JP3735975B2 - Wavelength conversion element - Google Patents

Description

【００２６】
この形態例は、非線形光学結晶５としてＢＢＯ単結晶と、ＢＢＯ単結晶側の第一層のＨｆＯ₂ １０と第二層のＭｇＦ₂ １１とからなる紫外光学薄膜８とで構成された波長変換素子９である。第一層のＨｆＯ₂ １０はイオンプレーティングにより成膜し、また第二層のＭｇＦ₂ １１は通常蒸着で成膜して２層構造の紫外光学薄膜８を形成する。
【００２７】
図４はこの紫外光学薄膜８の分光光度測定の測定結果を示す図で、５３２ｎｍの基本波に対して低反射特性が実現されていることが分かる。尚、図４において、横軸は測定光の波長を表し、縦軸は波長に対する反射率を表している。
【００２８】
また、図１０の曲線ａはこの紫外光学薄膜８の膜面上に出力１００ｍＷ、パワー密度1kＷ／ｃｍ² で波長２６６ｎｍの紫外光を照射し、反射、散乱、吸収に起因した損失の経時変化を測定した結果を示している。この損失が増加することは光学薄膜の劣化を意味するが、図１０の曲線ａから実施形態例１の紫外光学薄膜８は１００時間以上、紫外光に露光されていてもほとんど劣化していないことがわかる。
【００２９】
実施形態例２
実施形態例２の構成を表２に示す。
【表２】

【００３０】
この形態例は、実施形態例１と同一の構成で、第一層のＨｆＯ₂ １０と第二層のＭｇＦ₂ １１の膜厚が異なるものである。また、その紫外光学薄膜８の形成方法も実施形態例１と同一であり、ここでの説明は省略する。
【００３１】
図５はこの紫外光学薄膜８の分光光度測定の測定結果を示す図で、５３２ｎｍの基本波に対して低反射特性が実現されていることが分かる。尚、図５において、横軸は測定光の波長を表し、縦軸は波長に対する反射率を表している。
また、損失についても図示はしていないが、略実施形態例１と同様の結果が得られていて、紫外光に対する耐久性の高さが確認されている。
【００３２】
実施形態例３
実施形態例３の構成を表３に示す。
【表３】

【００３３】
この形態例は、実施形態例１と同一の構成で、実施形態例２と同様に第一層のＨｆＯ₂ １０と第二層のＭｇＦ₂ １１の膜厚が異なるものである。また、その紫外光学薄膜８の形成方法も実施形態例１と同一であり、ここでの説明は省略する。
【００３４】
図６はこの紫外光学薄膜８の分光光度測定の測定結果を示す図で、５３２ｎｍの基本波に対して低反射特性が実現されていることが分かる。尚、図６において、横軸は測定光の波長を表し、縦軸は波長に対する反射率を表している。
また、損失についても図示はしていないが、略実施形態例１と同様の結果が得られていて、紫外光に対する耐久性の高さが確認されている。
【００３５】
実施形態例４
実施形態例４の構成を表４に示す。
【表４】

【００３６】
この形態例は、実施形態例１と同一の構成で、実施形態例２および実施形態例３と同様に第一層のＨｆＯ₂ １０と第二層のＭｇＦ₂ １１の膜厚が異なるものである。また、その紫外光学薄膜８の形成方法も実施形態例１と同一であり、ここでの説明は省略する。
【００３７】
図７はこの紫外光学薄膜８の分光光度測定の測定結果を示す図で、５３２ｎｍの基本波に対して低反射特性が実現されていることが分かる。尚、図７において、横軸は測定光の波長を表し、縦軸は波長に対する反射率を表している。
また、損失についても図示はしていないが、略実施形態例１と同様の結果が得られていて、紫外光に対する耐久性の高さが確認されている。
【００３８】
実施形態例５
実施形態例５の構成を表５に示す。
【表５】

