215-222nm wavelength laser light generator

Abstract

The present invention pertains to a 215-222 nm wavelength laser beam generating apparatus which comprises: an excitation light source unit that converts laser beams with wavelengths of 1030-1064 nm into second harmonics and generates laser beams with wavelengths of 515-532 nm; an optical parametric oscillation unit that generates signal beams with wavelengths of 858-887 nm and idler beams with wavelengths of 1288-1330 nm by using the laser beams with the wavelengths of 515-532 nm as excitation light; a separation unit that separates the signal beams and the idler beams; a first wavelength conversion unit that generates fourth harmonics from the signal beams; a second wavelength conversion unit that generates deep ultraviolet rays with wavelengths of 215-222 nm from the idler beams through optical sum frequency generation with the second harmonics of the excitation light; and a coupling unit that couples the fourth harmonics from the first wavelength conversion unit with the deep ultraviolet rays from the second wavelength conversion unit. The present invention provides a laser beam generating apparatus that is able to generate simply and efficiently pulse laser beams with wavelengths of 215-222 nm, including a wavelength of 222 nm at which microorganisms are deactivated.

Description

[Technical Field]

[0001] The present invention relates to a laser light generator with a wavelength of 215 to 222 nm. More specifically, the present invention relates to an all-solid-state wavelength conversion laser generator that highly efficiently generates deep ultraviolet laser light with a wavelength of 215 to 222 nm, which is harmless to the human body and has a bactericidal effect (including virus inactivation; the same applies hereinafter). CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to Japanese Patent Application No. 2021-027496, filed February 24, 2021, the entire disclosure of which is expressly incorporated herein by reference. [Background technology]

[0002] Deep UV irradiation has long been used as a means of inactivating microorganisms such as bacteria and viruses. This method utilizes the fact that photochemical reactions such as hydration, dimer formation, and decomposition occur in DNA that has absorbed deep UV light, disrupting the helical structure of DNA and forming cyclobutane pyrimines, which kill bacterial cells.

[0003] Conventional deep ultraviolet light is not used on humans due to its effects on the human body. However, deep ultraviolet light with a wavelength of 222 nm has a sterilizing effect that is almost the same as conventional sterilizing ultraviolet light, or even greater depending on the type of bacteria, but it is absorbed by the stratum corneum of human skin and is therefore attracting attention because it has less effect on the human body than conventional ultraviolet light.

[0004] UV lamps, such as KrCl lamps, are known as sources of 222 nm light. However, the emission spectrum of UV lamps includes deep ultraviolet light with wavelengths other than 222 nm that are harmful to the human body, making it necessary to use a filter to block this light (see, for example, Patent Documents 1, 2, and 3). This has prevented efficient sterilization from being achieved. Furthermore, light-emitting diodes (LEDs), which have been attracting attention as alternative light sources to mercury lamps, currently only produce microwatt-order outputs at wavelengths of 265 nm or less.

[0005] Generally, laser light has a narrower spectrum than UV lamps, and a laser light source that emits only deep ultraviolet light with a wavelength of around 222 nm, which contributes to sterilization, would be extremely useful. Laser light has good directionality, making it possible to concentrate power on a small area, allowing a large amount of deep ultraviolet light to reach the DNA inside the cell walls and cell membranes of microorganisms, which is expected to have a sterilizing effect in a short period of time. In recent years, semiconductor lasers have been attracting attention as an alternative light source to mercury lamps. However, high-power oscillation at wavelengths below 270 nm has not been reported, and no laser light source that emits only deep ultraviolet light with a wavelength of around 222 nm is known.

[0006] A well-known example of a deep ultraviolet laser light source is a KrF laser device, but its oscillation wavelength is 248 nm. Alternatively, deep ultraviolet light with a wavelength of 266 nm is also known, generated by the fourth harmonic of an Nd:YAG laser oscillating at a wavelength of 1064 nm, but this wavelength is not 222 nm. Furthermore, these wavelengths are deep ultraviolet light that can have an effect on the human body.

