JP2012168498A - Wavelength conversion element, solid-state laser device, and laser system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain stable laser light.SOLUTION: A wavelength conversion element may include a non-linear crystal having a first surface, a first film bonded to the first surface and having at least one layer, and a first prism bonded to the first film. The bond between the first film and the first prism may be optical contact. The non-linear crystal may be a KBBF crystal.

Description

  The present disclosure relates to a wavelength conversion element, a solid-state laser device, and a laser system.

  Typical ultraviolet light source excimer lasers used in semiconductor lithography processes are a KrF excimer laser with a wavelength of approximately 248 nm and an ArF excimer laser with a wavelength of approximately 193 nm.

Most of such ArF excimer lasers are supplied to the market as a two-stage laser system including an oscillation stage laser and an amplification stage. The main configuration common to the oscillation stage laser and the amplification stage of the two-stage ArF excimer laser system will be described. The oscillation stage laser has a first chamber and the amplification stage has a second chamber. Laser gas (a mixed gas of F ₂ , Ar, Ne, and Xe) is sealed in the first and second chambers. The oscillation stage laser and amplification stage also have a high voltage pulse power supply that supplies electrical energy to excite the laser gas. Each of the oscillation stage laser and the amplification stage can have a high voltage pulse power supply, but can share one high voltage pulse power supply. A first discharge electrode including a first anode and a first cathode, each connected to the high voltage pulse power supply, is installed in the first chamber, and each of the first chambers is similarly provided in the second chamber. A second discharge electrode including a second anode and a second cathode connected to a voltage pulse power supply is provided.

  A configuration unique to the oscillation stage laser is, for example, a narrow-band module. Narrowband modules typically include one grating and at least one prism beam expander. The semi-transmissive mirror and the grating constitute an optical resonator, and the first chamber of the oscillation stage laser is installed between the semi-transmissive mirror and the grating.

  When a discharge is generated between the first anode and the first cathode of the first discharge electrode, the laser gas is excited and light is generated when the excitation energy is released. The light is output as a laser beam wavelength-selected by the narrowband module from the oscillation stage laser.

  A two-stage laser system when the amplification stage is a laser including a resonator structure is referred to as MOPO, and a two-stage laser system when the amplification stage does not include a resonator structure and is not a laser is referred to as MOPA. When laser light from the oscillation stage laser is present in the second chamber of the amplification stage, control is performed to generate a discharge between the second anode and the second cathode of the second discharge electrode. As a result, the laser gas in the second chamber is excited, and the laser beam is amplified and output from the amplification stage.

US Pat. No. 6,859,305 Patent No. 4074124

Overview

  A wavelength conversion device according to an aspect of the present disclosure includes a nonlinear crystal including a first surface, a first film bonded to the first surface and including at least one layer, and a first prism bonded to the first film. , May be provided.

  A solid-state laser device according to another aspect of the present disclosure includes a laser that outputs laser light, an amplification unit that amplifies the laser light, and the above-described wavelength conversion device that converts the wavelength of the laser light after amplification. May be.

  A laser system according to another aspect of the present disclosure may include the solid-state laser device described above and an amplifying device that amplifies laser light output from the solid-state laser device.

Several embodiments of the present disclosure are described below by way of example only and with reference to the accompanying drawings.
FIG. 1A shows a schematic configuration of an example of a solid-state laser device having a wavelength conversion element according to Embodiment 1 of the present disclosure and a two-stage laser device using the solid-state laser device. FIG. 1B shows a schematic configuration of an example of the amplifying apparatus shown in FIG. 1A. FIG. 2 shows a schematic configuration of a wavelength conversion element according to the second embodiment of the present disclosure. FIG. 3 shows a schematic configuration of the wavelength conversion element according to the third embodiment of the present disclosure. FIG. 4 shows a schematic configuration of a wavelength conversion element according to the fourth embodiment of the present disclosure. FIG. 5 shows a schematic configuration of a wavelength conversion element according to the fifth embodiment of the present disclosure. FIG. 6 shows a schematic configuration of a wavelength conversion element according to the sixth embodiment of the present disclosure. FIG. 7 shows a schematic configuration of a wavelength conversion element according to the mobile 7 according to the embodiment of the present disclosure.

Embodiment

  Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Embodiment described below shows an example of this indication and does not limit the contents of this indication. In addition, all the configurations and operations described in the embodiments are not necessarily essential as the configurations and operations of the present disclosure. In addition, the same referential mark is attached | subjected to the same component and the overlapping description is abbreviate | omitted. In addition, in the following description, it demonstrates along the flow of the following table of contents.

Table of contents Outline 2. 2. Explanation of terms Laser system including a solid-state laser device having a wavelength conversion element and an ArF amplifier (Embodiment 1)
3.1 Configuration 3.2 Operation 4. Wavelength conversion element in which two prisms are in optical contact with a nonlinear optical crystal (Embodiment 2)
4.1 Configuration 4.2 Operation 4.3 Action 5. A wavelength conversion element in which a prism provided with an oxide coating film and a nonlinear optical crystal are in optical contact (Embodiment 3)
5.1 Configuration 5.2 Action 6. Wavelength conversion element in which nonlinear optical crystal with oxide coating film or fluoride coating film and prism are in optical contact (Embodiment 4)
6.1 Configuration 6.2 Action 7. Wavelength converter with optical contact between prism film and nonlinear optical crystal film (Embodiment 5)
7.1 Configuration 7.2 Action 8. A wavelength conversion device in which a nonlinear optical crystal including a buffer layer and a film on each buffer layer is in optical contact with a prism (Embodiment 6)
8.1 Configuration 8.2 Action 9. A wavelength conversion element in which one prism is optically contacted with a nonlinear optical crystal coated with a coating film (Embodiment 7)
9.1 Configuration 9.2 Operation 9.3 Operation

1. Overview In the embodiments illustrated below, the surface of a nonlinear optical crystal can be coated with a film. This film can be in optical contact with the surface of the prism.