【００３９】
この形態例は、非線形光学結晶５としてＢＢＯ単結晶と、ＢＢＯ単結晶側の第一層のＨｆＯ₂ １０と第二層のＭｇＯ１２と第三層のＭｇＦ₂ １１とからなる紫外光学薄膜８とで構成された波長変換素子９である。第一層のＨｆＯ₂ １０はイオンプレーティングにより成膜し、また第二層のＭｇＯ１２および第三層のＭｇＦ₂ １１は通常蒸着で成膜して３層構造の紫外光学薄膜８を形成する。
【００４０】
図８はこの紫外光学薄膜８の分光光度測定の測定結果を示す図で、５３２ｎｍの基本波に対して低反射特性が実現されていることが分かる。尚、図８において、横軸は測定光の波長を表し、縦軸は波長に対する反射率を表している。
また、損失についても図示はしていないが、略実施形態例１と同様の結果が得られていて、紫外光に対する耐久性の高さが確認されている。
【００４１】
上述したように本発明の紫外光学薄膜を非線形光学結晶に用いてレーザ光の波長変換をする耐久性の高い波長変換素子を構成することができる。前記紫外光学薄膜はこれに限らず、他の紫外光に曝される光学部品に用いて効果が大きいことは論を待たない。
【００４２】
【発明の効果】
以上、説明したように本発明では、膜材料として熱伝導率が０．０１（Ｊ・ｃｍ−１・ｓｅｃ^−１・Ｋ^−１）以上の蒸着物質を使用することにより高出力の連続して発振する紫外光が照射されても、熱を逃がすことができるので長期信頼性のある紫外光学薄膜が得られる。従って、この紫外光学薄膜を光学結晶に用いて、その光学結晶の低反射化および高反射化ができ、高出力紫外光に対して長期信頼性のある波長変換素子が実現できる。
【００４３】
また、前述した光学薄膜は、光学結晶への水分の侵入を防ぎ、特にＢＢＯ単結晶の潮解性による表面の化学変化や表面の酸化に対する保護膜としての機能を有し、この点からも長期信頼性を確保することができる。
【図面の簡単な説明】
【図１】 レーザ光の短波長化に関し、波長変換素子を用いてレーザ光を短波長化するための概略構成を示す図である。
【図２】 レーザ光の短波長化に関し、波長変換素子を用いてレーザ光を短波長化するための、他の概略構成を示す図である。
【図３】 本発明の光学薄膜に関し、（ａ）は光学薄膜の一構成例であり、（ｂ）は他の構成例である。
【図４】 本発明の第一の実施形態例に係わる紫外光学薄膜の分光光度測定の測定結果を示す特性図である。
【図５】 本発明の第二の実施形態例に係わる紫外光学薄膜の分光光度測定の測定結果を示す特性図である。
【図６】 本発明の第三の実施形態例に係わる紫外光学薄膜の分光光度測定の測定結果を示す特性図である。
【図７】 本発明の第四の実施形態例に係わる紫外光学薄膜の分光光度測定の測定結果を示す特性図である。
【図８】 本発明の第五の実施形態例に係わる紫外光学薄膜の分光光度測定の測定結果を示す特性図である。
【図９】 従来におけるレーザ光の短波長化に関し、波長変換素子を用いてレーザ光を短波長化するための構成を示す図である。
【図１０】 本発明の第一の実施形態例に係わる紫外光学薄膜の経時変化と従来の紫外光学薄膜の経時変化を示す特性図である。
【符号の説明】
１…レーザ発振回路、２…半導体レーザ、３…固体レーザ、４，５…非線形光学結晶、６…レーザ光、７…紫外光、８…紫外光学薄膜、９…波長変換素子、１０…ＨｆＯ₂ 、１１…ＭｇＦ₂ 、１２…ＭｇＯ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a wavelength conversion element formed high ultraviolet optical thin durable surface optical crystal to ultraviolet light which oscillates continuously.
[0002]
[Prior art]
In recent years, there has been a remarkable development in the field of optoelectronics that performs information processing and measurement control using laser light. On the other hand, with the development, it is required to increase the processing speed, improve the control performance, and increase the amount of information to be handled. Therefore, it is important to shorten the wavelength and output of the laser light source. It has become to.
[0003]
As a method for shortening the wavelength of laser light, for example, as described in US Pat. No. 5,473,409, there is a method of generating second and fourth harmonics of fundamental light using a nonlinear optical crystal. FIG. 9 shows a configuration in which laser light is shortened using a nonlinear optical crystal that is a wavelength conversion element.
[0004]
However, it is difficult to oscillate a semiconductor laser in a short wavelength region. Therefore, a wavelength conversion element is configured using a nonlinear optical crystal to obtain short wavelength light. As shown in FIG. 9, the laser oscillation circuit 1 oscillates the semiconductor laser 2 and emits the laser beam 6. This laser beam 6 excites a solid-state laser 3 such as YAG. The laser light emitted from the excited solid-state laser 3 enters the nonlinear optical crystal 4 and is wavelength-converted by utilizing the phenomenon of second harmonic generation (SHG). The wavelength-converted laser light is incident on the nonlinear optical crystal 5 and further wavelength-converted by utilizing the phenomenon of fourth harmonic generation (FHG). The ultraviolet light 7 is obtained by this wavelength conversion.
[0005]
Although not shown, an ultraviolet optical thin film having a low reflectance with respect to the ultraviolet light 7 is formed on the surface of the nonlinear optical crystal 5 by vacuum deposition. However, the conventional ultraviolet optical thin film is broken by heat generated by the high-output ultraviolet light 7 in a short time, for example, in a few seconds to a few minutes, and does not have long-term reliability. For this reason, it has been impossible to obtain a wavelength conversion element that performs wavelength conversion efficiently.
[0006]
FIG. 10 shows the temporal change of the ultraviolet optical thin film. The state of change with time of the conventional ultraviolet optical thin film is shown by b in FIG. This shows the time-dependent change in loss caused by reflection, scattering, and absorption when an ultraviolet optical thin film for wavelength 266 nm is irradiated with ultraviolet light of wavelength 266 nm at an output of 100 mW and a power density of 1 kW / cm ² .
[0007]
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to form a thin film having excellent durability against high-power ultraviolet light on the surface of a nonlinear optical crystal that emits higher harmonics, thereby realizing an effective and long-term reduction in the wavelength of laser light. it is intended to provide a wavelength conversion element that have a reliability.
[0008]
[Means for Solving the Problems]
The wavelength conversion element of the present invention has a thermal conductivity of 0.01 (J · cm ⁻¹ · sec ⁻¹ · K ⁻¹ ) on the surface of an optical crystal that continuously generates ultraviolet light having a wavelength of 200 nm to 300 nm. In the wavelength conversion element in which the ultraviolet optical thin film is formed, hafnium oxide (HfO ₂ ) is used as a material for the ultraviolet optical thin film in the first layer formed in close contact with the surface of the optical crystal. Magnesium fluoride (MgF ₂ ) is used for the second layer formed on the first layer.
[0009]
The wavelength conversion element of the present invention has a thermal conductivity of 0.01 (J · cm ⁻¹ · sec ⁻¹ · K ^{− on} the surface of an optical crystal that continuously generates ultraviolet light having a wavelength of 200 nm to 300 nm. ¹ ) In the wavelength conversion element in which the above-described ultraviolet optical thin film is formed, hafnium oxide (HfO ₂ ) is used as the first layer formed in close contact with the surface of the optical crystal as the material of the ultraviolet optical thin film. Magnesium oxide (MgO) is used for the second layer formed on the first layer, and magnesium fluoride (MgF ₂ ) is used for the third layer formed on the second layer.