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 2016-220684 Patent Document 2: Japanese Patent Application Laid-Open No. 2017-136145 Patent Document 3: Japanese Patent Application Laid-Open No. 2018-114197 Patent Document 4: Japanese Patent Application Laid-Open No. 2007-86101 Patent Document 5: Japanese Patent Application Laid-Open No. 2003-5233 Patent Document 6: Japanese Patent Application Laid-Open No. 2003-280055 The entire disclosures of Patent Documents 1 to 6 are expressly incorporated herein by reference. Summary of the Invention [Problem to be solved by the invention]

[0008] Therefore, there is a need for a 222 nm laser light generator that uses an existing laser light source and can efficiently utilize the light from the light source. In particular, there is a desire for the emergence of a 222 nm laser light generator that is an all-solid-state system using nonlinear optical elements.

[0009] Although there is a demand for a compact, easy-to-maintain all-solid-state laser as a deep-ultraviolet light source that efficiently generates deep-ultraviolet light with a wavelength of 222 nm, devices using conventional semiconductor lasers or excimer lasers have not been able to provide sufficient performance.

[0010] For example, Patent Document 4 discloses a laser device that uses two semiconductor laser light sources to generate laser light in the deep ultraviolet region with a wavelength of 190 to 270 nm. In this device, a nonlinear optical element is used to obtain laser light with a wavelength of 227 nm, but there is no mention of generating laser light with a wavelength of 222 nm.

[0011] A deep ultraviolet laser light generator using a semiconductor laser light source and a nonlinear optical element is described in Patent Document 5, and a deep ultraviolet laser light generator using a semiconductor laser light source, a nonlinear optical element, and an optical parametric oscillator is described in Patent Document 6. However, the device described in Patent Document 5 targets a different ultraviolet wavelength, which is the fifth harmonic of the output light of a titanium sapphire laser with a wavelength of 788.145 nm generated by a KBBF crystal. It is not a laser light generator with a wavelength of 222 nm.

[0012] The device described in Patent Document 6 also targets a different ultraviolet wavelength and is not a laser light generator with a wavelength of 222 nm. Although it uses the output light of second harmonic pumped optical parametric oscillation of an Nd:YAG laser, it does not use idler light of optical parametric oscillation, which is different from the present invention.

[0013] The present invention has been made in view of the above background, and aims to provide a laser generating device using an all-solid-state system that efficiently generates laser light with wavelengths of 215 to 222 nm, including the 222 nm wavelength, which has no effect on the human body and has a sterilizing effect, for example, pulsed laser light. [Means for solving the problem]

