Ultraviolet laser light generator

Abstract

The present invention is a 399.08-nm ultraviolet laser light generation device including an excitation light source unit that converts 1064.2-nm laser light to a second harmonic to generate 532.1-nm laser light, an optical parametric oscillator that generates 798.15-nm signal light and 1596.3-nm idler light from the 532.1-nm laser light, a first wavelength conversion part that generates 399.08-nm light by sum-frequency generation from the idler light and the 532.1-nm light, and a second wavelength conversion part that generates a second harmonic from the signal light (the first wavelength conversion part and the second wavelength conversion part being listed in random order). The present invention relates to a 299.08-nm laser light generation device, and to a 228.04-nm ultraviolet laser light generation device that includes a third wavelength conversion part that generates 228.04-nm light by sum-frequency generation from 399.08-nm light and 532.1-nm light. The present invention provides a simple and highly efficient device for generating 228.04-nm laser light, which is a type of deep ultraviolet light, and a simple and highly efficient device for generating 399.08-nm laser light that serves as a light source for the aforementioned device.

Description

[Technical Field]

[0001] The present invention relates to an ultraviolet laser light generator, and more particularly to a 399.08 nm wavelength laser light generator and a 228.04 nm wavelength laser light generator. CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to Japanese Patent Application No. 2021-027497, filed February 24, 2021, the entire disclosure of which is hereby expressly incorporated by reference. [Background technology]

[0002] Laser light with wavelengths in the 200-280 nm range, also known as deep ultraviolet light, is used in a variety of fields, including semiconductor exposure equipment, wafer inspection, and sterilization equipment. While excimer lasers and semiconductor lasers are examples of light sources for deep ultraviolet laser light generators, excimer lasers have the drawback of using toxic gases and high maintenance costs. Semiconductor lasers also have low output power and are difficult to develop. Meanwhile, laser light generators that combine a solid-state laser oscillator with an oscillation wavelength in the 1 μm band as a fundamental light source with a wavelength conversion element using a nonlinear crystal or the like have been able to generate deep ultraviolet laser light of various wavelengths (Patent Documents 1 and 2). However, the laser light wavelengths obtained by wavelength conversion using harmonic generation are limited to wavelengths that are integer fractions of the wavelength of the fundamental light source. Furthermore, wavelength conversion using an optical parametric oscillator is used to obtain laser light of other wavelengths, but this method has the drawback of low overall system efficiency because the output of either the signal light or the idler light is not utilized.

[0003] In addition, multiple laser oscillators may be used to obtain laser light of a desired wavelength (Patent Documents 3 and 4). However, since this is a system using two lasers, there are concerns about reduced costs and 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 Laid-Open No. 2003-114454 Patent Document 4: Japanese Patent Application Laid-Open No. 2007-086104 The entire disclosures of Patent Documents 1 to 4 are expressly incorporated herein by reference. Summary of the Invention [Problem to be solved by the invention]

[0005] The first object of the present invention is to provide a laser light generating device that uses a single semiconductor laser oscillator and emits 228.04 nm deep ultraviolet light, which has not been previously available. The second object of the present invention is to provide a 399.08 nm ultraviolet laser light generating device that uses a single semiconductor laser oscillator and can be used as a light source for a 228.04 nm laser light generating device that emits deep ultraviolet light, which has not been previously available. [Means for solving the problem]