[0015]
Such a wavelength conversion element according to the present invention has a long-term reliability against continuously oscillating ultraviolet light because an ultraviolet optical thin film having high durability against ultraviolet light is formed on the surface of the optical crystal. The
[0016]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described with reference to FIGS.
[0017]
First, a configuration for reducing the wavelength of laser light will be described with reference to FIG. The laser oscillation circuit 1 oscillates the semiconductor laser 2 and emits laser light 6. This laser beam 6 excites a solid-state laser 3 such as YAG. The laser light emitted from the excited solid-state laser 3 enters the nonlinear optical crystal 4 and is wavelength-converted by utilizing the phenomenon of second harmonic generation (SHG). The wavelength-converted laser light is incident on the nonlinear optical crystal 5 and is further wavelength-converted using the phenomenon of fourth harmonic generation (FHG) to obtain ultraviolet light 7. On the surface of the nonlinear optical crystal 5, an ultraviolet optical thin film 8 having a low reflectance with respect to the ultraviolet light 7 is formed by vacuum deposition.
[0018]
Next, FIG. 2 shows a configuration example using a semiconductor laser having a relatively short wavelength. In this example, one nonlinear optical crystal 5 is used to generate ultraviolet light. The laser oscillation circuit 1 oscillates the semiconductor laser 2 and emits laser light 6. The laser beam 6 enters the nonlinear optical crystal 5 and is wavelength-converted using the phenomenon of second harmonic generation (SHG) to obtain ultraviolet light 7. On the surface of the nonlinear optical crystal 5, an ultraviolet optical thin film 8 having a low reflectance with respect to the ultraviolet light 7 is formed by vacuum deposition.
[0019]
The ultraviolet optical thin film 8 is formed using a vapor deposition material having a high thermal conductivity as a film material. It is a thin film with high durability and long-term reliability against ultraviolet light. That is, as shown in FIG. 3A, the first layer in contact with the nonlinear optical crystal 5 has a thermal conductivity of 0.01 (J · cm ⁻¹ · sec ⁻¹ · K ⁻¹ ) or more, which is HfO, which is a vapor deposition material. ₂ 10 [conductivity 0.016 (J · cm ⁻¹ · sec ⁻¹ · K ⁻¹ )] and MgF ₂ 11 [conductivity 0.15 (J · cm ⁻¹ · sec ⁻¹ · K ⁻¹ )] is used to form the ultraviolet optical thin film 8.
[0020]
The wavelength conversion element 9 is configured by forming the ultraviolet optical thin film 8 made of the above-described material on the surface of the nonlinear optical crystal 5. For example, the wavelength conversion element 9 is configured by forming the ultraviolet optical thin film 8 on the surface of the nonlinear optical crystal 5 having a fourth harmonic generation function for emitting ultraviolet light having a wavelength of 266 nm to incident light having a wavelength of 532 nm.
[0021]
The nonlinear optical crystal 5 is a single crystal such as potassium dihydrogen phosphate (KDP) or β-barium borate (BBO). In the paragraphs of Embodiment Examples 1 to 4 to be described later, with respect to a fundamental wave having a wavelength of 532 nm, a BBO single crystal is used as the nonlinear optical crystal 5 and the above-described ultraviolet optical thin film 8 having two layers is formed on the surface thereof. The wavelength conversion element 9 having a low reflectance will be described.
[0022]
FIG. 3B shows an ultraviolet optical thin film 8 in which a film of MgO 12 is formed between HfO ₂ 10 and MgF ₂ 11. This ultraviolet optical thin film 8 is also formed on the surface of the nonlinear optical crystal 5 to constitute the wavelength conversion element 9. In the section of Embodiment 5 to be described later, a BBO single crystal is used for the nonlinear optical crystal 5 and the above-described ultraviolet optical thin film 8 composed of three layers is formed on the surface thereof, and has a low reflectance with respect to a fundamental wave with a wavelength of 532 nm. The wavelength conversion element 9 will be described.
[0023]
Here, the wavelength dispersion formula of the uniaxial BBO single crystal is
n ₀ ² = 1.9595 + 0.7892λ ² / (λ ² −0.02161) (1)
^{_{n e 2 = 1.6932 + 0.6782λ 2}} / (λ 2 -0.01816) (2)
_{ne (} θ ₎ ² = 1 / (cos ² θ / n ₀ ² + sin ² θ / _ne ² ) (3)
Given in Incidentally, lambda is the wavelength, n _o is the ordinary refractive index, n _e is the extraordinary ray refraction index, n e _(θ) is the light incident from a direction at an angle theta from the optical axis of the single crystal abnormal It is a light refractive index. Therefore, from the wavelength dispersion equations (1) to (3), the phase matching condition of the BBO single crystal with respect to the fundamental wavelength of 532 nm is 47.6 °. When the fundamental wave light is incident on the BBO single crystal in this orientation, the fourth harmonic is generated most efficiently.
[0024]
Next, the configuration of the above-described ultraviolet optical thin film 8 and the wavelength conversion element 9 using a BBO single crystal as the nonlinear optical crystal 5 will be described with reference to FIGS. 4 to 7 and Tables 1 to 5. FIG. Tables 1 to 5 show the refractive indexes and phase film thicknesses of the substances constituting the wavelength conversion element 9 of Embodiments 1 to 5. The phase film thickness is obtained by multiplying the physical film thickness d by the refractive index n and dividing it by the fundamental wavelength λ _O and is represented by nd / λ _O. The refractive index is a value for light having a wavelength of 532 nm.
[0025]
Embodiment 1
Table 1 shows the configuration of the first embodiment.
[Table 1]

