Wavelength conversion device and wavelength conversion method

Abstract

To provide a wavelength conversion device and a wavelength conversion method that can improve stability of output light.SOLUTION: A wavelength conversion device comprises: storage means 101 which stores conversion efficiency maps MP by a plurality of temperature conditions of a nonlinear optical crystal 30, the conversion efficiency map MP containing wavelength conversion efficiency by a plurality input positions of input light on a reference surface 31 of the nonlinear optical crystal 30 which converts the wavelength of the output light from the wavelength of the input light associatively with the input positions; incidence position determination means 102 which determines an incidence position where the input light is made incident on the nonlinear optical crystal 30 based upon conversion efficiency maps MP under two or more temperature conditions selected from the storage means 101; and control means 103 which controls movement means 40 moving relative positions of the nonlinear optical crystal 30 and the input light so that the input light is made incident on the incidence position determined by the incidence position determination means 102.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a wavelength conversion device and a wavelength conversion method. [Background technology]

[0002] Patent Documents 1 to 9 disclose wavelength conversion devices using nonlinear optical crystals. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-055695 [Patent Document 2] Patent No. 5825642 [Patent Document 3] Japanese Patent Application Laid-Open No. 2003-057696 [Patent Document 4] Japanese Patent Application Laid-Open No. 2004-022946 [Patent Document 5] Japanese Patent Application Publication No. 10-268367 [Patent Document 6] Patent No. 4729093 [Patent Document 7] Japanese Patent Application Laid-Open No. 2006-317724 [Patent Document 8] Patent No. 4565207 [Patent Document 9] Patent No. 4572074 Summary of the Invention [Problem to be solved by the invention]

[0004] Stability of output light obtained by converting the wavelength of input light is desired.

[0005] The present disclosure has been made to solve the above problems, and aims to provide a wavelength conversion device and a wavelength conversion method that can improve the stability of output light. [Means for solving the problem]

[0006] The wavelength conversion device according to the present disclosure comprises a storage means for storing the conversion efficiency map for each of a plurality of temperature conditions of the nonlinear optical crystal, the conversion efficiency map being a conversion efficiency map storing wavelength conversion efficiencies for each of a plurality of input positions of the input light at a reference plane of the nonlinear optical crystal that converts the wavelength of the output light from the wavelength of the input light, the conversion efficiency being associated with the input position, an incident position determination means for determining an incident position at which the input light is incident on the nonlinear optical crystal based on the conversion efficiency map for two or more of the temperature conditions selected from the storage means, and a control means for controlling a moving means for moving the relative position between the nonlinear optical crystal and the input light so that the input light is incident on the incident position determined by the incident position determination means.

[0007] In the wavelength conversion device, the incident position determination means may identify compatible coordinates, which are coordinates of the input position at which the wavelength conversion efficiency under at least one of the temperature conditions is equal to or greater than a predetermined threshold, based on the conversion efficiency maps under the two or more selected temperature conditions, and determine the incident position from the compatible coordinates.

[0008] In the wavelength conversion device, the incident position determination means may identify a maximum conversion efficiency, which is the greatest wavelength conversion efficiency among the wavelength conversion efficiencies under a plurality of temperature conditions for each coordinate of the plurality of input positions, based on the conversion efficiency maps under the two or more selected temperature conditions, identify compatible coordinates, which are the coordinates of the input positions at which the maximum conversion efficiency is equal to or greater than a predetermined threshold, and determine the incident position from the compatible coordinates.

[0009] In the wavelength conversion device, the incident position determination means may identify compatible coordinates, which are coordinates of the input position at which the wavelength conversion efficiency under a plurality of the temperature conditions is equal to or greater than a predetermined threshold, based on the conversion efficiency maps under the two or more selected temperature conditions, and determine the incident position from the compatible coordinates.

[0010] In the wavelength conversion device, the incident position determining means may generate a path consisting of only a plurality of the fitted coordinates, and determine the incident position from the fitted coordinates within the path.

[0011] In the wavelength conversion device, the incident position determination means may determine a first matching coordinate in the path as the incident position, and then when determining the next incident position, determine a second matching coordinate in the path that is adjacent to the first matching coordinate as the next incident position, and repeat this process thereafter.

[0012] In the wavelength conversion device, the incident position determining means may determine the incident position so that the path is a single stroke.

[0013] In the wavelength conversion device, the nonlinear optical crystal is in contact with a temperature adjustment means that adjusts the temperature of the nonlinear optical crystal on a predetermined surface side, and the path includes a plurality of first line segments oriented along the predetermined surface and second line segments connecting the first line segments, and the length of the first line segments may be longer than the length of the second line segments.

[0014] In the wavelength conversion device, the path may be generated so that its starting point is the fitted coordinate belonging to the first line segment that is closest to the specified surface and its end point is the fitted coordinate belonging to the first line segment that is farthest from the specified surface, or it may be generated so that its starting point is the fitted coordinate belonging to the first line segment that is farthest from the specified surface and its end point is the fitted coordinate belonging to the first line segment that is closest to the specified surface.

[0015] In the wavelength conversion device, the nonlinear optical crystal is in contact with a temperature adjustment means that adjusts the temperature of the nonlinear optical crystal on a predetermined surface side, and the control means may cause the temperature adjustment means to adjust the temperature of the nonlinear optical crystal, using as a target temperature a temperature at which the wavelength conversion efficiency at the incident position identified based on the conversion efficiency map is equal to or greater than a predetermined threshold value.

[0016] In the wavelength conversion device, the control means may monitor the wavelength conversion efficiency while moving the incident position along the path, and cause the temperature adjustment means to adjust the temperature of the nonlinear optical crystal so as to maximize the wavelength conversion efficiency.

[0017] In the wavelength converter, the predetermined faces may include one to four faces of the nonlinear optical crystal excluding the incident face of the input light and the output face of the output light.

[0018] In the wavelength conversion device, the specified surface is one of the surfaces of the nonlinear optical crystal excluding the incident surface of the input light and the output surface of the output light, and the nonlinear optical crystal may be in contact with a holding member whose position is changed by the moving means on the surface side excluding the incident surface and the output surface.

[0019] In the wavelength conversion device, a temperature difference between adjacent temperatures under the temperature conditions corresponding to the selected plurality of conversion efficiency maps may be smaller than a temperature phase matching tolerance of the nonlinear optical crystal.

[0020] In the wavelength converter, a temperature difference between adjacent temperatures in the temperature conditions corresponding to the selected plurality of conversion efficiency maps may be equal to or less than half of a temperature phase matching tolerance of the nonlinear optical crystal.

[0021] In the wavelength conversion device, the incident position determination means may identify a reference temperature at which the wavelength conversion efficiency at a predetermined reference coordinate is maximized based on the conversion efficiency map, and determine the incident position based on the conversion efficiency map at the reference temperature and the conversion efficiency map for a temperature that is different from the reference temperature by a predetermined temperature.

[0022] In the wavelength conversion device, the input light may be composed of light in the ultraviolet region and light in the infrared region, and the nonlinear optical crystal may convert the wavelength by sum frequency mixing of the light in the ultraviolet region and the light in the infrared region.

[0023] In the wavelength conversion device, the conversion efficiency map may be generated under a plurality of temperature conditions and recorded in the storage means.

[0024] The wavelength conversion method according to the present disclosure includes a step of storing in a storage means a conversion efficiency map in which the wavelength conversion efficiency for each of a plurality of input positions of input light at a reference plane of a nonlinear optical crystal that converts the wavelength of output light from the wavelength of input light is stored in correspondence with the input position, the conversion efficiency map for each of a plurality of temperature conditions of the nonlinear optical crystal; a step of causing an incident position determination means to determine an incident position at which the input light is incident on the nonlinear optical crystal based on the conversion efficiency maps for two or more of the temperature conditions selected from the storage means; and a step of moving the relative position of the nonlinear optical crystal and the input light so that the input light is incident on the determined incident position. [Effects of the Invention]

