Gas laser amplifier, gas laser device, EUV light generating device and EUV exposure device

Abstract

A gas laser amplifier (10A) comprises a frame (11), a discharge electrode pair (20A, 20B) and an optical resonator (40). The frame (11) comprises: an incident window (12) into which a first laser is incident from the outside; and an exit window (13) from which the amplified first laser is emitted. The discharge electrode pair (20A, 20B) excites laser gas supplied between discharge electrodes (21A, 22A, 21B, 22B) arranged opposite to each other inside the frame (11). The optical resonator (40) oscillates a second laser by the gain of the excited laser gas in a non-incident state in which the first laser is not incident from the outside of the frame (11) into the inside of the frame (11) through the incident window (12), and stops the oscillation of the second laser in an incident state in which the first laser is incident from the incident window (12) into the inside of the frame (11).

Description

Technical Field

[0001] The present invention relates to a gas laser amplifier, a gas laser device, an EUV (Extreme UltraViolet) light generating device and an EUV exposure device which generate or amplify laser light by using gas as a laser medium. Background Art

[0002] The EUV light generating device comprises: a gas laser amplifier that generates laser light; and an EUV light generating unit that irradiates a target with the laser light emitted from the gas laser amplifier to generate EUV light. The gas laser amplifier comprises: a chamber that contains a laser gas containing a gas laser amplification medium, namely, CO2 gas; a first window that is disposed on the first surface of the chamber; and a second window that is disposed on the second surface opposite to the first surface. In addition, the gas laser amplifier comprises a pair of planar electrodes that are arranged relative to each other for applying a voltage to the space between the first concave mirror and the second concave mirror. In the gas laser amplifier as described above, if a high-frequency voltage is applied between the planar electrodes, a discharge region is formed and the laser gas is excited. In this state, the seed laser is incident into the chamber from the first window, and is amplified after passing through the discharge region to become amplified light. The amplified light is repeatedly reflected between the second concave mirror and the first concave mirror. Moreover, after a predetermined number of reflections, the amplified light is output from the first concave mirror through the second window from the chamber.

[0003] In the gas laser amplifier as described above, the natural radiation light generated in the discharge region is reflected between the first window and the second window, thereby generating self-oscillation. Therefore, Patent Document 1 discloses a gas laser amplifier having an aperture, wherein the aperture has an opening formed on an optical axis designed in the gas laser amplifier. Thus, the self-oscillation light generated in the gas laser amplifier is blocked by the aperture, and the self-oscillation light is suppressed from being emitted from the first window and the second window.

[0004] Patent Document 1: International Publication No. 2014 / 045889 Summary of the invention

[0005] However, in the above-mentioned conventional gas laser amplifier, it is possible to suppress the emission of self-excited oscillation light generated in an optical axis different from that of the seed laser from the first window and the second window, but it is impossible to suppress the emission of self-excited oscillation light generated in an optical axis substantially identical to that of the seed laser. The apertures in the gas laser amplifier described in Patent Document 1 are provided at the first window and the second window. The optical axis of the self-excited oscillation light oscillated by the apertures provided at the first window and the second window forming a reciprocating optical path becomes substantially identical to the optical axis of the seed laser in the gas laser amplifier. Even if the reflectivity of the laser in the aperture is set low, even a small amount of scattered light may self-oscillate between the apertures provided at the first window and the second window when the gain of the gas laser amplifier is large. In the gas laser amplifier of the above-mentioned EUV light generating device, there is a problem that, if self-excited oscillation light is generated in an optical axis substantially identical to that of the seed laser, the self-excited oscillation light may be irradiated to a target in the EUV light generating unit at an unexpected timing, causing a malfunction in the EUV light generating device.

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to obtain a gas laser amplifier capable of suppressing the generation of self-excited oscillation light in the same optical axis as that of a seed laser.

[0007] In order to solve the above-mentioned problems and achieve the purpose, the gas laser amplifier involved in the present invention has a frame, a discharge electrode pair and an optical resonator. The frame has an incident window into which the first laser is injected from the outside and an exit window from which the amplified first laser is emitted. The discharge electrode pair excites the laser gas supplied to the discharge electrodes arranged opposite to each other inside the frame. When the optical resonator is in a non-incident state where the first laser is not injected from the outside of the frame into the inside of the frame through the incident window, the gain of the excited laser gas causes the second laser to oscillate, and when the first laser is injected from the incident window into the inside of the frame in an incident state, the oscillation of the second laser is stopped.

[0008] Effects of the Invention

[0009] The gas laser amplifier according to the present invention has an effect of being able to suppress the generation of self-excited oscillation light in the same optical axis as the seed laser. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is a perspective view schematically showing an example of the structure of a gas laser device including the gas laser amplifier according to the first embodiment.

[0011] Figure 2 Observed from the Y direction Figure 1 Diagram of the interior of a gas laser amplifier.

[0012] Figure 3This is a diagram showing an example of a change in the output of a laser beam injected into a general gas laser amplifier with respect to time.

[0013] Figure 4 This is a diagram showing an example of a change in the output of laser light amplified by a general gas laser amplifier with respect to time.

[0014] Figure 5 This is a diagram showing an example of a change in the self-oscillation output with respect to time.

[0015] Figure 6 This is a diagram showing an example of a change in gain with respect to time in a general gas laser amplifier.

[0016] Figure 7 This is a diagram showing an example of a change in the output of laser light amplified by the gas laser amplifier according to the first embodiment with respect to time.

[0017] Figure 8 This is a diagram showing an example of changes in the optical resonator output with respect to time in the gas laser amplifier according to the first embodiment.

[0018] Fig. 9 This is a diagram showing an example of a change in the self-oscillation output with respect to time in the gas laser amplifier according to the first embodiment.

[0019] Fig.10 This is a diagram showing an example of a change in gain with respect to time in the gas laser amplifier according to the first embodiment.

[0020] Fig.11 This is a diagram showing an example of a change in the output of laser light amplified by the gas laser amplifier according to the first embodiment with respect to time.

[0021] Fig.12 This is a perspective view schematically showing an example of the structure of a gas laser device including a gas laser amplifier according to the second embodiment.

[0022] Fig.13 Observed from the Y direction Fig.12 Diagram of the interior of a gas laser amplifier.

[0023] Fig.14 This is a diagram showing an example of a change in the output of laser light amplified by the gas laser amplifier according to the second embodiment with respect to time.

[0024] Fig.15 This is a diagram showing an example of changes in the optical resonator output with respect to time in the gas laser amplifier according to the second embodiment.

[0025] Fig.16 This is a diagram showing an example of a change in the self-oscillation output with respect to time in the gas laser amplifier according to the second embodiment.

[0026] Fig.17 This is a diagram showing an example of a change in gain with respect to time in the gas laser amplifier according to the second embodiment.

[0027] Fig.18 This is a perspective view schematically showing an example of the structure of a gas laser device including a gas laser amplifier according to the third embodiment.

[0028] Fig.19 Observed from the Y direction Fig.18 Diagram of the interior of a gas laser amplifier.

[0029] Fig. 20 This is a perspective view schematically showing an example of the structure of a gas laser device including a gas laser amplifier according to the fourth embodiment.

[0030] Fig.21 Observed from the Y direction Fig. 20 Diagram of the interior of a gas laser amplifier.

[0031] Fig. 22 This is a perspective view schematically showing an example of the structure of a gas laser device including a gas laser amplifier according to the fifth embodiment.

[0032] Fig.23 Observed from the Y direction Fig. 22 Diagram of the interior of a gas laser amplifier.

[0033] Fig.24 This is a perspective view schematically showing an example of the structure of a gas laser device including a gas laser amplifier according to the sixth embodiment.

[0034] Fig.25 Observed from the Y direction Fig.24 Diagram of the interior of a gas laser amplifier.

[0035] Fig.26 This is an exploded perspective view schematically showing an example of the structure of a gas laser device including a gas laser amplifier according to the seventh embodiment.

[0036] Fig. 27 This is a diagram showing an example of changes in the output of laser light amplified by the gas laser amplifier according to the seventh embodiment with respect to time.

[0037] Fig.28This is a diagram showing an example of changes in the optical resonator output with respect to time in the gas laser amplifier according to the seventh embodiment.

[0038] Fig.29 This is a diagram showing an example of a change in the self-excited oscillation output with respect to time in the gas laser amplifier according to the seventh embodiment.

[0039] Fig.30 This is a diagram showing an example of a change in gain with respect to time in the first-stage gas laser amplifier according to the seventh embodiment.

[0040] Fig.31 This is a diagram showing an example of a change in gain with respect to time in the second-stage gas laser amplifier according to the seventh embodiment.

[0041] Fig.32 This is a perspective view schematically showing an example of the structure of a gas laser amplifier involved in embodiment 8.

[0042] Fig.33 This is a block diagram schematically showing an example of the structure of an EUV exposure device involved in Embodiment 9. DETAILED DESCRIPTION

[0043] Hereinafter, a gas laser amplifier, a gas laser device, an EUV light generating device, and an EUV exposure device according to embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to these embodiments.

[0044] Implementation method 1.

[0045] Figure 1 FIG. 1 is a perspective view schematically showing an example of the structure of a gas laser device having a gas laser amplifier according to Embodiment 1. Figure 1 In the figure, the direction of the optical axis OA1 of the seed laser in the gas laser amplifier 10A is set as the Z direction, and the direction perpendicular to the Z direction and in which the laser gas in the gas laser amplifier 10A flows is set as the X direction. In addition, the direction perpendicular to the Z direction and the X direction is set as the Y direction. In addition, the setting method of the X direction, the Y direction and the Z direction is the same in the subsequent figures. Figure 2 Observed from the Y direction Figure 1 Diagram of the interior of a gas laser amplifier.

[0046] The gas laser device 1 includes a laser light source 2 that emits seed laser light, which is laser light to be amplified, and a gas laser amplifier 10A that amplifies the seed laser light and emits the amplified seed laser light as amplified light.

[0047] The laser light source 2 outputs a linearly polarized first laser, namely a seed laser. The seed laser is a pulse laser or a continuous wave laser with a repetition frequency of several tens of kHz to several hundreds of kHz. Figure 1 In the example, the seed laser is P polarized light whose polarization direction PD1 is in the X direction.

[0048] The gas laser amplifier 10A has a frame 11 that seals a laser medium, i.e., a laser gas. The gas laser amplifier 10A has: a window 12, which is provided on a side surface 11A of the frame 11, for the seed laser from the laser light source 2 to enter; and a window 13, which is provided on a surface opposite to the side surface 11A, i.e., the side surface 11B, for emitting the amplified light amplified in the frame 11 to the outside. The window 12 and the window 13 are provided on the same straight line parallel to the Z direction. That is, in the frame 11, the optical axis OA1 connecting the window 12 and the window 13 becomes a straight line parallel to the Z direction. The window 12 is equivalent to the incident window, and the window 13 is equivalent to the exit window.

[0049] The gas laser amplifier 10A has polarizers 14, 15, a partial reflection mirror 16, a total reflection mirror 17, and a damper 18. The polarizers 14, 15 are arranged on the optical axis OA1 in the frame 11 sandwiched by the windows 12, 13. The polarizers 14, 15 transmit the seed laser and the amplified light having the same polarization direction PD1 as the seed laser, and reflect the laser light having the polarization direction PD2 orthogonal to the polarization direction PD1 of the seed laser. That is, the polarizers 14, 15 transmit the P polarized light, but reflect the S polarized light in the X direction. Thus, the S polarized light propagating on the optical axis OA1 is reflected in the X direction by the polarizers 14, 15.

[0050] The partial reflection mirror 16 transmits a part of the laser light reflected by the polarizer 14 and reflects the other laser light. The total reflection mirror 17 reflects the laser light reflected by the polarizer 15. The partial reflection mirror 16 and the total reflection mirror 17 constitute an optical resonator 40. The laser light generated by the optical resonator 40, that is, the laser light which is not the amplified light obtained by amplifying the seed laser light, reciprocates between the partial reflection mirror 16 and the total reflection mirror 17 to be amplified. The optical axis OA2 connecting the partial reflection mirror 16 and the total reflection mirror 17 becomes the optical axis of the optical resonator 40.

[0051] The damper 18 is arranged at the rear stage of the partial reflection mirror 16 on the optical axis OA2, and absorbs the laser light transmitted through the partial reflection mirror 16. In addition, the polarization direction PD2 of the laser light oscillated by the optical resonator 40 is polarized in the direction reflected by the polarizers 14 and 15, and is orthogonal to the polarization direction PD1 of the seed laser light. Therefore, the laser light oscillated by the optical resonator 40 is reflected by the polarizers 14 and 15 and is not emitted from the windows 12 and 13, and a part of the laser light transmitted through the partial reflection mirror 16 is absorbed by the damper 18.

[0052] The gas laser amplifier 10A has two discharge electrode pairs 20A and 20B, which are arranged in a frame 11 to excite the laser gas. The discharge electrode pair 20A has discharge electrodes 21A and 22A, and the discharge electrode pair 20B has discharge electrodes 21B and 22B. The discharge electrodes 21A and 22A are arranged to be spaced apart in the Y direction, and the electrode surfaces are parallel to each other, forming the discharge electrode pair 20A. The discharge electrodes 21B and 22B are arranged to be spaced apart in the Y direction, and the electrode surfaces are parallel to each other, forming the discharge electrode pair 20B. Figure 1 and Figure 2 In the example, the discharge electrodes 21A and 22A are arranged in the Z direction in the region between the center of the frame 11 and the window 12, and the discharge electrodes 21B and 22B are arranged in the Z direction in the region between the center of the frame 11 and the window 13. The gas laser amplifier 10A further includes a high frequency power supply (not shown) connected to the discharge electrodes 21A and 22A and the discharge electrodes 21B and 22B.