[0026]
In this embodiment, a wavelength conversion element composed of a BBO single crystal as the nonlinear optical crystal 5 and an ultraviolet optical thin film 8 made of the first layer HfO ₂ 10 and the second layer MgF ₂ 11 on the BBO single crystal side. Nine. The first layer of HfO ₂ 10 is formed by ion plating, and the second layer of MgF ₂ 11 is formed by ordinary vapor deposition to form the ultraviolet optical thin film 8 having a two-layer structure.
[0027]
FIG. 4 is a diagram showing the measurement result of the spectrophotometric measurement of the ultraviolet optical thin film 8, and it can be seen that the low reflection characteristic is realized with respect to the fundamental wave of 532 nm. In FIG. 4, the horizontal axis represents the wavelength of the measurement light, and the vertical axis represents the reflectance with respect to the wavelength.
[0028]
Curve a in FIG. 10 shows the time-dependent change in loss due to reflection, scattering, and absorption by irradiating the ultraviolet optical thin film 8 with ultraviolet light having an output of 100 mW and a power density of 1 kW / cm ² and a wavelength of 266 nm. The measurement results are shown. Increasing this loss means deterioration of the optical thin film. From the curve a in FIG. 10, the ultraviolet optical thin film 8 of Example 1 is hardly deteriorated even when exposed to ultraviolet light for 100 hours or more. I understand.
[0029]
Embodiment 2
Table 2 shows the configuration of the second embodiment.
[Table 2]