[0014] The present invention is as described below. [1] an excitation light source unit that converts laser light having a wavelength of 1030 to 1064 nm into a second harmonic to generate laser light having a wavelength of 515 to 532 nm; an optical parametric oscillator that generates signal light with a wavelength of 858 to 887 nm and idler light with a wavelength of 1288 to 1330 nm using laser light with a wavelength of 515 to 532 nm generated by a pumping light source as pumping light; a separation unit that separates signal light with wavelengths of 858 to 887 nm from idler light with wavelengths of 1288 to 1330 nm; a first wavelength conversion unit that generates a fourth harmonic having a wavelength of 215 to 222 nm from signal light having a wavelength of 858 to 887 nm; a second wavelength conversion unit that generates deep ultraviolet light having a wavelength of 215 to 222 nm from idler light having a wavelength of 1288 to 1330 nm by an optical sum frequency with 258 to 266 nm, which is the second harmonic of the excitation light; and A 215-222 nm wavelength laser light generating device including a combining section that combines the fourth harmonic having a wavelength of 215-222 nm from the first wavelength converting section with the deep ultraviolet light having a wavelength of 215-222 nm from the second wavelength converting section. [2] an excitation light source unit that converts laser light with a wavelength of 1064 nm into second harmonic to generate laser light with a wavelength of 532 nm; an optical parametric oscillator that generates signal light with a wavelength of 887 nm and idler light with a wavelength of 1330 nm using laser light with a wavelength of 532 nm generated by the pumping light source as pumping light; A separation unit that separates the signal light with a wavelength of 887 nm from the idler light with a wavelength of 1330 nm. a first wavelength conversion unit that generates a fourth harmonic having a wavelength of 222 nm from signal light having a wavelength of 887 nm; A second wavelength conversion unit that generates deep ultraviolet light having a wavelength of 222 nm from idler light having a wavelength of 1330 nm by an optical sum frequency with 266 nm, which is the second harmonic of the excitation light; and The laser light generating device according to [1] is a 222 nm wavelength laser light generating device, including a combining unit that combines the fourth harmonic of 222 nm wavelength from the first wavelength conversion unit and the deep ultraviolet light of 222 nm wavelength from the second wavelength conversion unit. [3] The laser light generating device according to [1] or [2], further comprising an Nd:YAG laser oscillator that generates laser light having a wavelength of 1030 to 1064 nm. [4] The laser light generator according to any one of [1] to [3], wherein the excitation light source unit includes a nonlinear optical crystal that converts laser light having a wavelength of 1030 to 1064 nm into a second harmonic. [5] The laser light generating device according to any one of [1] to [4], wherein the optical parametric oscillator is an optical parametric oscillator configured with a nonlinear optical crystal and two mirrors. [6] The laser light generating device according to any one of [1] to [5], wherein the first wavelength converting section is composed of two or more nonlinear optical crystals. [7] The laser light generating device according to any one of [1] to [6], wherein the second wavelength converting section is composed of two or more nonlinear optical crystals. [8] The laser light generating device according to any one of [1] to [7], further comprising a dichroic mirror between the pumping light source unit and the optical parametric oscillator unit, which reflects light with wavelengths of 1030 to 1064 nm contained in the light from the pumping light source unit and converts it into laser light with wavelengths of 515 to 532 nm. [9] The laser light generator according to any one of [1] to [8], further comprising a prism at the rear of the coupling part for separating light having wavelengths other than 215 to 222 nm.

[10] The laser light generating device according to any one of [1] to [9], wherein the laser light having a wavelength of 1030 to 1064 nm is pulsed laser light, and the pulse width is nanoseconds or picoseconds. [Effects of the Invention]

[0015] The present invention has the effect of providing a laser generator that is easy to operate and can generate laser light, for example, pulsed laser light, in the wavelength range of 215 to 222 nm, which includes 222 nm used for sterilization, with high efficiency and ease.

[0016] By using the above laser device for sterilization, sterilization can be performed effectively in a short time while avoiding any adverse effects on the human body. The laser light generating device according to this embodiment is a device that requires almost no maintenance because all necessary elements are solid-state systems. [Brief explanation of the drawings]

[0017] [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 fourth harmonic of the OPO signal light λs, the OPO idler light λi, and the optical sum-period generation wavelength of 266 nm light, which is the second harmonic of the 532 nm pump light, all coincide at 222 nm. DETAILED DESCRIPTION OF THE INVENTION

[0018] The 215 to 222 nm wavelength laser light generating device of the present invention is an excitation light source unit that converts laser light having a wavelength of 1030 to 1064 nm into a second harmonic to generate laser light having a wavelength of 515 to 532 nm; an optical parametric oscillator that generates signal light with a wavelength of 858 to 887 nm and idler light with a wavelength of 1288 to 1330 nm using laser light with a wavelength of 515 to 532 nm generated by a pumping light source as pumping light; a separation unit that separates signal light with wavelengths of 858 to 887 nm from idler light with wavelengths of 1288 to 1330 nm; a first wavelength conversion unit that generates a fourth harmonic having a wavelength of 215 to 222 nm from signal light having a wavelength of 858 to 887 nm; a second wavelength conversion unit that generates deep ultraviolet light having a wavelength of 215 to 222 nm from idler light having a wavelength of 1288 to 1330 nm by an optical sum frequency with 258 to 266 nm, which is the second harmonic of the excitation light; and The wavelength converter includes a coupling section that couples the fourth harmonic having a wavelength of 215 to 222 nm from the first wavelength converter with the deep ultraviolet light having a wavelength of 215 to 222 nm from the second wavelength converter.