2. Explanation of Terms A KBBF crystal is a nonlinear optical crystal represented by the chemical formula KBe ₂ BO ₃ F ₂ .
Burst oscillation is to output pulsed laser light at a predetermined repetition rate in a predetermined period.
An optical path is a path along which laser light propagates.
The optical contact is a joining method in which surfaces having a surface accuracy or surface roughness of a certain level or more are brought into close contact with each other. The surface accuracy or surface roughness required for each surface to be joined varies depending on the joining material. Furthermore, depending on the bonding material, the surfaces are brought into close contact with each other and then heated to increase the molecular motion at the interface and increase the bonding strength.

3. Laser system including a solid-state laser device having a wavelength conversion element and an ArF amplifier (Embodiment 1)
3.1 Configuration FIG. 1A shows a schematic configuration of an example of a two-stage laser apparatus according to Embodiment 1 of the present disclosure. FIG. 1B shows a schematic configuration of an example of the amplification device shown in FIG. 1A. 1B shows a schematic configuration of a cross section different from the cross section of the amplification device 3 shown in FIG. 1A.

  As shown in FIGS. 1A and 1B, a two-stage laser device (hereinafter referred to as a laser system) 1 may include a solid-state laser device 2 and an amplification device 3. The solid-state laser device 2 may have a wavelength conversion element, for example. The amplification device 3 may be, for example, a discharge excitation type ArF excimer amplifier. Between the solid-state laser device 2 and the amplifying device 3, a low coherence optical system 4 may be installed. As the low coherence optical system 4, an optical system such as an optical element group in which a collimating optical system is combined with an optical pulse stretcher or a random phase plate may be used.

  Next, the solid state laser device 2 will be described. The solid-state laser device 2 may include a pumping laser 5, a Ti: sapphire laser 6, an amplifier 7, a beam splitter 81, a high reflection mirror 82, a wavelength conversion device 9, and a high reflection mirror 11.

  The pumping laser 5 may be, for example, a laser that outputs the second harmonic light of a semiconductor laser pumped Nd: YAG laser. The Ti: sapphire laser 6 may include a Ti: sapphire crystal and an optical resonator. The amplifier 7 may be an amplifier including a Ti: sapphire crystal. The wavelength conversion device 9 may include a first wavelength conversion element 91 and a second wavelength conversion element 92. The first wavelength conversion element 91 may include an LBO crystal. The second wavelength conversion element 92 may include a KBBF crystal 101.

Next, the amplification device 3 will be described. The amplifying device 3 may include a chamber 20, a pair of discharge electrodes (anode 21 and cathode 22), an output coupling mirror 14, and high reflection mirrors 15, 16, and 17. Laser gas may be sealed in the chamber 20. This laser gas may be a mixed gas of Ar, Ne, F ₂ , or Xe. The anode 21 and the cathode 22 may be installed in the chamber 20. As shown in FIG. 1B, the anode 21 and the cathode 22 may be arranged at intervals in the direction along the paper surface. The anode 21 and the cathode 22 may be arranged at intervals in the direction perpendicular to the paper surface of FIG. 1B. A discharge space 23 may be provided between the anode 21 and the cathode 22. Windows 18 and 19 that transmit the pulse laser beam 32 may be attached to the chamber 20. Further, a high voltage pulse power supply (not shown) may be installed outside the chamber 20.

  The output coupling mirror 14 and the high reflection mirrors 15, 16, and 17 may constitute a ring type optical resonator. The output coupling mirror 14 may be an element that transmits part of light and reflects part of light.

3.2 Operation The solid-state laser device 2 may output pulsed laser light 31 having a wavelength of about 193 nm. The low coherence optical system 4 may reduce the coherency of the pulse laser beam 31. The amplifying device 3 may amplify the pulsed laser beam 32 with reduced coherency and output it as a pulsed laser beam 33. For example, the pulse laser beam 33 may be sent to a semiconductor exposure machine (not shown) and used for the exposure process.

  The pumping laser 5 may output pumping light (also called pumping light) 51 having a wavelength of about 532 nm. A part of the excitation light 51 may pass through the beam splitter 81. Another part of the excitation light 51 may be reflected by the beam splitter 81. The excitation light 51 a that has passed through the beam splitter 81 may excite the Ti: sapphire crystal of the Ti: sapphire laser 6. The excited Ti: sapphire laser 6 may output a pulsed laser beam 31a having a wavelength of approximately 773.6 nm. The Ti: sapphire laser 6 may include an optical resonator including a wavelength selection element (not shown). The Ti: sapphire laser 6 may output pulsed laser light 31a whose spectral width is narrowed by a wavelength selection element.

  On the other hand, among the excitation light 51 output from the pumping laser 5, the excitation light 51 b reflected by the beam splitter 81 may be further reflected by the high reflection mirror 82. The reflected excitation light 51b may enter the Ti: sapphire amplifier 7 and excite the Ti: sapphire crystal included therein. The amplifier 7 may amplify the pulse laser beam 31a output from the Ti: sapphire laser 6 by the excitation energy. As a result, the amplifier 7 may output a pulse laser beam 31b having a wavelength of approximately 773.6 nm.

  The pulsed laser light 31 b output from the Ti: sapphire amplifier 7 may enter the wavelength conversion device 9. The pulsed laser light 31 b incident on the wavelength conversion device 9 may first be incident on the first wavelength conversion element 91. Then, by passing through the pulse laser beam 31b and the LBO crystal which is a nonlinear optical crystal, the wavelength may be converted into the pulse laser beam 31b having a wavelength of about 386.8 nm (1/2 of the above-mentioned 773.6 nm). Next, the pulse laser beam 31b after wavelength conversion may be incident on the second wavelength conversion element 92. The pulse laser beam 31b may be further converted into the pulse laser beam 31 having a wavelength of about 193.4 nm (1/2 of the 386.8 nm) by passing through the KBBF crystal 101 which is a nonlinear optical crystal. .

  The pulse laser beam 31 that has passed through the KBBF crystal 101 may be incident on the low-coherence optical system 4 with its traveling direction changed by the high-reflection mirror 11. The coherence of the pulsed laser light 31 may be reduced by passing through the low-coherence optical system 4. The pulsed laser light 32 whose coherence is reduced may be incident on the amplification device 3.