[0030]
This embodiment has the same configuration as that of the first embodiment, and the film thicknesses of the first layer HfO ₂ 10 and the second layer MgF ₂ 11 are different. Further, the method for forming the ultraviolet optical thin film 8 is the same as that in the first embodiment, and the description thereof is omitted here.
[0031]
FIG. 5 is a diagram showing the measurement result of the spectrophotometric measurement of the ultraviolet optical thin film 8, and it can be seen that the low reflection characteristic is realized with respect to the fundamental wave of 532 nm. In FIG. 5, the horizontal axis represents the wavelength of the measurement light, and the vertical axis represents the reflectance with respect to the wavelength.
Although the loss is not shown in the figure, the same result as in the first embodiment is obtained, and the high durability against ultraviolet light is confirmed.
[0032]
Embodiment 3
Table 3 shows the configuration of the third embodiment.
[Table 3]

[0033]
This embodiment has the same configuration as that of the first embodiment, and the film thicknesses of the first layer of HfO ₂ 10 and the second layer of MgF ₂ 11 are different from those of the second embodiment. Further, the method for forming the ultraviolet optical thin film 8 is the same as that in the first embodiment, and the description thereof is omitted here.
[0034]
FIG. 6 is a diagram showing the measurement result of the spectrophotometric measurement of the ultraviolet optical thin film 8, and it can be seen that the low reflection characteristic is realized with respect to the fundamental wave of 532 nm. In FIG. 6, the horizontal axis represents the wavelength of the measurement light, and the vertical axis represents the reflectance with respect to the wavelength.
Although the loss is not shown in the figure, the same result as in the first embodiment is obtained, and the high durability against ultraviolet light is confirmed.
[0035]
Embodiment 4
Table 4 shows the configuration of the fourth embodiment.
[Table 4]

[0036]
This embodiment has the same configuration as that of the first embodiment, and the film thicknesses of the first layer of HfO ₂ 10 and the second layer of MgF ₂ 11 are different from those of the second and third embodiments. . Further, the method for forming the ultraviolet optical thin film 8 is the same as that in the first embodiment, and the description thereof is omitted here.
[0037]
FIG. 7 is a diagram showing the measurement result of the spectrophotometric measurement of the ultraviolet optical thin film 8, and it can be seen that the low reflection characteristic is realized with respect to the fundamental wave of 532 nm. In FIG. 7, the horizontal axis represents the wavelength of the measurement light, and the vertical axis represents the reflectance with respect to the wavelength.
Although the loss is not shown in the figure, the same result as in the first embodiment is obtained, and the high durability against ultraviolet light is confirmed.
[0038]
Embodiment 5
Table 5 shows the configuration of the fifth embodiment.
[Table 5]