[0053] In addition, the gas laser amplifier 10A has airflow generating parts 25A and 25B. The airflow generating parts 25A and 25B have: a laser gas supply part (not shown) that supplies laser gas; a blower (not shown) that causes the laser gas supplied to the frame 11 to flow in the X direction and circulates the laser gas in the frame 11; and a heat exchanger (not shown) that cools the laser gas that has passed through the optical axes OA1 and OA2. The airflow generating parts 25A and 25B cause the laser gas to flow in opposite directions in the X direction at different positions in the Z direction. That is, at Figure 1 In the example of , the airflow generating section 25A is arranged at the lower part of the discharge electrode 22A, and the airflow generating section 25B is arranged at the lower part of the discharge electrode 22B. Specifically, in the airflow generating section 25A, the laser gas is supplied from the laser gas supply section along the direction D1 between the discharge electrodes 21A and 22A in such a manner that the laser gas flows in the positive direction of the X-axis. In addition, in the airflow generating section 25B, the laser gas is supplied from the laser gas supply section along the direction D2 between the discharge electrodes 21B and 22B in such a manner that the laser gas flows in the negative direction of the X-axis. As the laser gas, CO2 gas can be used. The gas laser amplifier 10A using CO2 gas as the laser gas can be used as a light source of an EUV exposure device.

[0054] Laser gas flows in direction D1 between discharge electrodes 21A and 22A, and when a high frequency voltage is applied to discharge electrodes 21A and 22A, discharge space 23A is formed between discharge electrodes 21A and 22A. Discharge electrodes 21A and 22A are arranged so that discharge space 23A is formed upstream of optical axis OA1 in direction D1.

[0055] Laser gas flows in direction D2 between discharge electrodes 21B and 22B, and when high frequency voltage is applied to discharge electrodes 21B and 22B, discharge space 23B is formed between discharge electrodes 21B and 22B. Discharge electrodes 21B and 22B are arranged so that discharge space 23B is formed upstream of optical axis OA1 in direction D2.

[0056] like Figure 2 As shown, the gas laser amplifier 10A has apertures 31 on the optical axis OA1 between the window 12 and the discharge space 23A and between the window 13 and the discharge space 23B in the housing 11. The aperture 31 is a component that suppresses the self-excited oscillation light generated in an optical axis different from the optical axis OA1 from being emitted to the outside of the gas laser amplifier 10A. It is preferable to select the structural material of the aperture 31 so that the reflectivity of the laser light in the aperture 31 is reduced.

[0057] like Figure 1 As shown, the gas laser amplifier 10A is a three-axis orthogonal gas laser amplifier in which the X direction, the electrode gap direction, and the Z direction, the optical axis OA1 direction, are orthogonal.

[0058] Next, the operation of the gas laser amplifier 10A will be described. Figure 1 and Figure 2 The laser gas flows in the directions D1 and D2 shown. As a result, the laser gas flows between the discharge electrodes 21A and 22A and between the discharge electrodes 21B and 22B. A high-frequency voltage is applied between the discharge electrodes 21A and 22A and between the discharge electrodes 21B and 22B from a high-frequency power supply not shown in the figure, thereby forming discharge spaces 23A and 23B. The laser gas flowing into the discharge spaces 23A and 23B is excited. The excited laser gas flows into the optical axes OA1 and OA2 located on the downstream side of each discharge electrode pair 20A and 20B. The laser gas passing through the optical axes OA1 and OA2 is cooled by a heat exchanger not shown in the figure, flows to the discharge spaces 23A and 23B through a blower not shown in the figure, and circulates in the frame 11.

[0059] The seed laser emitted from the laser light source 2 provided outside the gas laser amplifier 10A is incident into the frame 11 from the window 12 along the optical axis OA1. Here, the seed laser is P-polarized light, so it is transmitted through the polarizer 14 and propagates toward the polarizer 15. In addition, the seed laser passes through the excited laser gas downstream of the discharge space 23A and the discharge space 23B, so the seed laser is amplified to become amplified light. Moreover, the P-polarized light, i.e., the amplified light, is transmitted through the polarizer 15 and emitted from the window 13 to the outside of the frame 11.

[0060] On the other hand, the laser light generated and amplified on an optical axis different from the optical axis OA1 of the gas laser amplifier 10A is blocked by the aperture 31 and is not emitted from the windows 12 and 13 .

[0061] In addition, in the housing 11, an optical resonator 40 is formed by a partial reflection mirror 16 and a total reflection mirror 17. The optical axis OA2 of the optical resonator 40 passes through the partial reflection mirror 16, the polarizer 14, the polarizer 15, and the total reflection mirror 17. Between the polarizer 14 and the polarizer 15, the laser light coaxial with the optical axis OA1 and oscillated by the optical resonator 40 passes through the excited laser gas. The polarization direction PD2 of the laser light oscillated by the optical resonator 40 is polarized in the direction reflected by the polarizers 14 and 15, and is orthogonal to the polarization direction PD1 of the seed laser light. The laser light is reflected and amplified between the partial reflection mirror 16 and the total reflection mirror 17, but is reflected by the polarizers 14 and 15, so it is not emitted to the outside of the housing 11. In addition, a part of the laser light reaching the partial reflection mirror 16 passes through the partial reflection mirror 16 and is absorbed by the damper 18. Therefore, the laser light oscillated by the optical resonator 40 is also not emitted to the outside of the housing 11. Furthermore, since the polarization component directed in the same direction as the seed laser light is not reflected by the polarizers 14 and 15 , it cannot resonate in the optical resonator 40 , and laser oscillation does not occur.

[0062] Here, an example of a situation in which self-oscillation occurs in a gas laser amplifier unrelated to the first embodiment will be described. Figure 3 is a diagram showing an example of a change in the output of a laser beam injected into a general gas laser amplifier with respect to time. Figure 4 This is a diagram showing an example of a change in the output of laser light amplified by a general gas laser amplifier with respect to time. Figure 5 is a diagram showing an example of the change in the self-oscillation output with respect to time. Figure 6 is a graph showing an example of the change in gain relative to time in a conventional gas laser amplifier. In these graphs, the horizontal axis represents time. Figure 3 The vertical axis represents the incident laser output, Figure 4 The vertical axis represents the laser amplifier output, Figure 5 The vertical axis represents the self-oscillation output, Figure 6 The vertical axis represents the gain g of the gas laser amplifier. a .

[0063] In addition, Figure 6 In the figure, g0 is the small signal gain, g s is the oscillation threshold gain of the self-oscillation, g p It is the gain when the laser is amplified. The small signal gain g0 is the amplification factor per unit length when the input is infinitely close to 0.

[0064] In the interval ΔT0, ΔT2, if Figure 3 As shown in the figure, this is when the seed laser is injected into the gas laser amplifier and amplified. Figure 4 As shown in FIG. 1 , the gain of the gas laser amplifier is used to amplify the laser light, and the amplified light is emitted to the outside of the gas laser amplifier. Figure 6 As shown, the gain g in the gas laser amplifier a Equal to the gain g when the seed laser is amplified p , below the oscillation threshold gain g of self-oscillation s , so if Figure 5 As shown, no self-oscillation occurs.

[0065] On the other hand, the interval ΔT1 is set as the interval in which the seed laser cannot be injected into the gas laser amplifier due to some problem. In this case, the seed laser is not amplified, so Figure 6 As shown, the gain g in the gas laser amplifier a rises, exceeding the oscillation threshold gain g of self-oscillation s ,like Figure 5 As shown, self-oscillation occurs.

[0066] In the first embodiment, the gas laser amplifier 10A is configured to suppress the occurrence of self-oscillation in the section ΔT1 in which the seed laser light is not incident on the gas laser amplifier 10A. Figure 7 FIG. 1 is a diagram showing an example of a change in the output of laser light amplified by the gas laser amplifier according to Embodiment 1 with respect to time. Figure 8 This is a diagram showing an example of changes in the optical resonator output with respect to time in the gas laser amplifier according to the first embodiment. Fig. 9 FIG. 1 is a diagram showing an example of a change in the self-excited oscillation output with respect to time in the gas laser amplifier according to the first embodiment. Fig.10 This is a diagram showing an example of a change in gain with respect to time in the gas laser amplifier according to the first embodiment. Fig.11 These are diagrams showing an example of changes in the output of laser light amplified by the gas laser amplifier according to Embodiment 1 with respect to time. In these diagrams, the horizontal axis represents time.

[0067] also, Figure 7 The laser amplification output shows the amplified output of the laser emitted from the window 13 after the seed laser is injected into the gas laser amplifier 10A along the optical axis OA1. Here, the repetition frequency shows the average output waveform of the pulsed laser with a repetition frequency of tens of kHz to hundreds of kHz. In addition, the instantaneous output waveform of the pulsed laser with a repetition frequency of tens of kHz to hundreds of kHz becomes Fig.11 shown.

[0068] Figure 8The optical resonator output is the output of the laser light output from the partial reflection mirror 16 of the optical resonator 40 and absorbed by the damper 18 . Fig. 9 The self-excited oscillation output is the output of self-excited oscillation generated by reflected or diffracted light from components such as the external components or the internal aperture 31 of the gas laser amplifier 10A. Fig.10 In the figure, g0 is the small signal gain, g s is the oscillation threshold gain of the self-oscillation, g r is the oscillation threshold gain of the optical resonator 40, g p is the gain of the laser when it is amplified.

[0069] The intervals ΔT10 and ΔT12 correspond to the incident state when the seed laser is incident on the gas laser amplifier 10A and amplified. In this case, as described above, the gain in the gas laser amplifier 10A is consumed by the incident seed laser. Fig.10 As shown, the gain g in the gas laser amplifier 10A is a Equal to the gain g when the seed laser is amplified p In the first embodiment, the oscillation threshold gain g of the optical resonator 40 is r Set to a gain g greater than that when the seed laser is amplified p Therefore, a value greater than or equal to the oscillation threshold gain g is not formed on the optical resonator 40 side. r The gain, such as Figure 8 As shown in FIG. 1 , laser light cannot be oscillated. That is, laser light is not emitted from the optical resonator 40. Fig.10 As shown, the oscillation threshold gain g of the self-oscillation s It also becomes the gain g when the seed laser is amplified p Large value, so Fig. 9 As shown, no self-oscillation occurs.

[0070] On the other hand, the interval ΔT11 is an interval in which the seed laser is not injected into the gas laser amplifier 10A, and corresponds to a non-incident state. Figure 7 As shown in Figure 2, when the laser amplifier output becomes 0, Fig.10 As shown, the gain g in the gas laser amplifier 10A is a The small signal gain g0 exceeds the oscillation threshold gain g of the optical resonator 40. r Therefore, if Figure 8 As shown, laser light is immediately oscillated in the optical resonator 40. At this time, the oscillation threshold gain g of the optical resonator 40 is r The oscillation threshold gain g of the self-oscillation s Since the laser beam is small, the laser beam is oscillated from the optical resonator 40 before the self-excited oscillation occurs. Fig. 9As shown, no self-oscillation occurs. Moreover, the gain g in the gas laser amplifier 10A a is consumed by the optical resonator 40, becoming equal to the oscillation threshold gain g of the optical resonator 40 r Therefore, the gain g in the gas laser amplifier 10A is a Below the oscillation threshold gain g for self-oscillation s , no self-oscillation occurs. That is, the gas laser amplifier 10A involved in embodiment 1 cannot suppress self-oscillation. Figure 8 As shown, part of the laser light oscillated by the optical resonator 40 passes through the partial reflection mirror 16 and is absorbed by the damper 18 .

[0071] Here, the gain per unit length when the seed laser is amplified on the optical axis OA1 in the incident state of the seed laser is denoted as g. p In addition, the output of the seed laser when injected into the gas laser amplifier 10A is denoted as P in The output of the amplified seed laser light emitted from the gas laser amplifier 10A is defined as P out The optical path length L of the range where the excited laser gas flows in the optical axis OA1 is p The gain of the seed laser amplification is expressed by the following equation (1).

[0072] [Formula 1]

[0073]

[0074] In addition, let the reflectivity of the partial reflection mirror 16 of the optical resonator 40 be R1, and let the gain per unit length when the optical resonator 40 oscillates, that is, the oscillation threshold gain be g r At this time, the optical path length L of the range into which the excited laser gas flows within the optical axis OA2 is r The gain of amplifying the laser light generated by the optical resonator 40 is expressed by the following equation (2).

[0075] [Formula 2]

[0076]

[0077] In order for the oscillation of the optical resonator 40 to automatically stop when the seed laser is incident, the condition of the following formula (3) must be satisfied.

[0078] g p L p <g r L r ···(3)

[0079] According to equations (1), (2), and (3), the reflectivity R1 of the partial reflection mirror 16 of the optical resonator 40 must satisfy the condition of the following equation (4).

[0080] [Formula 3]

[0081]

[0082] For example, it is assumed that a seed laser of 100 W is input and the amplification factor of the gas laser amplifier 10A reaches 25 kW of amplified light with a magnification of 250. The condition of the reflectivity R1 of the partial reflection mirror 16 at this time is expressed by the following equation (5).

[0083] R1<16×10 -6 ···(5)

[0084] On the other hand, the beam intensity of the seed laser at the time of injection is set to I in , the beam intensity of the amplified light during amplification is set to I out , set the saturation intensity to I s , the small signal gain is set to g0. The optical path length L of the range where the excited laser gas flows in the optical axis OA1 is p The small signal gain of is expressed by the following equation (6).

[0085] [Formula 4]

[0086]

[0087] For example, the saturation intensity I s 200W / cm 2 , the beam diameter of the amplified seed laser The small signal gain of the optical path length Lp in the range where the excited laser gas flows in the optical axis OA1 is expressed by the following equation (7) when the above-mentioned 100 W seed laser is input and 25 kW amplified light is output after amplification.

[0088] oeLh p ≒23···(7)

[0089] Self-excited oscillation is generated by reflected or diffracted light from components such as the external components or the internal aperture 31 of the gas laser amplifier 10A. Therefore, the feedback rate of light during self-excited oscillation is very small, and the oscillation threshold of self-excited oscillation is often approximately equal to the small signal gain g0. Therefore, before the self-excited oscillation light is generated, in order to oscillate in the optical resonator 40, the condition of the following formula (8) must be satisfied.

[0090] oeLh p >g r L r ···(8)

[0091] According to equations (2) and (7), the reflectivity R1 of the partial reflection mirror 16 of the optical resonator 40 must satisfy the condition of the following equation (9).

[0092] R1>7×10 -21 ···(9)

[0093] According to equations (5) and (9), the reflectivity R1 of the partial reflector 16 is set to be greater than 7×10 -21 , less than 16×10 -6 By setting a value of , it is possible to suppress the occurrence of self-oscillation in the gas laser amplifier 10A as described above.

