WO2010007938A1 - Ultraviolet laser device - Google Patents

Abstract

An ultraviolet laser device includes a visible laser oscillating section (laser 1) for generating a visible laser of a variable wavelength, a laser (laser 2) for generating a laser beam of a constant wavelength, and a wavelength converting section (conversion section 1) for generating a sum-frequency wave from the output light (output light a1) of the laser 1 and the output light (output light b) of the laser 2 and thereby producing an ultraviolet light.  The laser device is characterized in that the laser 1 includes an optical waveguide which has a core containing at least Pr as a laser medium and a semiconductor laser generating an excited light having a wavelength of larger than 400 nm and shorter than 480 nm as a pumping light source and ultraviolet light (output light c) having a wavelength of shorter than 250 nm is continuously outputted by using a ferroelectric fluoride crystal in the conversion section (1).

Description

UV laser equipment

The present invention relates to an ultraviolet laser device.

Background of the Invention

Conventionally, as an ultraviolet laser, an excimer laser such as a KrF laser, an ArF laser, or an F ₂ laser has been developed, and is widely applied to a stepper apparatus for semiconductor exposure. These ultraviolet lasers are gas lasers and have low repetition pulse laser oscillation, and it is difficult to maintain power stability and beam quality in continuous operation. In addition, the excimer laser is dangerous because it uses fluorine, and maintenance is troublesome. For this reason, the apparatus is expensive and large. Furthermore, since the excimer laser is a low repetition pulse laser, it is difficult to develop it for uses other than exposure. For example, in direct drawing microfabrication, it is desired to scan at a high speed in order to improve the processing efficiency, but in an excimer laser, scanning is difficult because repetition is slow. For this reason, although the ultraviolet light processing is applied to resin material processing and the like which are effective, the range is limited at present.

Also, continuous wave is useful for inspection and development of optical components used in equipment using excimer laser, because pulsed light reduces work efficiency. For this reason, light having the same wavelength as the excimer laser wavelength is cut out from the bright line of a high-pressure mercury lamp or white lamp light and used, but there is a problem in the light condensing property because it is not a laser. Concentration when using an excimer laser is often not sufficient even if advanced optical simulation is used, and it tends to be a trial-and-error development. For these reasons, development of a high-accuracy ultraviolet optical system requires a lot of time and money, and a large excimer laser optical system is very expensive. For efficient development, there is a need for continuous wave lasers at excimer laser wavelengths.

In contrast, solid-state lasers that do not require gas handling are being developed. For example, the wavelength conversion technology of an infrared solid-state laser has advanced, and an all-solid-state ultraviolet laser has been announced. These lasers can oscillate continuously or with high repetition and can be driven more stably than excimer lasers. Nd-doped YAG crystal (Nd: YAG) or Yb-doped fiber (YDF) is used as a laser that generates a continuous wave or a high repetition fundamental wave. The lasing wavelength of these lasers is almost 1064 nm for Nd: YAG and 1000 to 1100 nm for YDF. These lasers are wavelength-converted by nonlinear crystals such as LiNbO ₃ (LN), LiTaO ₃ (LT), KNbO ₃ (KN), BaB ₂ O ₄ (β-BBO).

Infrared lasers having a fundamental wavelength of 1 μm band can obtain ultraviolet light at the 2nd harmonic in the green region and 3-5 harmonics. Often used is the fourth harmonic of Nd: YAG, which generates 266 nm. As the nonlinear optical crystal for wavelength conversion, a bulk type and a quasi phase matching (QPM) type are known. The QPM type is capable of highly efficient wavelength conversion by a periodic polarization inversion technique. A plate-type bulk type and a waveguide type are known as the QPM element, and the waveguide type is considered to have high efficiency among the QPM elements because the optical confinement effect can be used.

The most well-known waveguide-type QPM element is a periodically poled LN crystal (PPLN), which is being widely used as a wavelength conversion element. For wavelength conversion, it has long been known that ferroelectric crystals having no central symmetry and refractive index anisotropy are useful. In particular, the search for materials having a high figure of merit for d33 and d32 has been continued. Yes. Recently, a QPM element and a periodically poled device using a ferroelectric fluoride crystal (Patent Document 1) that has been known for a short wavelength generation such as visible to ultraviolet have been studied (Non-Patent Document). 1, Non-Patent Document 2, Patent Document 2).