[0019] A 222 nm wavelength laser light generating apparatus, which is one embodiment of the laser light generating apparatus of the present invention, is as follows: an excitation light source unit that converts laser light with a wavelength of 1064 nm into second harmonic to generate laser light with a wavelength of 532 nm; an optical parametric oscillator that generates signal light with a wavelength of 887 nm and idler light with a wavelength of 1330 nm using laser light with a wavelength of 532 nm generated by the pumping light source as pumping light; A separation unit that separates the signal light with a wavelength of 887 nm from the idler light with a wavelength of 1330 nm. a first wavelength conversion unit that generates a fourth harmonic having a wavelength of 222 nm from signal light having a wavelength of 887 nm; A second wavelength conversion unit that generates deep ultraviolet light having a wavelength of 222 nm from idler light having a wavelength of 1330 nm by an optical sum frequency with 266 nm, which is the second harmonic of the excitation light; and The wavelength converter includes a coupling section that couples the fourth harmonic wave with a wavelength of 222 nm from the first wavelength converter with the deep ultraviolet light with a wavelength of 222 nm from the second wavelength converter.

[0020] FIG. 1 shows a schematic diagram of a laser light generating device according to the present invention, taking a laser light generating device with a wavelength of 222 nm as an example. Reference numeral 10 denotes a pumping light source section, 20 denotes an optical parametric oscillator section, 30 denotes a separator section, 40 denotes a first wavelength converter section, 50 denotes a second wavelength converter section, and 60 denotes a coupler section.

[0021] FIG. 2 is a schematic diagram of an example of a 222 nm wavelength laser light generating device as one embodiment of the laser light generating device of the present invention, and particularly shows that the first wavelength converting section 40 includes SHG 40a and SHG 40b, and the second wavelength converting section 50 includes SHG 50a and SFG 50b. FIG. 3 shows an explanatory diagram of an example of a 222 nm wavelength laser light generating apparatus, which is one embodiment of the laser light generating apparatus of the present invention.

[0022] The meanings of the abbreviations used in this specification are as follows: SHG: Second Harmonic Generation 4HG: Fourth Harmonic Generation SFG: Optical Sum Frequency Generation OPO: Optical parametric oscillator KTP:KTiOPO4 BBO: β-BaB2O4 LBO: LiB3O5 RTP:RbTiOPO4 KTA:KTiOAsO4 MgO:PPLT: MgO-doped periodically poled LiTaO3 KBBF:KBe2BO3F2

[0023] The laser light generating device of the present invention will be described below using a 222 nm wavelength laser light generating device as an example.

[0024] (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 nm into a second harmonic to generate a laser beam with a wavelength of 532 nm. The pumping light source that generates the laser beam with a wavelength of 1064 nm is, for example, Nd:YAG (Nd 3+ :Y3Al5O 12 The laser light with a wavelength of 1064 nm can be a pulsed laser light, and the pulse width can be nanoseconds or picoseconds. The light source that emits the laser light with a wavelength of 1030 to 1064 nm can be a Nd:YAG (Nd 3+ :Y3Al5O 12In addition to the 1064nm Nd:YVO4 laser, the 1053nm and 1047nm Nd:YLF (LiYF4), the 1030nm Yb:YAG, and the 1063nm Nd:GdVO4 laser are also available. The wavelength conversion of the above laser light sources utilizes the second-order nonlinear optical effect, so they are essentially pulsed light sources that generate a strong electric field. However, if a resonator is used in each process, wavelength conversion of continuous light is also possible.

[0025] The pumping light source unit 10 may include, for example, a pumping light source and a nonlinear optical crystal that converts this laser light into a 532 nm laser light, which is the second harmonic. The nonlinear optical crystal may be, for example, a KTP crystal, and is shown as crystal 1 in FIG. 3. In addition to a KTP crystal, crystal 1 may also be, for example, any of BBO, LBO, MgO:PPLT, and PPKTP. The PP in "PP+crystal name" stands for "Periodically Poled."

