JP2012137687A - Wavelength conversion device and ultraviolet light generating laser device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wavelength conversion device with high conversion efficiency and an ultraviolet light generation laser.SOLUTION: The wavelength conversion device may include: a wavelength conversion element that has a light incidence plane and a light emission plane and generate second harmonic light of light incident from the light incident plane; a liquid cell that includes an incident part through which the light incident on the wavelength conversion element passes, and an emission part through which the light emitted from the wavelength conversion element passes; and immersion liquid that is stored in the liquid cell along with the wavelength conversion element and in which the wavelength conversion element is immersed with at least the light emitting plane coming into contact with liquid.

Description

  The present disclosure relates to a wavelength conversion device and a laser device that generates ultraviolet light using the wavelength conversion device.

  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 F2, Ar, Ne, and Xe) is sealed in the first and second chambers. The oscillation stage laser and amplification stage also have a power supply that supplies electrical energy to excite the laser gas. Each of the oscillation stage laser and the amplification stage can have a power source, but a single power source can also be shared. A first discharge electrode including a first anode and a first cathode each connected to the power source is installed in the first chamber, and each is connected to the power source in the second chamber as well. A second discharge electrode including a second anode and a second cathode 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 1, 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.

Japanese Patent No. 4074124 Special table 2009-9075 Japanese Patent No. 3514073 Japanese Patent No. 3885529 US Pat. No. 6,859,305

Overview

  The wavelength conversion device according to the present disclosure includes a light incident surface and a light output surface, a wavelength conversion element that generates second harmonic light of light incident from the light incident surface, and light incident on the wavelength conversion element. A liquid cell comprising an incident part that passes through and an emission part through which light emitted from the wavelength conversion element passes, and is accommodated in the liquid cell together with the wavelength conversion element, and the wavelength conversion element has at least the light exit surface. An immersion liquid immersed in contact with the liquid.

Several embodiments of the present invention are described below by way of example only and with reference to the accompanying schematic drawings.
FIG. 1 is a diagram illustrating a schematic configuration of an example of a solid-state laser device having a wavelength conversion element according to an aspect of the present disclosure and a two-stage laser device using the solid-state laser device. FIG. 2 is a perspective view illustrating a schematic configuration of an example of a wavelength conversion device according to an aspect of the present disclosure. FIG. 3 is a top view showing a schematic configuration of the wavelength converter shown in FIG. FIG. 4 is a top view illustrating a schematic configuration of an example of a wavelength conversion device according to an aspect of the present disclosure. FIG. 5 is a top view illustrating a schematic configuration of an example of a wavelength conversion device according to an aspect of the present disclosure. FIG. 6 is a top view illustrating a schematic configuration of an example of a wavelength conversion device according to an aspect of the present disclosure. FIG. 7 is a top view illustrating a schematic configuration of an example of a wavelength conversion device according to an aspect of the present disclosure. FIG. 8 is a diagram for explaining the arrangement of the KBBF crystal and the reflection mirror of the wavelength converter shown in FIG. FIG. 9 is a top view illustrating a schematic configuration of an example of a wavelength conversion device according to an aspect of the present disclosure. FIG. 10 is a top view illustrating a schematic configuration of an example of a wavelength conversion device according to an aspect of the present disclosure. FIG. 11 is a top view illustrating a schematic configuration of an example of a wavelength conversion device according to an aspect of the present disclosure. FIG. 12 is a side view illustrating a schematic configuration of an example of a wavelength conversion device according to an aspect of the present disclosure.

Embodiment

1. Overview 1.1 Explanation of terms 2. General description of solid-state laser device having wavelength conversion element 2.1 Configuration 2.2 Operation 3. Description of Example of Wavelength Conversion Device According to One Aspect of Present Disclosure 3.1 Configuration 3.2 Operation 4. 4. Description of Example of Wavelength Conversion Device According to One Aspect of Present Disclosure 4.1 Configuration 4.2 Operation 5. 5. Description of Example of Wavelength Conversion Device According to One Aspect of Present Disclosure 5.1 Configuration 5.2 Operation 6. 6. Description of Example of Wavelength Conversion Device According to One Aspect of Present Disclosure 6.1 Configuration 6.2 Operation 7. 7. Description of Example of Wavelength Conversion Device According to One Aspect of Present Disclosure 7.1 Configuration 7.2 Operation 8. 8. Description of Example of Wavelength Conversion Device According to One Aspect of Present Disclosure 8.1 Configuration 8.2 Operation 9. 9. Description of Example of Wavelength Conversion Device According to One Aspect of Present Disclosure 9.1 Configuration 9.2 Operation 10. 10. Description of Example of Wavelength Conversion Device According to One Aspect of Present Disclosure 10.1 Configuration 10.2 Operation 11. Description of an example of a wavelength conversion device according to an aspect of the present disclosure 11.1 Configuration 11.2 Operation

1. Overview 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.

1.1 Explanation of Terms The KBBF crystal is a nonlinear optical crystal represented by the chemical formula KBe ₂ BO ₃ F ₂ and is a wavelength conversion element. The phase matching direction is a propagation direction of the incident light in the wavelength conversion element when the incident light is incident on the wavelength conversion element so as to satisfy the phase matching condition of the second harmonic generation. The phase matching angle is an angle formed by the normal line of the light incident surface of the wavelength conversion element and the phase matching direction. The conversion efficiency is an amount representing the ratio of the generated second harmonic light power to the incident light power.