[0006] The present invention is as follows. [1] an excitation light source unit that converts laser light having a wavelength of 1064.2 nm into a second harmonic to generate laser light having a wavelength of 532.1 nm; an optical parametric oscillator that generates signal light with a wavelength of 798.15 nm and idler light with a wavelength of 1596.3 nm using laser light with a wavelength of 532.1 nm generated by the pumping light source as pumping light; a first wavelength conversion unit that generates a sum frequency of idler light having a wavelength of 1596.3 nm and light having a wavelength of 532.1 nm to generate light having a wavelength of 399.08 nm; and a second wavelength conversion unit that generates second harmonic light of 399.08 nm wavelength from signal light of 798.15 nm wavelength, An ultraviolet laser light generating device with a wavelength of 399.08 nm, having an optical path for laser light in the order of an excitation light source unit, an optical parametric oscillator unit, a first wavelength conversion unit, and a second wavelength conversion unit, or in the order of an excitation light source unit, an optical parametric oscillator unit, a second wavelength conversion unit, and a first wavelength conversion unit. [2] The device according to [1], wherein the 532.1 nm light generated as a sum frequency by the first wavelength conversion unit is 532.1 nm light that has not been converted by the optical parametric oscillator unit. [3] The device according to [1] or [2], having an optical path for laser light that includes an excitation light source unit, an optical parametric oscillator unit, a first wavelength conversion unit, and a second wavelength conversion unit in this order. [4] [1] A 399.08 nm wavelength laser light generating device according to any one of [1] to [3], and An ultraviolet laser light generating device with a wavelength of 228.04 nm, including a third wavelength conversion unit that generates 228.04 nm light by generating the sum frequency of 399.08 nm light and 532.1 nm light. [5] The device according to [4], wherein the 532.1 nm light generated as a sum frequency by the third wavelength conversion unit is 532.1 nm light that has not been converted by the optical parametric oscillator unit. [6] The device according to [4] or [5], further comprising a separation unit that separates 228.04 nm light from light of other wavelengths, after the third wavelength conversion unit. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a laser generator with excellent operability that can generate laser light in the wavelength range of 228.04 nm, which is deep ultraviolet light that may be used for sterilization, with high efficiency and ease. According to the present invention, it is possible to provide a 399.08 nm ultraviolet laser light generator that can be used as a light source for a 228.04 nm laser light generator. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic explanatory diagram of a laser generating apparatus according to the present invention. [Figure 2] FIG. 2 is a schematic explanatory diagram of one embodiment of the laser generating device of the present invention. [Figure 3] FIG. 3 shows an embodiment of the laser generating device of the present invention. [Figure 4]Figure 4 shows an explanatory diagram illustrating that the wavelength of the optical sum period generated by the OPO between the idler light λi with a wavelength of 1596.3 nm and the pump light of 532.1 nm is 399.08 nm, which coincides with the 399.08 nm light that is the second harmonic of the signal light λs with a wavelength of 798.15 nm generated by the same OPO. DETAILED DESCRIPTION OF THE INVENTION

[0009] A first aspect of the laser light generating apparatus of the present invention is an ultraviolet laser light generating apparatus having a wavelength of 399.08 nm, which comprises: an excitation light source unit that converts laser light having a wavelength of 1064.2 nm into a second harmonic to generate laser light having a wavelength of 532.1 nm; an optical parametric oscillator that generates signal light with a wavelength of 798.15 nm and idler light with a wavelength of 1596.3 nm using laser light with a wavelength of 532.1 nm generated by the pumping light source as pumping light; a first wavelength conversion unit that generates a sum frequency of idler light having a wavelength of 1596.3 nm and light having a wavelength of 532.1 nm to generate light having a wavelength of 399.08 nm; and a second wavelength conversion unit that generates second harmonic light of 399.08 nm from signal light of 798.15 nm; The optical path of the laser light is in the order of pumping light source unit, optical parametric oscillator unit, first wavelength converter and second wavelength converter, or in the order of pumping light source unit, optical parametric oscillator unit, second wavelength converter and first wavelength converter.

[0010] A second aspect of the laser light generating device of the present invention is an ultraviolet laser light generating device with a wavelength of 228.04 nm, which includes the 399.08 nm wavelength laser light generating device of the first aspect of the present invention, and a third wavelength conversion unit that generates the sum frequency of 399.08 nm light and 532.1 nm light to generate 228.04 nm light.

[0011] FIG. 1 shows a schematic diagram of a laser light generating device according to the first and second aspects of the present invention, which has an optical path for laser light that includes an excitation light source unit, an optical parametric oscillator unit, a first wavelength conversion unit, and a second wavelength conversion unit in that order.

[0012] A laser light generation device according to a first aspect of the present invention is a device including components 10 to 40 in Fig. 1, where 10 is a pump light source unit, 20 is an optical parametric oscillator 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 may be reversed. A laser light generation device according to a second aspect of the present invention includes a third wavelength conversion unit 50 in addition to components 10 to 40 in Fig. 1.

[0013] FIG. 2 is a schematic diagram of one embodiment of the laser light generating device of the present invention, and particularly shows that the excitation light source section includes SHG, the first wavelength conversion section 30 includes SFG, the second wavelength conversion section 40 includes SHG, and the third wavelength conversion section 50 includes SFG. FIG. 3 shows an explanatory diagram of one embodiment of the laser light generating device of the present invention.

