possible to reduce the correlation between the eight types of speckle patterns of light.

[0166] According to the third embodiment, the deviation of the optical paths between the third transmitted light and the third one-time circular travel light, the deviation of the optical paths between the second transmitted light and the second one-time circular travel light, and the deviation of the optical paths between the first transmitted light and the first one-time circular travel light each include a deviation of the light emission position. Furthermore, the third deviation amount is between 1 / 80 and 1 / 40 of the beam width BPV of the first pulsed laser beam B1 in the second direction.

[0167] According to this, by setting the amount of deviation of the optical path so that the correlation of the speckle pattern becomes low, speckle can be effectively reduced.

[0168] In other respects, the third embodiment is similar to the first and second embodiments.

[0169] 5. Other 5.1 Modified Examples of Optical Pulse Stretcher Figure 19 schematically shows a first modified example of an optical pulse stretcher. While the fourth optical pulse stretcher OPS4 described with reference to Figure 3 includes an actuator 184f, the fourth optical pulse stretcher OPS4 shown in Figure 19 includes a wedge substrate 184g. The wedge substrate 184g is a plate with two non-parallel flat surfaces and high transmittance, and by changing the traveling direction of light B41, it generates a misalignment in the traveling direction between the transmitted light B50 and the single-circulation light B51. The attitude of the wedge substrate 184g may be changed by an actuator (not shown), allowing fine adjustment of the amount of misalignment in the traveling direction.

[0170] Fig. 20 schematically shows a second modified example of an optical pulse stretcher. While the fourth optical pulse stretcher OPS4 described with reference to Fig. 16 includes an actuator 184f, the fourth optical pulse stretcher OPS4 shown in Fig. 20 includes a plane-parallel substrate 184h. The plane-parallel substrate 184h is a plate having two parallel planes and high transmittance, and shifts the optical path axis of light B41 to cause a shift in the emission positions between transmitted light B50 and single-circulation light B51. The attitude of the plane-parallel substrate 184h may be changed by an actuator (not shown), allowing fine adjustment of the amount of shift in the emission positions.

[0171] 5.2 Supplementary Information The above description is intended to be illustrative rather than limiting. Thus, it will be apparent to those skilled in the art that modifications can be made to the embodiments of the present disclosure without departing from the scope of the claims. It will also be apparent to those skilled in the art that the embodiments of the present disclosure can be used in combination.

[0172] Terms used throughout this specification and claims should be construed as "open ended" unless expressly stated otherwise. For example, terms such as "comprise," "have," "comprise," and "equip" should be construed as meaning "without excluding the presence of elements other than those listed." In addition, the modifier "a" should be construed as meaning "at least one" or "one or more." In addition, the term "at least one of A, B, and C" should be construed as "A," "B," "C," "A+B," "A+C," "B+C," or "A+B+C," and should also be construed as including combinations other than "A," "B," and "C."

Claims

1. A laser oscillator including an optical resonator and a pair of electrodes for generating a discharge by applying a voltage to a laser gas, and for outputting a first pulsed laser beam; and a first optical pulse stretcher disposed in an optical path of the first pulsed laser beam, for transmitting a part of the first pulsed laser beam and causing another part to circulate once to output a first transmitted light and a first first circulating light, thereby outputting a second pulsed laser beam in which the pulse time width of the first pulsed laser beam is stretched, the first optical pulse stretcher being configured such that the optical path of the first transmitted light and the optical path of the first first circulating light are partially spatially overlapped with each other with a first deviation in a first direction; a second optical pulse stretcher that is disposed in an optical path of the second pulsed laser beam, and transmits a part of the second pulsed laser beam and causes another part to circulate once, thereby outputting a second transmitted light and a second one-time circulation light, thereby outputting a third pulsed laser beam having a stretched pulse time width of the second pulsed laser beam, wherein an optical path of the second transmitted light and an optical path of the second one-time circulation light are configured to spatially overlap each other by a second shift amount different from the first shift amount in the first direction.

2. A laser device according to claim 1, wherein the second deviation amount is greater than the first deviation amount.

3. A laser device according to claim 1, wherein the second deviation amount is at least twice as large as the first deviation amount.

4. A laser device as described in claim 1, further comprising a third optical pulse stretcher that is arranged in the optical path of the third pulsed laser light, and transmits a part of the third pulsed laser light and causes another part to circulate once to output a third transmitted light and a third one-time circulating light, thereby outputting a fourth pulsed laser light having a stretched pulse time width of the third pulsed laser light, wherein the optical path of the third transmitted light and the optical path of the third one-time circulating light are configured to spatially overlap in the first direction with a third shift amount different from both of the first and second shift amounts.