2. 2. General Description of Solid-State Laser Device Having Wavelength Conversion Element 2.1 Configuration FIG. 1 shows a schematic configuration of an example of a solid-state laser device having a wavelength conversion element according to one aspect of the present disclosure and a two-stage laser device using the same.
Reference numeral 1 denotes a two-stage laser apparatus, which roughly includes an oscillation stage laser 2 and an amplification stage 3. The oscillation stage laser 2 is a solid-state laser device having a wavelength conversion element in this figure. The amplification stage 3 is a discharge excitation type ArF excimer laser in this figure. Reference numeral 4 denotes a low-coherence optical system installed between the oscillation stage laser and the amplification stage. As the low-coherence optical system 4, a known system such as a random phase plate may be used.

Next, main components of the oscillation stage laser 2 will be described.
Reference numeral 5 denotes a semiconductor laser pumped YAG laser. 6 and 7 are Ti: sapphire lasers. 8a is a beam splitter, and 8b is a reflection mirror. 9 is an LBO crystal and 10 is a KBBF crystal. Reference numeral 11 denotes a reflection mirror.

Next, the amplification stage 3 will be described.
Reference numeral 12 denotes a chamber filled with laser gas. This laser gas may be a mixed gas of Ar, Ne, F ₂ and Xe. A pair of discharge electrodes (anode and cathode) (not shown) are installed inside the chamber 12. A power supply (not shown) is installed outside the chamber 12.
Reference numerals 13 and 14 are transflective mirrors. Reference numeral 15 denotes a high reflection mirror. The semi-transmissive mirror 14 and the highly reflective mirror 15 constitute an optical resonator.

2.2 Operation The oscillation stage laser 2 outputs a laser beam 16 having a wavelength of about 193 nm. The low coherence optical system 4 reduces the coherency of the laser beam 16. The amplification stage 3 amplifies the laser beam 17 with reduced coherency and outputs it as a laser beam 18. The laser beam 18 is sent to, for example, a semiconductor exposure machine (not shown) and used for exposure processing.
A part of the laser light having a wavelength of about 532 nm outputted from the semiconductor laser pumped YAG laser 5 is transmitted through the beam splitter 8a, and the other part is reflected by the beam splitter 8a. The laser beam that has passed through the beam splitter 8a excites the Ti: sapphire laser 6, and a laser beam having a wavelength of approximately 773.6 nm is output from the laser 6.

  Of the output light of the laser 5, the laser light reflected by the beam splitter 8 a and further reflected by the reflection mirror 8 b excites the Ti: sapphire laser 7, and the laser 7 uses the excitation energy to output laser from the laser 6. The light is amplified to output laser light having a wavelength of approximately 773.6 nm.

  The laser beam output from the Ti: sapphire laser 7 is transmitted through the LBO crystal 9 which is a wavelength conversion element, and the wavelength thereof is converted to approximately 386.8 nm (1/2 of 773.6 nm). Further, the laser beam having a wavelength of about 386.8 nm is transmitted through the KBBF crystal 10 which is a wavelength conversion element, and the wavelength is converted to about 193.4 nm (1/2 of the 386.8 nm).

The laser light 16 that has passed through the KBBF crystal 10 has its traveling direction changed by the reflecting mirror 11 and is incident on the low coherence optical system 4. The laser light 16 passes through the low-coherence optical system 4 and its coherence is reduced. The laser beam 17 whose coherence has been reduced enters the amplification stage 3.
The power source applies a voltage between the anode and the cathode.

  The semi-transmissive mirror 13 changes the traveling direction of the laser light 17 and advances it to the discharge space between the anode and the cathode. When the laser beam 17 is present in the discharge space, the laser beam 17 is amplified by performing control for generating a discharge in the discharge space. Further, the laser beam 17 reciprocates between the optical resonators formed by the transflective mirror 14 and the high reflection mirror 15, and continues to be amplified. A part of the laser beam 17 passes through the semi-transmissive mirrors 14 and 13 and is output as a laser beam 18.

3. Description of an Example of a Wavelength Conversion Device According to an Aspect of the Present Disclosure First, problems related to the KBBF crystal will be described.
The KBBF crystal is currently difficult to grow in directions other than the optical axis (Z axis). Moreover, it is difficult to grow the KBBF crystal at a thickness thicker than about 2.5 mm at present. Therefore, the KBBF crystal has a problem that a sufficient thickness cannot be obtained when it is cut along a plane perpendicular to the phase matching direction. Also, KBBF crystals are difficult to cut and optically polish on a plane perpendicular to the phase matching direction at present. Therefore, in the KBBF crystal, surfaces perpendicular to the optical axis direction may be used as the light incident surface and the light exit surface.

  In addition, when the KBBF crystal is disposed in the atmosphere, the second harmonic light generated in the KBBF crystal may be totally reflected at the interface between the atmosphere and the light exit surface. For this reason, the second harmonic light may not be extracted from the KBBF crystal.

On the other hand, Patent Document 5 discloses a technique in which a KBBF crystal is sandwiched between SiO ₂ or CaF ₂ prisms having a refractive index close to that of the KBBF crystal and optical contact is made. According to this technique, total reflection at the interface of the second harmonic light can be prevented.

