Ultraviolet laser light generating device

Abstract

The present application relates to a 399.08 nm ultraviolet laser generating device, comprising: an excitation light source section which converts 1064.2 nm laser light into a second harmonic to generate 532.1 nm laser light; an optical parametric oscillation section which generates 798.15 nm signal light and 1596.3 nm idler light from the 532.1 nm laser light; a first wavelength conversion section which generates 399.08 nm light by sum frequency generation of the idler light and the 532.1 nm light; and a second wavelength conversion section which generates a second harmonic from the signal light (the first wavelength conversion section and the second wavelength conversion section are not in a particular order). The present application relates to a 228.04 nm ultraviolet laser generating device, comprising: a 399.08 nm laser generating device; and a third wavelength conversion section which generates 228.04 nm light by sum frequency generation of the 399.08 nm light and the 532.1 nm light. The present application provides a high-efficiency and simple 228.04 nm laser generating device as one of deep ultraviolet rays and a high-efficiency and simple 399.08 nm laser generating device as a light source thereof.

Description

Technical Field

[0001] This invention relates to ultraviolet laser generating apparatuses. In particular, it relates to laser generating apparatuses with a wavelength of 399.08 nm and laser generating apparatuses with a wavelength of 228.04 nm. Cross-reference to related applications This application claims priority to Japanese Patent Application No. 2021-027497, filed on February 24, 2021, the entire contents of which are hereby incorporated as public information. Background Technology

[0002] Lasers with wavelengths in the 200–280 nm region are also known as deep ultraviolet (UV) lasers and are used in various fields such as semiconductor exposure equipment, wafer inspection, and sterilization equipment. Excimer lasers and semiconductor lasers can be cited as light sources for UV laser generation devices, but excimer lasers suffer from drawbacks such as the use of toxic gases and high maintenance costs. Furthermore, semiconductor lasers have weak output and are difficult to develop. On the other hand, various wavelengths of UV lasers can be obtained by using a solid-state laser oscillator with an oscillating wavelength in the 1 μm band as the basic light source and incorporating a wavelength conversion element using a nonlinear crystal, etc. (Patent Documents 1 and 2). However, the laser wavelength obtained by wavelength conversion based on higher harmonic generation is limited to an integer fraction of the wavelength of the basic light source. Additionally, to obtain lasers of other wavelengths, wavelength conversion is performed using an optical parametric oscillator, but since neither the signal light nor the idle light output is utilized at this time, the overall system efficiency is low.

[0003] In addition, multiple laser oscillators are sometimes used to obtain laser light of the desired wavelength (Patent Documents 3 and 4). However, since the system is based on two lasers, there are concerns about cost and reduced efficiency.

[0004] Patent Document 1: Japanese Patent Application Publication No. 09-292638 Patent Document 2: Japanese Patent Application Publication No. 11-258645 Patent Document 3: Japanese Patent Application Publication No. 2003-114454 Patent Document 4: Japanese Patent Application Publication No. 2007-086104 The complete descriptions in Patent Documents 1 to 4 are hereby introduced as public information. Summary of the Invention The problem that the invention aims to solve

[0005] The first objective of this invention is to provide a laser generating device that uses a separate semiconductor laser oscillator and is not previously available in deep ultraviolet light, i.e., 228.04 nm. The second objective of this invention is to provide a 399.08 nm ultraviolet laser generating device that can be used as a light source for a laser generating device that uses a separate semiconductor laser oscillator and is not previously available in deep ultraviolet light, i.e., 228.04 nm. Methods for solving problems