[0039]
This embodiment is composed of a BBO single crystal as the nonlinear optical crystal 5, and an ultraviolet optical thin film 8 composed of HfO ₂ 10 as the first layer, MgO 12 as the second layer, and MgF ₂ 11 as the third layer on the BBO single crystal side. This is a configured wavelength conversion element 9. The first layer of HfO ₂ 10 is formed by ion plating, and the second layer of MgO 12 and the third layer of MgF ₂ 11 are formed by ordinary vapor deposition to form the ultraviolet optical thin film 8 having a three-layer structure.
[0040]
FIG. 8 is a diagram showing the measurement result of the spectrophotometric measurement of the ultraviolet optical thin film 8, and it can be seen that the low reflection characteristic is realized with respect to the fundamental wave of 532 nm. In FIG. 8, the horizontal axis represents the wavelength of the measurement light, and the vertical axis represents the reflectance with respect to the wavelength.
Although the loss is not shown in the figure, the same result as in the first embodiment is obtained, and the high durability against ultraviolet light is confirmed.
[0041]
As described above, it is possible to configure a highly durable wavelength conversion element that converts the wavelength of laser light by using the ultraviolet optical thin film of the present invention for a nonlinear optical crystal. The ultraviolet optical thin film is not limited to this, and it is not a matter of course that the ultraviolet optical thin film is effective when used for other optical parts exposed to ultraviolet light.
[0042]
【The invention's effect】
As described above, in the present invention, a high output is continuously obtained by using a vapor deposition material having a thermal conductivity of 0.01 (J · cm−1 · sec ⁻¹ · K ⁻¹ ) or more as a film material. Even when irradiated with oscillating ultraviolet light, heat can be released, so that a long-term reliable ultraviolet optical thin film can be obtained. Therefore, by using this ultraviolet optical thin film for an optical crystal , the optical crystal can be reduced in reflection and reflection, and a wavelength conversion element having long-term reliability for high output ultraviolet light can be realized.
[0043]
The optical thin film described above prevents moisture from entering the optical crystal , and has a function as a protective film against surface chemical changes and surface oxidation due to deliquescence of the BBO single crystal. Sex can be secured.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration for shortening a wavelength of a laser beam by using a wavelength conversion element with respect to shortening the wavelength of the laser beam.
FIG. 2 is a diagram showing another schematic configuration for shortening the wavelength of laser light by using a wavelength conversion element with respect to shortening the wavelength of laser light.
3A is a structural example of an optical thin film, and FIG. 3B is another structural example of the optical thin film of the present invention.
FIG. 4 is a characteristic diagram showing the measurement result of the spectrophotometric measurement of the ultraviolet optical thin film according to the first embodiment of the present invention.
FIG. 5 is a characteristic diagram showing measurement results of spectrophotometric measurement of an ultraviolet optical thin film according to the second embodiment of the present invention.
FIG. 6 is a characteristic diagram showing a measurement result of spectrophotometric measurement of an ultraviolet optical thin film according to a third embodiment of the present invention.
FIG. 7 is a characteristic diagram showing a measurement result of spectrophotometric measurement of an ultraviolet optical thin film according to a fourth embodiment of the present invention.
FIG. 8 is a characteristic diagram showing a measurement result of spectrophotometric measurement of an ultraviolet optical thin film according to a fifth embodiment of the present invention.
FIG. 9 is a diagram showing a configuration for shortening the wavelength of a laser beam by using a wavelength conversion element with respect to shortening the wavelength of the conventional laser beam.
FIG. 10 is a characteristic diagram showing a change with time of an ultraviolet optical thin film according to the first embodiment of the present invention and a change with time of a conventional ultraviolet optical thin film.
[Explanation of symbols]
1 ... laser oscillator, 2 ... semiconductor laser, 3 ... solid-state laser, 4,5 ... nonlinear optical crystal, 6 ... laser light, 7 ... ultraviolet light, 8 ... ultraviolet optical thin film, 9 ... wavelength conversion element, 10 ... HfO ₂ 11 ... MgF ₂ , 12 ... MgO

Claims (2)

An ultraviolet optical thin film having a thermal conductivity of 0.01 (J · cm ⁻¹ · sec ⁻¹ · K ⁻¹ ) or more is formed on the surface of an optical crystal that continuously generates ultraviolet light having a wavelength of 200 nm or more and 300 nm or less. In the wavelength conversion element that has been
As a material for the ultraviolet optical thin film, hafnium oxide (HfO ₂ ) is used for the first layer formed in close contact with the surface of the optical crystal, and further, the second layer formed on the first layer is fluorinated. A wavelength conversion element characterized by using magnesium (MgF ₂ ). An ultraviolet optical thin film having a thermal conductivity of 0.01 (J · cm ⁻¹ · sec ⁻¹ · K ⁻¹ ) or more is formed on the surface of an optical crystal that continuously generates ultraviolet light having a wavelength of 200 nm or more and 300 nm or less. In the wavelength conversion element that has been
As a material for the ultraviolet optical thin film, hafnium oxide (HfO ₂ ) is used for the first layer formed in close contact with the surface of the optical crystal, and magnesium oxide (MgO) is used for the second layer formed on the first layer. ) And magnesium fluoride (MgF ₂ ) is used for the third layer formed on the second layer.

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