[0026] 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 its polarization direction to a 45-degree angle, and then passed through crystal 1 to be converted into a 532-nm laser light, which is the second harmonic. Type 2 phase matching is used for wavelength conversion. When an LBO or BBO crystal is used as crystal 1, the polarization direction is changed to perpendicular to the paper surface through a λ / 2 plate, and then passed through crystal 1 to be converted into a 532-nm laser light, which is the second harmonic. Furthermore, when an MgO:PPLT or PPKTP crystal is used as crystal 1, the λ / 2 plate is not required. Crystal 1 is positioned so that the polarization direction of this 532-nm laser light is horizontal to the paper surface. Note that type 2 phase matching refers to the generation of a second harmonic from incident light of different beams (i.e., orthogonal polarizations), and is distinct from type 1 phase matching, which generates a second harmonic with a polarization different from that of 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 harmonic wave all have the same extraordinary ray direction is called Type 0.

[0027] The types of crystals that can be used in the pumping light source unit, the optical parametric oscillator unit, the first wavelength conversion unit, and the second wavelength conversion unit, along with their functions, phase matching types, and polarizations, are listed in Table 1. Note that Table 1 lists an example in which the light source wavelength is 1064 nm, but the usable crystals listed for each of crystals 1 to 6 have the functions, phase matching types, and polarizations listed in Table 1 when the light source wavelength is in the range of 1030 to 1064 nm.

[0028] [Table 1]

[0029] In the polarization column of Table 1, o means ordinary wave, and e means extraordinary wave.

[0030] (Dichroic mirror M1) A dichroic mirror (M1 in Figure 3) can be installed between the pumping light source unit 10 and the OPO0. The dichroic mirror M1 reflects the 1064 nm light contained in the light from the pumping light source unit 10, converting it into 532 nm laser light. Since the 1064 nm light will not be used in subsequent processes, separating it from the 532 nm laser light will prevent unnecessary damage to optical elements and thermal stress on the crystal when focusing lasers of other wavelengths in subsequent processes. The 532 nm laser light that passes through the dichroic mirror M1 is incident on the OPO.

[0031] (Explanation of the optical parametric oscillator (OPO)) OPO 20 uses the 532 nm laser light generated by the pump light source as pump light to generate a signal light with a wavelength of 887 nm and an idler light with a wavelength of 1330 nm, and separates the generated signal light. The OPO consists of a nonlinear optical crystal and two mirrors. The nonlinear optical crystal can be, for example, KTP crystal or a related crystal, shown as crystal 2 in Figure 3. Examples of related crystals of KTP include RTP and KTA crystals, as well as BBO, MgO:PPLT, or PPKTP. Crystal 2 is cut to a phase-matching angle that generates a signal light with a wavelength of 887 nm (λs) and an idler light with a wavelength of 1330 nm (λi). Note that MgO:PPLT and PPKTP are adjusted to have a polarization 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. When the crystal 2 constituting the optical parametric oscillator 20 is a similar crystal to a KTP crystal, phase matching is a Type 2 process, so the pump light and idler light are polarized horizontally to the plane of the paper, and the signal light is polarized perpendicular to the plane of the paper. When the crystal 2 constituting the optical parametric oscillator 20 is a BBO crystal with Type 1 phase matching, the pump light is polarized horizontally to the plane of the paper, and the signal light and idler light are polarized perpendicular to the plane of the paper. When the crystal 2 constituting the optical parametric oscillator 20 is an MgO:PPLT or PPKTP crystal, phase matching is a Type 0 process, so the pump light, signal light, and idler light are polarized horizontally to the plane of the paper.

[0032] (separation part 30) A separator 30 is provided between the OPO and the first and second wavelength converters to separate the 887 nm signal light and the 1330 nm idler light. Considering subsequent processes, the separator 30 preferably transmits the 1330 nm idler light and the unconverted 532 nm pump light. The separator 30 can be, for example, a dichroic mirror (M2 in Figure 3). The dichroic mirror M2 reflects only the 887 nm signal light, out of the signal light and idler light converted by the OPO, and transmits the 1330 nm idler light and the unconverted 532 nm pump light. When the signal light and idler light have different polarization directions (type 2 phase matching), a polarizer can be used as the separator 30. In this case, horizontally polarized light passes through the polarizer, and vertically polarized light is reflected.