[0006] The present invention is described below. [1] An ultraviolet laser generating device with a wavelength of 399.08 nm, comprising: The excitation light source converts the 1064.2nm wavelength laser into a second harmonic, generating a 532.1nm wavelength laser. The optical parametric oscillation unit uses a 532.1 nm wavelength laser generated by the excitation source unit as the excitation light to produce a signal light with a wavelength of 798.15 nm and an idle light with a wavelength of 1596.3 nm. The first wavelength conversion unit performs a summation between idle light with a wavelength of 1596.3 nm and light with a wavelength of 532.1 nm to generate light with a wavelength of 399.08 nm; and The second wavelength conversion unit generates light with a wavelength of 399.08 nm as the second harmonic from the signal light with a wavelength of 798.15 nm. The ultraviolet laser generating device with a wavelength of 399.08 nm has a laser optical path in the order of excitation source section, optical parameter oscillation section, first wavelength conversion section and second wavelength conversion section, or in the order of excitation source section, optical parameter oscillation section, second wavelength conversion section and first wavelength conversion section. [2] According to the apparatus described in [1], wherein, The 532.1nm light generated by the sum-frequency conversion at the first wavelength conversion section is 532.1nm light that has not been converted by the optical parametric oscillation section. [3] The apparatus according to [1] or [2], wherein, The laser optical path consists of an excitation source section, an optical parametric oscillation section, a first wavelength conversion section, and a second wavelength conversion section. [4] An ultraviolet laser generating device with a wavelength of 228.04 nm, comprising: The 399.08 nm wavelength laser generating apparatus according to any one of [1] to [3]; and The third wavelength conversion unit generates 228.04nm light by combining 399.08nm light with 532.1nm light. [5] According to the apparatus described in [4], wherein, The 532.1nm light generated by the sum-frequency conversion at the wavelength conversion section is 532.1nm light that has not been converted by the optical parametric oscillation section. [6] The apparatus according to [4] or [5], wherein, The rear part of the third wavelength conversion section includes a separation section that separates 228.04nm light from light of other wavelengths. The effects of the invention

[0007] According to the present invention, a laser generating apparatus with excellent operability can be provided that can efficiently and easily generate deep ultraviolet laser light in the wavelength range of 228.04 nm, which can be used for sterilization. According to the present invention, a 399.08 nm ultraviolet laser generating apparatus can be provided that can be used as a light source for a 228.04 nm laser generating apparatus. Attached Figure Description

[0008] Figure 1 A schematic diagram illustrating the laser generating apparatus of the present invention is shown. Figure 2 A schematic diagram illustrating one embodiment of the laser generating apparatus of the present invention is shown. Figure 3 An embodiment of the laser generating apparatus of the present invention is shown. Figure 4 The diagram illustrates the situation where the wavelength of the idle light λi with a wavelength of 1596.3 nm generated in the OPO is the same as the wavelength of the second harmonic of the signal light λs with a wavelength of 798.15 nm generated in the same OPO, which is 399.08 nm. Detailed Implementation

[0009] The first aspect of the laser generating apparatus of the present invention is an ultraviolet laser generating apparatus with a wavelength of 399.08 nm, the apparatus comprising: The excitation light source converts the 1064.2nm wavelength laser into a second harmonic, generating a 532.1nm wavelength laser. The optical parametric oscillation unit uses a 532.1 nm wavelength laser generated by the excitation source unit as the excitation light to produce a signal light with a wavelength of 798.15 nm and an idle light with a wavelength of 1596.3 nm. The first wavelength conversion unit performs a summation between idle light with a wavelength of 1596.3 nm and light with a wavelength of 532.1 nm to generate light with a wavelength of 399.08 nm; and The second wavelength conversion unit generates light with a wavelength of 399.08 nm as the second harmonic from the signal light with a wavelength of 798.15 nm. The device has a laser optical path in the order of excitation source section, optical parameter oscillation section, first wavelength conversion section and second wavelength conversion section, or in the order of excitation source section, optical parameter oscillation section, second wavelength conversion section and first wavelength conversion section.

[0010] The second aspect of the laser generating apparatus of the present invention is an ultraviolet laser generating apparatus with a wavelength of 228.04 nm, which includes: the laser generating apparatus with a wavelength of 399.08 nm of the first aspect of the present invention; and a third wavelength conversion unit that generates 228.04 nm light by performing a sum-frequency conversion between 399.08 nm light and 532.1 nm light.