[0025] According to the present disclosure, it is possible to provide a wavelength conversion device and a wavelength conversion method that can improve the stability of output light. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a graph illustrating the conversion efficiency of a nonlinear optical crystal, in which the horizontal axis represents the temperature of the nonlinear optical crystal and the vertical axis represents the conversion efficiency. [Figure 2] 1 is a configuration diagram illustrating a wavelength conversion system according to a first embodiment. [Figure 3] FIG. 1(a) is a top view illustrating a nonlinear optical crystal in a wavelength conversion system according to embodiment 1, and FIG. 1(b) is a side view illustrating a nonlinear optical crystal in a wavelength conversion system according to embodiment 1. [Figure 4] 2 is a block diagram illustrating an information processing device in the wavelength conversion system according to the first embodiment. [Figure 5] 10 is a block diagram illustrating an information processing device in a wavelength conversion system according to another example of the first embodiment. [Figure 6]4 is a diagram illustrating a conversion efficiency map stored in a storage means of an information processing device in the wavelength conversion system according to the first embodiment. FIG. [Figure 7] FIG. 10 is a diagram illustrating a conversion efficiency map stored in a storage means of an information processing device in the wavelength conversion system according to the first embodiment, showing a conversion efficiency map obtained by changing the temperature by −1.2° C. from a predetermined temperature. [Figure 8] FIG. 10 is a diagram illustrating a conversion efficiency map stored in a storage means of an information processing device in the wavelength conversion system according to the first embodiment, showing a conversion efficiency map obtained by changing the temperature by −0.6° C. from a predetermined temperature. [Figure 9] FIG. 2 is a diagram illustrating a conversion efficiency map stored in a storage means of an information processing device in the wavelength conversion system according to the first embodiment, showing a conversion efficiency map obtained by changing the temperature by ±0° C. from a predetermined temperature. [Figure 10] FIG. 10 is a diagram illustrating a conversion efficiency map stored in a storage means of an information processing device in the wavelength conversion system according to the first embodiment, showing a conversion efficiency map obtained by changing the temperature by +0.6° C. from a predetermined temperature. [Figure 11] FIG. 10 is a diagram illustrating a conversion efficiency map stored in a storage means of an information processing device in the wavelength conversion system according to the first embodiment, showing a conversion efficiency map obtained by changing the temperature by +1.2° C. from a predetermined temperature. [Figure 12] FIG. 12 is a diagram illustrating a conversion efficiency map stored in a storage means of an information processing device in the wavelength conversion system according to the first embodiment, and is a diagram represented by the maximum wavelength conversion efficiency at each input position in FIGS. 7 to 11. [Figure 13] 3 is a diagram illustrating a path including an incident position determined by an incident position determining means in an information processing device in the wavelength conversion system according to the first embodiment. FIG. [Figure 14] FIG. 2 is a flowchart illustrating a wavelength conversion method using the wavelength conversion system according to the first embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0027] Hereinafter, a specific configuration of this embodiment will be described with reference to the drawings. The following description shows a preferred embodiment of the present disclosure, and the scope of the present disclosure is not limited to the following embodiment. In the following description, parts with the same reference numerals indicate substantially the same content.

[0028] First, in <Problems newly discovered by the inventors>, problems newly discovered by the inventors regarding wavelength conversion devices are described. Next, in <Embodiment 1>, a wavelength conversion device and a wavelength conversion method according to this embodiment are described. Note that the <Problems newly discovered by the inventors> are also within the scope of the technical idea of ​​this embodiment. Furthermore, the technical scope of the present invention is not limited to the applications and numerical values ​​described in the <Problems newly discovered by the inventors>.

[0029] <New problem discovered by the inventor> For example, photomask defect inspection devices may use a short-wavelength light source, particularly a deep ultraviolet light source with a wavelength of 250 nm or less, as an irradiation light source in order to improve optical resolution. It is desirable for photomask defect inspection devices to use a continuous, high-power light source to enable uninterrupted, high-speed inspection. To generate continuous light in such a deep wavelength range, second harmonic generation and sum frequency generation by external cavity conversion using light from a laser light source in the visible or infrared range are often used, as disclosed in Patent Document 1, for example. External cavity conversion involves placing a nonlinear optical crystal inside an external cavity.

[0030] The main nonlinear optical crystals for generating ultraviolet light are C S LiB6O 10 crystal (hereinafter referred to as CLBO crystal), β-BaB2O4 crystal (hereinafter referred to as BBO crystal), and LiB3O5 crystal (hereinafter referred to as LBO crystal) are used.

[0031] Second harmonic generation can be achieved with a single pump light source. In this respect, second harmonic generation is simpler and more efficient than sum frequency generation, which generally requires two light sources. However, the wavelength that can be generated with second harmonic generation is limited to 205 nm, at which phase matching can be achieved with BBO crystals. To generate light with wavelengths below 205 nm, sum frequency generation is required. CLBO crystals, BBO crystals, and LBO crystals can all be used as crystals for sum frequency generation.

[0032] For example, Patent Document 2 discloses a technique for generating continuous wave ultraviolet light with a wavelength of 233 to 234 nm by second harmonic generation using an external resonator with a BBO crystal, and further discloses a technique for generating light with a wavelength of 193.2 to 193.6 nm by sum frequency mixing light with a wavelength of 1111 to 1130 nm using a CLBO crystal placed in a second external resonator.

[0033] In both second harmonic generation and sum frequency generation, to generate practical ultraviolet light, it is essential to satisfy the so-called phase matching condition, which is a special condition regarding the relationship between the refractive index and wavelength of the incident light in the nonlinear optical crystal and the refractive index and wavelength of the generated light. The simplified phase matching condition for sum frequency generation is expressed by the following equation (1), where λ is the wavelength and n is the refractive index of the nonlinear optical crystal for each wavelength.

[0034] (n3 / λ3)=(n1 / λ1)+(n2 / λ2) (1)

[0035] As disclosed in Patent Document 2, when deep ultraviolet light with a wavelength of 193.2 to 193.6 nm is generated by sum frequency mixing ultraviolet light with a wavelength of 233 to 234 nm and infrared light with a wavelength of 1111 to 1130 nm using a CLBO crystal, the CLBO crystal can be operated under a special condition called non-critical phase matching, in which the angle between the incident optical axis and the crystal axis is orthogonal, thereby enabling the generation of deep ultraviolet light with high efficiency and high output.

[0036] However, the refractive index of a nonlinear optical crystal is a function of temperature, and in order to satisfy the above phase matching condition, it is necessary to precisely adjust and stabilize the temperature of the nonlinear optical crystal by means of a Peltier element or the like.

[0037] In the case of noncritical phase matching, the temperature dependence of the refractive index is particularly strong. For example, in the case of a 20 mm long CLBO crystal, a 0.3°C deviation from the optimum temperature calculated results in a 10% decrease in conversion efficiency, as shown in Figure 1. Figure 1 is a graph illustrating the wavelength conversion efficiency of a nonlinear optical crystal. The horizontal axis represents the relative temperature, with the temperature at which the conversion efficiency of the nonlinear optical crystal is maximized as 0, and the vertical axis represents the wavelength conversion efficiency. Therefore, to maintain a constant output power, it is necessary to stabilize the temperature as precisely as possible (for example, within ±0.05°C). The temperature range (full width at half maximum) within which the output power of the output light is not reduced by half is called the temperature phase matching tolerance. In the case of Figure 1, the temperature phase matching tolerance is 1.35°C.

[0038] Deep ultraviolet light with a wavelength of 193 nm has high photon energy. Therefore, if output light continues to be generated while the position of the CLBO crystal is fixed, optical damage will occur in the nonlinear optical crystal itself in a short period of time, resulting in a decrease in wavelength conversion efficiency. To solve this problem, many techniques have been proposed to change the position at which the laser light passes through the nonlinear optical crystal, as shown in Patent Documents 3 to 7.

[0039] However, CLBO crystals have low thermal conductivity. Therefore, when controlling the temperature from the surroundings using a Peltier element or the like, it is difficult to maintain a uniform temperature throughout the CLBO crystal. Therefore, when the CLBO crystal is translated, it is generally difficult to maintain the phase matching condition. This results in a problem of a decrease in the output power of the wavelength-converted output light.

[0040] As a means for solving this problem, a technology for adjusting the temperature of a nonlinear optical crystal has been proposed, as shown in Patent Document 8, for example. Specifically, in Patent Document 8, the nonlinear optical crystal is translated to adjust the output of incident light so that the output of wavelength-converted output light becomes approximately constant. At the same time, a temperature regulator is controlled to adjust the temperature of the nonlinear optical crystal so that the output of incident light becomes minimum during each of a plurality of temperature adjustment periods.

[0041] CLBO crystals do not necessarily have uniform conversion efficiency across the entire cross section perpendicular to their optical axis. This is because CLBO crystals are created through various processes that cause non-uniform conversion efficiency during their growth and processing. Because the quality of CLBO crystals is generally non-uniform, when the CLBO crystal is moved, input light may pass through a region of poor quality, and sufficient converted light output may not be obtained even if the temperature is optimized. This may hinder practical use in semiconductor inspection equipment, which requires continuous input of input light.

[0042] To solve this problem, Patent Document 9 proposes a wavelength converter equipped with a storage means for prestoring the output power of wavelength-converted output light when a nonlinear optical crystal is moved. Based on the output power stored in the storage means, this wavelength converter sequentially selects, from among the laser light input positions, an input position where the output power of the output light is equal to or greater than a predetermined threshold, and inputs the laser light. This method is used, for example, when generating ultraviolet light with a wavelength of 266 nm from visible light with a wavelength of 532 nm using a CLBO crystal.