[0094] As described above, by providing the optical resonator 40 in the gas laser amplifier 10A and appropriately setting the reflectivity R1 of the partial reflection mirror 16 of the optical resonator 40, the oscillation threshold gain of the laser light generated by the optical resonator 40 can be set to be larger than the gain when the seed laser light incident from the outside is amplified, and smaller than the threshold gain of the self-excited oscillation. In other words, the total resonator loss of the optical resonator 40 is set to have a value between the gain of the optical resonator 40 in the incident state and the gain of the optical resonator 40 in the non-incident state. In this way, the self-excited oscillation can be suppressed.

[0095] In addition, Figure 1 The polarization direction PD1 of the seed laser is set to the X direction which is the same as the air flow direction between the discharge electrodes 21A and 22A and between the discharge electrodes 21B and 22B, but the polarization direction PD1 of the seed laser can also be set to the discharge gap length direction, that is, the Y direction, and the polarization direction PD2 of the laser generated by the optical resonator 40 can be set to the X direction orthogonal thereto. That is, the polarizers 14 and 15 can be set to reflect P polarized light and transmit S polarized light.

[0096] In addition, Figure 1 In the embodiment, the optical resonator 40 is disposed inside the frame 11, but the polarizer 14, the partial reflector 16 and the damper 18 may be disposed outside the frame 11, or the polarizer 15 and the total reflector 17 may be disposed outside the frame 11. Figure 1 In the embodiment, the partial reflection mirror 16 and the damper 18 are arranged on the incident side of the seed laser, and the total reflection mirror 17 is arranged on the emission side of the seed laser, but their arrangement positions may be reversed. That is, the total reflection mirror 17 may be arranged on the incident side of the seed laser, and the partial reflection mirror 16 and the damper 18 may be arranged on the emission side of the seed laser.

[0097] In addition, Figure 1The light reciprocating in the optical resonator 40 is reflected by the polarizers 14 and 15 in the X direction, which is the direction of the airflow between the discharge electrodes 21A and 22A and between the discharge electrodes 21B and 22B, but it can also be reflected in the Y direction, which is the direction of the length of the electrode gap. Figure 1 In the embodiment, the optical axis OA1 of the seed laser of the gas laser amplifier 10A is a one-way structure that passes through the discharge spaces 23A and 23B only once, but as shown in the embodiment described later, it can also have a folded structure inside the frame 11 and pass through the discharge spaces 23A and 23B multiple times.

[0098] Furthermore, one or more gas laser amplifiers may be further provided in the subsequent stage to amplify the amplified light emitted from the window 13. The provided gas laser amplifier may be the gas laser amplifier 10A according to the first embodiment or a gas laser amplifier not related to the first embodiment.

[0099] In the first embodiment, the gas laser amplifier 10A has an optical resonator 40 that resonates the second laser light incident from the external laser light source 2 and has an optical axis OA2 that is partially common with the optical axis OA1 of the seed laser light amplified inside the housing 11. Polarizers 14 and 15 are provided on the optical axis OA1, and the polarizers 14 and 15 transmit the light polarized in the first direction and reflect the light polarized in the second direction orthogonal to the first direction. The optical resonator 40 is composed of a partial reflection mirror 16 arranged in the direction reflected by the polarizer 14 and a total reflection mirror 17 arranged in the direction reflected by the polarizer 15. A damper 18 that absorbs the laser light is arranged at the rear stage of the partial reflection mirror 16 of the optical axis OA2. In addition, the reflectivity R1 of the partial reflection mirror 16 is set so that the oscillation threshold gain of the laser light generated by the optical resonator 40 is greater than the gain when the seed laser light incident from the outside is amplified and is less than the threshold gain of the self-excited oscillation. Thus, when the seed laser is not emitted into the gas laser amplifier 10A, the optical resonator 40 performs laser oscillation before the self-excited oscillation light is generated, thereby suppressing the self-excited oscillation. In addition, when the laser light is generated on the same optical axis as the optical axis OA1 of the seed laser, the light having the polarization component in the first direction is not reflected by the polarizers 14 and 15, and is therefore not amplified by the optical resonator 40. In addition, the light having the polarization component in the second direction is amplified by the optical resonator 40, and a part of it is transmitted through the partial reflection mirror 16 and absorbed by the damper 18, and is not emitted to the outside of the gas laser amplifier 10A. As a result, there is an effect that the emission of the self-excited oscillation light generated on the same optical axis as the seed laser light can be suppressed in the gas laser amplifier 10A without using a device that temporally changes the loss of the optical resonator 40.

[0100] Implementation method 2.

[0101] Fig.12 This is a perspective view schematically showing an example of the structure of a gas laser device including a gas laser amplifier according to the second embodiment. Fig.13 Observed from the Y direction Fig.12 FIG. 1 is a diagram showing the interior of a gas laser amplifier. In addition, the parts different from those in Embodiment 1 are described below, and the parts identical to those in Embodiment 1 are denoted by the same reference numerals and their description is omitted.

[0102] In the first embodiment, the optical axis OA1 of the seed laser and the optical axis OA2 of the laser beam oscillated by the optical resonator 40 partially overlap. In the second embodiment, the optical axis OA1 of the seed laser and the optical axis OA2 of the laser beam oscillated by the optical resonator 41 do not overlap.

[0103] That is, no optical component other than aperture 31 is arranged on optical axis OA1 passing through windows 12 and 13. In addition, aperture 31 is provided between window 12 and a position corresponding to discharge space 23A on optical axis OA1 and between discharge space 23B and window 13 on optical axis OA1.

[0104] The gas laser amplifier 10B includes an optical resonator 41 in a housing 11. The optical resonator 41 includes a partial reflection mirror 16, a total reflection mirror 17, and a damper 18. The optical axis OA2 of the laser beam oscillated by the optical resonator 41 is arranged to be parallel to the optical axis OA1 at a position different from the optical axis OA1. Fig.12 and Fig.13 In the example of FIG. 1 , in the XZ plane, the optical axis OA2 is arranged parallel to the optical axis OA1 at a distance in the negative direction of the X axis. The damper 18 is arranged at a position where it can absorb the laser light transmitted through the partial reflection mirror 16. The laser light oscillated by the optical resonator 41 is output from the partial reflection mirror 16 and absorbed by the damper 18. As a result, all the laser light oscillated by the optical resonator 41 is absorbed by the damper 18, so that it is not emitted from the gas laser amplifier 10B to the outside.

[0105] The gas laser amplifier 10B also includes an aperture 32 on the optical axis OA2. The aperture 32 is disposed between the discharge space 23A and the partial reflection mirror 16 and between a position corresponding to the discharge space 23B on the optical axis OA2 and the total reflection mirror 17.

[0106] In Embodiment 2, discharge electrodes 21A and 22A are arranged so that discharge space 23A includes optical axis OA2 , and discharge electrodes 21B and 22B are arranged so that discharge space 23B includes optical axis OA1 .

[0107] Here, the operation of the gas laser amplifier 10B is described. Fig.12and Fig.13 The laser gas flows in the directions D1 and D2 shown. As a result, the laser gas flows between the discharge electrodes 21A and 22A and between the discharge electrodes 21B and 22B. A high-frequency voltage is applied between the discharge electrodes 21A and 22A and between the discharge electrodes 21B and 22B from a high-frequency power supply not shown in the figure, thereby forming discharge spaces 23A and 23B. The laser gas flowing into the discharge spaces 23A and 23B is excited. The excited laser gas flows into the optical axes OA1 and OA2 located on the downstream side of each discharge electrode pair 20A and 20B. The laser gas passing through the optical axes OA1 and OA2 is cooled by a heat exchanger not shown in the figure, flows to the discharge spaces 23A and 23B through a blower not shown in the figure, and circulates in the frame 11. In addition, the seed laser can be a pulse laser with a repetition frequency of tens of kHz to hundreds of kHz, or it can be a continuous wave laser.

[0108] The seed laser emitted from the laser light source 2 provided outside the gas laser amplifier 10B is incident into the frame 11 from the window 12 along the optical axis OA1. The seed laser passes through the excited laser gas when passing through the downstream of the discharge space 23A and the discharge space 23B, and is amplified to become amplified light. The amplified light is emitted from the window 13 to the outside of the frame 11.

[0109] Here, the reflectivity R1 of the partial reflection mirror 16 of the optical resonator 41 is set to the oscillation threshold gain g of the optical resonator 41. r The conditions shown below are met.

[0110] Fig.14 FIG. 1 is a diagram showing an example of a change in the output of a laser beam amplified by the gas laser amplifier according to Embodiment 2 with respect to time. Fig.15 This is a diagram showing an example of changes in the optical resonator output with respect to time in the gas laser amplifier according to the second embodiment. Fig.16 FIG. 1 is a diagram showing an example of a change in the self-excited oscillation output with respect to time in the gas laser amplifier according to the second embodiment. Fig.17 1 and 2 are diagrams showing an example of a change in gain with respect to time in a gas laser amplifier according to Embodiment 2. In these diagrams, the horizontal axis represents time.

[0111] exist Fig.17 In, g r’ is the gain on the optical axis OA1 when the optical resonator 41 oscillates, g p’ is the gain on the optical axis OA2 when the seed laser is amplified. Figure 7 , Figure 8 , Fig. 9 and Fig.10 The description of the parts that are the same as those described in is omitted.

[0112] In the intervals ΔT10 and ΔT12 where the seed laser is incident on the gas laser amplifier 10B and is being amplified, the oscillation threshold gain g of the optical resonator 41 is r Set to be greater than the gain g on the optical axis OA2 when the seed laser is amplified p’ Therefore, the seed laser is amplified, and when it is emitted from the window 13, no oscillation threshold gain g is formed on the optical resonator 41 side. r The gain, therefore, Fig.15 As shown in FIG. 1 , laser light cannot be oscillated. That is, laser light is not emitted from the optical resonator 41. Similarly, the oscillation threshold gain g of the self-excited oscillation is s It also becomes the gain g on the optical axis OA1 when the laser is amplified. p Large value, so Fig.16 As shown, no self-oscillation occurs.

[0113] On the other hand, in the interval ΔT11 where the seed laser is not injected into the gas laser amplifier 10B, Fig.14 As shown in Figure 2, when the laser amplifier output becomes 0, Fig.17 As shown, the gain g in the gas laser amplifier 10B a The oscillation threshold gain g of the optical resonator 41 is exceeded. r Therefore, if Fig.15 As shown in FIG. 1 , laser light is immediately oscillated from the optical resonator 41. At this time, the oscillation threshold gain g of the optical resonator 41 is r Less than the oscillation threshold gain g of self-oscillation s , so laser light is oscillated from the optical resonator 41 before self-oscillation occurs. Fig.16 As shown, no self-oscillation occurs. Moreover, the gain g on the optical axis OA1 in the gas laser amplifier 10B is a is consumed by the optical resonator 41, which is equal to the gain g on the optical axis OA1 when the optical resonator 41 oscillates. r’ Therefore, the gain g in the gas laser amplifier 10B is a Below the oscillation threshold gain g for self-oscillation s , no self-oscillation occurs. That is, the gas laser amplifier 10B involved in Embodiment 2 can suppress self-oscillation. Fig.15 As shown, part of the laser light oscillated by the optical resonator 41 passes through the partial reflection mirror 16 and is absorbed by the damper 18 .

[0114] As described above, in Embodiment 2, the optical resonator 41 is provided in the gas laser amplifier 10B, and its oscillation threshold gain is set to be larger than the gain when the seed laser incident from the outside is amplified, and is set to be smaller than the threshold gain of the self-excited oscillation. Thus, when the seed laser is not incident, the optical resonator 41 immediately oscillates the laser, so that the self-excited oscillation can be suppressed.

[0115] In addition, Fig.12 In the embodiment, the optical axis OA1 of the seed laser of the gas laser amplifier 10B has a single-pass structure that passes through the discharge spaces 23A and 23B only once, but may have a folded structure inside the frame 11 and pass through the discharge spaces 23A and 23B multiple times as in the embodiment described later.

[0116] And, in Fig.12 In the embodiment, the partial reflection mirror 16 and the damper 18 are arranged on the incident side of the seed laser, and the total reflection mirror 17 is arranged on the emission side of the seed laser, but these arrangement positions may be reversed. That is, the total reflection mirror 17 may be arranged on the incident side of the seed laser, and the partial reflection mirror 16 and the damper 18 may be arranged on the emission side of the seed laser.

[0117] Implementation method 3.

[0118] Fig.18 This is a perspective view schematically showing an example of the structure of a gas laser device including a gas laser amplifier according to the third embodiment. Fig.19 Observed from the Y direction Fig.18 FIG. 1 is a diagram showing the interior of a gas laser amplifier. In addition, the parts different from those in Embodiments 1 and 2 are described below, and the parts identical to those in Embodiments 1 and 2 are denoted by the same reference numerals and their description is omitted.

[0119] In the first and second embodiments, the window 12 and the window 13 are arranged on a straight line extending in the Z direction. However, in the third embodiment, the window 12 and the window 13 are not arranged on a straight line extending in the Z direction, but are arranged at different positions in the XY plane and the XZ plane. That is, the optical axis OA1 of the seed laser is folded back in the frame 11.

[0120] The gas laser amplifier 10C includes reflection mirrors 51, 52, 53, and 54. The reflection mirrors 51 and 53 are provided on the side surface 11B of the housing 11 where the window 13 is provided, and the reflection mirrors 52 and 54 are provided on the side surface 11A of the housing 11 where the window 12 is provided. The reflection mirrors 51, 52, 53, and 54 are arranged on the side surfaces 11A and 11B in the housing 11 so as to guide the seed laser incident from the window 12 to the window 13. Thus, an optical axis OA1 is formed which reaches the window 13 from the window 12 via the reflection mirrors 51, 52, 53, and 54.