[0011] Figure 1 The diagram shows a schematic illustration of a laser generating apparatus according to a first and a second embodiment of the present invention. The apparatus has a laser optical path arranged in the order of an excitation source unit, an optical parametric oscillation unit, a first wavelength conversion unit, and a second wavelength conversion unit.

[0012] The laser generating apparatus of the first aspect of the present invention comprises Figure 1 The apparatus comprises units 10 to 40, where 10 is an excitation light source, 20 is an optical parametric oscillation unit, 30 is a first wavelength conversion unit, and 40 is a second wavelength conversion unit. The order of the first wavelength conversion unit 30 and the second wavelength conversion unit 40 can also be reversed. The laser generating apparatus of the second aspect of the present invention, in addition to... Figure 1 In addition to wavelengths 10 to 40, it also includes a third wavelength conversion section 50.

[0013] Figure 2 This is a schematic diagram illustrating one aspect of the laser generating apparatus of the present invention, specifically showing a case where the excitation source unit includes an SHG, the first wavelength conversion unit 30 includes an SFG, the second wavelength conversion unit 40 includes an SHG, and the third wavelength conversion unit 50 includes an SFG. Figure 3 An explanatory diagram showing one embodiment of the laser generating apparatus of the present invention is provided.

[0014] In addition, the abbreviations used in this application have the following meanings. SHG: Second Harmonic Generation SFG: Sum Frequency Generation OPO: Optical Parametric Oscillator KTP: KTiOPO4 BBO: β-BaB2O4 LBO:LiB3O5 BiBO:BiB3O6 MgO:PPLT: Periodically Poled LiTaO3 with MgO KBBF: KBe2BO3F2

[0015] (Explanation of the excitation light source section) The excitation source unit 10 is a section that converts a 1064.2 nm wavelength laser into a second harmonic to generate a 532.1 nm wavelength laser. The excitation source for generating the 1064.2 nm wavelength laser can be, for example, Nd:YAG(Nd...) 3+ :Y3Al5O 12 The laser has a wavelength of 1064.2 nm and is a pulsed laser; the pulse duration can be nanoseconds or picoseconds. The excitation source unit 10 may, for example, include an excitation source and a nonlinear optical crystal that converts the laser light into a 532.1 nm laser as a second harmonic generation (SHG). The nonlinear optical crystal may, for example, be a KTP crystal. Figure 3 The image shows crystal 1. Besides KTP crystal, crystal 1 can also be any of BBO, LBO, MgO:PPLT with added MgO, or PPKTP. Additionally, "PP + crystal name" stands for "Periodically Poled".

[0016] More specifically, in the case of using KTP crystals in nonlinear optical crystals, such as Figure 3 As shown, the laser light from the excitation source is passed through a half-wave plate (λ / 2 plate) and its polarization direction is tilted at 45 degrees before passing through crystal 1, where it is converted into a 532.1 nm laser as a second harmonic. Phase matching in the wavelength conversion is of type 2. Alternatively, if crystal 1 is an LBO or BBO crystal, after passing through the λ / 2 plate and making the polarization direction perpendicular to the plane of the paper, the light is converted into a 532.1 nm laser as a second harmonic before passing through crystal 1.

[0017] Furthermore, when MgO:PPLT or PPKTP is used for crystal 1, a λ / 2 sheet is not required. Crystal 1 is positioned such that the polarization direction of the 532.1nm laser is horizontal with respect to the plane of the paper. Additionally, Type 2 phase matching means phase matching where second harmonics are generated from incident light of different rays (i.e., orthogonal and different polarizations), as opposed to Type 1 phase matching where second harmonics with different polarizations are generated from incident light of the same ray (i.e., same polarization). Furthermore, in this specification, phase matching where the direction of the incident light and the second harmonic are both the same is referred to as Type 0.

[0018] Table 1 below shows a list of the types of crystals that can be used in the excitation light source section, the optical parametric oscillation section, the first wavelength conversion section, the second wavelength conversion section, and the third wavelength conversion section, as well as their functions, phase matching types, and polarization.