  A high voltage pulse power source (not shown) electrically connected to the anode 21 and the cathode 22 in the chamber 20 may apply a high voltage pulse between the anode 21 and the cathode 22. Thereby, discharge may occur between the anode 21 and the cathode 22. The high voltage pulse may be applied between the anode 21 and the cathode 22 at a timing at which a discharge can be generated in the discharge space 23 when the pulse laser beam 32 exists in the discharge space 23.

  A part of the pulse laser beam 32 emitted from the low coherence optical system 4 may be transmitted through the output coupling mirror 14 and reflected by the high reflection mirror 15. The pulsed laser light 32 may pass through the window 18 and travel to the discharge space 23 between the anode 21 and the cathode 22. The pulse laser beam 32 may be amplified by performing control to cause discharge in the discharge space 23 when the pulse laser beam 32 exists in the discharge space 23. The amplified pulsed laser light 32 may be emitted from the chamber 20 through the window 19. The emitted pulsed laser light 32 may be highly reflected by the high reflection mirrors 16 and 17, and again travel through the window 19 to the discharge space 23 in the chamber 20 to be amplified. Then, the pulse laser beam 32 may be emitted from the chamber 20 through the window 18 this time. The emitted pulsed laser light 32 may be incident on the output coupling mirror 14. A part of the pulse laser beam 32 may pass through the output coupling mirror 14 and be emitted from the amplification device 3 as the pulse laser beam 33. Another part of the pulsed laser light 32 may be reflected back by the output coupling mirror 14 and returned to the ring optical resonator again as feedback light.

  In this description, the case where the amplifying apparatus 3 includes a ring optical resonator is illustrated, but the present invention is not limited to this example. For example, the amplifying apparatus 3 may include a Fabry-Perot resonator in which an optical resonator is disposed in an amplifier.

  In the first embodiment, a solid-state laser wavelength converter 9 and a laser system 1 using the same are illustrated. Here, the low-coherence optical system 4 and the amplifying device 3 in FIG. 1A are not essential components of the present disclosure. Further, the pulse laser beam 31 b before wavelength conversion by the wavelength conversion device 9 may not be a laser beam output from a laser device including the Ti: sapphire laser 6.

4). Wavelength conversion element in which two prisms are in optical contact with a nonlinear optical crystal (Embodiment 2)
Next, a second embodiment of the present disclosure will be described. In the second embodiment, the second wavelength conversion element 92 exemplified as the first embodiment will be described as a second embodiment of the wavelength conversion element 101A having a more specific configuration.

  Here, problems related to the KBBF crystal will be described. In the present situation, it is difficult for the KBBF crystal to grow in a direction other than the optical axis (Z axis). Also, at present, it is difficult to grow the KBBF crystal thicker than about 2.5 mm in the optical axis direction. Therefore, there is a problem that a sufficient thickness cannot be obtained when the KBBF crystal is cut along a plane perpendicular to the phase matching direction. Also, since the KBBF crystal has a strong cleavage property, there is a problem that it is difficult to perform satisfactory cutting on a surface perpendicular to the phase matching direction and optical polishing on this surface at present. For this reason, the KBBF crystal may be used as a light incident surface and a light emission surface in the plane perpendicular to the optical axis direction.

  KBBF crystals have a high refractive index. For this reason, when the KBBF crystal is disposed in the atmosphere, there is a condition that the second harmonic light (193.4 nm) generated in the KBBF crystal is totally reflected at the interface between the atmosphere and the light exit surface. Therefore, there are cases where the second harmonic light cannot be extracted from the KBBF crystal.

  Therefore, a film may be coated on each of the incident surface and the exit surface of the KBBF crystal. Then, the KBBF crystal coated with the film may be sandwiched between two prisms from the incident surface side and the output surface side. The film may have a thickness sufficient to obtain a surface roughness sufficient for the surface to form an optical contact. By forming the film, the surface roughness of the surface can be made the surface roughness of the film even if the incident surface and the exit surface of the KBBF crystal have a certain surface roughness. Thereby, an optical contact can be formed by the flat film and the prism. According to such a configuration, total reflection at the interface of the second harmonic light can be prevented.

4.1 Configuration FIG. 2 shows a schematic configuration of the wavelength conversion element 101A in the wavelength conversion device according to the second embodiment. Below, the KBBF crystal 101 is illustrated as a nonlinear optical crystal.

  As shown in FIG. 2, the wavelength conversion element 101A is formed on the KBBF crystal 101, the coating film (third film) 102a formed on one main surface of the KBBF crystal 101, and the other main surface of the KBBF crystal 101. The coated film (first film) 103a may be provided. Hereinafter, one main surface is referred to as an incident surface 101a, and the other main surface is referred to as an output surface 101b. The film thickness of the coating films 102a and 103a may be such a thickness that the surface can obtain a surface roughness sufficient to form an optical contact.

  Furthermore, the wavelength conversion element 101A may include a prism (second prism) 102 and a prism (first prism) 103. The prism 102 may be provided on the incident surface 101a side of the KBBF crystal 101 with the coating film 102a interposed therebetween. The prism 102 may be bonded to the coating film 102a by an optical contact.

  The prism 103 may be provided on the emission surface 101b of the KBBF crystal 101 with the coating film 103a interposed therebetween. The prism 103 may be bonded to the coating film 103a by optical contact.

4.2 Operation For example, the pulse laser beam 31 b (386.8 nm) transmitted through the first wavelength conversion element 91 may be incident on the prism 102. The pulsed laser light 31b may pass through a surface where the prism 102 and the coating film 102a are joined by optical contact. Thereafter, the pulse laser beam 31 b may pass through the coating film 102 a and enter the KBBF crystal 101. Then, in the KBBF crystal 101, the second harmonic light 31c (193.4 nm) having the pulsed laser light 31b as the fundamental wave light (386.8 nm) can be generated. The pulsed laser light 31b and the second harmonic light 31c may pass through the coating film 103a and may pass through the surface where the coating film 103a and the prism 103 are joined by optical contact. Thereafter, the pulsed laser light 31 b and the second harmonic light 31 c may pass through the prism 103 and be emitted from the prism 103. At this time, the pulsed laser light 31b and the second harmonic light 31c have different refraction angles, and thus can be separated and emitted from the prism 103. The second harmonic light 31 c may be output from the wavelength conversion device 9 as the pulsed laser light 31. The pulse laser beam 31 may be amplified by an amplification device 3 such as an ArF excimer amplifier.