[0033] (First wavelength converting section 40) The first wavelength conversion section 40 is a 4HG portion that converts signal light of 887 nm wavelength to 222 nm wavelength, and specifically, as shown in FIG. 2, can include an SHG 40a that converts 887 nm signal light to 444 nm blue light and an SHG 40b that converts 444 nm light to 222 nm deep ultraviolet light.

[0034] When the separator 30 is a dichroic mirror M2, the SHG 40a converts the reflected 887 nm signal light into 444 nm blue light. The SHG 40a can be a nonlinear optical crystal, such as an LBO or BBO crystal, and is shown as crystal 3 in FIG. 3. This crystal 3 is cut at an angle that allows Type 1 phase matching of the 887 nm fundamental wave with the 444 nm SHG. The polarization direction of the 444 nm light is horizontal. When the crystal 2 constituting the optical parametric oscillator 20 is an MgO:PPLT or PPKTP crystal, the SHG 40a is an MgO:PPLT crystal with a polarization reversal periodic length that generates the 888 nm SHG. In this case, the polarization direction of the 444 nm light is also horizontal to the plane of the paper.

[0035] SHG 40b converts 444 nm light into 222 nm deep ultraviolet light and can be a nonlinear optical crystal such as BBO. In Figure 3, this is represented by crystal 4. The 444 nm light is incident on the BBO crystal 4 and further converted into 222 nm deep ultraviolet light. Crystal 4 can be a nonlinear optical crystal other than BBO, such as KBBF, and is cut or sandwiched between quartz prisms so that the fundamental wave propagates at an angle that is Type 1 phase-matched to the 222 nm SHG. The polarization direction of the 222 nm light is perpendicular to the paper. The generated 222 nm light is combined with the 222 nm light generated on the other side at coupling section 60.

[0036] The first wavelength conversion section 40 can be composed of two or more crystals. When the SHG 40a and SHG 40b each consist of one crystal, the first wavelength conversion section 40 consists of two crystals. The SHG 40a and SHG 40b can each be two crystals with the same length and cut angle arranged in tandem, which can increase the conversion efficiency. In this case, the first wavelength conversion section 40 can be composed of three or more crystals.

[0037] (Second wavelength converting section 50) The second wavelength conversion unit 50 generates deep ultraviolet light with a wavelength of 222 nm by optical sum frequency mixing with the 266 nm second harmonic of the pump light from the idler light with a wavelength of 1330 nm separated by the separation unit 30. As shown in Fig. 2, the second wavelength conversion unit includes an SHG 50a that converts the pump light with a wavelength of 532 nm to a wavelength of 266 nm, and an SFG 50b that receives the deep ultraviolet light with a wavelength of 266 nm and the idler light with a wavelength of 1330 nm generated by the OPO again and generates 222 nm by optical sum frequency mixing.

[0038] The SHG 50a can be a nonlinear optical crystal such as BBO or CLBO, and is shown as crystal 5 in FIG. 3. Of the pump light and idler light that have passed through the dichroic mirror M2, which is the separator 30, the pump light with a wavelength of 532 nm is incident on crystal 5 and converted to a wavelength of 266 nm by SHG. Crystal 5 is cut at an angle that allows type-1 phase matching of the 532 nm fundamental wave with the 266 nm SHG. The polarization direction of the 266 nm light at this time is vertical.

[0039] SFG 50b can be made of a nonlinear optical crystal such as a CLBO crystal, shown as crystal 6 in Figure 3. The 266 nm deep-ultraviolet light converted by crystal 5 and the 1330 nm idler light generated by the OPO are re-entered into crystal 6, where 222 nm light is generated by optical sum frequency mixing. Crystal 6 can be a nonlinear optical crystal other than CLBO, such as BBO, and is cut to achieve type 2 phase matching. The polarization direction of the generated 222 nm light is horizontal. When crystal 2 constituting optical parametric oscillator 20 is BBO with type 1 phase matching, crystal 6 is cut to achieve type 1 phase matching.