However, according to an actual measurement by the present applicants, a color center is generated on the optical contact surface of the KBBF crystal even when the energy density of incident laser light is 1 J / cm ² or less. It has been confirmed through experiments conducted by the present applicants that when the color center is formed, damage occurs on the optical contact surface of the KBBF crystal.

  Therefore, when the optical contact surface exists in the KBBF crystal, the life of the KBBF crystal may be shortened. As a result, there is a possibility that the running cost and the maintenance cost of the wavelength converter using the KBBF crystal are increased. Moreover, since the energy density of the laser light incident on the KBBF crystal is limited, there is a possibility that the second harmonic light with high energy and high average power cannot be obtained.

  Hereinafter, an example of the wavelength conversion device according to an aspect of the present disclosure will be described.

3.1 Configuration FIG. 2 is a perspective view illustrating a schematic configuration of an example of a wavelength conversion device according to an aspect of the present disclosure.
The wavelength conversion device 20 may include a KBBF crystal 10, water 21, a liquid cell 22, and a mounting table 23. The liquid cell 22 may include optical windows 22a and 22b.

  The liquid cell 22 may accommodate the KBBF crystal 10, the water 21, and the mounting table 23. The mounting table 23 may mount the KBBF crystal 10. The mounting table 23 may be made of a material having a high thermal conductivity, such as a metal or diamond. The KBBF crystal 10 may be immersed in the water 21.

  FIG. 3 is a top view showing a schematic configuration of the wavelength converter shown in FIG. In FIG. 3, the mounting table 23 is not shown. The laser beam L1 having a wavelength of about 386.8 nm and outputted from the LBO crystal 9 in FIG. 1 can pass through the optical window (incident part) 22a. A non-reflective coating may be applied to the atmosphere side of the optical window 22a. The optical window 22a may be arranged at an angle that makes a Brewster angle with respect to the laser light L1.

  The KBBF crystal 10 may include a light incident surface 10a and a light emitting surface 10b. The light incident surface 10a and the light emitting surface 10b may be parallel to each other. Here, broken lines in the figure indicate normal lines of the light incident surface 10a and the light emitting surface 10b. In the KBBF crystal 10, surfaces perpendicular to the optical axis direction may be used as the light incident surface 10a and the light emitting surface 10b. At this time, the phase matching direction of the KBBF crystal 10 is inclined by 55.61 degrees with respect to the normal line of the light incident surface 10a.

  The KBBF crystal 10 may be arranged such that the laser beam L1 is incident at an incident angle θ1 from the light incident surface 10a. The laser beam L1 may be collimated by a collimating lens before entering the KBBF crystal 10.

  The laser beam L1 and the second harmonic light L2 generated in the KBBF crystal 10 can pass through the optical window (emission part) 22b. A non-reflective coating may be applied to the atmosphere side of the optical window 22b. The optical window 22b may be disposed at an angle that makes a Brewster angle with respect to the laser light L1 or the second harmonic light L2.

3.2 Operation Next, the operation of the wavelength conversion device 20 will be described.
The KBBF crystal 10 is arranged so that the laser beam L1 is incident from the light incident surface 10a at an incident angle θ1 such that the refraction angle is the phase matching angle θ2. The incident angle θ1 can be expressed using the following equation. θ1 = arcsin [(refractive index of KBBF crystal 10 / refractive index of water 21) × sin (θ2)]. The refractive index of the water 21 at the wavelength of the laser beam L1 (approximately 386.8 nm) is 1.344. The phase matching angle θ2 of the KBBF crystal 10 is 55.61 degrees. The refractive index of the KBBF crystal 10 at the wavelength of the laser beam L1 is 1.493. Accordingly, the incident angle θ1 needs to be set to arcsin [1.493 / 1.344 × sin (55.61)] = 66.4 degrees.

  The KBBF crystal 10 generates the second harmonic light L2 having a wavelength of about 193.4 nm when the laser light L1 is incident so as to satisfy the phase matching condition. The second harmonic light L2 corresponds to the laser light 16 in FIG.

  In this wavelength conversion device 20, the KBBF crystal 10 is immersed in water 21. Therefore, the medium in contact with the light exit surface 10 b of the KBBF crystal 10 is water 21. The refractive index of the water 21 at the wavelength of the second harmonic light L2 is 1.44. In this case, the critical angle of total reflection is θm = arcsin (1.44 / 1.493) = 74.69 degrees. That is, the critical angle θm is larger than the incident angle of the second harmonic light L2 on the light exit surface 10b (in this case, the phase matching angle θ2). Therefore, the second harmonic light L2 can be extracted from the light exit surface 10b to the outside of the KBBF crystal 10. Note that the emission angle θ3 of the second harmonic light L2 at the light emission surface 10b is about 55 degrees in consideration of the walk-off angle.

  In this wavelength converter 20, since the KBBF crystal 10 is immersed in the water 21, the light incident surface 10a and the light emitting surface 10b of the KBBF crystal 10 have no optical contact surface. Therefore, the generation of the color center by the laser light L1 or the second harmonic light L2 in the KBBF crystal 10 and the occurrence of damage due to the generation are suppressed. As a result, the wavelength conversion device 20 can realize reduction in running cost and maintenance cost, and generation of second energy light with high energy and high average power.

  The water 21 is preferable because the light absorption is substantially zero at the wavelength of the laser light L1 and the light absorption is small at about 3% / cm at the wavelength of the second harmonic light L2, and the light loss is small. Note that fluorine oil may be used in place of the water 21. Perfluoropolyether oil (for example, Fomblin (registered trademark)) may be used as the fluorinated oil. Fluorine-based oil is preferable because light absorption is almost zero and light loss is small at the wavelengths of the laser light L1 and the second harmonic light L2.