5. A laser device as described in claim 4, wherein when the first transmitted light is a=0, the first one-time circumnavigation light is a=1, the second transmitted light is b=0, the second one-time circumnavigation light is b=1, the third transmitted light is c=0, and the third one-time circumnavigation light is c=1, and light contained in the fourth pulse laser light is represented as Pabc depending on whether the light has been transmitted or circumnavigated once in each of the first, second, and third optical pulse stretchers, the optical paths of light P000, P100, P010, P110, P001, P101, P011, and P111 are shifted from each other.

6. A laser device according to claim 4, wherein the second deviation amount is at least twice as large as the first deviation amount, and the third deviation amount is at least twice as large as the second deviation amount.

7. A laser device as described in claim 6, further comprising: a fourth optical pulse stretcher that is disposed in an optical path of the fourth pulse laser light, and transmits a part of the fourth pulse laser light and causes another part to circulate once to output a fourth transmitted light and a fourth one-time circulating light, thereby outputting a fifth pulse laser light having a stretched pulse time width of the fourth pulse laser light, wherein the optical path of the fourth transmitted light and the optical path of the fourth one-time circulating light are configured to spatially overlap with each other by a fourth shift amount in the first direction, and the fourth shift amount is equal to or greater than twice the third shift amount.

8. A laser device according to claim 1, wherein the first direction is perpendicular to both the direction of the discharge and the direction of the optical path axis of the optical resonator.

9. A laser device as described in claim 8, wherein the shift in the optical paths between the second transmitted light and the second first-circulation light, and the shift in the optical paths between the first transmitted light and the first first-circulation light each include a shift in the direction of light propagation, and the smaller of the second shift amount and the first shift amount is greater than or equal to 1 / 20 and less than or equal to 1 / 10 of the beam divergence in the first direction of the first pulsed laser light.

10. A laser device as described in claim 9, wherein the larger of the second shift amount and the first shift amount is less than the beam divergence of the first pulsed laser light in the first direction.

11. A laser device according to claim 8, further comprising a third optical pulse stretcher disposed in an optical path of the third pulse laser beam, transmitting a portion of the third pulse laser beam and causing another portion to circulate once to output a third transmitted beam and a third first circulating beam, thereby outputting a fourth pulse laser beam having a pulse time width stretched from the third pulse laser beam, the third optical pulse stretcher being configured such that an optical path of the third transmitted beam and an optical path of the third first circulating beam are partially overlapped in space, wherein the first transmitted beam is a=0, the first first circulating beam is a=1, the second transmitted beam is b=0, the second first circulating beam is b=1, the third transmitted beam is c=0, and the third first circulating beam is c=1, a difference between a total shift amount in the first direction of each of optical paths of light P000, P100, P010, P110, P001, P101, P011, and P111 and a total shift amount in the first direction of optical paths other than the total shift amount in the first direction of each of light P000, P100, P010, P110, P001, P101, P011, and P111 is equal to or greater than 1 / 20 of a beam divergence in the first direction of the first pulse laser beam.

12. A laser device as described in claim 8, wherein the shift in the optical path between the second transmitted light and the second first-circulation light, and the shift in the optical path between the first transmitted light and the first first-circulation light each include a shift in the light emission position, and the smaller of the second shift amount and the first shift amount is greater than or equal to 1 / 20 and less than or equal to 1 / 10 of the beam width of the first pulse laser light in the first direction.

13. A laser device as described in claim 12, wherein the larger of the second shift amount and the first shift amount is less than the beam width of the first pulse laser light in the first direction.

14. A laser device according to claim 8, further comprising a third optical pulse stretcher disposed in an optical path of the third pulse laser beam, transmitting a portion of the third pulse laser beam and causing another portion to circulate once to output a third transmitted beam and a third first circulating beam, thereby outputting a fourth pulse laser beam having a pulse time width stretched from the third pulse laser beam, the third optical pulse stretcher being configured such that an optical path of the third transmitted beam and an optical path of the third first circulating beam are partially overlapped in space, wherein the first transmitted beam is a=0, the first first circulating beam is a=1, the second transmitted beam is b=0, the second first circulating beam is b=1, the third transmitted beam is c=0, and the third first circulating beam is c=1, a difference between a total shift amount in the first direction of each of optical paths of light P000, P100, P010, P110, P001, P101, P011, and P111 and a total shift amount in the first direction of optical paths other than the total shift amount in the first direction of each of light P000, P100, P010, P110, P001, P101, P011, and P111 is equal to or greater than 1 / 20 of a beam width of the first pulse laser light in the first direction.