[0019] [Table 1]

[0020] In Table 1, "o" in the polarization column refers to ordinary wave, and "e" refers to extraordinary wave.

[0021] (Dialect mirror M1) A dichroic mirror can be installed between the excitation light source 10 and the OPO 20. Figure 3 The dichroic mirror M1 reflects the 1064.2nm light from the excitation source 10 to obtain a 532.1nm laser. Since the 1064.2nm light is not used in subsequent processes, separating it from the 532.1nm laser avoids unnecessary damage to optical components or temperature load on the crystal when focusing other wavelengths of laser light in subsequent processes. The 532.1nm laser light transmitted through the dichroic mirror M1 is then incident on the OPO.

[0022] (Explanation of the Optical Parametric Oscillator (OPO)) OPO 20 is a section that uses a 532.1 nm wavelength laser generated by the excitation source as the excitation light to produce a signal light with a wavelength of 798.15 nm and an idle light with a wavelength of 1596.3 nm, and separates the generated signal light. OPO includes a nonlinear optical crystal and two mirrors. The nonlinear optical crystal can be, for example, a BBO crystal or a BiBO crystal, or any of MgO:PPLT or PPKTP. Crystal 2 is cut to produce a phase-matching angle for the signal light λs with a wavelength of 798.15 nm and the idle light λi with a wavelength of 1596.3 nm. Furthermore, MgO:PPLT and PPKTP are adjusted to have a polarization reversal period length capable of producing the aforementioned signal light and idle light wavelengths. The two wavelengths emitted from this crystal are amplified by a resonator containing two mirrors to obtain OPO oscillation. Regarding the crystal 2 constituting the optical parametric oscillator 20, as shown in Table 1, in the case of a phase matching process of type 1, if the excitation light is polarized horizontally with respect to the paper surface, then the signal light and the idle light are polarized in a direction perpendicular to the paper surface.

[0023] Regarding the wavelength accuracy of the signal light in the optical parametric oscillation unit 20, it is preferable to narrow the band at the seed light based on the semiconductor laser, and control the crystal 2 to about 0.1 nm or less through temperature tuning. This allows the spectral width and variation of the 399.08 nm violet light wavelength to be about 0.05 nm or less.

[0024] (First wavelength conversion unit 30) The first wavelength conversion unit 30 is a unit that generates light with a wavelength of 399.08 nm by mixing idle light with a wavelength of 1596.3 nm generated by the OPO and light with a wavelength of 532.1 nm generated by the excitation light source unit that has passed through the OPO. The 532.1 nm light generated by the mixing and frequency conversion at the first wavelength conversion unit 30 is 532.1 nm light that has not been converted by the OPO 20. Figure 3 The crystal 3 shown can be, for example, a nonlinear optical crystal such as a BBO crystal. If MgO:PPLT is used in addition to BBO in crystal 3, then MgO:PPLT is used as crystal 2 in the optical parametric oscillator 20. In this case, crystal 3 is adjusted to produce a polarization reversal period length for the summation frequency of idle light with a wavelength of 1596.3 nm and light with a wavelength of 532.1 nm. The polarization direction of the 399.08 nm light is horizontal to the plane of the paper.

[0025] (Second wavelength conversion unit 40) The second wavelength conversion unit 40 is the SHG section that converts the signal light with a wavelength of 798.15nm to the SHG section with a wavelength of 399.08nm. Figure 3 The crystal 4 shown can be, for example, a nonlinear optical crystal such as an LBO or BBO crystal. Besides LBO or BBO, it can also be, for example, a nonlinear optical crystal such as MgO:PPLT. In the case where crystal 4 is MgO:PPLT, MgO:PPLT is used as crystal 2 in the optical parametric oscillator 20. At this time, crystal 4 is adjusted to provide the polarization reversal period length generated by the SHG with a wavelength of 798.15 nm. The polarization direction of the 399.08 nm light is also horizontal to the plane of the paper.