[0043] The inventors have found that when a CLBO crystal is used that generates deep ultraviolet light with a wavelength of about 193 nm by sum frequency mixing infrared light with a wavelength of about 1110 nm and ultraviolet light with a wavelength of about 234 nm, it may be difficult to put the device configuration disclosed in Patent Document 9 and the like into practical use.

[0044] The main reason is as follows: the power of the wavelength-converted output light varies not only with the quality of the nonlinear optical crystal, but also with the nonuniformity of the temperature distribution in the nonlinear optical crystal. This is because, if there is a nonuniform temperature distribution in the region through which the input light passes (both in-plane and along the optical axis), the phase matching condition expressed by equation (1) is only partially maintained.

[0045] Furthermore, the temperature distribution in a diamond-shaped nonlinear optical crystal called a Brewster cut, which is used to continuously output wavelength-converted output light, is more non-uniform and complex than in a rectangular parallelepiped crystal. The inventors have discovered that such diamond-shaped nonlinear optical crystals have regions with low wavelength conversion efficiency, even if the overall quality is good.

[0046] In addition, CLBO crystals, which generate deep ultraviolet light with a wavelength of around 193 nm by sum-frequency mixing infrared light with a wavelength of around 1110 nm and ultraviolet light with a wavelength of around 234 nm, enable highly efficient wavelength conversion through noncritical phase matching. However, the trade-off is that the wavelength conversion efficiency is extremely sensitive to the temperature of the nonlinear optical crystal through which the input light passes.

[0047] In the example mentioned above, a temperature change of 0.67°C reduces the output light power by half. For example, we found that even a commonly used CLBO crystal measuring 5 x 5 x 20 mm has a temperature distribution of at least 1°C due to its low thermal conductivity. If the temperature changes by 1°C, the output light power of a wavelength of 193 nm will not reach even 20% of the power that would be obtained if the temperature were optimized.

[0048] For wavelength conversion devices that continuously output light for a long period of time, such as semiconductor inspection equipment, nonlinear optical crystals with a relatively large cross-sectional area are required. However, for example, a nonlinear optical crystal measuring 8 x 8 x 20 mm may experience a temperature difference of 2°C or more within the crystal. In addition, there is the problem that the optimal temperature for maximizing the wavelength conversion efficiency of the nonlinear optical crystal changes over time due to the absorption of the output light itself, which generates a wavelength of 193 nm.

[0049] Therefore, the method of detecting and recording the wavelength-converted output light while moving a nonlinear optical crystal requires finding the optimal temperature and measuring the output light each time the nonlinear optical crystal is moved. For example, if the cross section of a nonlinear optical crystal is divided into 50 x 40 = 2,000 measurement points and the temperature that maximizes wavelength conversion efficiency at all measurement points is found to obtain a two-dimensional distribution, assuming that measurements can be taken in 5 minutes per measurement point, a total of 10,000 minutes, or 167 hours, would be required. However, a method requiring such a long measurement time would accelerate damage to the nonlinear optical crystal. Therefore, this method is not practical for semiconductor inspection equipment, which is required to operate 24 hours a day, 365 days a year.

[0050] Therefore, the inventors conducted extensive research into the characteristics of nonlinear optical crystals, such as CLBO crystals, that generate deep ultraviolet light with a wavelength of approximately 193 nm by sum-frequency mixing infrared light with a wavelength of approximately 1110 nm and ultraviolet light with a wavelength of approximately 235 nm. The inventors then changed the holding temperature of the nonlinear optical crystal five or more times and obtained a two-dimensional distribution (conversion efficiency map) of the cross section of the nonlinear optical crystal of the ratio of the output light with a wavelength of 193 nm to the output light with a wavelength of 235 nm (output light output / input light output). The inventors discovered that a practical distribution can be obtained by using the maximum ratio at each point as the evaluation value for that point.

[0051] <Embodiment 1> Next, a wavelength conversion device according to the first embodiment will be described. FIG. 2 is a configuration diagram illustrating a wavelength conversion system 1 according to the first embodiment. As shown in FIG. 2, the wavelength conversion system 1 includes a light source 10, an optical system 20, a nonlinear optical crystal 30, a moving means 40, a temperature adjusting means 50, an optical output detecting means 61, an optical output detecting means 62, a temperature controller 70, a cavity length control device 80, a driver 90, and an information processing device 100. In this embodiment, the entire wavelength conversion system 1 including the information processing device 100 may be referred to as a wavelength conversion device, or the information processing device 100 may be referred to as a wavelength conversion device. Furthermore, the information processing device 100 plus some of the components constituting the wavelength conversion system 1 may be referred to as a wavelength conversion device.

[0052] The light source 10 includes, for example, an ultraviolet light source 11 and an infrared light source 12. The ultraviolet light source 11 generates laser light L11 including ultraviolet light having a wavelength λ of 233 to 235 nm. The laser light L11 may have a center wavelength of λ of 234 nm, for example. The infrared light source 12 generates laser light L12 including infrared light having a wavelength λ of 1090 to 1130 nm. The laser light L12 may have a center wavelength of λ of 1110 nm, for example. Note that the light source 10 is not limited to the ultraviolet light source 11 and the infrared light source 12, and may be a light source that generates light of another wavelength as long as the nonlinear optical crystal 30 outputs output light that has been wavelength-converted from input light.

[0053] The optical system 20 includes a mirror 21, a mirror 22, and a resonator 23. The mirror 21 reflects a portion of the laser light L11 toward an optical output detection means 61. The mirror 22 reflects a portion of the output light wavelength-converted in the nonlinear optical crystal 30 toward an optical output detection means 62. The mirrors 21 and 22 may be half mirrors, non-polarizing beam splitters, or the like.

[0054] The resonator 23 includes, for example, a mirror 24, a mirror 25, a mirror 26, and a mirror 27. The resonator 23 may include other optical members. The multiple mirrors 24 to 27 are arranged in the resonator 23 so that the laser light L11 and the laser light L12 are sum-frequency mixed in the nonlinear optical crystal 30. The multiple mirrors 24 to 27 may be, for example, half mirrors, non-polarizing beam splitters, etc. For example, the multiple mirrors 24 to 27 are arranged so that the optical axis of the laser light L11 and the optical axis of the laser light L12 overlap in the nonlinear optical crystal 30.

[0055] For example, laser light L11 is incident on mirror 24. After passing through mirror 24, laser light L11 is incident on nonlinear optical crystal 30. After passing through nonlinear optical crystal 30, laser light L11 is transmitted through mirror 25.

[0056] For example, laser light L12 is incident on mirror 26. The laser light L12 that has passed through mirror 26 is incident on mirror 27. The laser light L12 that has been reflected by mirror 27 is incident on mirror 24. The laser light L12 that has been reflected by mirror 24 is incident on nonlinear optical crystal 30. The laser light L12 that has passed through nonlinear optical crystal 30 is reflected by mirror 25. The laser light L12 that has been reflected by mirror 25 is incident on mirror 26. The laser light L12 that has been reflected by mirror 26 overlaps with the laser light L12 from infrared light source 12 on the same axis and is incident on mirror 27.

[0057] In this way, the resonator 23 is configured to increase the intensity of the laser light L12 by using the four mirrors 24 to 27. Note that the resonator 23 is not limited to the four mirrors 24 to 27, and may be configured to increase the intensity of the laser light L12 by using three or less or five or more mirrors.

[0058] The cavity length control device 80 controls the cavity length of the cavity 23. For example, the cavity length control device 80 is connected to an actuator 63 that moves the position of the mirror 27, and servo-controls the position of the mirror 27 so that the intensity of the laser light L12 circulating inside the cavity 23 continues to increase due to the positive interference effect.

[0059] FIG. 3(a) is a top view illustrating the nonlinear optical crystal 30 in the wavelength conversion system 1 according to the first embodiment, and FIG. 3(b) is a side view illustrating the nonlinear optical crystal 30 in the wavelength conversion system 1 according to the first embodiment. As shown in FIGS. 3(a) and 3(b), the nonlinear optical crystal 30 is fixed to a holding member 39. As a result, the holding member 39 holds the nonlinear optical crystal 30. The holding member 39 is also fixed to a moving means 40. As a result, the moving means 40 moves the holding member 39 and the nonlinear optical crystal 30. The temperature adjusting means 50 is attached to the holding member 39 or directly to the nonlinear optical crystal 30. The temperature sensor 51 may be attached so as to be in contact with the holding member 39. Alternatively, the temperature sensor 51 may be disposed near the nonlinear optical crystal 30. The temperature sensor 51 senses the temperature at a predetermined position in the nonlinear optical crystal 30.