  Fomblin has a refractive index of, for example, 1.29 at the wavelength of the laser beam L1. The refractive index of Fomblin is 1.33 at the wavelength of the second harmonic light L2, for example. Therefore, the incident angle θ1 of the laser beam L1 needs to be set to arcsin [1.493 / 1.29 × sin (55.61)] = 72.8 degrees. Further, the emission angle θ3 of the second harmonic light L2 at the light exit surface 10b is about 62 degrees in consideration of the walk-off angle.

  Further, other immersion liquid may be used instead of the water 21. The immersion liquid preferably has a refractive index such that when the KBBF crystal 10 is immersed, the critical angle θm of total reflection is larger than the incident angle of the second harmonic light L2 with respect to the light exit surface 10b. In addition, the immersion liquid preferably has a small light absorption at the wavelengths of the laser light L1 and the second harmonic light L2. It is preferable that the light absorption amount of the immersion liquid is a light absorption amount that does not halve the power of the laser beam L1 before reaching the KBBF crystal 10 at most. Further, it is preferable that the light absorption amount of the immersion liquid is a light absorption amount that does not halve the power of the second harmonic light L2 until it is emitted to the outside of the liquid cell 22 at most.

  Further, instead of the KBBF crystal 10, another wavelength conversion element may be used. This wavelength conversion element is preferably such that the incident angle of the second harmonic light to the light exit surface is equal to or greater than the critical angle of total reflection of the second harmonic light at the interface between the light exit surface and the atmosphere. The immersion liquid used at this time has a refractive index such that when the wavelength conversion element is immersed, the critical angle of total reflection of the second harmonic becomes larger than the incident angle of the second harmonic light to the light exit surface. It is good to have.

4). 4. Description of Example of Wavelength Conversion Device According to One Aspect of Present Disclosure 4.1 Configuration FIG. 4 is a top view illustrating a schematic configuration of an example of a wavelength conversion device according to an aspect of the present disclosure.
The wavelength conversion device 30 may include the KBBF crystal 10, the immersion liquid 31, and the liquid cell 32. The immersion liquid 31 may include water 21 and silicon-based oil 31A. The liquid cell 32 may include optical windows 22a and 22b and separation walls 32c and 32d.

  The immersion liquid 31 may be accommodated in the liquid cell 32. The KBBF crystal 10 may be immersed in the immersion liquid 31. The water 21 that is the first immersion liquid may be in contact with the light emitting surface 10b. The silicon-based oil 31A that is the second immersion liquid may be in contact with the light incident surface 10a. The separation walls 32c and 32d may separate the water 21 and the silicon-based oil 31A and prevent them from mixing. The KBBF crystal 10 may be arranged such that the laser beam L1 is incident at an incident angle θ4 from the light incident surface 10a.

4.2 Operation Next, the operation of the wavelength conversion device 30 will be described.
The KBBF crystal 10 is arranged so that the laser light L1 is incident from the light incident surface 10a at an incident angle θ4 such that the refraction angle becomes the phase matching angle θ2. The refractive index of the silicon-based oil 31A at the wavelength of the laser beam L1 (approximately 386.8 nm) is 1.4. The phase matching angle θ2 of the KBBF crystal 10 is 55.61 degrees. The refractive index of the KBBF crystal 10 at the wavelength of the laser beam L1 is 1.493. Therefore, the refractive index of the silicon-based oil 31A at the wavelength of the laser light L1 is closer to the refractive index of the KBBF crystal 10 than the refractive index of the atmosphere and the refractive index of the water 21 (1.493). At this time, the incident angle θ4 needs to be set to arcsin [1.493 / 1.4 × sin (55.61)] = 61.6 degrees. The incident angle θ4 is smaller than the value (66.4 degrees) of the incident angle θ1 in the wavelength conversion device 20 shown in FIG. Therefore, it is possible to reduce light loss due to the reflection of the laser light L1 at the light incident surface 10a. Note that the silicon-based oil 31A is preferable because light absorption is small and light loss is small at the wavelength of the laser light L1.

  Further, in this wavelength conversion device 30, the light output surface 10 b side of the KBBF crystal 10 is immersed in water 21, as in the wavelength conversion device 20 shown in FIG. 2. Therefore, similarly to the wavelength conversion device 20, the second harmonic light L2 can be extracted to the outside of the KBBF crystal 10 from the light emitting surface 10b. Also in this wavelength converter 30, there is no optical contact surface on the light incident surface 10 a and the light emitting surface 10 b of the KBBF crystal 10. As a result, the wavelength conversion device 30 can realize reduction in running cost and maintenance cost, and generation of high energy and high average power second harmonic light.

  Note that fluorine oil may be used in place of the water 21. Further, another first immersion liquid may be used instead of the water 21. When the first immersion liquid is in contact with the light exit surface 10b side of the KBBF crystal 10, the refraction is such that the critical angle θm of total reflection is larger than the incident angle of the second harmonic light L2 with respect to the light exit surface 10b. Those with rates are good. The first immersion liquid preferably has a small light absorption at the wavelength of the second harmonic light L2.