4.3 Action In the wavelength conversion element 101A, the pulse laser beam 31b or the second harmonic light 31c is provided at each interface between the prism 102, the coating film 102a, the KBBF crystal 101, the coating film 103a, and the prism 103. Can be prevented from being totally reflected. When the prism is directly bonded to the KBBF crystal 101 by optical contact, the interface between the KBBF crystal 101 and the prism may be damaged by the pulse laser beam. Therefore, the lifetime of the KBBF crystal 101 may be shortened. On the other hand, in the second embodiment, a film may be coated on the surface of the KBBF crystal 101, and the film and the prism may be in optical contact. Thereby, damage received by the pulse laser beam can be reduced. Thereby, the lifetime of the wavelength conversion element 101A can be improved.

  In the second embodiment, coating films 102a and 103a are formed on both sides of the entrance surface 101a and the exit surface 101b of the KBBF crystal 101. Also, these coating films 102a and 103a and the prisms 102 and 103 are joined by optical contact. However, it is not limited to this configuration. For example, the wavelength conversion element 101A may be configured to include only one of the coating films 102a and 103a. At this time, in the KBBF crystal 101, a film may be coated on the interface that is more damaged by the pulse laser beam 31b, the pulse laser beam 31b, or the second harmonic light 31c. The surface not coated with the film may be in direct optical contact between the KBBF crystal 101 and the prism.

5. Wavelength conversion element optically contacted using oxide (Embodiment 3)
Next, a more specific configuration of the wavelength conversion element 101A exemplified as the second embodiment will be described as a third embodiment. Below, the KBBF crystal 101 is illustrated as a nonlinear optical crystal.

5.1 Configuration FIG. 3 shows a schematic configuration of the wavelength conversion element 101B in the wavelength conversion device according to the third embodiment. As shown in FIG. 3, the wavelength conversion element 101B includes a KBBF crystal 101, a coating film (third film) 112a, a coating film (first film) 113a, a prism (second prism) 112, and a prism (first prism). 1 prism) 113.

  The coating film 112 a may be formed on the incident surface 101 a of the KBBF crystal 101. The coating film 113 a may be formed on the emission surface 101 b of the KBBF crystal 101. The film thickness of the coating films 112a and 113a may be such a thickness that the surface can obtain a sufficient surface roughness to form an optical contact.

  The prism 112 may be bonded to the coating film 112a formed on the incident surface 101a of the KBBF crystal 101 by optical contact. The prism 113 may be bonded to the coating film 113a formed on the emission surface 101b of the KBBF crystal 101 by optical contact. The prism 112, the coating film 112a, the coating film 113a, and the prism 113 may be formed of a material having a refractive index that does not totally reflect laser light at each interface.

  The coating film 112a may be a film containing at least one of oxide and fluoride. Alternatively, the coating film 112 a may be a multilayer film including a layer (second layer) including at least one of oxide and fluoride on a surface in contact with the prism 112. Similarly, the coating film 113a may be a film including at least one of an oxide and a fluoride. Alternatively, the coating film 113a may be a multilayer film including a layer (first layer) containing at least one of oxide and fluoride on a surface in contact with the prism 113.

The material of the coating film 112a or the layer (second layer) that forms the surface in contact with the prism 112 in the coating film 112a may include at least one of SiO ₂ , MgF ₂ , LaF ₃ , and GdF ₃ . Similarly, the material of the coating film 113a or the layer (first layer) forming the surface in contact with the prism 113 in the coating film 113a may include at least one of SiO ₂ , MgF ₂ , LaF ₃ , and GdF _3. Good.

The material of the prism 112 may include at least one of SiO ₂ crystal, CaF ₂ crystal, and MgF ₂ crystal. Similarly, the material of the prism 113 may include at least one of SiO ₂ crystal, CaF ₂ crystal, and MgF ₂ crystal.

  By using materials having the same molecular composition for the coating film 112a and the prism 112, the adhesion strength of the coating film 112a to the prism 112 can be improved. Also, index matching can be facilitated by using materials having the same molecular composition. Similarly, by using materials having the same molecular composition for the coating film 113a and the prism 113, the adhesion strength of the coating film 113a to the prism 113 can be improved. Moreover, refractive index matching can be facilitated by using materials having the same molecular composition.

  For the prisms 112 and 113, for example, synthetic quartz or quartz may be used.

  For the formation of the coating films 112a and 113a, an electron beam method, a sputtering method, or the like may be used. However, the present invention is not limited to this, and various film formation methods can be used. By forming the coating films 112a and 113a, the surface roughness of the entrance surface 101a and the exit surface 101b of the KBBF crystal 101 can be planarized by the coating films 112a and 113a, respectively.

5.2 Action According to the third embodiment, the prism and the film having the same molecular composition can be in optical contact. Thereby, the damage which an interface receives with a pulse laser beam can be reduced, and the lifetime of the wavelength conversion element 101B can be improved.

Note that in the case where quartz is used for the prism 112 or 113, the prism may be manufactured so that the optical axis of the quartz coincides with the polarization direction of the pulsed laser light 31b. Further, as the coating films 112a and 113a, a SiO ₂ film formed by a sputtering method may be used. Thereby, the compaction of the SiO ₂ film generated by the second harmonic light 31c can be suppressed. Quartz is thought to be less susceptible to compaction due to laser light having a wavelength of 193.4 nm compared to synthetic quartz. Accordingly, the quartz prism is particularly preferably used for the first prism.

6). Wavelength conversion element in optical contact using oxide and fluoride (Embodiment 4)
Next, another specific configuration of the wavelength conversion element 101A illustrated as the second embodiment will be described as a fourth embodiment. Below, the KBBF crystal 101 is illustrated as a nonlinear optical crystal.