[0060] The nonlinear optical crystal 30 converts the wavelengths of the laser beams L11 and L12 incident thereon. The nonlinear optical crystal 30 outputs wavelength-converted output beam L13. The nonlinear optical crystal 30 includes, for example, a CLBO crystal. Note that the nonlinear optical crystal 30 is not limited to a CLBO crystal, and may be a BBO crystal or an LBO crystal as long as it is a crystal that converts the wavelength of the output beam from the wavelength of the input beam. Note that in the above description, the laser beam L11 transmitted through the nonlinear optical crystal 30 is transmitted through the mirror 25. However, instead, the laser beam L11 transmitted through the nonlinear optical crystal 30 may be reflected by the mirror 25, and the laser beam L11 may resonate as follows: That is, the laser beam L11 is reflected by the mirror 25 and enters the mirror 26. The laser beam L11 reflected by the mirror 26 enters the mirror 27. The laser beam L11 reflected by the mirror 27 enters the mirror 24. The laser beam L11 reflected by the mirror 24 is superimposed on the same axis as the laser beam L11 from the ultraviolet light source 11 and enters the nonlinear optical crystal 30.

[0061] The nonlinear optical crystal 30 has a reference plane 31. The reference plane 31 is a plane on which the laser beams L11 and L12 are incident. For example, the reference plane 31 is formed at an incident angle θ of the laser beam L11. 11 and the incident angle θ of the laser light L12 12 It is preferable that all of the laser beams L11 and L12 are arranged so that they are near the Brewster angle, at most 10° or less. This makes it possible to reduce the reflection loss of the incident laser beams L11 and L12. The nonlinear optical crystal 30 also has a rhombic cross section so that the laser beams L11 and L12 traveling through it are approximately parallel to the four faces excluding the input and output faces. This type of shape of the nonlinear optical crystal 30 is called a Brewster cut. The laser beams L11 and L12 enter the interior of the nonlinear optical crystal 30 at a refraction angle θ2 with respect to the incident face. The laser beams L11 and L12 are arranged so that they are near the Brewster angle (incident angle θ 12 + refraction angle θ2=90°) so that the laser light L12 is not reflected by the reference surface 31. In this case, the incident θ 11 In order for the laser light L11 and the laser light L12 to overlap (become equal in refraction angle θ2) in the nonlinear optical crystal 30, the incident angle θ of the laser light L11 with a short wavelength must be 11 is the angle of incidence θ 12 By utilizing this phenomenon, the mirrors 24 and 25 may be configured so that the laser light L11 is neither reflected nor transmitted by them.

[0062] The nonlinear optical crystal 30 may have a predetermined surface 32. The nonlinear optical crystal 30 may be in contact with a temperature adjustment means 50 that adjusts the temperature of the nonlinear optical crystal 30 on the predetermined surface 32 side. The predetermined surface 32 may be one of the surfaces of the nonlinear optical crystal 30 excluding the incident surface of the input light (e.g., reference surface 31) and the output surface of the output light. The nonlinear optical crystal 30 may be in contact with a holding member 39 to which a moving means 40 that moves the incident position of the nonlinear optical crystal 30 is fixed. The surface of the nonlinear optical crystal 30 in contact with the holding member 39 to which the moving means 40 is fixed may be a surface excluding the incident surface (e.g., reference surface 31) and the output surface of the output light. The surface of the nonlinear optical crystal 30 in contact with the holding member 39 to which the moving means 40 is fixed may be, for example, the same surface as the surface of the nonlinear optical crystal 30 in contact with the temperature adjustment means 50 (predetermined surface 32), a surface opposite to the predetermined surface 32, or a surface other than these. Note that predetermined surface 32 may include one to four surfaces of nonlinear optical crystal 30 excluding the incident surface of input light and the output surface of output light. For example, predetermined surface 32 may include four surfaces of the surfaces connecting the incident surface and the output surface. By including multiple surfaces in predetermined surface 32, the temperature uniformity of nonlinear optical crystal 30 can be improved.

[0063] The moving means 40 changes the incident position at which the input light is incident on the nonlinear optical crystal 30. That is, the moving means 40 changes the relative position between the nonlinear optical crystal 30 and the input light. The moving means 40, for example, two-dimensionally moves the reference plane 31 of the nonlinear optical crystal 30 in a plane parallel to the reference plane 31. As shown in FIG. 3 , in the case of a Brewster cut type nonlinear optical crystal 30, the moving means 40 moves the nonlinear optical crystal 30 parallel to the reference plane 31. In the following example, the moving means 40 will be described as changing the position of the nonlinear optical crystal 30 to change the relative position between the nonlinear optical crystal 30 and the input light. However, the moving means 40 may also change the positions of the ultraviolet light source 11, the infrared light source 12, the mirror 21, etc. to change the relative position between the nonlinear optical crystal 30 and the input light.

[0064] The movement means 40 includes, for example, a driving device such as a motor, an encoder, etc. The movement means 40 is connected to the driver 90 in a state in which information can be transmitted via a signal line that includes at least one of a wireless and a wired connection. The movement means 40 changes the incident position based on a signal from the driver 90. Note that the movement means 40 may be connected to the information processing device 100 in a state in which information can be transmitted via a signal line without going through the driver 90, and may change the incident position based on a signal from the information processing device 100 that has the function of the driver 90.

[0065] The temperature adjustment means 50 heats or cools the nonlinear optical crystal 30. The temperature adjustment means 50, together with the temperature sensor 51, is connected to the temperature controller 70 via a signal line in a state in which information can be transmitted. The temperature controller 70 controls the temperature adjustment means 50 so that the set temperature specified by the information processing device 100 matches the temperature measured by the temperature sensor 51. Note that the temperature adjustment means 50 may be connected to the information processing device 100 via a signal line in a state in which information can be transmitted, without going through the temperature controller 70, and may heat or cool the nonlinear optical crystal 30 based on a signal from the information processing device 100 having the function of the temperature controller 70.

[0066] The optical output detection means 61 detects the output of input light such as laser light L11 and laser light L12 incident on the nonlinear optical crystal 30. The optical output detection means 61 is connected to the information processing device 100 via a signal line in a state in which information can be transmitted. The optical output detection means 61 outputs the detected output of the input light to the information processing device 100.

[0067] The optical output detecting means 62 detects the output power of the output light wavelength-converted in the nonlinear optical crystal 30. The optical output detecting means 62 is connected to the information processing device 100 via a signal line in a state in which information can be transmitted. The optical output detecting means 62 outputs the detected output power of the output light to the information processing device 100.

[0068] Fig. 4 is a block diagram illustrating an information processing device 100 in the wavelength conversion system 1 according to the first embodiment. As shown in Fig. 4, the information processing device 100 includes a storage unit 101, an incident position determination unit 102, and a control unit 103. The information processing device 100 includes information processing devices such as a PC, a server, and a smartphone. Fig. 5 is a block diagram illustrating an information processing device 100a in the wavelength conversion system 1 according to another example of the first embodiment. As shown in Fig. 5, the information processing device 100a may further include a processing unit 104.

[0069] FIG. 6 is a diagram illustrating a conversion efficiency map MP stored in the storage means 101 of the information processing device 100 in the wavelength conversion system 1 according to the first embodiment. In FIG. 6, some reference numerals are omitted to avoid cluttering the drawing. This also applies to the subsequent drawings. As shown in FIG. 6, the storage means 101 stores the conversion efficiency map MP. The conversion efficiency map MP is a map in which the wavelength conversion efficiency for each of a plurality of input positions IP of input light on the reference surface 31 of the nonlinear optical crystal 30 is stored in association with the input position IP. Note that the position at which the input light is incident in the conversion efficiency map MP is referred to as the input position IP, and the position at which the input light is incident, determined by the incident position determination means 102 (described later), is referred to as the incident position to distinguish between the two.

[0070] The conversion efficiency map MP does not have to be created in the wavelength conversion system 1 as long as it is stored in the storage means 101. The conversion efficiency map MP may be created by the wavelength conversion system 1 in the following manner. In this case, an information processing device 100a shown in FIG. 5 is used.

[0071] First, a predetermined position of the nonlinear optical crystal 30 is adjusted to a predetermined temperature. The predetermined position may be, for example, near the center of the nonlinear optical crystal 30. In this case, the nonlinear optical crystal 30 is positioned by the moving means 40 so that the input light and output light pass through a predetermined position, such as near the center of the reference surface 31 of the nonlinear optical crystal 30.

[0072] Next, the temperature of nonlinear optical crystal 30 is adjusted by temperature adjustment means 50 to find the temperature of nonlinear optical crystal 30 at which the output light detected by optical output detection means 62 is maximized. Then, while maintaining the temperature at a predetermined position, reference surface 31 of nonlinear optical crystal 30 is scanned two-dimensionally by movement means 40. As a result, the outputs detected by optical output detection means 61 and optical output detection means 62 when input light is incident on each input position IP on reference surface 31 are input into information processing device 100a, along with the input positions IP.