[0014] The meanings of the abbreviations used in this specification are as follows: SHG: Second Harmonic Generation SFG: Optical Sum Frequency Generation OPO: Optical parametric oscillator KTP:KTiOPO4 BBO: β-BaB2O4 LBO: LiB3O5 BiBO:BiB3O6 MgO:PPLT: MgO-doped periodically poled LiTaO3 KBBF:KBe2BO3F2

[0015] (Explanation of the excitation light source unit) The pumping light source unit 10 is a part that converts a laser beam with a wavelength of 1064.2 nm into a second harmonic to generate a laser beam with a wavelength of 532.1 nm. The pumping light source that generates the laser beam with a wavelength of 1064.2 nm is, for example, Nd:YAG (Nd 3+ :Y3Al5O 12) laser. The laser light with a wavelength of 1064.2 nm is pulsed laser light, and the pulse width can be nanoseconds or picoseconds. The pumping light source unit 10 can include, for example, a pumping light source and a nonlinear optical crystal that converts this laser light into 532.1 nm laser light, which is second harmonic generation (SHG). The nonlinear optical crystal can be, for example, a KTP crystal, and is shown as crystal 1 in FIG. 3. In addition to KTP crystal, crystal 1 can also be, for example, BBO, LBO, MgO-doped MgO:PPLT, or PPKTP. Note that PP in "PP+crystal name" stands for "Periodically Poled."

[0016] More specifically, when a KTP crystal is used as the nonlinear optical crystal, as shown in Figure 3, the laser light from the pump light source is passed through a half-wave plate (λ / 2 plate) to change the polarization direction to a 45-degree angle, and then passed through crystal 1 to be converted into a 532.1 nm laser light, which is the second harmonic. Phase matching in the wavelength conversion is Type 2. Furthermore, when an LBO or BBO crystal is used as crystal 1, the polarization direction is changed to a direction perpendicular to the paper surface through a λ / 2 plate, and then passed through crystal 1 to be converted into a 532.1 nm laser light, which is the second harmonic.

[0017] Furthermore, if MgO:PPLT or PPKTP is used for crystal 1, a λ / 2 plate is not required. Crystal 1 is installed so that the polarization direction of this 532.1 nm laser light is horizontal to the paper surface. Note that type 2 phase matching refers to phase matching that generates second harmonics from incident light of different beams (i.e., different orthogonal polarizations), and is distinguished from type 1 phase matching that generates second harmonics with a different polarization from the incident light from incident light of the same beam (i.e., the same polarization). Furthermore, in this specification, phase matching in which the incident light and the second harmonics all have the same extraordinary ray direction is referred to as type 0.

[0018] Table 1 below lists the types of crystals that can be used in the pump light source section, the optical parametric oscillator 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 polarizations.

[0019] [Table 1]

[0020] In the polarization column of Table 1, o means ordinary wave, and e means extraordinary wave.

[0021] (Dichroic mirror M1) A dichroic mirror (M1 in Figure 3) can be installed between the pumping light source unit 10 and the OPO 20. The dichroic mirror M1 reflects the 1064.2 nm light contained in the light from the pumping light source unit 10, converting it into 532.1 nm laser light. Since the 1064.2 nm light is not used in subsequent processes, separating it from the 532.1 nm laser light prevents unnecessary damage to optical elements and thermal stress on the crystal when focusing lasers of other wavelengths in subsequent processes. The 532.1 nm laser light that passes through the dichroic mirror M1 is incident on the OPO.

[0022] (Explanation of the optical parametric oscillator (OPO)) OPO 20 uses the 532.1 nm laser light generated by the pump light source as pump light to generate a 798.15 nm signal light and a 1596.3 nm idler light, and then separates the generated signal light. The OPO consists of a nonlinear optical crystal and two mirrors. The nonlinear optical crystal can be, for example, a BBO crystal or a BiBO crystal, or alternatively, MgO:PPLT or PPKTP. Crystal 2 is cut to a phase-matching angle that generates a 798.15 nm signal light λs and a 1596.3 nm idler light λi. The MgO:PPLT and PPKTP are adjusted to have a polarization reversal periodicity that allows the generation of the signal and idler light wavelengths. The two wavelengths emitted from this crystal are amplified in a resonator composed of two mirrors, resulting in OPO oscillation. As shown in Table 1, in the case of the phase matching type 1 process, the crystal 2 constituting the optical parametric oscillator 20 has the pump light polarized horizontally to the plane of the paper, and the signal light and idler light polarized vertically to the plane of the paper.