[0121] The gas laser amplifier 10C includes partial reflection mirrors 16 and 19 and a damper 18. The partial reflection mirrors 16 and 19 constitute an optical resonator 42. The partial reflection mirrors 16 and 19 are arranged in the housing 11 so that the optical axis OA2 of the laser beam oscillated by the optical resonator 42 crosses the optical axis OA1 of the seed laser beam. Fig.18 and Fig.19 In the example, the partial reflector 16 is disposed in the area between the side 11A where the window 12 is disposed and the discharge electrode pair 20A arranged on the incident side of the seed laser and flows into the upstream side of the gas flow between the discharge electrodes 21A and 22A. In addition, the partial reflector 19 is disposed in the area between the side 11B where the window 13 is disposed and the discharge electrode pair 20B arranged on the emission side of the seed laser and flows into the upstream side of the gas flow between the discharge electrodes 21B and 22B. Therefore, both ends of the optical axis OA2 of the optical resonator 42 close to the partial reflectors 16 and 19 pass through the upstream side of the gas flow relative to the optical axis OA1. In addition, the central portion of the optical axis OA2 that crosses the optical axis OA1 substantially shares the excited laser gas with the optical axis OA1.

[0122] The damper 18 is configured to absorb the laser light transmitted through the partial reflection mirrors 16 and 19. A part of the laser light oscillated by the optical resonator 42 is emitted from the partial reflection mirrors 16 and 19 and is completely absorbed by the damper 18. Fig.18 and Fig.19 In the embodiment, the partial reflection mirrors 16 and 19 and the damper 18 of the optical resonator 42 are arranged outside the housing 11 , but they may also be arranged outside the housing 11 .

[0123] The gas laser amplifier 10C has apertures 31, 32, and 33 on the optical axes OA1 and OA2. The aperture 31 is arranged between the position corresponding to the discharge space 23A on the optical axis OA1 and the window 12, and between the position corresponding to the discharge space 23B on the optical axis OA1 and the window 13. The aperture 33 is arranged between the reflector 51 and the discharge space 23B on the optical axis OA1, between the position corresponding to the discharge space 23A on the optical axis OA1 and the reflector 52, between the position corresponding to the discharge space 23B on the optical axis OA1 and the reflector 53, and between the discharge space 23A and the reflector 54 on the optical axis OA1. The aperture 32 is arranged between the discharge space 23A and the partial reflector 16 on the optical axis OA2, and between the discharge space 23B and the partial reflector 19.

[0124] In the third embodiment, discharge electrodes 21B and 22B are arranged so that a portion of the optical axis connecting window 12 and reflector 51 in optical axis OA1 is included in discharge space 23B. Also, discharge electrodes 21A and 22A are arranged so that a portion of the optical axis connecting reflector 54 and window 13 in optical axis OA1 is included in discharge space 23A.

[0125] Here, the operation of the gas laser amplifier 10C is described. Fig.18 and Fig.19 The laser gas flows in the directions D1 and D2 shown. As a result, the laser gas flows between the discharge electrodes 21A and 22A and between the discharge electrodes 21B and 22B. A high-frequency voltage is applied between the discharge electrodes 21A and 22A and between the discharge electrodes 21B and 22B from a high-frequency power supply not shown in the figure, thereby forming discharge spaces 23A and 23B. The laser gas flowing into the discharge spaces 23A and 23B is excited. The excited laser gas flows into the optical axis OA1 located on the downstream side of each discharge electrode pair 20A and 20B. In addition, the optical axis OA2 is configured to pass through the discharge spaces 23A and 23B in most of it. The laser gas passing through the optical axes OA1 and OA2 is cooled by a heat exchanger not shown in the figure, flows into the discharge spaces 23A and 23B through a blower not shown in the figure, and circulates in the frame 11. In addition, the seed laser can be a pulse laser with a repetition frequency of tens of kHz to hundreds of kHz, or it can be a continuous wave laser.

[0126] The seed laser emitted from the laser light source 2 provided outside the gas laser amplifier 10C is incident into the frame 11 through the window 12, and propagates along the optical axis OA1. Then, the seed laser passes through the excited laser gas, is reflected by the reflector 51, passes through the excited laser gas again, and is reflected by the reflector 52. Then, it is reflected by the reflectors 53 and 54 in the same manner. Each time the seed laser is reflected by the reflectors 51, 52, 53, and 54, it passes through the excited laser gas, and is thereby amplified. The finally amplified seed laser, i.e., the amplified light, passes through the window 13 and is emitted to the outside of the frame 11. As described above, in Fig.18 and Fig.19 In the example, the seed laser is amplified while being folded back five times in the excited laser gas. In addition, here, the case of folding back four times is shown as an example, but the number of folding backs may be greater than or equal to two times.

[0127] Here, the reflectances R1 and R2 of the partial reflection mirrors 16 and 19 of the optical resonator 42 are set to the oscillation threshold gain g of the optical resonator 42. r The following conditions are satisfied. In addition, the diagram showing the operation of the gas laser amplifier 10C in the third embodiment is similar to that in the second embodiment. Figures 14 to 17The figures shown are the same and therefore refer to Figures 14 to 17 For explanation.

[0128] In the intervals ΔT10 and ΔT12 where the seed laser is incident on the gas laser amplifier 10C and amplified, the oscillation threshold gain g of the optical resonator 42 formed by the partial reflection mirrors 16 and 19 is r Set to be greater than the gain g on the optical axis OA2 when the laser is amplified p’ Therefore, if Fig.15 As shown, the seed laser is amplified, and when emitted from the window 13, a gain g greater than or equal to the oscillation threshold value is not formed on the optical resonator 42 side. r Therefore, laser light cannot be oscillated. That is, laser light is not emitted from the optical resonator 42. Similarly, the oscillation threshold gain g of the self-excited oscillation is s It also becomes the gain g on the optical axis OA1 when the seed laser is amplified. p Large value, so Fig.16 As shown, no self-oscillation occurs.

[0129] On the other hand, in the interval ΔT11 where the seed laser is not incident on the gas laser amplifier 10C, Fig.14 As shown in Figure 2, when the laser amplifier output becomes 0, Fig.17 As shown, the gain g in the gas laser amplifier 10C is a The oscillation threshold gain g of the optical resonator 42 is exceeded. r Therefore, if Fig.15 As shown in FIG. 1 , laser light is immediately oscillated from the optical resonator 42. At this time, the oscillation threshold gain g of the optical resonator 42 is r Less than the oscillation threshold gain g of self-oscillation s , so laser light is oscillated by the optical resonator 42 before self-oscillation occurs. Fig.16 As shown, no self-oscillation occurs. Moreover, the gain g on the optical axis OA1 in the gas laser amplifier 10C is a is consumed by the optical resonator 42 and becomes equal to the gain g on the optical axis OA1 when the optical resonator 42 oscillates. r’ Therefore, the gain g in the gas laser amplifier 10C is a Below the oscillation threshold gain g for self-oscillation s , no self-excited oscillation occurs. That is, the gas laser amplifier 10C involved in Embodiment 3 can suppress self-excited oscillation. Fig.15 As shown, part of the laser light oscillated by the optical resonator 42 passes through the partial reflection mirrors 16 and 19 and is absorbed by the damper 18 .

[0130] In the third embodiment, the reflecting mirrors 51, 52, 53, and 54 are arranged on the path in the housing 11 from the window 12 to the window 13, and the length of the optical axis OA1 of the excited laser gas is longer than that in the first and second embodiments. Thus, the seed laser can emit amplified light with a large output in addition to the effects of the first and second embodiments, as compared with the first and second embodiments.

[0131] Implementation method 4.

[0132] Fig. 20 This is a perspective view schematically showing an example of the structure of a gas laser device including a gas laser amplifier according to the fourth embodiment. Fig.21 Observed from the Y direction Fig. 20 FIG. 1 is a diagram showing the interior of a gas laser amplifier. In addition, the parts different from those in Embodiments 1, 2, and 3 are described below, and the parts identical to those in Embodiments 1, 2, and 3 are denoted by the same reference numerals and their description is omitted.

[0133] The gas laser amplifier 10D of the fourth embodiment has the same optical components constituting the optical axis OA1 for amplifying the seed laser as the third embodiment, but the structure of the optical resonator 43 is different from that of the third embodiment. In the fourth embodiment, the optical axis OA2 of the laser beam oscillated by the optical resonator 43 partially overlaps with the optical axis OA1 of the seed laser beam.

[0134] The gas laser amplifier 10D has polarizers 14, 15, partial reflectors 16, 19, and a damper 18. The polarizers 14, 15 are arranged on the optical axis OA1 outside the frame 11. The polarizer 14 is arranged on the optical axis OA1 outside the window 12, and the polarizer 15 is arranged on the optical axis OA1 outside the window 13. The polarizers 14, 15 transmit the seed laser and the amplified light having the same polarization direction PD1 as the seed laser, and reflect the laser having the polarization direction PD2 orthogonal to the polarization direction PD1. That is, the polarizers 14, 15 transmit the P polarized light, but reflect the S polarized light in the X direction. The polarizers 14, 15 are configured to reflect the S polarized light in the X direction.

[0135] The partial reflection mirror 16 transmits a part of the laser light reflected in the X direction by the polarizer 14 and reflects the remaining laser light toward the polarizer 14. The partial reflection mirror 19 transmits a part of the laser light reflected in the X direction by the polarizer 15 and reflects the remaining laser light toward the polarizer 15.

[0136] The damper 18 is disposed so as to absorb the laser light transmitted through the partial reflection mirrors 16 and 19 . The laser light oscillated by the optical resonator 43 is output from the partial reflection mirrors 16 and 19 , and all of it is absorbed by the damper 18 .

[0137] The partial reflection mirror 16 and the partial reflection mirror 19 constitute the optical resonator 43. The optical axis OA2 of the laser oscillated by the optical resonator 43 overlaps with the optical axis OA1 between the polarizer 14 and the polarizer 15. The laser oscillated by the optical resonator 43 is amplified by reciprocating between the partial reflection mirrors 16 and 19. In addition, the polarization direction PD2 of the laser oscillated by the optical resonator 43 is polarized in the direction reflected by the polarizers 14 and 15, and is orthogonal to the polarization direction PD1 of the seed laser. Therefore, the laser oscillated by the optical resonator 43 is reflected by the polarizers 14 and 15 and is not emitted from the gas laser amplifier 10D. In addition, a part of the laser that has passed through the partial reflection mirrors 16 and 19 is absorbed by the damper 18.

[0138] The gas laser amplifier 10D has an aperture 32 on the optical axis OA2. The aperture 32 is disposed between the polarizer 14 and the partial reflection mirror 16 and between the polarizer 15 and the partial reflection mirror 19 on the optical axis OA2.

[0139] Here, the operation of the gas laser amplifier 10D is described. Fig. 20 and Fig.21 The laser gas flows in the directions D1 and D2 shown. As a result, the laser gas flows between the discharge electrodes 21A and 22A and between the discharge electrodes 21B and 22B. A high-frequency voltage is applied between the discharge electrodes 21A and 22A and between the discharge electrodes 21B and 22B from a high-frequency power supply not shown in the figure, thereby forming discharge spaces 23A and 23B. The laser gas flowing into the discharge spaces 23A and 23B is excited. The excited laser gas flows into the optical axes OA1 and OA2 located on the downstream side of each discharge electrode pair 20A and 20B. The laser gas passing through the optical axes OA1 and OA2 is cooled by a heat exchanger not shown in the figure, flows into the discharge spaces 23A and 23B through a blower not shown in the figure, and circulates in the frame 11. In addition, the seed laser can be a pulse laser with a repetition frequency of tens of kHz to hundreds of kHz, or it can be a continuous wave laser.

[0140] The seed laser emitted from the laser light source 2 provided outside the gas laser amplifier 10D propagates along the optical axis OA1. Here, the seed laser is P-polarized light, and therefore passes through the polarizer 14 and is emitted into the frame 11 from the window 12. Furthermore, the seed laser passes through the excited laser gas, is reflected by the reflector 51, passes through the excited laser gas again, and is reflected by the reflector 52. Then, it is reflected by the reflectors 53 and 54 in the same manner. The seed laser passes through the excited laser gas each time it is reflected by the reflectors 51, 52, 53, and 54, and thereby the seed laser is amplified. The finally amplified seed laser, i.e., the amplified light, passes through the window 13. The amplified light emitted to the outside of the frame 11 is P-polarized light, and therefore passes through the polarizer 15.

[0141] As mentioned above, in Fig. 20 and Fig.21 In the embodiment, the seed laser is amplified while being folded back five times in the excited laser gas. In addition, here, the case where the seed laser is folded back four times is shown as an example, but the number of folding backs may be greater than or equal to two times.

[0142] On the other hand, laser light generated and amplified on an optical axis different from the optical axis OA1 of the gas laser amplifier 10D is blocked by the apertures 31 and 33 and is not emitted from the windows 12 and 13 .

[0143] In addition, laser light propagating on the same optical axis as the optical axis OA1 of the gas laser amplifier 10D is sometimes generated in the frame 11. As described above, the optical resonator 43 is formed by partial reflectors 16 and 19 outside the frame 11. The optical axis OA2 of the optical resonator 43 passes through the partial reflector 16, the polarizer 14, the polarizer 15, and the partial reflector 19. Between the polarizers 14 and 15, it becomes coaxial with the optical axis OA1 and passes through the excited laser gas. The polarization direction PD2 of the laser light oscillated by the optical resonator 43 is polarized in the direction reflected by the polarizers 14 and 15, and is orthogonal to the polarization direction PD1 of the seed laser. Therefore, the laser light is reflected between the partial reflectors 16 and 19 and amplified, but is reflected by the polarizers 14 and 15, so it is separated from the optical axis OA1 outside the frame 11. In addition, a part of the laser light reaching the partial reflectors 16 and 19 is transmitted through the partial reflectors 16 and 19 and absorbed by the damper 18. Thus, the laser light oscillated by the optical resonator 43 is not emitted to the outside. Furthermore, since the polarization component oriented in the same direction as the seed laser light is not reflected by the polarizers 14 and 15 , it cannot be resonated by the optical resonator 43 and laser oscillation does not occur.

[0144] Here, the conditions of the reflectances R1 and R2 of the partial reflection mirrors 16 and 19 for performing the above-mentioned operation in the gas laser amplifier 10D according to the fourth embodiment are described. Figures 7 to 10 The figures shown are the same and therefore refer to Figures 7 to 10 However, in the fourth embodiment, Figure 8 The optical resonator output is the sum of the laser outputs output from the partial reflection mirrors 16 and 19 of the optical resonator 43 and absorbed by the damper 18 .