[0040] The second wavelength conversion section 50 can be composed of two or more crystals. When the SHG 50a and SFG 50b each consist of one crystal, the second wavelength conversion section 50 consists of two crystals. The SHG 50a and SFG 50b can each be two crystals arranged in tandem, each having the same length and cut angle, which can increase the conversion efficiency. In this case, the second wavelength conversion section 50 can be composed of three or more crystals.

[0041] (Connection part 60) The combining unit 60 combines the 222 nm light generated in the first wavelength-converting unit 40 (SHG 40b in FIG. 2) and the 222 nm light generated in the second wavelength-converting unit 50 (SFG 50b in the figure). The combining unit 60 can be, for example, a polarizer.

[0042] A separator 70 (not shown in FIGS. 1 and 2) can be provided behind the combiner 60 to separate the laser light of various wavelengths generated during the wavelength conversion process and extract the 222 nm light. The separator 70 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 222 nm generated during the wavelength conversion process, but can be, for example, a quartz prism or an MgF2 prism. The separator 70 separates the light of wavelengths other than 222 nm to obtain laser light of 222 nm wavelength.

[0043] The example shown in Figure 3 is for a Type 2 optical parametric oscillator, but examples of combinations of crystals 2 to 6 for Type 0 and Type 1 are shown in Table 2 below, along with the Type 2 example shown in Figure 3. However, these examples are merely illustrative, and the present invention is not intended to be limited to these examples. Note that the example combinations of crystals 2 to 6 shown in Table 2 are for a light source wavelength of 1064 nm, but when the light source wavelength is in the range of 1030 to 1064 nm, combinations similar to those of crystals 2 to 6 shown in Table 2 can be used.

[0044] [Table 2]

[0045] (Mechanism of generating laser light with wavelengths of 215 to 222 nm) The mechanism for generating laser light with a wavelength of 215 to 222 nm in the device of the present invention will be explained below, taking 222 nm as an example. In an optical parametric oscillator (OPO), the following relationship holds when the pump light wavelength is λp, the signal light wavelength is λs, and the idler light wavelength is λi.

[0046] (Equation 1) 1 / λs+1 / λi=1 / λp

[0047] 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.

[0048] (Equation 2) 1 / λ1+1 / λ2=1 / λ3

[0049] 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.

[0050] In the present invention, as described above, an OPO pumped at 532 nm generates 887 nm signal light λs and 1330 nm idler light λi, which are second harmonic waves of a 1064 nm laser beam. As shown in Figure 4, the first wavelength converter generates the fourth harmonic wave λs from the 887 nm signal light λs, which has a wavelength of 222 nm. This utilizes the characteristic that the wavelength of the optical sum period generated from the 1330 nm idler light λi and the 266 nm light, which is the second harmonic wave of the 532 nm pump light, in the subsequent second wavelength converter matches. This mechanism functions similarly when generating deep ultraviolet light in the wavelength range of 215 to 222 nm using a laser light source with a wavelength range of 1030 to 1064 nm.

[0051] In the present invention, both the signal and idler output beams of the OPO can be used to generate deep-ultraviolet light with a wavelength of 215 to 222 nm, thereby realizing a more efficient deep-ultraviolet laser light generator with a wavelength of 215 to 222 nm.

[0052] The 222 nm wavelength laser light generated by the device of the present invention may vary depending on the specifications of each component and operating conditions, but is generally laser light with a wavelength in the range of 221.5 to 222.1 nm. Similarly, laser light with wavelengths other than 222 nm also has a wavelength that falls within a range of approximately ±0.5 nm depending on the specifications of each component and operating conditions.

[0053] The 222 nm wavelength laser light obtained by the device of the present invention is only deep ultraviolet light with a wavelength of 222 nm, which contributes to the sterilizing effect. Therefore, unlike when a KrCl lamp tube with a wide spectral width is used as the light source, there is no need for a bandpass filter to cut out excess deep ultraviolet light that can have an adverse effect on the human body.