6.1 Configuration FIG. 4 shows a schematic configuration of the wavelength conversion element 101C in the wavelength conversion device according to the fourth embodiment. As shown in FIG. 4, the wavelength conversion element 101C includes a KBBF crystal 101, a coating film (third film) 122a, a coating film (first film) 123a, a prism (second prism) 122, and a prism (first prism). 1 prism) 123.

  The coating film 122 a may be formed on the incident surface 101 a of the KBBF crystal 101. The coating film 123 a may be formed on the emission surface 101 b of the KBBF crystal 101. The film thickness of the coating films 122a and 123a may be such a thickness that the surface can obtain a surface roughness sufficient to form an optical contact.

  The prism 122 may be bonded to the coating film 122a formed on the incident surface 101a of the KBBF crystal 101 by optical contact. The prism 123 may be bonded to the coating film 123a formed on the emission surface 101b of the KBBF crystal 101 by optical contact. The prism 122, the coating film 122a, the coating film 123a, and the prism 123 may be formed of a material having a refractive index so that laser light is not totally reflected at each interface.

For example, an oxide may be used as the material of the coating film 122a and the prism 122 positioned on the incident side of the pulse laser beam 31b. The coating film 122a may be a multilayer film including a layer containing an oxide (second layer) on the surface in contact with the prism 122. By making the contact surfaces of both the coating film 122a and the prism 122 into oxides, the ease of joining them can be improved. Moreover, refractive index matching can be facilitated by using oxides for both. The oxide used for the coating film 122a and the prism 122 may be SiO ₂ crystal or the like. Note that fluoride may be used as the material of the coating film 122a and the prism 122.

On the other hand, for example, fluoride may be used as the material of the coating film 123a and the prism 123 positioned on the emission side of the pulse laser beam 31b and the second harmonic light 31c. The fluoride material has a lower absorptance with respect to laser light having a wavelength of 193.4 nm than the oxide material. Therefore, it can be considered that the fluoride material is less likely to be compacted by the second harmonic light 31c than the oxide material. The coating film 123 a may be a multilayer film including a layer (first layer) containing fluoride on a surface in contact with the prism 123. By making the contact surfaces of both the coating film 123a and the prism 123 into fluorides, the ease of joining them can be improved. Moreover, refractive index matching can be facilitated by using fluoride for both. The fluoride used for the coating film 123a may be MgF ₂ , LaF ₃ , GdF ₃ or the like. The fluoride used for the prism 123 may be CaF ₂ , MgF ₂ or the like.

  For the formation of the coating films 122a and 123a, an electron beam method, a sputtering method, or the like may be used. However, the present invention is not limited to this, and various film formation methods can be used. By forming the coating films 122a and 123a, the surface roughness of the entrance surface 101a and the exit surface 101b of the KBBF crystal 101 can be planarized by the coating films 122a and 123a, respectively.

6.2 Action According to the fourth embodiment, the prism and the film made of the material having the same composition can be in optical contact with each of the entrance surface 101a side and the exit surface 101b side of the KBBF crystal 101. Thereby, the damage which an interface receives with a pulse laser beam can be reduced, and the lifetime of the wavelength conversion element 101C can be improved.

In addition, when MgF ₂ is used as the material of the prism 123, the prism 123 may be manufactured so that the optical axis of the prism 123 and the polarization direction of the pulsed laser light 31b coincide.

7). Wavelength conversion element having optical contact between prism film and crystal film (Embodiment 5)
Next, another specific configuration of the wavelength conversion element 101A exemplified as the second embodiment will be described as a fifth embodiment. Below, the KBBF crystal 101 is illustrated as a nonlinear optical crystal.

7.1 Configuration FIG. 5 shows a schematic configuration of the wavelength conversion element 101D in the wavelength conversion device according to the fifth embodiment. As shown in FIG. 5, the wavelength conversion element 101D includes a KBBF crystal 101, a coating film 132a (third film), a coating film (first film) 133a, a prism (second prism) 132, and a prism (first prism). 1 prism) 133. The prism (first prism) 133 may include a coating film (second film) 133b on the surface in contact with the coating film (first film) 133a.

  The coating film 132 a may be formed on the incident surface 101 a of the KBBF crystal 101. The coating film 133 a may be formed on the emission surface 101 b of the KBBF crystal 101. The coating film 133b may be formed on the surface of the prism 133 on the KBBF crystal 101 side. The film thickness of the coating films 132a and 133a may be such a thickness that the surface can obtain a sufficient surface roughness to form an optical contact. Similarly, the film thickness of the coating film 133b may be such a thickness that the surface can obtain a surface roughness sufficient to form an optical contact.

  The prism 132 may be bonded to the coating film 132a formed on the incident surface 101a of the KBBF crystal 101 by optical contact. As for the prism 133, the coating film 133b may be bonded to the coating film 133a formed on the emission surface 101b of the KBBF crystal 101 by optical contact. In this case, since the coating films are bonded to each other by optical contact, they can be bonded suitably. Note that a coating film may be formed on the prism 132 also on the incident surface 101a side of the KBBF crystal 101, and this coating film and the coating film 132a of the KBBF crystal 101 may be joined by optical contact. . The prism 132 and the coating film 132a, the coating film 132a and the KBBF crystal 101, the KBBF crystal 101 and the coating film 133a, the coating film 133a and the coating film 133b, and the coating film 133b and the prism 133 are not totally reflected at the respective interfaces. It may be formed of a material having a large refractive index.

For example, an oxide may be used as the material of the coating film 132a and the prism 132 positioned on the incident side of the pulse laser beam 31b. The coating film 132a may be a multilayer film including a layer containing an oxide (second layer) on the surface in contact with the prism 132. By making the contact surfaces of both the coating film 132a and the prism 132 into oxides, the ease of joining them can be improved. Moreover, refractive index matching can be facilitated by using oxides for both. The oxide used for the coating film 132a and the prism 132 may be SiO ₂ or the like. The material of the coating film 132a may be fluoride. The fluoride may include at least one of MgF ₂ , LaF ₃ , and GdF ₃ . The material of the prism 132 is not limited to SiO ₂ crystal, but may be a material containing at least one of CaF ₂ crystal and MgF ₂ crystal. Further, as a material for forming the coating film on the prism 132, a material containing at least one of MgF ₂ , LaF ₃ , GdF ₃ , and SiO ₂ may be used.