[0145] In the intervals ΔT10 and ΔT12 where the seed laser is incident on the gas laser amplifier 10D and amplified, the gain in the gas laser amplifier 10D is consumed by the incident seed laser. Fig.10 As shown, the gain g in the gas laser amplifier 10D a Equal to the gain g when the seed laser is amplifiedp In the fourth embodiment, the oscillation threshold gain g of the optical resonator 43 is r Set to a gain g greater than that when the seed laser is amplified p Therefore, on the optical resonator 43 side, a gain greater than or equal to the oscillation threshold gain g is not formed. r The gain, such as Figure 8 As shown, laser light cannot be oscillated. That is, laser light is not emitted from the optical resonator 43. Similarly, the oscillation threshold gain g of the self-excited oscillation is s It also becomes the gain g when the seed laser is amplified p High value, so Fig. 9 As shown, no self-oscillation occurs.

[0146] On the other hand, in the interval ΔT11 where the seed laser is not incident on the gas laser amplifier 10D, Figure 7 As shown in Figure 2, when the laser amplifier output becomes 0, Fig.10 As shown, the gain g in the gas laser amplifier 10D a The small signal gain g0 exceeds the oscillation threshold gain g of the optical resonator 43. r Therefore, if Figure 8 As shown in FIG. 1 , laser light is immediately oscillated from the optical resonator 43. At this time, the oscillation threshold gain g of the optical resonator 43 is r Less than the oscillation threshold gain g of self-oscillation s , so laser light is oscillated by the optical resonator 43 before self-oscillation occurs. Fig. 9 As shown, no self-oscillation occurs. Moreover, the gain g in the gas laser amplifier 10D a is consumed by the optical resonator 43 and becomes equal to the oscillation threshold gain g of the optical resonator 43 r Therefore, the gain g in the gas laser amplifier 10D is a Below the oscillation threshold gain g for self-oscillation s , no self-oscillation occurs. That is, the gas laser amplifier 10D involved in the fourth embodiment can suppress self-oscillation. Figure 8 As shown, part of the laser light oscillated by the optical resonator 43 passes through the partial reflection mirrors 16 and 19 and is absorbed by the damper 18 .

[0147] Here, the optical path length L of the range into which the excited laser gas flows within the optical axis OA1 of the gas laser amplifier 10D is denoted as p The gain of the seed laser amplification is expressed by equation (1) as described above.

[0148] In addition, the reflectances of the partial reflection mirrors 16 and 19 of the optical resonator 43 are respectively set to R1 and R2. At this time, the optical path length L of the optical resonator 43 in the range where the excited laser gas flows in the optical axis OA2 is r The gain during oscillation is expressed by the following equation (10).

[0149] [Formula 5]

[0150]

[0151] When the seed laser is incident, the optical resonator 43 must satisfy the condition of equation (3) in order to automatically stop the oscillation. According to equations (1), (10) and (3), the reflectivities R1 and R2 of the partial reflectors 16 and 19 of the optical resonator 43 must satisfy the condition of the following equation (11).

[0152] [Formula 6]

[0153]

[0154] For example, assuming that a 100 W seed laser is input, the amplification factor of the gas laser amplifier 10D that reaches an output of 25 kW of amplified light is 250 times. The conditions of the reflectances R1 and R2 of the partial reflection mirrors 16 and 19 at this time are expressed by the following equation (12).

[0155] R1R2<16×10 -6 ···(12)

[0156] On the other hand, the optical path length L of the range into which the excited laser gas flows within the optical axis OA1 is p The small signal gain of is expressed by equation (6).

[0157] For example, the saturation intensity I s 200W / cm 2 , the beam diameter of the amplified seed laser The optical path length L of the range where the excited laser gas flows in the optical axis OA1 is 30 mm when the above-mentioned 100 W laser is input and outputted to 25 kW after amplification. p The small signal gain of is expressed by equation (7).

[0158] Self-excited oscillation is generated by reflected or diffracted light from external components or internal apertures 31, 32, 33 of the gas laser amplifier 10D. Therefore, the feedback rate of light during self-excited oscillation is very small, and the oscillation threshold of self-excited oscillation is often roughly equal to the small signal gain. Therefore, before self-excited oscillation light is generated, in order to oscillate by the optical resonator 43, the condition of formula (8) must be satisfied.

[0159] By substituting equation (10) and equation (7) into equation (8), the conditions of reflectances R1 and R2 of the partial reflection mirrors 16 and 19 of the optical resonator 43 are obtained according to the following equation (13).

[0160] R1R2>7×10 -21 ···(13)

[0161] According to equations (12) and (13), the product of the reflectivity R1 of the partial reflector 16 and the reflectivity R2 of the partial reflector 19 is set to be greater than 7×10 -21 And less than 16×10 -6 By setting the value of , the occurrence of self-oscillation in the gas laser amplifier 10D can be suppressed as described above.

[0162] As described above, in the fourth embodiment, the optical resonator 43 is provided in the gas laser amplifier 10D, and the reflectances R1 and R2 of the partial reflection mirrors 16 and 19 of the optical resonator 43 are appropriately set. As a result, the oscillation threshold gain of the laser light generated by the optical resonator 43 is larger than the gain when the seed laser light incident from the outside is amplified and smaller than the threshold gain of the self-excited oscillation. As a result, the self-excited oscillation can be suppressed without using a device that changes the loss of the optical resonator 43 over time.

[0163] In addition, Fig. 20 In the embodiment, the polarization direction PD1 of the seed laser is set to the X direction which is the same as the air flow direction between the discharge electrodes 21A and 22A and between the discharge electrodes 21B and 22B, but the polarization direction PD1 of the seed laser can also be set to the discharge gap length direction, that is, the Y direction, and the polarization direction PD2 of the laser light generated by the optical resonator 43 can be set to the X direction orthogonal thereto. That is, the polarizers 14 and 15 can be set to reflect the P polarized light and transmit the S polarized light.

[0164] In addition, Fig. 20 In the embodiment, the optical resonator 43 is arranged outside the frame 11, but the polarizer 14, the partial reflector 16 and the damper 18 can also be arranged inside the frame 11, and the polarizer 15, the partial reflector 19 and the damper 18 can also be arranged inside the frame 11.

[0165] And, in Fig. 20 In the embodiment, the light reciprocating in the optical resonator 43 is reflected by the polarizers 14 and 15 in the X direction, which is the direction of the airflow between the discharge electrodes 21A and 22A and between the discharge electrodes 21B and 22B, but it can also be reflected in the Y direction, which is the direction of the length of the electrode gap. Fig. 20In the embodiment, the optical axis OA1 of the seed laser of the gas laser amplifier 10D is a four-pass structure that passes through the discharge space four times, but it can also be a one-pass structure that passes through the discharge space 23A, 23B without the reflectors 51, 52, 53, 54 only once as in embodiment 1, or it can be a structure that passes through the discharge space 23A, 23B multiple times other than four times.

[0166] According to the fourth embodiment, the same effects as those of the third embodiment can be obtained.

[0167] Implementation method 5.

[0168] Fig. 22 This is a perspective view schematically showing an example of the structure of a gas laser device including a gas laser amplifier according to the fifth embodiment. Fig.23 Observed from the Y direction Fig. 22 FIG. 1 is a diagram showing the interior of a gas laser amplifier. In addition, the parts different from those in Embodiments 1, 2, 3, and 4 are described below, and the parts identical to those in Embodiments 1, 2, 3, and 4 are denoted by the same reference numerals and their description is omitted.

[0169] The gas laser amplifier 10E further includes a beam splitter 56 and dampers 57a and 57b in the structure of the gas laser amplifier 10D of the fourth embodiment. The beam splitter 56 is arranged between the partial reflection mirror 16 and the polarizer 14. The damper 57a absorbs the laser light reflected from the beam splitter 56 by incident on the frame 11 side. The damper 57b absorbs the laser light reflected from the beam splitter 56 by incident on the partial reflection mirror 16 side. In addition, the other structures in the gas laser amplifier 10E are the same as those in the fourth embodiment.

[0170] The operation of the gas laser amplifier 10E according to the fifth embodiment is the same as that described in the fourth embodiment. However, when the laser light amplified by the optical resonator 43 propagates from the window 12 to the partial reflection mirror 16, a part of the laser light is reflected by the beam splitter 56 and absorbed by the damper 57a. In addition, at the partial reflection mirror 16, a part of the laser light is transmitted and absorbed by the damper 18, but the remaining laser light is reflected and propagates along the optical axis OA2 to the partial reflection mirror 19. At this time, a part of the reflected laser light is reflected by the beam splitter 56 and absorbed by the damper 57b.

[0171] Here, the conditions of the reflectances R1 and R2 of the partial reflection mirrors 16 and 19 and the transmittance T of the beam splitter 56 for performing the above-mentioned operation in the gas laser amplifier 10E according to the fifth embodiment are described. Figures 7 to 10 The figures shown are the same and therefore refer to Figures 7 to 10However, in Embodiment 5, Figure 8 The optical resonator output is the sum of the laser output output from the partial reflection mirrors 16 and 19 of the optical resonator 43 and absorbed by the damper 18 and the laser output split by the beam splitter 56 and absorbed by the dampers 57a and 57b.

[0172] In the intervals ΔT10 and ΔT12 where the seed laser is incident on the gas laser amplifier 10E and amplified, the gain in the gas laser amplifier 10E is consumed by the incident seed laser. Fig.10 As shown, the gain g in the gas laser amplifier 10E a Equal to the gain g when the seed laser is amplified p In the fifth embodiment, the oscillation threshold gain g of the optical resonator 43 formed by the partial reflection mirrors 16 and 19 is r Set to a gain g greater than that when the seed laser is amplified p Therefore, a value greater than or equal to the oscillation threshold gain g is not formed on the optical resonator 43 side. r The gain, such as Figure 8 As shown, laser light cannot be oscillated. That is, laser light is not emitted from the optical resonator 43. Similarly, the oscillation threshold gain g of the self-excited oscillation is s It also becomes the gain g when the seed laser is amplified p High value, so Fig. 9 As shown, no self-oscillation occurs.

[0173] On the other hand, in the interval ΔT11 where the seed laser is not incident on the gas laser amplifier 10E, Figure 7 As shown in Figure 2, when the laser amplifier output becomes 0, Fig.10 As shown, the gain g in the gas laser amplifier 10E a The small signal gain g0 exceeds the oscillation threshold gain g of the optical resonator 43. r Therefore, if Figure 8 As shown in FIG. 1 , laser light is immediately oscillated from the optical resonator 43. At this time, the oscillation threshold gain g of the optical resonator 43 is r Less than the oscillation threshold gain g of self-oscillation s , so laser light is oscillated by the optical resonator 43 before self-oscillation occurs. Fig. 9 As shown, no self-oscillation occurs. Moreover, the gain g in the gas laser amplifier 10E a is consumed by the optical resonator 43 and becomes equal to the oscillation threshold gain g of the optical resonator 43 r Therefore, the gain g in the gas laser amplifier 10E is a Below the oscillation threshold gain g for self-oscillation s, no self-oscillation occurs. That is, the gas laser amplifier 10E involved in Embodiment 5 can suppress self-oscillation. In addition, Figure 8 As shown, part of the laser light oscillated by the optical resonator 43 is transmitted through the partial reflection mirrors 16 and 19 or is reflected by the beam splitter 56 and is absorbed by the dampers 18, 57a, and 57b.

[0174] Here, the optical path length L of the range into which the excited laser gas flows within the optical axis OA1 is p The gain of the seed laser amplification is expressed by equation (1) as described above.

[0175] In addition, the reflectances of the partial reflection mirrors 16 and 19 of the optical resonator 43 are respectively set to R1 and R2, and the transmittance of the beam splitter 56 is set to T. At this time, the optical path length L of the optical resonator 43 in the range where the excited laser gas flows in the optical axis OA2 is r The gain during oscillation is expressed by the following equation (14).

[0176] [Formula 7]

[0177]

[0178] When the seed laser is injected, in order for the oscillation of the optical resonator 43 to stop automatically, the condition of formula (3) must be satisfied. According to formulas (1), (14) and (3), the reflectances R1 and R2 of the partial reflectors 16 and 19 of the optical resonator 43 and the transmittance T of the spectrometer 56 must satisfy the condition of the following formula (15).

[0179] [Formula 8]

[0180]

[0181] For example, assuming that a 100W seed laser is input, the amplification factor of the gas laser amplifier 10E that reaches an output of 25kW of amplified light is 250 times. The conditions of the reflectances R1 and R2 of the partial reflection mirrors 16 and 19 and the transmittance T of the beam splitter 56 are as follows (16).

[0182] R1R2T 2 <16×10 -6 ···(16)

[0183] On the other hand, the optical path length L of the range into which the excited laser gas flows within the optical axis OA1 is p The small signal gain of is expressed by equation (6).

[0184] For example, the saturation intensity I s 200W / cm 2 , the beam diameter of the amplified seed laser The optical path length L of the range where the excited laser gas flows in the optical axis OA1 is 30 mm when the above-mentioned 100 W laser is input and 25 kW is output after amplification. p The small signal gain of is expressed by equation (7).

[0185] Self-excited oscillation is generated by reflected or diffracted light from external components or internal apertures 31, 32, 33 of the gas laser amplifier 10E. Therefore, the feedback rate of light during self-excited oscillation is very small, and the oscillation threshold of self-excited oscillation is often roughly equal to the small signal gain. Therefore, before the self-excited oscillation light is generated, in order to oscillate by the optical resonator 43, the condition of formula (8) must be satisfied.

[0186] By substituting equations (14) and (7) into equation (8), the conditions of the reflectances R1 and R2 of the partial reflection mirrors 16 and 19 of the optical resonator 43 and the transmittance T of the spectrometer 56 are obtained by the following equation (17).

[0187] R1R2T 2 >7×10 -21 ···(17)

[0188] According to equations (16) and (17), the product of the reflectivity R1 of the partial reflecting mirror 16, the reflectivity R2 of the partial reflecting mirror 19, and the square of the transmittance T of the beam splitter 56 is set to be 7×10 -21 Larger than 16×10 -6 By setting a small value, it is possible to suppress the occurrence of self-oscillation in the gas laser amplifier 10E as described above.