[0054] The laser light generator of the present invention can achieve relatively high output, making it possible to irradiate a wide area with deep ultraviolet light at a wavelength of 222 nm and to irradiate liquids such as water, making it useful for applications such as sterilizing entrances and exits of facilities with unspecified access and liquids. In addition, the generated laser light can be irradiated onto a target object via a laser light guide such as an optical fiber, as needed. Therefore, it is easy to irradiate ultraviolet light onto areas such as the backside of a structure, for example. [Industrial Applicability]

[0055] 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]

[0056] 10. Excitation light source section 20 Optical parametric oscillator 30 Separation part 40 First wavelength conversion unit 50 Second wavelength conversion unit 60 Joint

Claims

1. an excitation light source unit that converts laser light having a wavelength of 1030 to 1064 nm into a second harmonic to generate laser light having a wavelength of 515 to 532 nm; an optical parametric oscillator that generates signal light with a wavelength of 858 to 887 nm and idler light with a wavelength of 1288 to 1330 nm using laser light with a wavelength of 515 to 532 nm generated by a pumping light source as pumping light; a separation unit for separating signal light having a wavelength of 858 to 887 nm from idler light having a wavelength of 1288 to 1330 nm; a first wavelength conversion unit that generates fourth harmonics having a wavelength of 215 to 222 nm from signal light having a wavelength of 858 to 887 nm; a second wavelength conversion unit that generates deep ultraviolet light having a wavelength of 215 to 222 nm from idler light having a wavelength of 1288 to 1330 nm by an optical sum frequency with 258 to 266 nm, which is the second harmonic of the excitation light; and A laser light generating device having a wavelength of 215 to 222 nm, comprising a combining section for combining the fourth harmonic having a wavelength of 215 to 222 nm from the first wavelength converting section and the deep ultraviolet light having a wavelength of 215 to 222 nm from the second wavelength converting section.

2. an excitation light source unit that converts laser light having a wavelength of 1064 nm into second harmonic to generate laser light having a wavelength of 532 nm; an optical parametric oscillator that generates signal light with a wavelength of 887 nm and idler light with a wavelength of 1330 nm using laser light with a wavelength of 532 nm generated by a pumping light source as pumping light; a separation unit for separating signal light having a wavelength of 887 nm from idler light having a wavelength of 1330 nm; a first wavelength conversion unit that generates a fourth harmonic having a wavelength of 222 nm from signal light having a wavelength of 887 nm; a second wavelength conversion unit that generates deep ultraviolet light having a wavelength of 222 nm from idler light having a wavelength of 1330 nm by an optical sum frequency with 266 nm, which is the second harmonic of the excitation light; and 2. The laser light generating device according to claim 1, comprising a combining section that combines the fourth harmonic having a wavelength of 222 nm from the first wavelength converting section and the deep ultraviolet light having a wavelength of 222 nm from the second wavelength converting section.

3. 3. The laser light generating device according to claim 1, further comprising an Nd:YAG laser oscillator for generating laser light having a wavelength of 1030 to 1064 nm.

4. 4. The laser light generating device according to claim 1, wherein the pumping light source section includes a nonlinear optical crystal that converts laser light having a wavelength of 1030 to 1064 nm into a second harmonic.

5. 5. The laser light generating device according to claim 1, wherein the optical parametric oscillator is an optical parametric oscillator comprising a nonlinear optical crystal and two mirrors.

6. 6. The laser light generating device according to claim 1, wherein the first wavelength converting portion is composed of two or more nonlinear optical crystals.

7. 7. The laser light generating device according to claim 1, wherein the second wavelength converting portion is composed of two or more nonlinear optical crystals.

8. 8. The laser light generating device according to claim 1, further comprising a dichroic mirror between the pumping light source unit and the optical parametric oscillator unit, which reflects light with a wavelength of 1030 to 1064 nm contained in the light from the pumping light source unit and converts it into laser light with a wavelength of 515 to 532 nm.

9. 9. The laser light generating device according to claim 1, further comprising a prism disposed behind the coupling section for separating light having wavelengths other than 215 to 222 nm.

10. 10. The laser light generating device according to claim 1, wherein the laser light having a wavelength of 1030 to 1064 nm is a pulsed laser light, and the pulse width is nanoseconds or picoseconds.

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