On the other hand, as materials for the coating film 133a, the coating film 133b, and the prism 133 positioned on the emission side of the pulse laser beam 31b and the second harmonic light 31c, for example, fluoride or oxide may be used. The fluoride material has a lower absorptance with respect to laser light having a wavelength of 193.4 nm than the oxide material. Therefore, it can be considered that the fluoride material is less likely to be compacted by the second harmonic light 31c than the oxide material. The coating film 133a may be a multilayer film including a layer (first layer) containing an oxide or fluoride on a surface in contact with the coating film 133b. The coating film 133b may be a multilayer film including a layer containing an oxide or fluoride on a surface in contact with the coating film 133a. A material having the same composition may be used for each of the relative surfaces of the coating film 133a and the coating film 133b. By using a material having the same composition on each of the relative surface sides of the coating film 133a and the coating film 133b, it is possible to improve the ease of joining the two. Furthermore, refractive index matching can be facilitated. The material used for the coating films 133a and 133b may include MgF ₂ , LaF ₃ , GdF ₃ , SiO ₂ and the like. The material used for the prism 133 may be a material including at least one of CaF ₂ crystal and MgF ₂ crystal. In particular, SiO ₂ may be used for the coating films 133a and 133b, and CaF ₂ crystal may be used for the prism 133. Note that a SiO ₂ crystal may be used as the material of the prism 133.

  The coating films 132a and 133a may be formed on the entrance surface 101a and the exit surface 101b of the KBBF crystal 101 by using an electron beam method, a sputtering method, or the like. The coating film 133b may be formed on the surface of the prism 133 on the KBBF crystal 101 side by using an electron beam method, a sputtering method, or the like. However, the present invention is not limited to this, and various film formation methods can be used. By forming the coating films 132a and 133a, the surface roughness of the entrance surface 101a and the exit surface 101b of the KBBF crystal 101 can be improved. The surface roughness of the prism 133 on the KBBF crystal 101 side surface can be flattened by the coating film 133b.

7.2 Operation According to the fifth embodiment, on the incident surface 101a side of the KBBF crystal 101, a prism made of a material having the same composition and the film can be in optical contact. Further, on the emission surface 101b side of the KBBF crystal 101, a film made of a material having the same composition can be in optical contact. Thereby, the damage which an interface receives with the pulse laser beam 31b can be reduced, and the lifetime of the wavelength conversion element 101D can be improved.

As the material of the prism 133, when using a fluoride crystal material such as CaF _2, as compared with the case of using an oxide material, it may further improve the durability of the wavelength conversion element 101D.

8). A wavelength conversion element in which a nonlinear optical crystal including a buffer layer and a film on each buffer layer is optically contacted with a prism (Embodiment 6)
Next, another specific configuration of the wavelength conversion element 101A exemplified as the second embodiment will be described as a sixth embodiment. Below, the KBBF crystal 101 is illustrated as a nonlinear optical crystal.

8.1 Configuration FIG. 6 shows a schematic configuration of the wavelength conversion element 101E in the wavelength conversion device according to the sixth embodiment. As shown in FIG. 6, the wavelength conversion element 101E includes a KBBF crystal 101, a coating film (third film) 142a, a coating film (first film) 143a, a buffer layer (second buffer layer) 142c, and a buffer. A layer (first buffer layer) 143c, a prism (second prism) 142, and a prism (first prism) 143 may be provided.

  The buffer layer 142 c may be formed on the incident surface 101 a of the KBBF crystal 101. The coating film 142a may be formed on the buffer layer 142c. The buffer layer 143c may be formed on the emission surface 101b of the KBBF crystal 101. The coating film 143a may be formed on the buffer layer 143c. The total film thickness of the buffer layer 142c and the coating film 142a may be such a thickness that the surface can obtain a surface roughness sufficient to form an optical contact. Similarly, the total film thickness of the buffer layer 143c and the coating film 143a may be a thickness that allows the surface to obtain a surface roughness sufficient to form an optical contact.

  The prism 142 may be bonded to the coating film 142a formed on the incident surface 101a side of the KBBF crystal 101 by optical contact. The prism 143 may be bonded to the coating film 143a formed on the emission surface 101b side of the KBBF crystal 101 by optical contact. The prism 142 and the coating film 142a, the coating film 142a and the buffer layer 142c, the buffer layer 142c and the KBBF crystal 101, the KBBF crystal 101 and the buffer layer 143c, the buffer layer 143c and the coating film 143a, and the coating film 143a and the prism 143 have their interfaces. The laser beam may be formed of a material having a refractive index so that the laser beam is not totally reflected.

For the material of the coating films 142a and 143a and the material of the prisms 142 and 143, for example, a material containing at least one of fluoride and oxide may be used. The coating film 142 a may be a multilayer film including a layer (second layer) containing an oxide or fluoride on a surface in contact with the prism 142. The coating film 143a may be a multilayer film including a layer (first layer) containing an oxide or fluoride on a surface in contact with the prism 143. On the entrance surface 101a side or the exit surface 101b side of the KBBF crystal 101, a material having the same composition may be used for the prism 142 or 143 and the coating film 142a or 143a. By using a material having a similar composition, it is possible to improve the ease of joining the two. Moreover, refractive index matching can be facilitated by using fluoride for both. The material used for the coating films 142a and 143a may be a material containing at least one of MgF ₂ , LaF ₃ , GdF ₃ , and SiO ₂ . The material used for the prisms 142 and 143 may be a material including at least one of CaF ₂ crystal, MgF ₂ crystal, and SiO ₂ crystal. In particular, SiO ₂ may be used for the coating films 142a and 143a, and synthetic quartz (SiO ₂ ) may be used for the prisms 142 and 143.