[0023] The wavelength precision of the signal light from the optical parametric oscillator 20 is preferably controlled to approximately 0.1 nm or less by narrowing the bandwidth with seed light from a semiconductor laser and by temperature tuning the crystal 2. This allows the spectral width and fluctuation of the violet light wavelength of 399.08 nm to be approximately 0.05 nm or less.

[0024] (First wavelength converting section 30) The first wavelength conversion unit 30 generates 399.08 nm light by optical sum frequency mixing using the 1596.3 nm idler light generated by the OPO and the 532.1 nm light generated by the pump light source and transmitted through the OPO. The 532.1 nm light generated as a sum frequency by the first wavelength conversion unit 30 is the 532.1 nm light not converted by the OPO 20. The crystal 3 shown in FIG. 3 can be a nonlinear optical crystal such as a BBO crystal. In addition to BBO, if MgO:PPLT is used as the crystal 3, MgO:PPLT is also used as the crystal 2 of the optical parametric oscillator 20. The crystal 3 is adjusted to a polarization periodicity sufficient to generate the 1596.3 nm idler light and the 532.1 nm sum frequency. The polarization direction of the 399.08 nm light is horizontal to the plane of the paper.

[0025] (Second wavelength converting section 40) The second wavelength conversion section 40 is a section that converts the signal light of 798.15 nm to the SHG wavelength of 399.08 nm. The crystal 4 shown in FIG. 3 can be a nonlinear optical crystal such as LBO or BBO. Other than LBO or BBO, it can also be a nonlinear optical crystal such as MgO:PPLT. When the crystal 4 is MgO:PPLT, MgO:PPLT is used as the crystal 2 of the optical parametric oscillator 20. The crystal 4 is adjusted to a polarization inversion periodic length that generates 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 converter 30 and the second wavelength converter 40 can be reversed. That is, the 399.08 nm wavelength ultraviolet laser light generator (first embodiment) of the present invention can have an optical path for laser light in the order of the pumping light source unit 10, the optical parametric oscillator unit 20, the first wavelength converter 30, and the second wavelength converter 40, or in the order of the pumping light source unit 10, the optical parametric oscillator unit 20, the second wavelength converter 40, and the first wavelength converter 30.

[0027] The order of the first wavelength-converting section 30 and the second wavelength-converting section 40 can be reversed.

[0028] (Third wavelength converting section 50) The third wavelength conversion section 50 generates 228.04 nm light by optical sum frequency mixing from 532.1 nm light generated by the pumping light source section and transmitted through the OPO 20, first wavelength conversion section 30, and second wavelength conversion section 40, and 399.08 nm light generated by the first wavelength conversion section 30 and second wavelength conversion section 40. The 532.1 nm light generated as a sum frequency by the third wavelength conversion section 50 is 532.1 nm light that was not converted by the OPO 20 and transmitted through the first wavelength conversion section 30 and second wavelength conversion section 40. The crystal 5 shown in FIG. 3 can be, for example, a nonlinear optical crystal such as BBO or KBBF crystal.

[0029] (separation part 60) A separator 60 (not shown in FIGS. 1 and 2) can be provided behind the third wavelength converter 50 to separate the laser light of various wavelengths generated during the wavelength conversion process and extract the 228.04 nm light. The separator 60 can be, for example, a prism (see FIG. 3). The prism is not particularly limited as long as it can remove laser light of wavelengths other than 228.04 nm generated during the wavelength conversion process, and can be, for example, a quartz prism or an MgF2 prism. The separator 60 separates the light of wavelengths other than 228.04 nm to obtain laser light of 228.04 nm wavelength.

[0030] 3 is an example in which the optical parametric oscillator is phase-matched to type 1, but when the optical parametric oscillator is phase-matched to type 0, MgO:PPLT is used for both crystal 3 and crystal 4. However, these examples are merely illustrative, and the present invention is not intended to be limited to these examples.

[0031] (228.04nm laser light generation mechanism) In an OPO, when the pump light wavelength is λp, the signal light wavelength is λs, and the idler light wavelength is λi, the following relationship holds:

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

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

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

[0035] In ultraviolet laser generation methods using wavelength conversion, there are various combinations using (Equation 1) and (Equation 2), but coherent light of the desired wavelength is generated using the above relationship. Normally, deep ultraviolet laser light is generated by using either the signal light or the idler light output in (Equation 1) for wavelength conversion, and the other output light is not used and is cut by a filter, which has the disadvantage of low conversion efficiency to deep ultraviolet light for the entire system.