15. A laser device as described in claim 1, further comprising a third optical pulse stretcher arranged in an optical path of the third pulsed laser light, transmitting a part of the third pulsed laser light and causing another part to circulate once to output a third transmitted light and a third one-time circulating light, thereby outputting a fourth pulsed laser light having a stretched pulse time width of the third pulsed laser light, wherein the optical path of the third transmitted light and the optical path of the third one-time circulating light are configured to spatially overlap with each other by a third amount of deviation in a second direction, wherein the first direction is a direction perpendicular to both the direction of the discharge and the direction of the optical path axis of the optical resonator, and the second direction is the direction of the discharge.

16. A laser device according to claim 15, wherein the third amount of deviation is smaller than both the first and second amounts of deviation.

17. A laser device as described in claim 15, wherein the deviation in the optical paths between the third transmitted light and the third first-circulation light, the deviation in the optical paths between the second transmitted light and the second first-circulation light, and the deviation in the optical paths between the first transmitted light and the first first-circulation light each include a deviation in the direction of light propagation, and the third deviation amount is greater than or equal to 1 / 80 and less than or equal to 1 / 40 of the beam divergence in the second direction of the first pulsed laser light.

18. A laser device as described in claim 15, wherein the deviation in the optical paths between the third transmitted light and the third first-circulation light, the deviation in the optical paths between the second transmitted light and the second first-circulation light, and the deviation in the optical paths between the first transmitted light and the first first-circulation light each include a deviation in the light emission position, and the third deviation amount is greater than or equal to 1 / 80 and less than or equal to 1 / 40 of the beam width of the first pulsed laser light in the second direction.

19. A laser device according to claim 1, further comprising: a third optical pulse stretcher disposed in an optical path of the third pulsed laser beam, which transmits a part of the third pulsed laser beam and causes another part to circulate once to output third transmitted light and third first-circulation light, thereby outputting a fourth pulsed laser beam having a pulse time width stretched from the third pulsed laser beam, the third optical pulse stretcher being configured so that an optical path of the third transmitted light and an optical path of the third first-circulation light are spatially overlapped; and a fourth optical pulse stretcher disposed in the optical path of the fourth pulsed laser beam, which transmits a part of the fourth pulsed laser beam and causes another part to circulate once to output fourth transmitted light and fourth first-circulation light, thereby outputting a fifth pulsed laser beam having a pulse time width stretched from the fourth pulsed laser beam, the fourth optical pulse stretcher being configured so that an optical path of the fourth transmitted light and an optical path of the fourth first-circulation light are spatially overlapped; one of the third and fourth optical pulse stretchers is configured to shift an optical path in the first direction by a shift amount different from either the first or second shift amount in one revolution, and the other is configured to shift an optical path in a second direction in one revolution, the first direction is a direction perpendicular to both the direction of the discharge and the direction of the optical path axis of the optical resonator, and the second direction is the direction of the discharge.

20. A method for manufacturing an electronic device, comprising: a laser oscillator including an optical resonator and a pair of electrodes for generating a discharge by applying a voltage to a laser gas, and outputting a first pulsed laser beam; and a first optical pulse stretcher disposed in an optical path of the first pulsed laser beam, for transmitting a part of the first pulsed laser beam and causing another part to circulate once to output a first transmitted light and a first first circulating light, thereby outputting a second pulsed laser beam in which the pulse time width of the first pulsed laser beam is stretched, the first optical pulse stretcher being configured such that the optical path of the first transmitted light and the optical path of the first first circulating light are spatially partially overlapped with each other with a first deviation in a first direction; a second optical pulse stretcher that is arranged in an optical path of the second pulsed laser beam, and transmits a part of the second pulsed laser beam and causes another part to circulate once, thereby outputting a second transmitted light and a second one-time circulation light, thereby outputting a third pulsed laser beam having a stretched pulse time width of the second pulsed laser beam, wherein an optical path of the second transmitted light and an optical path of the second one-time circulation light are configured to spatially overlap with each other by a second shift amount different from the first shift amount in the first direction;

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