[0189] That is, by using the beam splitter 56 , the degree of freedom in selecting the reflectances R1 and R2 of the partial reflecting mirrors 16 and 19 and the transmittance T of the beam splitter 56 increases compared to the case of the fourth embodiment.

[0190] As described above, in the fifth embodiment, the optical resonator 43 is provided in the gas laser amplifier 10E, and the reflectances R1 and R2 of the partial reflection mirrors 16 and 19 of the optical resonator 43 and the transmittance T of the spectrometer 56 are appropriately set. As a result, the oscillation threshold gain of the laser light generated by the optical resonator 43 is larger than the gain when the seed laser light incident from the outside is amplified, and is smaller than the threshold gain of the self-excited oscillation. As a result, the self-excited oscillation can be suppressed without using a device that changes the loss of the optical resonator 43 over time.

[0191] In addition, Fig. 22In the embodiment, the polarization direction PD1 of the seed laser is set to the X direction which is the same as the air flow direction between the discharge electrodes 21A and 22A and between the discharge electrodes 21B and 22B, but the polarization direction PD1 of the seed laser can also be set to the discharge gap length direction, that is, the Y direction, and the polarization direction PD2 of the laser light generated by the optical resonator 43 can be set to the X direction orthogonal thereto. That is, the polarizers 14 and 15 can be set to reflect the P polarized light and transmit the S polarized light.

[0192] In addition, Fig. 22 In the embodiment, the optical resonator 43 is arranged outside the frame 11, but the polarizer 14, the spectrometer 56, the partial reflector 16 and the dampers 18, 57a, 57b can also be arranged inside the frame 11, and the polarizer 15, the partial reflector 19 and the damper 18 can also be arranged inside the frame 11.

[0193] And, in Fig. 22 In the embodiment, the light reciprocating in the optical resonator 43 is reflected by the polarizers 14 and 15 in the X direction, which is the direction of the airflow between the discharge electrodes 21A and 22A and between the discharge electrodes 21B and 22B, but it can also be reflected in the Y direction, which is the direction of the length of the electrode gap. Fig. 22 In the embodiment, the optical axis OA1 of the seed laser is a four-pass structure in which the optical axis OA1 passes through the discharge space four times, but it can also be a one-pass structure in which the discharge spaces 23A and 23B without the reflectors 51, 52, 53, and 54 are passed only once as in the first embodiment, or it can be a structure in which the discharge spaces 23A and 23B are passed multiple times other than four times. Fig. 22 , a structure in which one beam splitter 56 is provided is shown, but a plurality of beam splitters 56 may be provided on the optical axis OA2 between the polarizer 14 and the partial reflection mirror 16 or on the optical axis OA2 between the polarizer 15 and the partial reflection mirror 19 .

[0194] According to the fifth embodiment, the same effects as those of the third embodiment can be obtained.

[0195] Implementation method 6.

[0196] Fig.24 This is a perspective view schematically showing an example of the structure of a gas laser device including a gas laser amplifier according to the sixth embodiment. Fig.25 Observed from the Y direction Fig.24 FIG. 1 is a diagram showing the interior of a gas laser amplifier. In addition, the parts different from those in Embodiments 1, 2, 3, 4, and 5 are described below, and the parts identical to those in Embodiments 1, 2, 3, 4, and 5 are denoted by the same reference numerals and their description is omitted.

[0197] The gas laser amplifier 10F further includes a spectrometer 56 and dampers 57a and 57b in the structure of the gas laser amplifier 10C of the third embodiment. The spectrometer 56 is arranged between the partial reflection mirror 16 and the aperture 32. The damper 57a absorbs the laser light reflected from the spectrometer 56 by incident on the side of the frame 11. The damper 57b absorbs the laser light reflected from the spectrometer 56 by incident on the side of the partial reflection mirror 16. In addition, the other structures in the gas laser amplifier 10F are the same as those in the third embodiment.

[0198] The operation of the gas laser amplifier 10F according to the sixth embodiment is the same as that described in the third embodiment. However, when the laser light amplified by the optical resonator 42 propagates from the partial reflection mirror 19 to the partial reflection mirror 16, a part of the laser light is reflected by the beam splitter 56 and absorbed by the damper 57a. In addition, a part of the laser light is transmitted by the partial reflection mirror 16 and absorbed by the damper 18, but the remaining laser light is reflected and propagates along the optical axis OA2 to the partial reflection mirror 19. At this time, a part of the reflected laser light is reflected by the beam splitter 56 and absorbed by the damper 57b.

[0199] Here, the reflectances R1 and R2 of the partial reflection mirrors 16 and 19 of the optical resonator 42 and the transmittance T of the beam splitter 56 are set to the oscillation threshold gain g of the optical resonator 42. r The following conditions are satisfied. In addition, the diagram showing the operation of the gas laser amplifier 10F in the sixth embodiment is similar to that in the second embodiment. Figures 14 to 17 The figures shown are the same and therefore refer to Figures 14 to 17 However, in the case of the sixth embodiment, Fig.15 The optical resonator output is the sum of the laser output output from the partial reflection mirrors 16 and 19 of the optical resonator 42 and absorbed by the damper 18 and the laser output reflected by the beam splitter 56 and absorbed by the dampers 57a and 57b.

[0200] The intervals ΔT10 and ΔT12 are when the seed laser is incident on the gas laser amplifier 10F and amplified. In this case, as described above, the gain in the gas laser amplifier 10F is consumed by the incident seed laser. In addition, the gain of the optical resonator 42 during amplification on the optical axis OA2 at this time is g p’ .

[0201] In the sixth embodiment, the oscillation threshold gain g of the optical resonator 42 formed by the partial reflection mirrors 16 and 19 is r Set to be greater than the gain g on the optical axis OA2 when the laser is amplified p’ Therefore, if Fig.15 As shown, the seed laser is amplified, and when emitted from the window 13, a gain g greater than or equal to the oscillation threshold value is not formed on the optical resonator 42 side.r Therefore, laser light cannot be oscillated. That is, laser light is not emitted from the optical resonator 42. Similarly, the oscillation threshold gain g of the self-excited oscillation is s It also becomes the gain g on the optical axis OA1 when the laser is amplified. p Large value, so Fig.16 As shown, no self-oscillation occurs.

[0202] On the other hand, the interval ΔT11 is an interval in which the seed laser is not incident on the gas laser amplifier 10F. Fig.14 As shown in Figure 2, when the laser amplifier output becomes 0, Fig.17 As shown, the gain g in the gas laser amplifier 10F a The oscillation threshold gain g of the optical resonator 42 is exceeded. r Therefore, if Fig.15 As shown in FIG. 1 , laser light is immediately oscillated from the optical resonator 42. At this time, the oscillation threshold gain g of the optical resonator 42 is r Less than the oscillation threshold gain g of self-oscillation s , so laser light is oscillated by the optical resonator 42 before self-oscillation occurs. Fig.16 As shown, no self-oscillation occurs. Moreover, the gain g on the optical axis OA1 in the gas laser amplifier 10F is a is consumed by the optical resonator 42 and becomes equal to the gain g on the optical axis OA1 when the optical resonator 42 oscillates. r’ Therefore, the gain g in the gas laser amplifier 10F is a Below the oscillation threshold gain g for self-oscillation s , no self-oscillation occurs. That is, the gas laser amplifier 10F involved in Embodiment 6 can suppress self-oscillation. Fig.15 As shown, part of the laser light oscillated by the optical resonator 42 passes through the partial reflection mirrors 16 and 19 and is absorbed by the damper 18. In addition, part of the laser light oscillated by the optical resonator 42 is reflected by the beam splitter 56 and is absorbed by the dampers 57a and 57b.

[0203] Further, similarly to the fifth embodiment, the degree of freedom in selecting the reflectances R1 and R2 of the partial reflecting mirrors 16 and 19 and the transmittance T of the beam splitter 56 is increased compared to the third embodiment.

[0204] According to the sixth embodiment, the same effects as those of the third embodiment can be obtained.

[0205] Implementation method 7.

[0206] Fig.261 is an exploded perspective view schematically showing an example of the structure of a gas laser device having a gas laser amplifier according to Embodiment 7. The gas laser device 1 includes a laser light source 2, a gas laser amplifier 10D according to Embodiment 4, and a gas laser amplifier 10A according to Embodiment 1. Here, the gas laser amplifier 10A is connected in such a manner that the seed laser from the laser light source 2 is incident on the window 12 of the gas laser amplifier 10D according to Embodiment 4, and the amplified light emitted from the gas laser amplifier 10D is incident on the window 12 of the gas laser amplifier 10A according to Embodiment 1. That is, in the gas laser device 1, the gas laser amplifier 10D having a folding structure of mirrors 51, 52, 53, and 54 for reflecting the seed laser from the laser light source 2 in the housing 11 is arranged at the front stage, and the gas laser amplifier 10A having a single-pass structure without a mirror for reflecting the seed laser is arranged at the rear stage. In one example, the laser light source 2 and the gas laser amplifier 10D and the gas laser amplifier 10D and the gas laser amplifier 10A are connected by optical fibers.

[0207] In the gas laser device 1 as described above, the seed laser emitted from the laser light source 2 is incident into the frame 11 along the optical axis OA1 through the window 12 of the gas laser amplifier 10D, and is amplified by passing through the excited laser gas. In the gas laser amplifier 10D, the optical axis OA1 is folded back multiple times in the frame 11, so the seed laser is amplified multiple times. The amplified seed laser is emitted to the outside of the frame 11 through the window 13 of the gas laser amplifier 10D, and is incident to the window 12 of the gas laser amplifier 10A configured in the subsequent stage. The amplified light incident into the frame 11 of the gas laser amplifier 10A from the window 12 is further amplified by passing through the excited laser gas, and is emitted to the outside through the window 13.

[0208] Here, conditions of the reflectances R1 and R2 of the partial reflection mirrors 16 and 19 of the gas laser amplifier 10D according to the seventh embodiment and the reflectances R3 and R4 of the partial reflection mirror 16 and the total reflection mirror 17 of the gas laser amplifier 10A are described.

[0209] Fig. 27 FIG. 1 is a diagram showing an example of a change in the output of a laser beam amplified by the gas laser amplifier according to Embodiment 7 with respect to time. Fig.28 This is a diagram showing an example of changes in the optical resonator output with respect to time in the gas laser amplifier according to the seventh embodiment. Fig.29 This is a diagram showing an example of a change in the self-excited oscillation output with respect to time in the gas laser amplifier according to the seventh embodiment. Fig.30 is a diagram showing an example of a change in gain with respect to time in the first-stage gas laser amplifier according to Embodiment 7. Fig.31These are diagrams showing an example of a change in gain with respect to time in the second-stage gas laser amplifier according to Embodiment 7. In these diagrams, the horizontal axis represents time.

[0210] also, Fig. 27 The laser amplification output of φ represents the output of the seed laser amplified by the two gas laser amplifiers 10D and 10A connected along the optical axis OA1. Fig.28 The optical resonator output is the laser output output from the partial reflection mirrors 16 and 19 of the optical resonators 43 and 40 in the gas laser amplifiers 10D and 10A connected along the optical axis OA1 and absorbed by the damper 18. Curve C1 shows the laser output of the optical resonator 43 in the first-stage gas laser amplifier 10D, and curve C2 shows the laser output of the optical resonator 40 in the second-stage gas laser amplifier 10A. Fig.30 The gain g of the first-stage gas laser amplifier 10D is shown as a1 , Fig.31 The gain g of the second-stage gas laser amplifier 10A is shown as a2 In addition, Fig.30 and Fig.31 In, g r1 , g r2 are the oscillation threshold gains of the optical resonators 43 and 40 in the first-stage and second-stage gas laser amplifiers 10D and 10A, respectively, and g p1 , g p2 These are the gains in the first-stage and second-stage gas laser amplifiers 10D and 10A, respectively, when the seed laser is amplified.

[0211] In the interval ΔT10 and ΔT12, when the seed laser is injected into the gas laser amplifier 10D and 10A and amplified, as described above, the gain in the gas laser amplifier 10D and 10A is consumed by the injected seed laser. Fig.30 and Fig.31 As shown, the gain g in the first and second stage gas laser amplifiers 10D and 10A is a1 , g a2 are equal to the gain g when the seed laser is amplified p1 , g p2 In the seventh embodiment, the oscillation threshold gain g of the optical resonator 43, 40 in the first-stage and second-stage gas laser amplifiers 10D, 10A is r1 , g r2 The gain g is set to be greater than that when the laser is amplified. p1 , g p2 Therefore, no oscillation threshold gain g is formed on the optical resonator 43, 40 side of each gas laser amplifier 10D, 10A. r1 , gr2 The gain, such as Fig.28 As shown, laser light cannot be oscillated. That is, laser light is not emitted from each optical resonator 43, 40. Similarly, the oscillation threshold gain g of the self-excited oscillation is s It also becomes the gain g when the seed laser is amplified p1 , g p2 Large value, so Fig.29 As shown, no self-oscillation occurs.

[0212] On the other hand, the interval ΔT11 is an interval in which the seed laser is not incident on the gas laser amplifiers 10D and 10A. Fig. 27 As shown in Figure 2, when the laser amplifier output becomes 0, Fig.30 and Fig.31 As shown, the gain g in the gas laser amplifiers 10D and 10A is a1 , g a2 The small signal gain g0 exceeds the oscillation threshold gain g of the optical resonator 43, 40 in each of the gas laser amplifiers 10D, 10A. r1 , g r2 Therefore, if Fig.28 As shown in the curves C1 and C2, laser light is immediately oscillated from the optical resonators 43 and 40 in the gas laser amplifiers 10D and 10A. At this time, the oscillation threshold gain g of the optical resonators 43 and 40 in the gas laser amplifiers 10D and 10A is r1 , g r2 Less than the oscillation threshold gain g of self-oscillation s Therefore, in each gas laser amplifier 10D, 10A, laser light is oscillated by the optical resonator 43, 40 before self-excited oscillation occurs. Fig.29 As shown, no self-oscillation occurs. Moreover, the gain g in the gas laser amplifiers 10D and 10A is a1 , g a2 is consumed by the optical resonators 43 and 40, and becomes equal to the oscillation threshold gain g of the optical resonators 43 and 40 in the respective gas laser amplifiers 10D and 10A. r1 , g r2 Therefore, the gain g in each gas laser amplifier 10D, 10A is a1 , g a2 Below the oscillation threshold gain g for self-oscillation s , no self-oscillation occurs. That is, the gas laser device 1 involved in embodiment 7 can suppress self-oscillation. In addition, Fig.28 As shown, part of the laser light oscillated by the optical resonators 43 and 40 passes through the partial reflection mirrors 16 and 19 and is absorbed by the damper 18 .