[0073] Next, the processing means 104 of the information processing device 100a calculates and maps the wavelength conversion efficiency at each input position IP. The wavelength conversion efficiency is, for example, as described above, the ratio of the output of output light with a wavelength of 193 nm to the output of input light with a wavelength of 235 nm (output of output light / output of input light). In this way, as shown in FIG. 6, the information processing device 100a can create a conversion efficiency map MP, which is a distribution map of wavelength conversion efficiency at the reference plane 31 of the nonlinear optical crystal 30. Note that, in order to perform actual wavelength conversion processing with enhanced reproducibility of the relationship between the wavelength conversion efficiency and temperature conditions shown in the conversion efficiency map MP generated by the above procedure and stored in the storage means 101, it is preferable to keep the positional relationship between the nonlinear optical crystal 30 and the temperature adjustment means 50 the same when the conversion efficiency map MP is generated and when the wavelength conversion processing is performed using the conversion efficiency map MP. For example, it is preferable to keep the contact surface between the nonlinear optical crystal 30 and the temperature adjustment means 50 the same when the conversion efficiency map MP is generated and when the wavelength conversion processing is performed using the conversion efficiency map MP.

[0074] In Figure 6, input positions IP with wavelength conversion efficiencies of 50% or more are shown in white, input positions IP with wavelength conversion efficiencies of 45% to 50% are shown in light gray, input positions IP with wavelength conversion efficiencies of 40% to 45% are shown in dark gray, and input positions IP with wavelength conversion efficiencies less than 40% are shown in black.

[0075] 6 shows an example of measurements on a CLBO crystal with a special shape called a Brewster cut. The region where high wavelength conversion efficiency can be obtained due to this special shape is located obliquely on the reference plane 31 of this embodiment. Furthermore, on the reference plane 31 of this embodiment, a region where wavelength conversion efficiency is low exists on the left side. Note that the shapes of the region with high wavelength conversion efficiency and the region with low wavelength conversion efficiency are merely examples, and other shapes may also be used.

[0076] In the related art, this result is utilized to sequentially use input positions IP with high wavelength conversion efficiency as the incident position of input light. However, as in the related art, when outputting 193 nm light using non-critical phase matching, the temperature tolerance of phase matching is very narrow. Therefore, in the related art, the area on the reference surface 31 of the nonlinear optical crystal 30 that can be used as an incident position is limited to a limited part in the central portion.

[0077] In contrast, in this embodiment, the temperature of the nonlinear optical crystal 30 is changed to create a conversion efficiency map MP at multiple temperatures. Then, the region with high wavelength conversion efficiency at each temperature is used as the incident position. For example, even if the central portion of the reference surface 31 is usable as the incident position at one temperature, the peripheral portion of the reference surface 31 may be usable as the incident position at another temperature. Therefore, by changing the temperature of the nonlinear optical crystal 30, a wide range of the reference surface 31 can be used as the incident position.

[0078] 7 to 11 are diagrams illustrating conversion efficiency maps MP stored in the storage means 101 of the information processing device 100 in the wavelength conversion system 1 according to the first embodiment, showing conversion efficiency maps MP obtained by varying the predetermined temperature by −1.2° C., −0.6° C., ±0° C., +0.6° C., and +1.2° C., respectively. As shown in FIGS. 7 to 11, the storage means 101 may store conversion efficiency maps MP for each of a plurality of temperature conditions of the nonlinear optical crystal 30. Note that the temperature condition may be a set temperature for the nonlinear optical crystal 30. For example, it may be a controlled temperature for the temperature adjustment means 50, or it may be a temperature at a predetermined position of the nonlinear optical crystal 30 (for example, the contact surface between the nonlinear optical crystal 30 and the temperature adjustment means 50) changed by heating or cooling with the temperature adjustment means 50. Alternatively, it may be a temperature at a predetermined position of the holding member 39.

[0079] As shown in FIG. 7, when the temperature is −1.2°C from the predetermined temperature, the region where high wavelength conversion efficiency can be obtained is distributed at the bottom of the conversion efficiency map MP. As shown in FIG. 8, when the temperature is −0.6°C from the predetermined temperature, the region where high wavelength conversion efficiency can be obtained is distributed below the center of the conversion efficiency map MP. As shown in FIG. 9, when the temperature is ±0°C from the predetermined temperature, the region where high wavelength conversion efficiency can be obtained is distributed in the central part of the conversion efficiency map MP. As shown in FIG. 10, when the temperature is +0.6°C from the predetermined temperature, the region where high wavelength conversion efficiency can be obtained is distributed above the center of the conversion efficiency map MP. As shown in FIG. 11, when the temperature is +1.2°C from the predetermined temperature, the region where high wavelength conversion efficiency can be obtained is distributed at the top of the conversion efficiency map MP.

[0080] The incident position determination means 102 determines the incident position at which the input light is incident on the nonlinear optical crystal 30, based on the conversion efficiency maps MP under two or more temperature conditions selected from the storage means 101. In FIGS. 7 to 11, the incident position determination means 102 selects the conversion efficiency maps MP under five temperature conditions (-1.2°C, -0.6°C, ±0°C, +0.6°C, and +1.2°C from the predetermined temperature). In this way, the incident position determination means 102 may select the conversion efficiency maps MP under five or more temperature conditions. This allows a wide range of the conversion efficiency maps MP to be used as the incident position. However, the incident position determination means 102 is not limited to this, and may select the conversion efficiency maps MP under four or fewer temperature conditions, or may select the conversion efficiency maps MP under six or more temperature conditions.

[0081] The temperature difference between each temperature condition is set to 0.6°C. This temperature difference of 0.6°C corresponds to a value less than half the temperature phase matching tolerance of 1.35°C of the nonlinear optical crystal 30 of this embodiment. In this way, by setting the temperature difference between the temperature conditions corresponding to the selected multiple conversion efficiency maps MP to less than half the temperature phase matching tolerance of the nonlinear optical crystal 30, the wavelength conversion efficiency at each input position IP approaches its maximum for one of the conversion efficiency maps with different temperature conditions. The temperature difference may be made smaller to create and select conversion efficiency maps MP under more temperature conditions. For example, the temperature difference may be set to 0.3°C, and nine temperature conditions may be created: -1.2°C, -0.9°C, -0.6°C, -0.3°C, ±0°C, +0.3°C, +0.6°C, +0.9°C, and +1.2°C. The temperature range may also be wider than ±1.2°C. Although this increases the number of conversion efficiency maps and increases the time required for creation, it enables the creation of MPs with higher accuracy.

[0082] The incident position determination means 102 identifies the coordinates of the input position IP at which the wavelength conversion efficiency under at least one temperature condition is equal to or greater than a predetermined threshold, based on the conversion efficiency map MP under two or more selected temperature conditions. The coordinates of the input position IP at which the wavelength conversion efficiency is equal to or greater than a predetermined threshold are called "compatible coordinates." The incident position determination means 102 then determines the incident position from the identified compatible coordinates.

[0083] Specifically, for example, the incident position determining means 102 identifies the coordinates of the input position IP in the conversion efficiency map MP where the wavelength conversion efficiency is 50% or more as the suitable coordinates. That is, in the examples of Fig. 7 to Fig. 11, the incident position determining means 102 determines the incident position from the area shown in white in the conversion efficiency map MP. Note that the predetermined threshold is not limited to 50% and may be another value.

[0084] Furthermore, the incident position determination means 102 may specify the suitable coordinates of the input position where the wavelength conversion efficiency under a plurality of temperature conditions is equal to or greater than a predetermined threshold value, based on the conversion efficiency map MP under the selected two or more temperature conditions, and then determine the incident position from the suitable coordinates.

[0085] 12 is a diagram illustrating a conversion efficiency map MP1 stored in the storage means 101 of the information processing device 100 in the wavelength conversion system 1 according to the first embodiment, and is represented by the maximum wavelength conversion efficiency at each input position IP in FIGS. 7 to 11. As shown in FIG. 12, each input position IP in the conversion efficiency map MP has a maximum conversion efficiency at which the wavelength conversion efficiency is maximized within a varied temperature range. For example, input position IP1 exhibits a maximum conversion efficiency (≧50%) at a temperature (−1.2°C from a predetermined temperature). input position IP2 exhibits a maximum conversion efficiency (≧50%) at a temperature (+1.2°C from a predetermined temperature). input position IP3 exhibits a maximum conversion efficiency (≧50%) at a temperature (−1.2°C from a predetermined temperature).

[0086] As shown in Fig. 12, by changing the temperature of the nonlinear optical crystal 30, high wavelength conversion efficiency can be obtained not only in the central region of the conversion efficiency map MP shown in Fig. 9 but also over a wide range of the conversion efficiency map MP1. However, it can also be seen that there are regions in the conversion efficiency map MP1 where sufficient wavelength conversion efficiency cannot be obtained.