However, in the wavelength conversion of an all-solid-state laser using a crystal as the laser medium, the wavelength range that can be oscillated by the original solid-state crystal laser is as narrow as several nanometers or less, so the wavelength is close to a fixed state and a desired wavelength can be obtained. It is difficult. In order to obtain a desired wavelength, the original laser serving as a fundamental wave is required to have variability in a wavelength (frequency) range as wide as possible. Among infrared solid-state lasers having a wide wavelength tunable, an Er-doped fiber (EDF) laser has progressed, and high output has been achieved. The fundamental wave of the 1550 nm band can be tunable over a wide range from 1500 nm to 1600 nm, and there is a possibility that ultraviolet light having a desired wavelength can be obtained.

However, since the EDF laser has a laser oscillation wavelength as long as the 1550 nm band, in order to obtain ultraviolet light, multistage high-order wavelength conversion of 5th harmonic or higher is required. Furthermore, if the fundamental wave is adjusted to a wavelength of 1546.4 nm to obtain an 8th harmonic wave, 193.3 nm of the ArF excimer laser wavelength may be obtained. In the conversion, the conversion efficiency with respect to the fundamental wave is as low as 1% or less, so that the power density in the wavelength conversion crystal is lowered during the conversion, making it difficult to obtain an ultraviolet continuous wave laser. As another broadband wavelength tunable solid-state laser, a Ti: sapphire laser is well known, and can oscillate in a very wide wavelength range from 650 nm to 1100 nm. For this reason, it is most often used as a broadband wavelength variable light source (Patent Document 3). However, the Ti: sapphire laser requires a high-power laser in the 500 nm band as an excitation source, which not only increases the size of the apparatus but also consumes a large amount of power because of its low electro-optical conversion efficiency.

Recently, since the semiconductor laser technology has advanced, a technique for adjusting the laser wavelength to a desired wavelength although using a semiconductor laser adjusted to a predetermined wavelength has been advanced. This technique uses a sum frequency generation (SFG) technique that adds the frequencies of lasers of different wavelengths, and achieves practical conversion efficiency using a waveguide wavelength conversion element such as PPLN. For example, fluorescent dye excitation light sources for biological observation have been put into practical use by SFG technology. However, the laser output obtained by sum frequency generation using a semiconductor laser as a fundamental wave is only tens to hundreds mW in the blue to red visible light region. Even if the wavelength of a laser having such an output is further converted to obtain ultraviolet light, the output is about several mW or less, which is not practical. To increase output, it is necessary to increase the output of a custom-made semiconductor laser adjusted to a specific wavelength and to fix the wavelength by using a fiber grating adjusted to a specific wavelength, and specialization is inevitable. Further, the semiconductor laser has a problem that the beam quality is easily deteriorated due to the high output, and the light condensing property is remarkably lowered. For this reason, even if a high-power semiconductor laser is used, the wavelength conversion efficiency is lowered, and as a result, it becomes difficult to obtain ultraviolet light with sufficient power after wavelength conversion.

On the other hand, a fiber laser capable of obtaining a high-quality laser output even at high output is considered useful as a fundamental wave, and an ultraviolet continuous wave laser light source using sum frequency generation using at least one fiber laser has been proposed (Patent Document 4). ). Here, a method is disclosed in which two wavelengths are selected from three discrete wavelengths between 950 nm and 1580 nm, and one of them is used as a high-order harmonic to finally obtain ultraviolet light. However, since CsLiB ₆ O ₁₀ (CLBO) crystal or BBO crystal is used as the nonlinear optical crystal for generating the sum frequency, transparency is not always sufficient due to the problem of the ultraviolet absorption edge of the oxide crystal. It cannot be said that the wavelength conversion efficiency is high in the region. Furthermore, although CLBO is a high-performance crystal as a known ultraviolet wavelength conversion crystal, it is not only difficult to handle because of deliquescence, but also because a dielectric multilayer film cannot be formed directly on the crystal surface, Restrictions and restrictions on the usage environment are very strict. In addition, since existing fiber lasers are lasers in the infrared wavelength region, the second harmonic is not sufficient for the generation of ultraviolet light, and the higher harmonics such as the third and fourth harmonics. Therefore, there is a problem that the efficiency is remarkably lowered.