[0036] In the present invention, as described above, a 532.1-nm pumped OPO generates a 798.15-nm signal light λs and a 1596.3-nm idler light λi, which are second harmonics of a 1064.2-nm laser beam. The first wavelength converter generates an optical sum period from the 1596.3-nm idler light λi and the 532.1-nm pump light at a wavelength of 399.08 nm. This wavelength coincides with the 399.08-nm second harmonic generated from the 798.15-nm signal light λs at the second wavelength converter (see FIG. 4). This allows for the realization of a more efficient 399.08-nm ultraviolet laser beam generator.

[0037] In addition, in this invention, both the signal and idler output beams of the OPO can be used to generate UV light with a wavelength of 399.08 nm, and furthermore, optical sum-period generation generated from this 399.08 nm light and the 532.1 nm pump light enables the generation of deep-UV light with a wavelength of 228.04 nm, thereby realizing a more efficient deep-UV laser light generator with a wavelength of 228.04 nm.

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

[0039] The laser light with a wavelength of 228.04 nm obtained by the device of the present invention is thought to have a sterilizing effect because it is close to the wavelength of 222 nm.

[0040] The laser beam generator of the present invention can utilize both signal and idler beams, enabling more efficient generation of deep-ultraviolet laser beams. This allows for irradiation of a wide range of ultraviolet light with wavelengths of 399.08 nm or 228.04 nm, or irradiation of liquids such as water, making it useful for applications such as sterilizing entrances and exits of facilities with unspecified access and liquids. Additionally, the generated laser beam can be irradiated onto a target object via a laser beam guide such as a fiber, as needed. Therefore, for example, it is easy to irradiate ultraviolet light onto areas such as the backside of a structure. [Industrial Applicability]

[0041] The present invention is effective not only in medical settings but also in disinfection work in large facilities. Furthermore, since it does not use toxic gases such as ozone or ethylene oxide, it is easy to handle and has little effect on the human body. Furthermore, since it does not use liquids such as alcohol disinfectants, it can also be used to disinfect paper media that cannot be wetted, such as books. [Explanation of symbols]

[0042] 10. Excitation light source section 20 Optical parametric oscillator 30 First wavelength conversion unit 40 Second wavelength conversion unit 50 Third wavelength conversion unit

Claims

1. an excitation light source unit that converts laser light having a wavelength of 1064.2 nm into a second harmonic to generate laser light having a wavelength of 532.1 nm; an optical parametric oscillator that generates signal light with a wavelength of 798.15 nm and idler light with a wavelength of 1596.3 nm using laser light with a wavelength of 532.1 nm generated by a pumping light source as pumping light; a first wavelength conversion unit that generates a sum frequency of idler light having a wavelength of 1596.3 nm and light having a wavelength of 532.1 nm to generate light having a wavelength of 399.08 nm; and a second wavelength conversion unit that generates second harmonic light having a wavelength of 399.08 nm from signal light having a wavelength of 798.15 nm; An ultraviolet laser light generating device with a wavelength of 399.08 nm, having an optical path for laser light in the order of an excitation light source unit, an optical parametric oscillator unit, a first wavelength conversion unit, and a second wavelength conversion unit, or in the order of an excitation light source unit, an optical parametric oscillator unit, a second wavelength conversion unit, and a first wavelength conversion unit.

2. 2. The device according to claim 1, wherein the 532.1 nm light generated as a sum frequency by the first wavelength conversion section is 532.1 nm light that has not been converted by the optical parametric oscillator section.

3. 3. The device according to claim 1, further comprising an optical path for the laser light that includes an excitation light source section, an optical parametric oscillator section, a first wavelength converter section, and a second wavelength converter section in this order.

4. A 399.08 nm wavelength laser light generating device according to any one of claims 1 to 3, and An ultraviolet laser light generating device having a wavelength of 228.04 nm, comprising a third wavelength conversion unit that generates a sum frequency of 399.08 nm light and 532.1 nm light to generate light having a wavelength of 228.04 nm.

5. 5. The apparatus according to claim 4, wherein the 532.1 nm light generated as a sum frequency by the third wavelength conversion section is 532.1 nm light that has not been converted by the optical parametric oscillator section.

6. 6. The device according to claim 4, further comprising a separation section for separating the 228.04 nm light from light of other wavelengths after the third wavelength conversion section.

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