[0087] For example, the lower right region of the conversion efficiency map MP1 shows that the wavelength conversion efficiency is not high, regardless of the temperature of the nonlinear optical crystal 30. This phenomenon may be reproduced even if the nonlinear optical crystal 30 is replaced with another one. Therefore, it is possible that the efficiency does not depend on the quality of the nonlinear optical crystal 30. After detailed investigation, we found that the efficiency depends on the shape of the nonlinear optical crystal 30. We found that the nonlinear optical crystal 30 has a large difference in temperature distribution in the direction parallel to its optical axis, and that perfect phase matching may not be maintained throughout the entire direction of light propagation. Related technologies have difficulty grasping this fact, leading to the problem of setting a region in which sufficient output light cannot be obtained as a usable region.

[0088] FIG. 13 is a diagram illustrating a path RT including an incident position determined by the incident position determination means 102 in the information processing device 100 in the wavelength conversion system 1 according to the first embodiment. As shown in FIG. 13, the incident position determination means 102 identifies the maximum wavelength conversion efficiency among the wavelength conversion efficiencies under multiple temperature conditions for each of the coordinates of multiple input positions IP based on the conversion efficiency maps MP under two or more selected temperature conditions. The incident position determination means 102 then identifies the coordinates at which the maximum conversion efficiency is equal to or greater than a predetermined threshold. The coordinates at which the maximum conversion efficiency is equal to or greater than a predetermined threshold are also called compatible coordinates because they are equal to or greater than the predetermined threshold. In this way, the incident position determination means 102 may determine the incident position from the compatible coordinates.

[0089] Specifically, the incident position determination means 102 identifies the maximum conversion efficiency for each input position IP based on the conversion efficiency map MP under five temperature conditions (temperatures of -1.2°C, -0.6°C, ±0°C, +0.6°C, and +1.2°C from the predetermined temperature). For example, the maximum conversion efficiency of input position IP1 is ≧50%, and the maximum conversion efficiency of input position IP2 is ≧50%. The maximum conversion efficiency of input position IP3 is also ≧50%. When the predetermined threshold is set to 50%, the incident position determination means 102 determines the coordinates of input positions IP1, IP2, IP3, etc., where the maximum conversion efficiency is ≧50% as compatible coordinates, and determines the incident position from the compatible coordinates.

[0090] The incident position determination means 102 may generate a route RT consisting of only a plurality of matching coordinates. Then, the incident position determination means 102 may determine the incident position from the matching coordinates within the route RT. Specifically, for example, when determining the next incident position after determining the first matching coordinate (input position IP1) within the route RT as the incident position, the incident position determination means 102 determines the second matching coordinate (input position IP3) which is a matching coordinate within the route RT and adjacent to the first matching coordinate as the next incident position. The incident position determination means 102 repeats this process thereafter.

[0091] In this way, the incident position determination means 102 may generate a route RT from the input position IP1 to the input position IP2 where the maximum conversion efficiency is ≧50%. Therefore, the route RT includes compatible coordinates where the maximum conversion efficiency is equal to or greater than a predetermined threshold.

[0092] Furthermore, the incident position determining means 102 may specify a reference temperature at which the wavelength conversion efficiency at a predetermined reference coordinate is maximized, based on the conversion efficiency map MP. Specifically, for example, as shown in Fig. 9, the reference coordinate may be the coordinate of the central part of the reference surface 31, and the reference temperature (predetermined temperature) at which the wavelength conversion efficiency at the central part of the reference surface 31 is maximized may be specified based on the conversion efficiency map MP. Then, the incident position determining means 102 may determine the incident position based on the conversion efficiency map MP at the reference temperature and the conversion efficiency maps MP for temperatures that are different from the reference temperature by a predetermined temperature (for example, -1.2°C, -0.6°C, +0.6°C, and +1.2°C).

[0093] The bottom sides of the conversion efficiency maps MP and MP1 correspond to the predetermined plane 32. In this case, the path RT may include a plurality of first line segments RT10 oriented along the predetermined plane 32 and second line segments RT20 connecting the first line segments RT10. The first line segments RT11, RT15, ​​RT19, etc. in FIG. 13 are collectively referred to as the first line segment RT10. The length of the first line segment RT10 may be longer than the length of the second line segment RT20.

[0094] Because the temperature adjustment means 50 is in contact with the predetermined surface 32 of the nonlinear optical crystal 30, the temperature of the nonlinear optical crystal 30 exhibits a distribution in which the temperature decreases with increasing distance from the predetermined surface 32. Therefore, the temperatures at which the maximum conversion efficiency is achieved are approximately equal for each coordinate on the first line segment RT10 oriented along the predetermined surface 32. In other words, the temperature difference at which the maximum conversion efficiency is achieved for each coordinate on the first line segment RT10 oriented along the predetermined surface 32 is small. Therefore, even if the temperature control of the nonlinear optical crystal 30 by the temperature adjustment means 50 is limited when the incident position is scanned along the first line segment RT10, or even with only a small temperature change, good conversion efficiency can be achieved at each coordinate.

[0095] Furthermore, the route RT is generated so that its starting point is the fitted coordinates belonging to the first line segment RT11 that is closest to the predetermined surface 32, and its ending point is the fitted coordinates belonging to the first line segment RT19 that is farthest from the predetermined surface 32. Alternatively, the route RT is generated so that its starting point is the fitted coordinates belonging to the first line segment RT19 that is farthest from the predetermined surface 32, and its ending point is the fitted coordinates belonging to the first line segment RT11 that is closest to the predetermined surface 32. In this way, the incident position determination means 102 may determine the incident position so that the route RT is drawn in one stroke. Furthermore, the route RT may be a round trip, or the route RT may be different when moving away from the predetermined surface and when approaching it.

[0096] The control means 103 controls the moving means 40 that moves the nonlinear optical crystal 30 so that the input light is incident on the incident position determined by the incident position determining means 102. Specifically, the control means 103 controls the moving means 40 via the driver 90 to change the position at which the input light is incident on the nonlinear optical crystal 30 toward the incident position determined by the incident position determining means 102.

[0097] In addition, the control means 103 controls the temperature adjustment means 50 to adjust the temperature of the nonlinear optical crystal 30 to a target temperature at which the wavelength conversion efficiency at the incident position identified based on the conversion efficiency map MP is equal to or greater than a predetermined threshold value.

[0098] Specifically, as shown in Figure 13, when the incident position is moved along the first line segment RT11, the control means 103 controls the temperature adjustment means 50 to adjust the temperature of the nonlinear optical crystal 30 to a target temperature (-1.2°C from a predetermined temperature) at which the wavelength conversion efficiency at the incident position along the first line segment RT11 is ≧50%.

[0099] Furthermore, when the incident position is moved along the first line segment RT15, ​​the control means 103 controls the temperature adjustment means 50 to adjust the temperature of the nonlinear optical crystal 30 to a target temperature (±0°C from a predetermined temperature) at which the wavelength conversion efficiency at the incident position along the first line segment RT15 is ≧50%.

[0100] Furthermore, when the incident position is moved along the first line segment RT19, the control means 103 controls the temperature adjustment means 50 to adjust the temperature of the nonlinear optical crystal 30 to a target temperature (+1.2°C from the specified temperature) at which the wavelength conversion efficiency at the incident position along the first line segment RT19 is ≧50%.

[0101] The control means 103 may not necessarily target the temperature at the time of acquiring the conversion efficiency map MP, but may appropriately control the temperature adjustment means 50 in a direction that increases the conversion efficiency as the incident position moves. That is, the control means 103 monitors the wavelength conversion efficiency while moving the incident position along the path RT, and controls the temperature adjustment means 50 to adjust the temperature of the nonlinear optical crystal 30 so that the wavelength conversion efficiency is maximized. The control means 103 may also control the output of the laser beams L11 and L12 when acquiring the conversion efficiency map MP. The control means 103 may also control the input wavelength. Specifically, the control means 103 may control the light source 10 to oscillate laser beams L11 and L12 having predetermined wavelengths. The control means 103 may also control the cavity length of the resonator 23 that mixes the sum wavelengths. Specifically, the control means 103 controls the cavity length control device 80 to control the cavity length of the resonator 23.

[0102] Next, a description will be given of a wavelength conversion method using the wavelength conversion system 1 of this embodiment. Fig. 14 is a flow chart illustrating an example of a wavelength conversion method using the wavelength conversion system 1 according to the first embodiment.

[0103] 14, a conversion efficiency map MP is stored. For example, the control means 103 stores in the storage means 101 a conversion efficiency map MP at the reference plane 31 of the nonlinear optical crystal 30, the conversion efficiency map MP for each of a plurality of temperature conditions of the nonlinear optical crystal 30. The conversion efficiency map MP may be one created in the wavelength conversion system 1.