[0213] Here, the gain per unit length when the seed laser light on the optical axis OA1 is amplified when the seed laser light is incident on the first-stage gas laser amplifier 10D, that is, the residual gain is denoted as g. p1 In addition, the output of the seed laser when it is injected into the first-stage gas laser amplifier 10D is denoted as P1 in The output of the amplified seed laser, i.e., the amplified light emitted from the first-stage gas laser amplifier 10D is defined as P1. out The optical path length L of the range into which the excited laser gas in the first-stage gas laser amplifier 10D flows within the optical axis OA1 is p1 The gain of the seed laser amplification is expressed by the following equation (18).

[0214] [Formula 9]

[0215]

[0216] In addition, the reflectances of the partial reflection mirrors 16 and 19 of the first-stage optical resonator 43 are respectively represented by R1 and R2, and the gain per unit length when the optical resonator 43 oscillates, that is, the oscillation threshold gain is represented by g r1 At this time, the optical path length L of the range into which the excited laser gas flows within the optical axis OA2 is r1 The gain of laser amplification generated by the optical resonator 43 is expressed by the following equation (19).

[0217] [Formula 10]

[0218]

[0219] In the first-stage gas laser amplifier 10D, when the seed laser is incident, the oscillation of the optical resonator 43 automatically stops, and the condition of the following equation (20) must be satisfied.

[0220] g p1 L p1 <g r1 L r1 ···(20)

[0221] According to equations (18), (19), and (20), the reflectivities R1 and R2 of the partial reflection mirrors 16 and 19 of the optical resonator 43 must satisfy the condition of the following equation (21).

[0222] [Formula 11]

[0223]

[0224] For example, assuming that a seed laser of 100 W or less is input, the amplification factor of the gas laser amplifier 10D reaching 10 kW of amplified light is 100 times or more. The conditions of the reflectances R1 and R2 of the partial reflection mirrors 16 and 19 at this time are as follows (22).

[0225] R1R2<100×10 -6 ···(twenty two)

[0226] On the other hand, the beam intensity of the seed laser at the time of injection is set to I1 in , the beam intensity of the amplified light after being amplified by the first-stage gas laser amplifier 10D is set to I1 out , set the saturation intensity to I s , the small signal gain of the first-stage gas laser amplifier 10D is set to g 01 The optical path length L of the range into which the excited laser gas flows within the optical axis OA1 is p1 The small signal gain of is expressed by the following equation (23).

[0227] [Formula 12]

[0228]

[0229] For example, the saturation intensity I s 200W / cm 2 , the beam diameter of the seed laser after being amplified by the first-stage gas laser amplifier 10D is The optical path length L of the range where the excited laser gas flows in the optical axis OA1 is 15 mm when the above-mentioned 100 W laser is input and 10 kW amplified light is output after amplification. p1 The small signal gain of is expressed by the following equation (24).

[0230] g 01 L p1 ≒33···(24)

[0231] Self-excited oscillation is generated by reflected or diffracted light from external components or internal apertures 31, 32, 33 and other components of the first-stage gas laser amplifier 10D. Therefore, the feedback rate of light during self-excited oscillation is very small, and the oscillation threshold of self-excited oscillation is often roughly equal to the small signal gain. Therefore, before the self-excited oscillation light is generated, in order to oscillate by the optical resonator 43, the following condition (25) must be satisfied.

[0232] g 01 L p1 >g r1 L r1 ···(25)

[0233] According to equations (19) and (24), the reflectivities R1 and R2 of the partial reflection mirrors 16 and 19 of the optical resonator 43 must satisfy the condition of the following equation (26).

[0234] R1R2>48×10 -30 ···(26)

[0235] According to equations (22) and (26), the product of the reflectivity R1 of the partial reflector 16 and the reflectivity R2 of the partial reflector 19 is set to be 48×10 -30 Larger than 100×10 -6 By setting the value to be small, the occurrence of self-oscillation in the first-stage gas laser amplifier 10D can be suppressed as described above.

[0236] In addition, the gain per unit length when the laser light on the optical axis OA1 is amplified when the amplified light is incident in the second-stage gas laser amplifier 10A, that is, the residual gain is denoted as g. p2 In addition, the output of the amplified light when it is incident on the second-stage gas laser amplifier 10A is referred to as P2 in The output of the amplified light emitted from the second-stage gas laser amplifier 10A is defined as P2 out The optical path length L of the range into which the excited laser gas in the second-stage gas laser amplifier 10A flows within the optical axis OA1 is p2 The gain of the seed laser amplification is expressed by the following equation (27).

[0237] [Formula 13]

[0238]

[0239] In addition, the reflectances of the partial reflection mirror 16 and the total reflection mirror 17 of the second-stage optical resonator 40 are respectively set to R3 and R4, and the gain per unit length during oscillation of the optical resonator 40, that is, the oscillation threshold gain, is set to g r2 At this time, the laser light generated by the optical resonator 40 has an optical path length L within the range where the excited laser gas flows in the optical axis OA2. r2 The amplified gain is expressed by the following equation (28).

[0240] [Formula 14]

[0241]

[0242] In the second-stage gas laser amplifier 10A, when the amplified light is injected, the oscillation of the optical resonator 40 is automatically stopped, and the condition of the following formula (29) must be satisfied.

[0243] g p2 Lp2 <g r2 L r2 ···(29)

[0244] According to equations (27), (28), and (29), the reflectivity R3 of the partial reflection mirror 16 and the reflectivity R4 of the total reflection mirror 17 of the optical resonator 40 must satisfy the condition of the following equation (30).

[0245] [Formula 15]

[0246]

[0247] For example, assuming that a seed laser of 100W or less is input, the amplification factor of the second-stage gas laser amplifier 10A reaches 25kW or more when the output of the amplified light reaches 2.5 times or more. At this time, the reflectivity R3 of the partial reflection mirror 16 and the reflectivity R4 of the total reflection mirror 17 are given by the following equation (31).

[0248] R3R4<160×10 -3 ···(31)

[0249] On the other hand, the beam intensity of the amplified light when incident on the second-stage gas laser amplifier 10A is denoted as I2 in The beam intensity of the amplified light after being amplified by the second-stage gas laser amplifier 10A is set to I2 out , set the saturation intensity to I s , the small signal gain of the second-stage gas laser amplifier 10A is set to g 02 The optical path length L of the range into which the excited laser gas flows within the optical axis OA1 is p2 The small signal gain of is expressed by the following equation (32).

[0250] [Formula 16]

[0251]

[0252] For example, the saturation intensity I s 200W / cm 2 , the beam diameter of the seed laser amplified by the second-stage gas laser amplifier 10A is The optical path length L of the range where the excited laser gas flows in the optical axis OA1 is 30 mm, when the above-mentioned 10 kW laser is input and 25 kW amplified light is output after amplification. p2 The small signal gain of is expressed by the following equation (33).

[0253] g 02 L p2 ≒11.5···(33)

[0254] Self-excited oscillation is generated by reflected or diffracted light from external components or internal aperture 31 of the second-stage gas laser amplifier 10A. Therefore, the feedback rate of light during self-excited oscillation is very small, and the oscillation threshold of self-excited oscillation is often roughly equal to the small signal gain. Therefore, before the self-excited oscillation light is generated, in order to oscillate by the optical resonator 40, the condition of the following formula (34) must be satisfied.

[0255] g 02 L p2 >g r2 L r2 ···(34)

[0256] According to equations (28) and (33), the reflectivities R3 and R4 of the partial reflection mirror 16 and the total reflection mirror 17 of the optical resonator 40 must satisfy the condition of the following equation (35).

[0257] R3R4>1×10 -10 ···(35)

[0258] According to equations (31) and (35), the product of the reflectivity R3 of the partial reflection mirror 16 and the reflectivity R4 of the total reflection mirror 17 is set to be a ratio of 1×10 -10 Larger than 160×10 -3 By setting the value to be small, it is possible to suppress the occurrence of self-oscillation in the second-stage gas laser amplifier 10A as described above.

[0259] As described above, by connecting two or more gas laser amplifiers 10D and 10A, and appropriately setting the reflectivity R1, R2, R3, and R4 of the partial reflection mirrors 16 and 19 or the partial reflection mirror 16 and the total reflection mirror 17 of the optical resonator 43 and 40 in each gas laser amplifier 10D and 10A, the oscillation threshold gain of the laser light generated by the optical resonator 43 and 40 can be set to be larger than the gain when amplifying the seed laser light incident from the outside, and smaller than the threshold gain of the self-excited oscillation. Thus, the self-excited oscillation can be suppressed without using a device that temporally changes the loss of the optical resonator 43 and 40.

[0260] also, Fig.26 The gas laser device 1 shown in the embodiment 1 and 4 has a structure in which the gas laser amplifiers 10A and 10D shown in the embodiment 1 and 4 are connected, but the embodiment is not limited to this. In one example, the connected gas laser amplifiers can use any method shown in the embodiment 1 to the embodiment 6. In addition, the number of gas laser amplifiers connected by the gas laser device 1 can be set to any number.

[0261] in addition, Fig.26The gas laser device 1 shown in the figure has a structure in which one optical resonator 43 or 40 is provided for each housing 11 of the gas laser amplifiers 10D or 10A, but the embodiment is not limited thereto. In one example, the gas laser device 1 has a structure in which one optical resonator is provided over a plurality of housings 11 .

[0262] According to the seventh embodiment, the same effects as those of the first to sixth embodiments can be obtained.

[0263] Implementation method 8.

[0264] Fig.32 is a perspective view schematically showing an example of the structure of a gas laser amplifier according to Embodiment 8. Fig.32 The frame 11 is omitted in the figure. Fig.32 In the embodiment, the height direction is defined as the Y direction in the housing 11 (not shown). In addition, the incident direction of the seed laser is defined as the Z direction in the direction perpendicular to the Y direction, and the direction perpendicular to the Z direction is defined as the X direction.

[0265] The gas laser amplifier 10G includes a housing 11 (not shown) and windows 12 and 13 provided on one side surface of the housing 11. The seed laser from the laser light source 2 is incident on the window 12. The amplified light amplified in the housing 11 is emitted from the window 13.

[0266] The gas laser amplifier 10G includes: an optical component that forms a first optical path OP1 that guides the laser light incident from the window 12 into a square shape in the XZ plane; and an optical component that forms a second optical path OP2 that guides the laser light from the first optical path OP1 into a square shape in the XZ plane until it reaches the window 13 .

[0267] The optical components constituting the first optical path OP1 include: two discharge tubes 68 extending in the Z direction, a polarizer 60, two discharge tubes 69 extending in the X direction, a reflector 61, two discharge tubes 70 extending in the Z direction, a reflector 62, two discharge tubes 71 extending in the X direction, and a reflector 63. The polarizer 60 reflects the laser light having the same polarization direction as the polarization direction PD1 of the seed laser light, and transmits the laser light having the polarization direction PD2 orthogonal to the polarization direction PD1 of the seed laser light. The reflectors 61 and 62 reflect the laser light incident from the Z direction toward the X direction, and conversely reflect the laser light incident from the X direction toward the Z direction. The reflector 63 reflects the laser light incident from the X direction toward the Y direction, and conversely reflects the laser light from the Y direction toward the X direction.

[0268] The optical components constituting the second optical path OP2 include a reflector 64, two discharge tubes 72 extending in the X direction, a reflector 65, two discharge tubes 73 extending in the Z direction, a reflector 66, two discharge tubes 74 extending in the X direction, a polarizer 67, and two discharge tubes 75 extending in the Z direction. The reflectors 65 and 66 reflect the laser light incident from the Z direction toward the X direction, and conversely reflect the laser light incident from the X direction toward the Z direction. The reflector 64 reflects the laser light incident from the X direction toward the Y direction, and conversely reflects the laser light from the Y direction toward the X direction. The polarizer 67 reflects the laser light of the same polarization direction as the polarization direction PD1 of the seed laser light, and transmits the laser light of the polarization direction PD2 orthogonal to the polarization direction PD1 of the seed laser light.

[0269] Laser gas flows in the discharge tubes 68, 69, 70, 71, 72, 73, 74, 75. The laser gas flows in the direction D3. The two discharge tubes 68, 69, 70, 71, 72, 73, 74, 75 arranged on one side of the square optical path are arranged at a distance from each other in the center of one side. Laser gas is supplied from the center to each discharge tube 68, 69, 70, 71, 72, 73, 74, 75, and the laser gas flows in the direction D3. The gas laser amplifier 10G is not shown in the figure, but also includes electrodes arranged around the discharge tubes 68, 69, 70, 71, 72, 73, 74, 75, a high-frequency power supply for supplying a high-frequency voltage to the electrodes, and a blower for flowing the laser gas. While laser gas is supplied to discharge tubes 68 , 69 , 70 , 71 , 72 , 73 , 74 , 75 , a high-frequency voltage is applied to the electrodes from a high-frequency power supply, thereby exciting the laser gas in discharge tubes 68 , 69 , 70 , 71 , 72 , 73 , 74 , 75 .

[0270] The optical axis OA1 of the seed laser light propagating in the gas laser amplifier 10G is constituted by a first optical path OP1 and a second optical path OP2 .

[0271] In addition, the gas laser amplifier 10G has partial reflection mirrors 81, 82 and dampers 83, 84. The partial reflection mirrors 81, 82 reflect a part of the laser light and transmit the remaining laser light. The partial reflection mirror 81 is arranged at a position where the laser light from the reflection mirror 66 is transmitted through the polarizer 67. The damper 83 absorbs the laser light that has transmitted through the partial reflection mirror 81. The partial reflection mirror 82 is arranged at a position where the laser light from the reflection mirror 61 is transmitted through the polarizer 60. The damper 84 absorbs the laser light that has transmitted through the partial reflection mirror 82.