  Further, another second immersion liquid may be used instead of the silicon-based oil 31A. The second immersion liquid preferably has a refractive index closer to the refractive index of the KBBF crystal 10 than the refractive index of the atmosphere at the wavelength of the laser beam L1. The second immersion liquid preferably has a small light absorption at the wavelength of the laser beam L1.

  Further, instead of the KBBF crystal 10, another wavelength conversion element may be used. This wavelength conversion element is preferably such that the incident angle of the second harmonic light to the light exit surface is equal to or greater than the critical angle of total reflection of the second harmonic light at the interface between the light exit surface and the atmosphere. Further, when the first immersion liquid used at this time is in contact with the light exit surface of the wavelength conversion element, the critical angle of total reflection of the second harmonic wave is larger than the incident angle of the second harmonic light to the light exit surface. What has a refractive index which becomes large is good. In addition, the second immersion liquid used at this time preferably has a refractive index closer to the refractive index of the wavelength conversion element than the refractive index of the atmosphere at the wavelength of the incident light.

5. 5. Description of Example of Wavelength Conversion Device According to One Aspect of Present Disclosure 5.1 Configuration FIG. 5 is a top view illustrating a schematic configuration of an example of a wavelength conversion device according to an aspect of the present disclosure.
The wavelength conversion device 20 </ b> A may include two KBBF crystals 10, water 21, and a liquid cell 22. The wavelength conversion device 20A may include a mounting table on which the two KBBF crystals 10 are mounted.

  The two KBBF crystals 10 may be arranged such that the light emitting surface 10b and the light incident surface 10a facing each other are parallel to each other.

5.2 Operation Next, the operation of the wavelength conversion device 20A will be described.
The KBBF crystal 10 located on the left side of the drawing is arranged so that the laser light L1 is incident from the light incident surface 10a at an incident angle θ1. As a result, the left KBBF crystal 10 generates the second harmonic light L2 and emits it from the light exit surface 10b. At the same time, laser light L1 that has not undergone wavelength conversion is also emitted from the left KBBF crystal 10.

  Laser light L1 emitted from the left KBBF crystal 10 is incident on the KBBF crystal 10 located on the right side of the paper surface from the light incident surface 10a at an incident angle θ1. Thereby, the right KBBF crystal 10 generates the second harmonic light L2 and emits it from the light exit surface 10b. The second harmonic light L2 emitted from the left KBBF crystal 10 passes through the right KBBF crystal 10 and propagates in parallel with the second harmonic light L2 generated in the right KBBF crystal 10.

  In this wavelength conversion device 20A, since the two KBBF crystals 10 each generate the second harmonic light L2, higher conversion efficiency can be obtained. Also in this wavelength conversion device 20A, there are no optical contact surfaces on the light incident surface 10a and the light emitting surface 10b of the two KBBF crystals 10, respectively. As a result, the wavelength conversion device 20A can realize reduction in running cost and maintenance cost, and generation of high energy and high average power second harmonic light.

  The wavelength conversion device 20A is not limited to the two KBBF crystals 10, and may include more KBBF crystals 10.

6). 6. Description of Example of Wavelength Conversion Device According to One Aspect of Present Disclosure 6.1 Configuration FIG. 6 is a top view illustrating a schematic configuration of an example of a wavelength conversion device according to an aspect of the present disclosure.
The wavelength conversion device 40 may include two liquid cells 22, a relay lens 41, and a dichroic mirror 42.

  The two liquid cells 22 may each contain the KBBF crystal 10 and the water 21. The relay lens 41 that is a condensing element may be disposed between the two liquid cells 22. The dichroic mirror 42 may reflect the laser light L1 and transmit the second harmonic light L2. The dichroic mirror 42 may be disposed on the opposite side (right side of the drawing) to the two liquid cells 22 from which the laser light L1 is input.

6.2 Operation Next, the operation of the wavelength conversion device 40 will be described.
The KBBF crystal 10 accommodated in the liquid cell 22 located on the left side of the paper surface is arranged so that the laser light L1 is incident from the light incident surface 10a at an incident angle θ1. Thus, when the laser beam L1 is incident on the left KBBF crystal 10, the second harmonic light L2 is generated and emitted from the light emitting surface 10b. At the same time, the left-side KBBF crystal 10 emits laser light L1 that has not undergone wavelength conversion.

  The relay lens 41 condenses the laser light L1 emitted from the left KBBF crystal 10 and makes it incident on the KBBF crystal 10 accommodated in the liquid cell 22 located on the right side of the paper. The right KBBF crystal 10 is arranged so that the laser light L1 emitted from the left KBBF crystal 10 is incident from the light incident surface 10a at an incident angle θ1. Thus, when the laser beam L1 is incident on the right KBBF crystal 10, the second harmonic light L2 is generated and emitted from the light emitting surface 10b. The second harmonic light L2 emitted from the left KBBF crystal 10 passes through the right KBBF crystal 10, and is emitted while being superimposed on the second harmonic light L2 generated there. The dichroic mirror 42 angularly separates the superimposed second harmonic light L2 and the remaining laser light L1.

  In this wavelength converter 40, since the two KBBF crystals 10 respectively generate the second harmonic light L2, higher conversion efficiency can be obtained. The relay lens 41 condenses the laser light L1 emitted from the left KBBF crystal 10 and makes it incident on the right KBBF crystal 10 in a state where the intensity density of the light is increased. As a result, the conversion efficiency in the right KBBF crystal 10 is increased. Also in this wavelength conversion device 40, there is no optical contact surface on each of the light incident surface 10a and the light emitting surface 10b of the two KBBF crystals 10. As a result, the wavelength conversion device 40 can realize reduction in running cost and maintenance cost, and generation of second energy light with high energy and high average power.