[0104] Next, as shown in step S12, an incident position is determined. Specifically, control means 103 causes incident position determination means 102 to determine an incident position at which input light is incident on nonlinear optical crystal 30, based on conversion efficiency maps MP under two or more temperature conditions selected from storage means 101. For example, incident position determination means 102 may identify, based on the conversion efficiency maps MP under the selected two or more temperature conditions, suitable coordinates of the input position IP at which the wavelength conversion efficiency is equal to or greater than a predetermined threshold, and determine the incident position from the suitable coordinates.

[0105] The incident position determination means 102 may also identify the maximum conversion efficiency for each coordinate based on the conversion efficiency map MP, and determine the incident position from the compatible coordinates at which the maximum conversion efficiency is equal to or greater than a predetermined threshold. Furthermore, the incident position determination means 102 may generate a route RT consisting of only a plurality of compatible coordinates, and determine the incident position from the compatible coordinates within the route RT.

[0106] Next, as shown in step S13, the nonlinear optical crystal 30 is moved. Specifically, the control means 103 moves the nonlinear optical crystal 30 to the moving means 40 so that the input light is incident on the determined incident position. In this way, the wavelength conversion system 1 can output output light obtained by converting the wavelength of the input light.

[0107] Next, the effects of this embodiment will be described. In the wavelength conversion system 1 of this embodiment, the incident position determining means 102 determines the incident position at which input light is incident on the nonlinear optical crystal 30 based on the conversion efficiency map MP. As a result, the wavelength conversion system 1 causes input light to be incident at an incident position where wavelength conversion efficiency is appropriate. This can improve the stability of the output light.

[0108] As an example, the wavelength conversion system 1 of this embodiment uses a CLBO crystal that generates ultraviolet light with a wavelength of 193 nm by sum frequency generation. The wavelength conversion system 1 measures the wavelength conversion efficiency of the CLBO crystal across the reference plane 31 at multiple temperatures in advance. Therefore, the wavelength conversion system 1 moves the incident position of input light onto the CLBO crystal along the region of the reference plane 31 with high wavelength conversion efficiency while controlling the temperature. The conversion efficiency map MP is based on the wavelength conversion efficiency and is generated as a result of taking into account all factors that affect the wavelength conversion efficiency, such as optical absorption in the nonlinear optical crystal 30, refractive index nonuniformity, and temperature nonuniformity of the nonlinear optical crystal 30. Therefore, the wavelength conversion system 1 enables stable generation of high-power light with a wavelength of 193 nm over a long period of time.

[0109] In this way, according to the present disclosure, by appropriately controlling the temperature of the nonlinear optical crystal 30 when the input light passes through, it is possible to set the incident position in a moving region where the required wavelength conversion efficiency can be obtained, thereby extending the time during which deep ultraviolet light is continuously generated by one nonlinear optical crystal 30.

[0110] For example, when generating 193 nm ultraviolet light with an output of 100 mW, if the speed of movement of the incident position is about 10 μm per hour and the output power reduction of the output light is less than 5%, if the total movement distance can be secured at 100 mm, continuous use for 10,000 hours is possible. 2This can be achieved by using more than 50% of the area of ​​a crystal with a cross section. For example, when dividing the cross section of a nonlinear optical crystal into 50 x 40 = 2000 measurement points and obtaining a MAP at a certain temperature, 2 seconds of measurement time at each measurement point is sufficient. In other words, one MAP can be obtained in about 4000 seconds (= 67 minutes). If the temperature conditions are changed in five ways, and it takes 5 minutes to adjust the temperature, all of the MAPs can be obtained in 67 x 5 + 5 x 4 = 355 minutes, or about 6 hours.

[0111] As described above, according to the present disclosure, it is possible to make maximum use of the CLBO crystal, which is a key component in a 193 nm wavelength light source that can be used in semiconductor inspection equipment and the like that requires continuous operation 24 hours a day, 365 days a year, and to construct a highly reliable wavelength conversion system 1.

[0112] Although the embodiments of the present disclosure have been described above, the present disclosure includes appropriate modifications that do not impair the objects and advantages thereof, and is not limited to the above-described embodiments. Furthermore, appropriate omissions and combinations of the configurations of embodiment 1 are also within the scope of the technical concept of the present disclosure. Furthermore, the following configurations are also within the scope of the technical concept of the embodiments.

[0113] (Appendix 1) a step of storing a conversion efficiency map in a storage means, the conversion efficiency map being stored in association with a plurality of input positions of input light on a reference surface of a nonlinear optical crystal that converts the wavelength of output light from the wavelength of input light, the conversion efficiency map being stored in association with the input positions, the conversion efficiency map being stored in association with a plurality of temperature conditions of the nonlinear optical crystal; a step of causing an incident position determining means to determine an incident position at which the input light is incident on the nonlinear optical crystal based on the conversion efficiency maps under two or more of the temperature conditions selected from the storage means; a step of moving a relative position between the nonlinear optical crystal and the input light by a moving means so that the input light is incident on the determined incident position; A wavelength conversion method comprising: (Appendix 2) In the step of causing the incident position determining means to determine the incident position, The incident position determining means identifying, based on the conversion efficiency maps under the two or more selected temperature conditions, compatible coordinates that are coordinates of the input position at which the wavelength conversion efficiency under at least one of the temperature conditions is equal to or greater than a predetermined threshold; determining the incident position from the fitted coordinates; 2. The wavelength conversion method according to claim 1. (Appendix 3) In the step of causing the incident position determining means to determine the incident position, The incident position determining means Identifying a maximum conversion efficiency, which is the maximum wavelength conversion efficiency among the wavelength conversion efficiencies under the plurality of temperature conditions for each coordinate of the plurality of input position coordinates, based on the conversion efficiency maps under the two or more selected temperature conditions; identifying a matching coordinate, which is a coordinate of the input position where the maximum conversion efficiency is equal to or greater than a predetermined threshold; determining the incident position from the fitted coordinates; 2. The wavelength conversion method according to claim 1. (Appendix 4) In the step of causing the incident position determining means to determine the incident position, The incident position determining means Identifying compatible coordinates, which are coordinates of the input position at which the wavelength conversion efficiency under the plurality of temperature conditions is equal to or greater than a predetermined threshold, based on the conversion efficiency maps under the two or more selected temperature conditions; determining the incident position from the fitted coordinates; 2. The wavelength conversion method according to claim 1. (Appendix 5) In the step of causing the incident position determining means to determine the incident position, The incident position determining means generating a path consisting of only a plurality of said matching coordinates; determining the incident position from the fitted coordinates within the path; 5. A wavelength conversion method according to any one of claims 2 to 4. (Appendix 6) In the step of causing the incident position determining means to determine the incident position, the incident position determination means determines a second fitted coordinate that is the fitted coordinate within the path and adjacent to the first fitted coordinate as the next incident position when determining the next incident position after determining a first fitted coordinate within the path as the incident position, and thereafter repeats this process; 6. A wavelength conversion method according to claim 5. (Appendix 7) In the step of causing the incident position determining means to determine the incident position, the incident position determining means determines the incident position so that the path is a single stroke. 7. A wavelength conversion method according to claim 6. (Appendix 8) the nonlinear optical crystal is in contact with a temperature adjusting means for adjusting the temperature of the nonlinear optical crystal on a predetermined surface side; the path includes a plurality of first line segments oriented along a predetermined plane and second line segments connecting the first line segments; The length of the first line segment is longer than the length of the second line segment. 6. A wavelength conversion method according to claim 5. (Appendix 9) The path is generated so as to have a starting point at the fitted coordinates belonging to the first line segment closest to the specified surface and an end point at the fitted coordinates belonging to the first line segment farthest from the specified surface, or so as to have a starting point at the fitted coordinates belonging to the first line segment farthest from the specified surface and an end point at the fitted coordinates belonging to the first line segment closest to the specified surface. 9. A wavelength conversion method according to claim 8. (Appendix 10) the nonlinear optical crystal is in contact with a temperature adjusting means for adjusting the temperature of the nonlinear optical crystal on a predetermined surface side; The method further comprises a step of causing the temperature adjusting means to adjust the temperature of the nonlinear optical crystal, with the target temperature being a temperature at which the wavelength conversion efficiency at the incident position specified based on the conversion efficiency map is equal to or greater than a predetermined threshold value. 2. The wavelength conversion method according to claim 1. (Appendix 11) The wavelength conversion efficiency is monitored while the incident position is moved along the path, and the temperature of the nonlinear optical crystal is adjusted by a temperature adjusting means so that the wavelength conversion efficiency is maximized. 2. The wavelength conversion method according to claim 1. (Appendix 12) The predetermined surfaces include one to four surfaces of the nonlinear optical crystal excluding the incident surface of the input light and the output surface of the output light. 11. A wavelength conversion method according to claim 10. (Appendix 13) the predetermined surface is one of the surfaces of the nonlinear optical crystal excluding the incident surface of the input light and the output surface of the output light, the nonlinear optical crystal is in contact with a holding member whose position is changed by the moving means on a surface side other than the incident surface and the exit surface; 11. A wavelength conversion method according to claim 10. (Appendix 14) a temperature difference between adjacent temperatures under the temperature conditions corresponding to the selected plurality of conversion efficiency maps is smaller than a temperature phase matching tolerance of the nonlinear optical crystal; 2. The wavelength conversion method according to claim 1. (Appendix 15) a temperature difference between adjacent temperatures in the temperature conditions corresponding to the selected plurality of conversion efficiency maps is equal to or less than half of a temperature phase matching tolerance of the nonlinear optical crystal; 2. The wavelength conversion method according to claim 1. (Appendix 16) In the step of causing the incident position determining means to determine the incident position, The incident position determining means Identifying a reference temperature at which the wavelength conversion efficiency at a predetermined reference coordinate is maximized based on the conversion efficiency map; determining the incident position based on the conversion efficiency map at the reference temperature and the conversion efficiency map at a temperature different from the reference temperature by a predetermined temperature; 16. A wavelength conversion method according to claim 15. (Appendix 17) the input light is composed of ultraviolet light and infrared light, the nonlinear optical crystal converts the wavelength by sum frequency mixing of the ultraviolet light and the infrared light; 2. The wavelength conversion method according to claim 1. (Appendix 18) The method further comprises generating the conversion efficiency map under a plurality of temperature conditions and recording the map in the storage means. 2. The wavelength conversion method according to claim 1. [Explanation of symbols]