As the material of the buffer layers 142c and 143c, a material including at least one of Al ₂ O ₃ , HfO ₂ , ZrO ₂ , and ScO ₂ may be used. By forming the laminated film of the coating film 142a and the buffer layer 142c, and the laminated film of the coating film 143a and the buffer layer 143c, the surface roughnesses on the entrance surface 101a and the exit surface 101b of the KBBF crystal 101 are respectively determined as the coating film. 142a and the buffer layer 142c, and the coating film 143a and the buffer layer 143c.

  For the formation of the buffer layers 142c and 143c, a sputtering method, a CVD method, an ALD (Atomic Layer Deposition) method, or the like may be used. The coating films 142a and 143a may be formed on the buffer layers 142c and 143c formed on the KBBF crystal 101 by using an electron beam method, a sputtering method, or the like. However, the present invention is not limited to this, and various film formation methods can be used.

8.2 Action According to the sixth embodiment, the prism and the film made of the material having the same composition can be in optical contact with each of the entrance surface 101a side and the exit surface 101b side of the KBBF crystal 101. Thereby, the damage which an interface receives with the pulse laser beam 31b can be reduced, and the lifetime of the wavelength conversion element 101E can be improved.

The KBBF crystal 101 is a fluoride crystal. For this reason, when SiO ₂ is used as the material of the coating films 142a and 143a, the KBBF crystal 101 and the SiO ₂ coating film may come into contact with each other to generate SiF ₄ or the like. Since SiF ₄ absorbs ultraviolet rays, the conversion efficiency of the wavelength conversion element may be lowered. According to the sixth embodiment, by forming the buffer layers 142c and 143c on the entrance surface 101a and the exit surface 101b of the KBBF crystal 101, respectively, the possibility that SiF ₄ or the like is generated can be reduced. . As a result, the absorption of ultraviolet light by SiF ₄ can be reduced, and the possibility that the conversion efficiency of the wavelength conversion element will be reduced can be reduced.

  Further, by providing the buffer layer 142c between the KBBF crystal 101 and the coating film 142a, internal stress caused by the difference in thermal expansion coefficient between the KBBF crystal 101 and the coating film 142a can be reduced. Similarly, by providing the buffer layer 143c between the KBBF crystal 101 and the coating film 143a, the internal stress caused by the difference in thermal expansion coefficient between the KBBF crystal 101 and the coating film 143a can be reduced. As a result, the possibility of mechanical destruction of the wavelength conversion element caused by internal stress accompanying temperature change can be reduced.

9. A wavelength conversion element in which one prism is optically contacted with a nonlinear optical crystal coated with a coating film (Embodiment 7)
Next, a wavelength conversion element 101F, which is another specific configuration of the second wavelength conversion element 92 exemplified as the first embodiment, will be described as a seventh embodiment.

9.1 Configuration In the above-described second to third embodiments, the two opposing surfaces of the KBBF crystal 101 which is a nonlinear optical crystal are the laser light incident surface 101a and the light emitting surface 101b, and a prism is provided on each of them via a coating film. The case where it was provided was illustrated. However, the present invention is not limited to this, and one surface of the KBBF crystal 101 may be a laser light incident / exit surface, and a prism may be provided on this surface via a coating film.

  FIG. 7 shows a schematic configuration of the wavelength conversion element 101F in the wavelength conversion device according to the seventh embodiment. As shown in FIG. 7, the wavelength conversion element 101F may include a KBBF crystal 101, a coating film (first film) 152a, and a prism (first prism) 152.

  The coating film 152 a may be formed on the incident / exit surface 101 c of the KBBF crystal 101. The prism 152 may be bonded to the coating film 152a formed on the incident / exit surface 101c of the KBBF crystal 101 by optical contact. The prism 152 and the coating film 152a may be formed of a material having a refractive index such that the laser beam is not totally reflected at the interface.

  The material of the prism 152 and the coating film 152a may be the prism material and the coating film material exemplified in the above-described second to sixth embodiments. Preferably, the material of the prism 152 and the coating film 152a may be a fluoride material having a low absorption rate for laser light having a wavelength of 193.4 nm. The coating film 152a may be the multilayer film described above.

  In addition, prism 152 may include a coating film (second film) similar to that of the above-described fifth embodiment on a surface that contacts coating film 152a. Furthermore, a buffer layer (first buffer layer) similar to that of the above-described sixth embodiment may be provided on the KBBF crystal 101, and the coating film 152a may be provided on the buffer layer.

9.2 Operation For example, the pulse laser beam 31b (386.8 nm) transmitted through the first wavelength conversion element 91 may be incident on the prism 152. The pulse laser beam 31b may pass through the prism 152 and may enter the KBBF crystal 101 via the coating film 152a.

  At least part of the pulsed laser light 31b having a wavelength of 386.8 nm can be converted into the second harmonic light 31c having a wavelength of 193.4 nm by transmitting through the KBBF crystal 101. The pulsed laser light 31b and the wavelength-converted second harmonic light 31c may be highly reflected by a surface 101d facing the incident / exit surface 101c of the KBBF crystal 101. Here, the pulse laser beam 31b and the second harmonic light 31c can be highly reflected by the surface 101d by entering the surface 101d at a total reflection angle determined by the refractive index of the KBBF crystal 101 and the refractive index of air.

  The pulsed laser light 31b and the second harmonic light 31c that are highly reflected by the surface 101d may pass through the KBBF crystal 101 again. At this time, the pulsed laser light 31b and the second harmonic light 31c may travel on different optical paths depending on the difference in refractive index depending on the wavelength.

  The pulsed laser beams 31b and 31c propagating in different optical paths may be incident on the prism 152 again via the coating film 152a, and the optical path may be refracted by the prism 152 and output. As a result, the pulsed laser light 31b and the second harmonic light 31c can be output from the wavelength conversion element 101F through different optical paths.

9.3 Operation According to the seventh embodiment, since only one prism is used, the configuration of the wavelength conversion element 101F can be simplified. Furthermore, since the pulse laser beam 31b reciprocates in the KBBF crystal 101, the optical path length of the pulse laser beam 31b in the KBBF crystal 101 can be increased. As a result, the conversion efficiency from the pulsed laser light 31b to the second harmonic light 31c can be improved.