[0026] The order of the first wavelength conversion unit 30 and the second wavelength conversion unit 40 can be interchanged. That is, the ultraviolet laser generating device (first mode) with a wavelength of 399.08 nm of the present invention can have a laser optical path in the order of excitation light source unit 10, optical parameter oscillation unit 20, first wavelength conversion unit 30 and second wavelength conversion unit 40, or in the order of excitation light source unit 10, optical parameter oscillation unit 20, second wavelength conversion unit 40 and first wavelength conversion unit 30.

[0027] The order of the first wavelength conversion unit 30 and the second wavelength conversion unit 40 can be interchanged.

[0028] (Third wavelength conversion unit 50) The third wavelength conversion unit 50 is a section that generates light with a wavelength of 228.04 nm by mixing light with frequency from the excitation light source unit, which has passed through the OPO 20, the first wavelength conversion unit 30, and the second wavelength conversion unit 40, with light with a wavelength of 399.08 nm generated by the first wavelength conversion unit 30 and the second wavelength conversion unit 40. The 532.1 nm light generated by frequency mixing at the third wavelength conversion unit 50 is 532.1 nm light that has not been converted by the OPO 20 and has passed through the first wavelength conversion unit 30 and the second wavelength conversion unit 40. Figure 3 The crystal 5 shown can be, for example, a nonlinear optical crystal such as a BBO or KBBF crystal.

[0029] (Separation section 60) A separation section 60 may be provided at the rear of the third wavelength conversion section 50. Figure 1 and Figure 2 (Not shown in the figure), the separation unit 60 is used to separate the laser light of various wavelengths generated during the wavelength conversion process and extract the 228.04nm light. The separation unit 60 can be, for example, a prism (see Figure 1). Figure 3 There are no particular restrictions as long as the laser light with wavelengths other than 228.04 nm generated during the wavelength conversion process can be removed; for example, it can be a quartz prism, MgF2 prism, etc. The separation unit 60 separates the light with wavelengths other than 228.04 nm to obtain laser light with a wavelength of 228.04 nm.

[0030] Figure 3 The examples shown represent the case where the optical parametric oscillator (OPO) has a type 1 phase match. However, in the case where the OPO has a type 0 phase match, both crystal 3 and crystal 4 use MgO:PPLT. These examples are merely illustrative and are not intended to limit the invention to these specific examples.

[0031] (Mechanism for generating 228.04nm laser light) In an OPO, when the excitation wavelength is λp, the signal wavelength is λs, and the idle wavelength is λi, the following relationship exists.

[0032] (Equation 1) 1 / λs + 1 / λi = 1 / λp

[0033] In addition, when the incident light wavelength is λ1, another incident light wavelength is λ2, and the light sum frequency wavelength is λ3, the SFG exhibits the following relationship.

[0034] (Equation 2) 1 / λ1 + 1 / λ2 = 1 / λ3

[0035] In wavelength-conversion-based ultraviolet laser generation methods, various combinations of (Equation 1) and (Equation 2) are used to generate coherent light of the desired wavelength through the aforementioned relationship. Typically, deep ultraviolet lasers are generated by using the output light of either the signal light or the idle light in (Equation 1) for wavelength conversion, while the output light of the other light is not used but is cut off by a filter. Therefore, there is a disadvantage of low conversion efficiency to deep ultraviolet light for the entire system.

[0036] In this invention, as described above, an OPO excited by the second harmonic of a 1064.2 nm laser (i.e., 532.1 nm) generates a 798.15 nm signal light λs and a 1596.3 nm idle light λi. The following characteristic is utilized: the wavelength generated by the sum of the frequencies of the light generated at the first wavelength conversion section from the 1596.3 nm idle light λi and the 532.1 nm excitation light is 399.08 nm, which coincides with the wavelength of the second harmonic generated at the second wavelength conversion section from the 798.15 nm signal light λs (refer to...). Figure 4 Therefore, a more efficient ultraviolet laser generating device with a wavelength of 399.08 nm can be realized.