  The wavelength conversion device 40 is not limited to the two liquid cells 22 and may include more liquid cells 22. A relay lens 41 may be disposed between the KBBF crystals 10 accommodated in these liquid cells 22. The liquid cell 22 may contain a plurality of KBBF crystals 10. The relay lens 41 may be accommodated in the liquid cell 22 and disposed between the plurality of KBBF crystals 10.

7). 7. Description of Example of Wavelength Conversion Device According to One Aspect of Present Disclosure 7.1 Configuration FIG. 7 is a top view illustrating a schematic configuration of an example of a wavelength conversion device according to an aspect of the present disclosure.
The wavelength conversion device 50 may include a KBBF crystal 10, water 21, a liquid cell 22, a dichroic mirror 51, and a reflection mirror 52.

  The dichroic mirror 51 may be disposed on the side where the laser light L1 is input (the left side of the paper) with respect to the liquid cell 22. The dichroic mirror 51 may reflect the laser light L1 and transmit the second harmonic light L2. The reflection mirror 52, which is a reflection element, may be disposed on the opposite side (right side of the drawing) to the liquid cell 22 from which the laser light L1 is input.

7.2 Operation Next, the operation of the wavelength conversion device 50 will be described.
The dichroic mirror 51 reflects the laser light L1 toward the liquid cell 22. Laser light L1 is incident on the KBBF crystal 10 accommodated in the liquid cell 22 from the light incident surface 10a at an incident angle θ1. Thus, when the laser beam L1 is incident on the KBBF crystal 10, the second harmonic light L2 is generated and emitted from the light emitting surface 10b. At the same time, laser light L1 that has not undergone wavelength conversion is also emitted from the KBBF crystal 10.

  The reflection mirror 52 reflects and collects the laser light L1 and the second harmonic light L2 emitted from the KBBF crystal 10 and makes them enter the KBBF crystal 10 again. Laser light L1 reflected by the reflection mirror 52 is incident on the KBBF crystal 10 from the light exit surface 10b at an incident angle θ1. Thereby, in the KBBF crystal 10, the second harmonic light L2 is further generated and emitted from the light incident surface 10a. On the other hand, the second harmonic light L2 reflected by the reflection mirror 52 and incident on the KBBF crystal 10 is transmitted through the KBBF crystal 10 and emitted. The dichroic mirror 51 separates the two second harmonic light L2 in a direction different from the incident direction of the laser light L1.

  In this wavelength converter 50, the laser beam is incident twice on one KBBF crystal 10, and the second harmonic light L2 is generated. Therefore, higher conversion efficiency can be obtained by one KBBF crystal 10.

  Here, FIG. 8 is a diagram for explaining the arrangement of the KBBF crystal 10 and the reflection mirror 52 of the wavelength converter 50 shown in FIG. A point where the two optical paths of the laser beam L1 and the second harmonic beam L2 emitted from the KBBF crystal 10 to the right side of the drawing intersect is a point F. The reflection mirror 52 has a spherical shape with a curvature radius R of the reflection surface 52a. The reflection mirror 52 may be disposed such that the reflection surface 52a coincides with a spherical surface having a radius R with the point F as the center.

  With this arrangement, the reflection mirror 52 can reflect the laser light L1 and the second harmonic light L2 so that the reciprocal optical paths by reflection coincide with each other. By making the reciprocating optical paths coincide with each other, the laser light L1 surely enters the KBBF crystal 10 from the light emitting surface 10b at the incident angle θ1. The reflection mirror 52 reflects and collects the laser beam L1, and enters the KBBF crystal 10 with the intensity density of the light increased. As a result, the conversion efficiency in the KBBF crystal 10 is increased. In addition, the optical path of the second harmonic light L2 generated by the KBBF crystal 10 and reflected by the reflecting mirror 52 is parallel to the optical path of the second harmonic light L2 generated by the reflected laser light L1. As a result, the two beams of the second harmonic light L2 can be easily combined.

  Also in this wavelength converter 50, the light incident surface 10a and the light emitting surface 10b of the KBBF crystal 10 have no optical contact surface. As a result, the wavelength conversion device 50 can realize reduction in running cost and maintenance cost and generation of second energy light with high energy and high average power.

8). 8. Description of Example of Wavelength Conversion Device According to One Aspect of Present Disclosure 8.1 Configuration FIG. 9 is a top view illustrating a schematic configuration of an example of a wavelength conversion device according to an aspect of the present disclosure.
The wavelength conversion device 60 may include the KBBF crystal 10, the water 21, the liquid cell 22, the liquid circulation device 61, and the pipe 62.

  The pipe 62 may connect the liquid cell 22 and the liquid circulation device 61. The liquid circulation device 61 may be a pump.

8.2 Operation Next, the operation of the wavelength conversion device 60 will be described.
The liquid circulation device 61 circulates the water 21 in which the KBBF crystal 10 is immersed through the pipe 62. Thereby, the temperature rise of the KBBF crystal 10 due to the incidence of the laser light and the generation of the second harmonic light is suppressed. Therefore, shortening of the lifetime of the KBBF crystal 10 is suppressed. Also in this wavelength converter 60, the light incident surface 10a and the light emitting surface 10b of the KBBF crystal 10 have no optical contact surface. As a result, the wavelength conversion device 60 can realize further reduction in running cost and maintenance cost, and generation of second harmonic light with higher energy and higher average power.