[0272] An optical resonator is formed by the partial reflection mirrors 81 and 82. The optical axis OA2 of the laser light oscillated by the optical resonator passes through the partial reflection mirror 81, the polarizer 67, the reflection mirrors 66, 65, 64, 63, 62, 61, the polarizer 60, and the partial reflection mirror 82.

[0273] Here, the operation of the gas laser amplifier 10G is described. First, the operation when the seed laser is incident from the window 12 is described. The seed laser emitted from the laser light source 2 provided on the outside of the gas laser amplifier 10G is incident from the window 12 into the frame 11 along the optical axis OA1. In addition, the seed laser becomes a linearly polarized light polarized in the polarization direction PD1, and becomes a direction reflected by the polarizers 60 and 67. Moreover, the seed laser propagates while being amplified in the discharge tube 68 where the excited laser gas flows. The amplified seed laser, i.e., the amplified light, is reflected by the polarizer 60 and incident on the next discharge tube 69. Then, the amplified light is amplified while propagating through the reflector 61, the discharge tube 70, the reflector 62, the discharge tube 71, the reflector 63, the reflector 64, the discharge tube 72, the reflector 65, the discharge tube 73, the reflector 66, and the discharge tube 74 in sequence. Moreover, the amplified light is reflected by the polarizer 67, and after being further amplified by the discharge tube 75, it is emitted through the window 13. That is, in Fig.32 A high-speed axial flow laser amplifier is shown in which the direction D3 in which the laser gas flows is the same as the direction in which the laser propagates.

[0274] exist Fig.32 In the figure, the laser gas flows through the discharge tubes 68, 69, 70, 71, 72, 73, 74, 75 from the center of one side of the square optical path toward the end where the polarizers 60, 67 or the reflectors 61, 62, 63, 64, 65, 66 are arranged. However, the laser gas may flow through the discharge tubes 68, 69, 70, 71, 72, 73, 74, 75 from the end where the polarizers 60, 67 or the reflectors 61, 62, 63, 64, 65, 66 are arranged on one side of the square optical path toward the center. The airflow of the laser gas is formed by a blower (not shown).

[0275] Next, the operation when the seed laser is not incident from the window 12 is described. When the seed laser is not incident, light is generated from the laser gas excited by the discharge and propagates along the optical axis OA2 in the discharge tube. At this time, the component of the polarization direction PD2 whose polarization direction is orthogonal to the polarization direction PD1 of the seed laser passes through the polarizers 60 and 67, and is therefore reflected by the partial reflection mirrors 81 and 82. That is, an optical resonator is formed between the partial reflection mirrors 81 and the partial reflection mirrors 82. The laser light reflected by the partial reflection mirrors 81 and 82 propagates back and forth in the excited laser gas, thereby performing laser oscillation. In addition, a part of the laser light oscillated between the partial reflection mirrors 81 and 82 passes through the partial reflection mirrors 81 and 82 and is absorbed by the dampers 83 and 84. In addition, the laser light oscillated between the partial reflection mirrors 81 and 82 has the polarization direction PD2 orthogonal to the polarization direction PD1 of the seed laser as described above, and is not reflected by the polarizers 60 and 67, so it will not pass through the windows 12 and 13 to be emitted to the outside of the gas laser amplifier 10G.

[0276] In addition, Fig.32 In the embodiment, the polarization direction PD1 of the seed laser light is in the Y direction, but it may be in the X direction. In this case, the polarization direction PD2 of the laser light oscillated by the optical resonator is in the Y direction which is different from the seed laser light by 90 degrees.

[0277] In the gas laser amplifier 10G according to the eighth embodiment, either the seed laser or the laser light generated by the optical resonator always exists to consume the gain in the gas laser amplifier 10G. Therefore, unexpected self-oscillation does not occur in the gas laser amplifier 10G, and there is an effect that light other than the amplified light amplified by the seed laser light is not emitted from the gas laser amplifier 10G.

[0278] Implementation method 9.

[0279] Fig.33 1 is a block diagram schematically showing an example of the configuration of an EUV exposure apparatus according to Embodiment 9. The EUV exposure apparatus 100 includes a laser light source 2 , a laser amplification unit 110 , an EUV light generation unit 120 , and an exposure processing unit 140 .

[0280] The laser light source 2 is composed of a laser oscillator that generates a seed laser. The laser amplifier 110 has one or more gas laser amplifiers. In addition, one or more gas laser amplifiers included in the laser amplifier 110 are composed of the gas laser amplifiers 10A, 10B, 10C, 10D, 10E, 10F, and 10G described in Embodiments 1, 2, 3, 4, 5, 6, and 8. Fig.33In the example, the laser amplification unit 110 has a structure in which four gas laser amplifiers 111, 112, 113, and 114 are connected in series along the optical axis OA1. Fig.33 , the laser amplifier 110 is illustrated in which four gas laser amplifiers 111, 112, 113, and 114 are connected in series. However, the number of gas laser amplifiers 111, 112, 113, and 114 in the laser amplifier 110 only needs to be greater than or equal to one, and is not limited to four.

[0281] The EUV light generating unit 120 irradiates the pulse laser from the laser amplifying unit 110 onto the dripping tin (Sn) droplets, thereby generating EUV light. The generated EUV light passes through the transmission optical path 130 and enters the exposure processing unit 140.

[0282] The exposure processing unit 140 irradiates the resist layer applied on a substrate such as a semiconductor substrate with EUV light through a photomask provided with a predetermined pattern, thereby exposing the resist layer. The exposure processing unit 140 includes a substrate stage (not shown) for holding the substrate and a photomask stage (not shown) for holding the photomask. In addition, the exposure processing unit 140 includes an illumination optical system (not shown) for adjusting the irradiation range of the EUV light to the photomask and a projection optical system (not shown) for reducing and projecting the EUV light reflected by the photomask onto the substrate.

[0283] In addition, the gas laser device 1 is composed of the laser light source 2 and the laser amplifier 110. That is, the gas laser device 1 includes one or more gas laser amplifiers 10A, 10B, 10C, 10D, 10E, 10F, 10G described in Embodiments 1, 2, 3, 4, 5, 6, and 8. In addition, the laser light source 2, the laser amplifier 110, and the EUV light generator 120 constitute an EUV light generator 121. That is, the EUV light generator 121 includes one or more gas laser amplifiers 10A, 10B, 10C, 10D, 10E, 10F, 10G described in Embodiments 1, 2, 3, 4, 5, 6, and 8.

[0284] The operation of the EUV exposure device 100 is described. The seed laser emitted from the laser light source 2 is incident on the laser amplifier 110 along the optical axis OA1. In the laser amplifier 110, the seed laser is incident on the gas laser amplifier 111, amplified internally, and the amplified light is emitted from the gas laser amplifier 111. Then, the emitted amplified light is similarly amplified and emitted by the gas laser amplifiers 112, 113, and 114. The amplified light amplified by the laser amplifier 110 is incident on the EUV light generating unit 120. In the EUV light generating unit 120, the laser is focused and irradiated onto a target of tin in the form of droplets dripping at a predetermined period. If the laser is irradiated onto the target of tin, EUV light is generated from the tin. The generated EUV light is guided to the exposure processing unit 140 through the transmission optical path 130. In the exposure processing unit 140, the EUV light reflected by the photomask is irradiated onto the resist layer applied on the substrate, and the resist layer is exposed.

[0285] The EUV exposure device 100 according to the ninth embodiment includes the gas laser amplifier 10A, 10B, 10C, 10D, 10E, 10F, 10G described in any one of the first, second, third, fourth, fifth, sixth, and eighth embodiments. Therefore, when the seed laser is not incident on the gas laser amplifier 10A, 10B, 10C, 10D, 10E, 10F, 10G, no self-excited oscillation light is generated. In addition, the laser light oscillated by the optical resonator in the gas laser amplifier 10A, 10B, 10C, 10D, 10E, 10F, 10G is not emitted to the outside of the gas laser amplifier 10A, 10B, 10C, 10D, 10E, 10F, 10G. Therefore, the laser light oscillated by the self-excited oscillation light or the optical resonator is not irradiated to the target in the EUV light generating unit 120 or the laser light source 2 of the seed laser. As a result, there is an effect of being able to suppress the possibility of problems occurring in the EUV exposure apparatus 100 and the EUV light generating apparatus 121 due to unexpected irradiation of laser light.

[0286] The configuration described in the above embodiment is an example of the content of the present invention, and can be combined with other known technologies. Part of the configuration can be omitted or changed without departing from the scope of the present invention.

[0287] Description of the label

[0288] 1 Gas laser device, 2 Laser light source, 10A, 10B, 10C, 10D, 10E, 10F, 10G, 111, 112, 113, 114 Gas laser amplifier, 11 Frame, 11A, 11B Side, 12, 13 Window, 14, 15, 60, 67 Polarizer, 16, 19, 81, 82 Partial reflector, 17 Total reflector, 18, 57a, 57b, 83, 84 Damper, 20A, 20B Discharge electrode pair, 21A, 22A, 21B, 22B Discharge electrode, 23A, 23B discharge space, 25A, 25B air flow generating unit, 31, 32, 33 apertures, 40, 41, 42, 43 optical resonators, 51, 52, 53, 54, 61, 62, 63, 64, 65, 66 reflecting mirrors, 56 spectrometer, 68, 69, 70, 71, 72, 73, 74, 75 discharge tubes, 100 EUV exposure device, 110 laser amplification unit, 120 EUV light generating unit, 121 EUV light generating unit, 130 transmission light path, 140 exposure processing unit, OA1, OA2 optical axes.

Claims

1. A gas laser amplifier, characterized in that: have: a frame having an incident window into which the first laser beam is incident from the outside, and an exit window from which the amplified first laser beam is emitted; a discharge electrode pair for exciting laser gas supplied between discharge electrodes disposed opposite to each other inside the frame; and An optical resonator that causes a second laser to oscillate by the gain of the excited laser gas when the first laser is in a non-incident state where the first laser is not incident from the incident window into the interior of the frame from the outside of the frame, and stops the oscillation of the second laser when the first laser is in an incident state where the first laser is incident from the incident window into the interior of the frame.

2. The gas laser amplifier according to claim 1, characterized in that: The total resonator loss of the optical resonator has a value between the gain of the optical resonator in the incident state and the gain of the optical resonator in the non-incident state.

3. The gas laser amplifier according to claim 1 or 2, characterized in that: The first laser light is linearly polarized light polarized in a first direction. The second laser beam is linearly polarized light polarized in a second direction orthogonal to the first direction.

4. The gas laser amplifier according to claim 1 or 2, characterized in that: The optical resonator has: a partial reflection mirror that reflects a portion of the second laser light and transmits the remaining portion; a total reflection mirror, which reflects the second laser light; as well as The first damper absorbs the second laser beam transmitted through the partial reflection mirror.

5. The gas laser amplifier according to claim 4, characterized in that: The reflectivity of the partial reflector is greater than 7×10 -21 And less than 16×10 -6 .

6. The gas laser amplifier according to claim 1 or 2, characterized in that: The optical resonator has: a first partial reflector that reflects a portion of the second laser beam and transmits the remaining portion; a second partial reflector that reflects a portion of the second laser light and transmits the remaining portion; a first damper that absorbs the remaining portion of the second laser beam transmitted through the first partial reflector; as well as The second damper absorbs the remaining portion of the second laser beam transmitted through the second partial reflection mirror.

7. The gas laser amplifier according to claim 6, characterized in that: The product of the reflectivity of the first partial reflector and the reflectivity of the second partial reflector is greater than 7×10 -21 And less than 16×10 -6 .

8. The gas laser amplifier according to claim 6, characterized in that The optical resonator also has: A spectrometer is disposed on the optical path of the optical resonator; and a third damper that absorbs the second laser beam separated by the spectrometer.

9. The gas laser amplifier according to claim 8, characterized in that: The product of the reflectivity of the first partial reflector, the reflectivity of the second partial reflector and the square of the transmittance of the beam splitter is greater than 7×10 -21 And less than 16×10 -6 .

10. The gas laser amplifier according to claim 1 or 2, characterized in that: A reflecting mirror is further provided, and the reflecting mirror reflects the first laser light in the frame. The optical axis of the first laser beam is folded back within the frame between the incident window and the emission window by the reflection mirror.

11. The gas laser amplifier according to claim 1 or 2, characterized in that: The optical axis of the second laser beam overlaps with a portion of the optical axis of the first laser beam passing through the incident window and the exit window.

12. The gas laser amplifier according to claim 1 or 2, characterized in that: The device further includes a gas flow generating section configured to flow the laser gas in a direction of an optical axis of the first laser light in a region including between the discharge electrodes.

13. The gas laser amplifier according to claim 1 or 2, characterized in that: The optical axis of the second laser beam is independent of the optical axis of the first laser beam passing through the incident window and the exit window.

14. The gas laser amplifier according to claim 13, characterized in that: The optical resonator is disposed so that an optical axis of the second laser beam intersects a portion of an optical axis of the first laser beam.

15. The gas laser amplifier according to claim 1 or 2, characterized in that: The device further comprises a gas flow generating section for causing the laser gas to flow in a region including between the discharge electrodes. The gas flow generating unit causes the two laser gases to flow in a third direction which is perpendicular to the first direction in which the first laser is incident and perpendicular to the second direction, that is, the direction of the gap between the discharge electrodes, at different positions in the first direction. The two laser gases are directed toward each other.

16. The gas laser amplifier according to claim 14, characterized in that The invention also comprises an airflow generating unit which makes the two laser gases flow at different positions in the first direction in a third direction which is perpendicular to the first direction in which the first laser is incident and perpendicular to the second direction in which the gap between the discharge electrodes is formed. The two laser gases are directed toward each other. A portion of the optical axis of the second laser light passes upstream of the optical axis of the first laser light in the direction in which the laser gas flows.

17. The gas laser amplifier according to claim 1 or 2, characterized in that: The first laser light is a pulse laser light.

18. A gas laser device, characterized in that: have: A laser amplification unit, comprising one or more of the gas laser amplifiers according to any one of claims 1 to 17; and The laser light source is provided outside the housing of the gas laser amplifier and emits the first laser light.

19. An EUV light generating device, characterized in that: A gas laser device according to claim 18.

20. An EUV exposure device, characterized in that: A gas laser device according to claim 18.

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