[0037] Furthermore, in this invention, the output light from both the signal light and idle light of the OPO can be used to generate ultraviolet light with a wavelength of 399.08 nm. More specifically, by generating a light-frequency combination from the 399.08 nm light and the 532.1 nm excitation light, deep ultraviolet light with a wavelength of 228.04 nm can be generated. Therefore, a more efficient deep ultraviolet laser generation device with a wavelength of 228.04 nm can be realized.

[0038] The laser with a wavelength of 399.08 nm obtained by the device of the present invention can also be combined with nonlinear crystals and the like to be used as a light source of other wavelengths.

[0039] The laser with a wavelength of 228.04 nm obtained in the device of the present invention is considered to have a bactericidal effect because it is similar to the wavelength of 222 nm.

[0040] In the laser generating apparatus of the present invention, since both signal light and idle light can be utilized, deep ultraviolet laser can be generated more efficiently. Therefore, it is possible to irradiate a wide range of ultraviolet light with wavelengths of 399.08 nm or 228.04 nm, or to irradiate liquids such as water, which is useful for applications such as entrances and exits of facilities with unspecified access, and for the sterilization of liquids. Furthermore, the generated laser can be directed to a target object via a laser conductor such as an optical fiber, as needed. Therefore, for example, ultraviolet irradiation of parts such as the back side of a structure becomes easy. Industrial availability

[0041] This invention is effective not only in medical settings but also in disinfection operations at large facilities. Furthermore, it has minimal impact on human health because it does not use toxic gases such as ozone or ethylene oxide, making it easy to manage and handle. Additionally, since it does not use liquid disinfectants such as alcohol, it can also be used for disinfecting paper media that cannot be wetted, such as books. Explanation of the label

[0042] 10 Excitation Light Source Section 20 Optical Parametric Oscillation Section 30 First Wavelength Conversion Section 40 Second Wavelength Conversion Section 50 Third Wavelength Conversion Section

Claims

1. An ultraviolet laser generating device with a wavelength of 228.04 nm, comprising: The excitation light source converts the 1064.2nm wavelength laser into a second harmonic to generate a pump light with a wavelength of 532.1nm. The beam splitter divides the pump light with a wavelength of 532.1 nm into at least a first pump light and a second pump light. The second pump light is the pump light with a wavelength of 532.1 nm that is retained after passing through the optical parametric oscillation section and is not converted. The optical parametric oscillator is excited by the first pump light and generates signal light with a wavelength of 798.15 nm and idle light with a wavelength of 1596.3 nm, and allows at least a portion of the pump light with a wavelength of 532.1 nm to be output as unconverted pump light with a wavelength of 532.1 nm. The separation unit separates the signal light from the idle light on the optical path and leads them out. The first wavelength conversion unit has its optical input end optically connected to the output optical path of the idle light and the output optical path of the unconverted wavelength 532.1nm pump light, so as to generate a sum-frequency combination of the idle light and the unconverted wavelength 532.1nm pump light, thereby generating light with a wavelength of 399.08nm. The second wavelength conversion unit has its optical input end optically connected to the output optical path of the signal light to generate a second harmonic of the signal light, thereby generating light with a wavelength of 399.08nm. An ultraviolet laser generating device with a wavelength of 399.08 nm, having a laser optical path in the order of excitation source section, optical parameter oscillation section, first wavelength conversion section and second wavelength conversion section, or excitation source section, optical parameter oscillation section, second wavelength conversion section and first wavelength conversion section; and The third wavelength conversion unit generates light with a wavelength of 228.04nm by performing a summation of 399.08nm light and 532.1nm light.

2. The apparatus according to claim 1, wherein, The laser optical path consists of an excitation source section, an optical parametric oscillation section, a first wavelength conversion section, and a second wavelength conversion section.

3. The apparatus according to claim 1, wherein, The 532.1nm light generated by the sum-frequency conversion at the third wavelength conversion section is the 532.1nm light that has not been converted by the optical parametric oscillation section.

4. The apparatus according to claim 3, wherein, The rear part of the third wavelength conversion section includes a separation section that separates 228.04nm light from light of other wavelengths.

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