9. Description of Example of Wavelength Conversion Device According to One Aspect of Present Disclosure 9.1 Configuration FIG. 10 is a top view illustrating a schematic configuration of an example of a wavelength conversion device according to an aspect of the present disclosure.
The wavelength conversion device 60A may include the KBBF crystal 10, the water 21, the liquid cell 22, the liquid circulation device 61, the pipe 62, and the liquid temperature control device 63. The liquid temperature control device 63 may include a temperature detector, a cooler or a heater, and a control unit.

  The pipe 62 may connect the liquid cell 22, the liquid circulation device 61, and the liquid temperature control device 63. The temperature detector of the liquid temperature control device 63 may be a thermistor. The cooler of the liquid temperature control device 63 may be an electronic cooling element. The heater of the liquid temperature control device 63 may be an electric heater. The control unit of the liquid temperature control device 63 may control the cooler.

9.2 Operation Next, the operation of the wavelength conversion device 60A will be described.
The liquid circulation device 61 circulates the water 21 in which the KBBF crystal 10 is immersed through the pipe 62. The temperature detector of the liquid temperature control device 63 detects the liquid temperature of the water 21. The liquid temperature control device 63 controls the temperature of the water 21 so that the controller controls the cooler or the heater so that the detected liquid temperature is within a predetermined range. Thereby, the water 21 is kept at a liquid temperature within a predetermined range. Therefore, the KBBF crystal 10 immersed in the water 21 is also maintained at a temperature within a predetermined range. In this wavelength conversion device 60A, the change in conversion efficiency of the KBBF crystal 10 due to temperature is small, so that the power of the generated second harmonic light is stabilized.

  In this wavelength converter 60A, the temperature rise of the KBBF crystal 10 due to the incidence of the laser light and the generation of the second harmonic light is suppressed. The wavelength converter 60A also has no optical contact surface on the light incident surface 10a and the light emitting surface 10b of the KBBF crystal 10. As a result, the wavelength conversion device 60A can realize further reduction in running cost and maintenance cost, and generation of second harmonic light with higher energy and higher average power.

10. 10. Description of Example of Wavelength Conversion Device According to One Aspect of Present Disclosure 10.1 Configuration FIG. 11 is a top view illustrating a schematic configuration of an example of a wavelength conversion device according to an aspect of the present disclosure.
The wavelength conversion device 70 may include the KBBF crystal 10, the water 21, the liquid cell 22, the mounting table 23, the element temperature control device 71, the heat transfer body 72, and the temperature detector 73. The element temperature control device 71 may include at least one of a cooler or a heater and a control unit.

  The KBBF crystal 10 may be mounted on the mounting table 23. The heat transfer body 72 may be connected to the element temperature control device 71 and a place near the KBBF crystal 10 on the mounting table 23. The heat transfer body 72 may be made of a material having a high thermal conductivity, such as a metal or diamond, or may have a high thermal conductivity such as a heat pipe. The temperature detector 73 may be installed at a location near the KBBF crystal 10 of the heat transfer body 72. The cooler or the heater of the element temperature control device 71 may be connected to the heat transfer body 72.

10.2 Operation Next, the operation of the wavelength conversion device 70 will be described.
The temperature detector 73 detects the temperature in the vicinity of the KBBF crystal 10. In the element temperature control device 71, the control unit controls the cooler or the heater, and controls the temperature of the KBBF crystal 10 so that the temperature detected by the temperature detector 73 falls within a predetermined range. The cooling or heating is performed via the cooler or the heat transfer body 72 connected to the heater and the mounting table 23. As a result, the KBBF crystal 10 is kept at a device temperature within a predetermined range. Therefore, since the change in the conversion efficiency of the KBBF crystal 10 becomes small, the power of the generated second harmonic light is stabilized.

  Also in this wavelength conversion device 70, the temperature rise of the KBBF crystal 10 due to the incidence of the laser light and the generation of the second harmonic light is suppressed. The wavelength converter 70 also has no optical contact surface on the light incident surface 10a and the light emitting surface 10b of the KBBF crystal 10. As a result, the wavelength conversion device 70 can realize further reduction in running cost and maintenance cost and generation of second harmonic light with higher energy and higher average power.

11. Description of an Example of a Wavelength Conversion Device According to an Aspect of the Present Disclosure 11.1 Configuration FIG. 12 is a side view illustrating a schematic configuration of an example of a wavelength conversion device according to an aspect of the present disclosure.
The wavelength converter 80 includes the KBBF crystal 10, the water 21, the liquid cell 22, the mounting table 23, the element temperature controller 81, the heat transfer body 82, the temperature detector 83, the folder 84, and the heat insulator. 85 may be provided. The element temperature control device 81 may include at least one of a cooler or a heater and a control unit. Note that the description of the optical window of the liquid cell 22 is omitted.

  The folder 84 may hold the KBBF crystal 10. The folder 84 may be made of a material having a high thermal conductivity, such as a metal or diamond. The KBBF crystal 10 may be held on the folder 84 and mounted on the mounting table 23. The mounting table 23 may be mounted on the heat insulator 85. The cooler may be an electronic cooler. The heat transfer body 82 may be connected to the element temperature control device 81 and the folder 84. The heat transfer body 82 may be made of a material such as a metal or diamond having a high thermal conductivity, or may have a high thermal conductivity such as a heat pipe. The temperature detector 83 may be installed in the folder 84. The cooler or the heater of the element temperature control device 81 may be connected to the heat transfer body 82.