[0114] 1. Wavelength conversion system 10 light source 11 Ultraviolet light source 12 Infrared light source 20 Optical system 21, 22, 24, 25, 26, 27 Mirror 23 Resonator 30 Nonlinear optical crystals 31 Reference plane 32 specified surface 39 Retaining member 40 Transportation 50 Temperature adjustment means 51 Temperature Sensor 61, 62 Optical output detection means 63 Actuator 70 Temperature Controller 80 Resonator length control device 90 Drivers 100, 100a Information processing device 101 Memory means 102 Injection position determining means 103 Control Means 104 Processing means IP Input Position L11, L12 laser light L13 output light MP, MP1 conversion efficiency map RT pathway RT10, RT11, RT15, ​​RT19 First line RT20 2nd line

Claims

1. a storage means for storing a conversion efficiency map in which wavelength conversion efficiencies for a plurality of input positions of input light on a reference surface of a nonlinear optical crystal that converts the wavelength of output light from the wavelength of the input light are stored in association with the input positions, the storage means storing the conversion efficiency map for a plurality of temperature conditions of the nonlinear optical crystal; an incident position determining means for determining an incident position at which the input light is incident on the nonlinear optical crystal based on the conversion efficiency maps under two or more of the temperature conditions selected from the storage means; a control means for controlling a moving means for moving a relative position between the nonlinear optical crystal and the input light so that the input light is incident on the incident position determined by the incident position determining means; A wavelength conversion device comprising:

2. The incident position determining means identifying, based on the conversion efficiency maps under the two or more selected temperature conditions, compatible coordinates that are coordinates of the input position at which the wavelength conversion efficiency under at least one of the temperature conditions is equal to or greater than a predetermined threshold; determining the incident position from the fitted coordinates; 2. The wavelength conversion device according to claim 1.

3. The incident position determining means Identifying a maximum conversion efficiency, which is the maximum wavelength conversion efficiency among the wavelength conversion efficiencies under the plurality of temperature conditions for each coordinate of the plurality of input position coordinates, based on the conversion efficiency maps under the two or more selected temperature conditions; identifying a matching coordinate, which is a coordinate of the input position where the maximum conversion efficiency is equal to or greater than a predetermined threshold; determining the incident position from the fitted coordinates; 2. The wavelength conversion device according to claim 1.

4. The incident position determining means Identifying compatible coordinates, which are coordinates of the input position at which the wavelength conversion efficiency under the plurality of temperature conditions is equal to or greater than a predetermined threshold, based on the conversion efficiency maps under the two or more selected temperature conditions; determining the incident position from the fitted coordinates; 2. The wavelength conversion device according to claim 1.

5. The incident position determining means generating a path consisting of only a plurality of said matching coordinates; determining the incident position from the fitted coordinates within the path; The wavelength conversion device according to any one of claims 2 to 4.

6. the incident position determination means determines a second fitted coordinate which is the fitted coordinate within the path and is adjacent to the first fitted coordinate as the next incident position when determining the next incident position after determining a first fitted coordinate within the path as the incident position, and thereafter repeats this process; 6. The wavelength conversion device according to claim 5.

7. the incident position determining means determines the incident position so that the path is a single stroke.

7. The wavelength conversion device according to claim 6.

8. the nonlinear optical crystal is in contact with a temperature adjusting means for adjusting the temperature of the nonlinear optical crystal on a predetermined surface side; the path includes a plurality of first line segments oriented along a predetermined plane and second line segments connecting the first line segments; The length of the first line segment is longer than the length of the second line segment.

6. The wavelength conversion device according to claim 5.

9. The path is generated so as to have a starting point at the fitted coordinates belonging to the first line segment closest to the specified surface and an end point at the fitted coordinates belonging to the first line segment farthest from the specified surface, or the path is generated so as to have a starting point at the fitted coordinates belonging to the first line segment farthest from the specified surface and an end point at the fitted coordinates belonging to the first line segment closest to the specified surface.

9. The wavelength conversion device according to claim 8.

10. the nonlinear optical crystal is in contact with a temperature adjusting means for adjusting the temperature of the nonlinear optical crystal on a predetermined surface side; the control means controls the temperature adjustment means to adjust the temperature of the nonlinear optical crystal to a target temperature that is a temperature at which the wavelength conversion efficiency at the incident position specified based on the conversion efficiency map is equal to or greater than a predetermined threshold.

2. The wavelength conversion device according to claim 1.

11. the control means monitors the wavelength conversion efficiency while moving the incident position on the path, and controls the temperature adjustment means to adjust the temperature of the nonlinear optical crystal so as to maximize the wavelength conversion efficiency.

2. The wavelength conversion device according to claim 1.

12. the predetermined surfaces include one to four surfaces of the nonlinear optical crystal excluding an incident surface of the input light and an output surface of the output light; The wavelength conversion device according to claim 10.

13. the predetermined surface is one of the surfaces of the nonlinear optical crystal excluding an incident surface of the input light and an output surface of the output light, the nonlinear optical crystal is in contact with a holding member whose position is changed by the moving means on a surface side other than the incident surface and the output surface; The wavelength conversion device according to claim 10.

14. a temperature difference between adjacent temperatures under the temperature conditions corresponding to the selected plurality of conversion efficiency maps is smaller than a temperature phase matching tolerance of the nonlinear optical crystal; 2. The wavelength conversion device according to claim 1.

15. a temperature difference between adjacent temperatures under the temperature conditions corresponding to the selected plurality of conversion efficiency maps is equal to or less than half of a temperature phase matching tolerance of the nonlinear optical crystal; 2. The wavelength conversion device according to claim 1.

16. The incident position determining means Identifying a reference temperature at which the wavelength conversion efficiency at a predetermined reference coordinate is maximized based on the conversion efficiency map; determining the incident position based on the conversion efficiency map at the reference temperature and the conversion efficiency map at a temperature different from the reference temperature by a predetermined temperature; 16. The wavelength conversion device according to claim 15.

17. the input light is composed of ultraviolet light and infrared light, the nonlinear optical crystal converts the wavelength by sum frequency mixing of the ultraviolet light and the infrared light; 2. The wavelength conversion device according to claim 1.

18. generating the conversion efficiency map under a plurality of temperature conditions and recording the map in the storage means; 2. The wavelength conversion device according to claim 1.

19. a step of storing a conversion efficiency map in a storage means, the conversion efficiency map being stored in association with a plurality of input positions of input light on a reference surface of a nonlinear optical crystal that converts the wavelength of output light from the wavelength of input light, the conversion efficiency map being stored in association with the input positions, the conversion efficiency map being stored in association with a plurality of temperature conditions of the nonlinear optical crystal; a step of causing an incident position determining means to determine an incident position at which the input light is incident on the nonlinear optical crystal based on the conversion efficiency maps under the two or more temperature conditions selected from the storage means; a step of moving a relative position between the nonlinear optical crystal and the input light by a moving means so that the input light is incident on the determined incident position; A wavelength conversion method comprising:

Images