  The above description is intended to be illustrative only and not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the embodiments of the present disclosure without departing from the scope of the appended claims.

  Terms used throughout this specification and the appended claims should be construed as "non-limiting" terms. For example, the terms “include” or “included” should be interpreted as “not limited to those described as included”. The term “comprising” should be interpreted as “not limited to what is described as having”. Also, the indefinite article “a” or “an” in the specification and the appended claims should be interpreted to mean “at least one” or “one or more”.

In the above-described embodiment, an example in which there is one amplifier 7 has been shown, but a plurality of amplifiers 7 may be used. The Ti: sapphire laser 6 and the amplifier 7 are pumped by the common pumping laser 5, but separate pumping lasers may be used. Further, as the pumping laser 5, a laser that outputs the second harmonic light of an Nd: YLF laser or an Nd: YVO ₄ laser may be used. Instead of the Ti: sapphire laser 6, a laser that generates the second harmonic light of an erbium-doped optical fiber laser may be used. This laser may be pumped by a semiconductor laser. Further, the wavelength conversion device 9 is not limited to the configuration of the present disclosure, and the light incident on the wavelength conversion device 9 is converted into light having an amplification wavelength band of the amplification device 3, for example, light having a wavelength of about 193.4 nm. Anything can be used. For example, as the nonlinear optical crystal included in the wavelength converter 9, a CLBO crystal may be used instead of the LBO crystal.

1 Two-stage laser equipment (laser system)
2 Solid-state laser device 3 Amplifying device 31, 31a, 32, 33 Pulse laser light 31b Pulse laser light 31c Second harmonic light 4 Low coherence optical system 5 Pumping laser 51, 51a, 51b Excitation light 6 Ti: sapphire laser 7 Amplifier 81 Beam splitter 82 High reflection mirror 9 Wavelength conversion device 91 First wavelength conversion element 92 Second wavelength conversion element 101 KBBF crystal 101a Incident surface 101b Outgoing surface 101c Incoming / exiting surface 14 Output coupling mirrors 15 to 17 High reflection mirror 18, 19 Window 20 Chamber 21 Anode 22 Cathode 23 Discharge space 101A, 101B, 101C, 101D, 101E, 101F Wavelength conversion element 102, 112, 122, 132, 142, 103, 113, 123, 133, 143, 152 Priz 102a, 112a, 122a, 132a, 142a, 103a, 113a, 123a, 133a, 143a, 133b, 152a Coating film 142c, 143c Buffer layer

Claims (23)

A nonlinear crystal comprising a first surface;
A first film bonded to the first surface and including at least one layer;
A first prism bonded to the first film;
A wavelength conversion device comprising:   The wavelength converter according to claim 1, wherein the joint between the first film and the first prism is an optical contact.   The wavelength conversion device according to claim 1, wherein the nonlinear crystal is a KBBF crystal.   2. The wavelength conversion device according to claim 1, wherein the first film includes a first layer containing at least one of an oxide and a fluoride on a joint surface with the first prism. _2. The wavelength conversion device according to claim 1, wherein the first film includes a first layer including at least one of SiO ₂ , MgF ₂ , LaF ₃ , and GdF _{3 on} a bonding surface with the first prism. The wavelength conversion device according to claim 1, wherein the material of the first prism includes at least one of SiO ₂ crystal, CaF ₂ crystal, and MgF ₂ crystal.   The wavelength conversion device according to claim 1, wherein the first prism includes a second film including at least one layer on a joint surface with the first film. The wavelength conversion device according to claim 7, wherein the second film includes a film including at least one of SiO ₂ , MgF ₂ , LaF ₃ , and GdF _{3 on} the joint surface with the first film.   The wavelength conversion device according to claim 1, wherein the first layer includes a first buffer layer on a joint surface with the first prism. The wavelength conversion device according to claim 9, wherein the material of the first buffer layer includes at least one of Al ₂ O ₃ , HfO ₂ , ZrO ₂ , and ScO ₂ . The wavelength conversion device according to claim 10, wherein the material of the first prism includes at least one of SiO ₂ crystal, CaF ₂ crystal, and MgF ₂ crystal. A third film that is bonded to the second surface opposite to the first surface of the nonlinear crystal and includes at least one layer;
A second prism joined to the third film;
The wavelength converter of Claim 1 provided with.   The wavelength conversion device according to claim 12, wherein the joint between the third film and the second prism is an optical contact.   The wavelength conversion device according to claim 12, wherein the third film includes a second layer including at least one of an oxide and a fluoride on a joint surface with the second prism. The wavelength conversion device according to claim 12, wherein the third film includes a second layer including at least one of SiO ₂ , MgF ₂ , LaF ₃ , and GdF _{3 on} a bonding surface with the second prism. The wavelength conversion device according to claim 12, wherein the material of the second prism includes at least one of SiO ₂ crystal, synthetic quartz glass, fused silica glass, CaF ₂ crystal, and MgF ₂ crystal.   The wavelength conversion device according to claim 12, wherein the third film includes a second buffer layer on a joint surface with the first prism. The wavelength conversion device according to claim 17, wherein the material of the second buffer layer includes at least one of Al ₂ O ₃ , HfO ₂ , ZrO ₂ , and ScO ₂ . The wavelength conversion device according to claim 18, wherein the material of the second prism includes at least one of SiO ₂ crystal, synthetic quartz glass, fused silica glass, CaF ₂ crystal, and MgF ₂ crystal. A laser that outputs laser light;
An amplifying unit for amplifying the laser beam;
The wavelength conversion device according to claim 1, wherein the wavelength of the amplified laser light is converted.
A solid-state laser device. A laser that outputs laser light;
An amplifying unit for amplifying the laser beam;
The wavelength converter according to claim 12, which converts the wavelength of the laser beam after amplification;
A solid-state laser device. A solid-state laser device according to claim 20,
An amplifying device for amplifying the laser beam output from the solid-state laser device;
A laser system comprising: A solid-state laser device according to claim 21;
An amplifying device for amplifying the laser beam output from the solid-state laser device;
A laser system comprising:

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