11.2 Operation Next, the operation of the wavelength converter 80 will be described.
The temperature detector 83 detects the temperature in the vicinity of the KBBF crystal 10 via the folder 84. In the element temperature control device 81, the control unit controls the electronic cooler or the heater, and controls the temperature of the KBBF crystal 10 so that the temperature detected by the temperature detector 83 falls within a predetermined range. The cooling or heating is performed via an electronic cooler or a heat transfer body 82 connected to the heater and a folder 84. As a result, the KBBF crystal 10 is kept at a device temperature within a predetermined range. Therefore, since the change in the conversion efficiency of the KBBF crystal 10 becomes small, the power of the generated second harmonic light is stabilized.

  Also in this wavelength converter 80, the temperature rise of the KBBF crystal 10 due to the incidence of the laser light and the generation of the second harmonic light is suppressed. The wavelength converter 80 also has no optical contact surface on the light incident surface and the light output surface of the KBBF crystal 10. As a result, the wavelength conversion device 80 can realize further reduction in running cost and maintenance cost, and generation of second harmonic light with higher energy and higher average power.

  In the above-described embodiment, light incident on the wavelength conversion element and light emitted from the wavelength conversion element are transmitted through separate optical windows. However, light incident on the wavelength conversion element and light emitted from the wavelength conversion element may pass through the same optical window. 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”.

DESCRIPTION OF SYMBOLS 1 Laser apparatus 10 KBBF crystal 10a Light output surface 10b Light output surface 20, 20A, 30, 40, 50, 60, 60A, 70, 80 Wavelength converter 21 Water 22, 32 Liquid cell 22a, 22b Optical window 23 Mounting table 31 Immersion liquid 31A Silicon oil 32c, 32d Separation wall 41 Relay lens 42, 51 Dichroic mirror 52 Reflection mirror 52a Reflection surface 61 Liquid circulation device 62 Piping 63 Liquid temperature control device 71, 81 Element temperature control device 72, 82 Heat transfer body 73 83 Temperature detector 84 Folder 85 Heat insulator L1 Laser light L2 Second harmonic light θ1, θ4 Incident angle θ2 Phase matching angle θ3 Output angle

Claims (13)

A wavelength conversion element that includes a light incident surface and a light exit surface, and generates second harmonic light of light incident from the light incident surface;
A liquid cell comprising an incident part through which light incident on the wavelength conversion element passes; and an emission part through which light emitted from the wavelength conversion element passes;
An immersion liquid that is contained in the liquid cell together with the wavelength conversion element, and in which the wavelength conversion element is immersed so that at least the light exit surface is in contact with the liquid;
A wavelength conversion device comprising: In the wavelength conversion element, an incident angle to the light emitting surface when the second harmonic light is emitted is equal to or greater than a critical angle of total reflection of the second harmonic light at the interface between the light emitting surface and the atmosphere. Yes,
The refractive index of the immersion liquid is such that the critical angle of total reflection of the second harmonic wave at the interface with the light exit surface is larger than the incident angle of the second harmonic light to the light exit surface. is there,
The wavelength conversion device according to claim 1. In the wavelength conversion element, an incident angle to the light emitting surface when the second harmonic light is emitted is equal to or greater than a critical angle of total reflection of the second harmonic light at the interface between the light emitting surface and the atmosphere. Yes,
The immersion liquid is in contact with the light exit surface, and the critical angle of total reflection of the second harmonic at the interface with the light exit surface is greater than the incident angle of the second harmonic light on the light exit surface. A first immersion liquid having a refractive index that increases, and a second immersion liquid in contact with the light incident surface and having a refractive index closer to the refractive index of the wavelength conversion element than the refractive index of the atmosphere at the wavelength of the incident light. Including,
The wavelength conversion device according to claim 1.   The wavelength conversion device according to claim 1, wherein the wavelength conversion element is a KBBF crystal.   The wavelength converter according to claim 1, wherein the immersion liquid is at least one of water and fluorine-based oil.   The wavelength converter according to claim 3, wherein the first immersion liquid is at least one of water and fluorine-based oil.   The wavelength conversion device according to claim 3, wherein the second immersion liquid is a silicon-based oil. A plurality of the wavelength conversion elements;
A condensing element that is disposed between the plurality of wavelength conversion elements, and makes the incident light emitted from one wavelength conversion element enter the other wavelength conversion element;
The wavelength converter of Claim 1 provided with.   The wavelength conversion device according to claim 1, further comprising a reflection element for causing the incident light emitted from the wavelength conversion element to enter the wavelength conversion element again.   The wavelength converter of Claim 1 provided with the liquid circulation apparatus for circulating the said immersion liquid.   The wavelength converter of Claim 1 provided with the liquid temperature control apparatus which controls the temperature of the said immersion liquid in the predetermined range.   The wavelength converter of Claim 1 provided with the element temperature control apparatus which controls the temperature of the said wavelength converter within the predetermined range. A laser device for outputting laser light;
The wavelength converter according to claim 1, wherein the laser light is input as the incident light;
An ultraviolet light generation laser device comprising:

Images