US Pat. No. 3,982,136 International Publication No. 2001/090812 Japanese Patent Laid-Open No. 10-341054 JP 2006-73970 A

As described above, it is difficult to realize a compact and highly efficient laser with a continuous wave solid-state ultraviolet laser whose laser oscillation wavelength is sufficiently close to that of a conventional excimer laser. For this reason, there is a demand for a continuous-wave all-solid-state ultraviolet laser that can be adjusted to an excimer laser wavelength and that can be used for ultraviolet laser processing by laser drawing, design of excimer laser devices, component inspection, and the like. Further, for spectroscopic measurement applications, a continuous wave all solid-state ultraviolet laser whose wavelength is variable in the ultraviolet wavelength region is desired.

Therefore, an object of the present invention is to provide a continuous wave ultraviolet laser that can be tuned to a specific wavelength in the ultraviolet wavelength region or can be tunable within a certain wavelength range.

As a result of intensive studies to achieve the above object, the inventors of the present invention have developed a fundamental wave in an ultraviolet laser device using a sum frequency generation technology that continuously oscillates a laser beam that can be tuned to an existing excimer laser wavelength. In order to avoid efficiency degradation due to higher-order wavelength conversion, a laser light source with a short wavelength as much as possible is used as a fundamental wave. The present inventors have found that the above object can be achieved by using a nonlinear optical crystal that maintains sufficient transparency even in the light wavelength region, and have reached the present invention.

According to the present invention, a visible laser oscillation unit (laser 1) having a variable wavelength, a laser (laser 2) that generates laser light having a constant wavelength, an output light (output light a1), and a laser of laser 1 In a laser device including a wavelength conversion unit (conversion unit 1) that generates ultraviolet light by generating a sum frequency based on output light (output light b), the laser 1 contains at least Pr as a laser medium in the core An optical waveguide and a semiconductor laser that generates excitation light having a wavelength of 400 nm or more and 480 nm or less as an excitation light source, and using a ferroelectric fluoride crystal for the conversion unit 1, ultraviolet light having a wavelength of 250 nm or less (output light) An ultraviolet laser device (first device) is provided that continuously outputs c).

The first apparatus uses an ultraviolet laser in which the laser oscillation wavelength of the laser 1 is in the range of 700 nm to 715 nm and the laser 2 has a wavelength in the range of more than 250 nm to 300 nm. It may be a device (second device).

The first apparatus uses a laser having a laser oscillation wavelength of 598 nm or more and 715 nm or less and a wavelength of 400 nm or more and 550 nm or less as the laser 2, and further, the laser 1 and the conversion A wavelength conversion unit (conversion unit 2) for converting the wavelength of the output light a1 is provided between the units 1, and the ultraviolet light is generated by the sum frequency generation based on the output light (output light a2) whose wavelength is converted and the output light b. It may be an ultraviolet laser device (third device) characterized by being generated.

Any one of the first to fourth devices has a composition in which the ferroelectric fluoride crystal is represented by XMgF ₄ , XZnF ₄ , XAlF ₅ , Na ₂ MgAlF ₇ , or Na ₂ ZnAlF ₇ (where X is , One element selected from any one of Ca, Sr, and Ba).

It is a figure which shows the structural example of the laser 1 of this invention. It is a figure which shows another structural example of the laser 1 of this invention. It is a figure which shows the structural example of the laser of this invention. It is a figure which shows the relationship between the wavelength of the laser 1 of this invention, and an ultraviolet light wavelength. It is a figure which shows the ultraviolet light output spectrum of this invention. It is a figure which shows the ultraviolet light output stability of this invention. It is a figure which shows the structural example of the laser of this invention.

Detailed description

According to the present invention, it is possible to provide a continuous wave ultraviolet laser that can be tuned to a specific wavelength in the ultraviolet wavelength region or can be tunable within a certain wavelength range. Further, an ultraviolet CW laser whose wavelength is tuned to an existing excimer laser can be provided.

The present invention includes a visible laser oscillation unit (laser 1) having a variable wavelength, a laser (laser 2) that generates laser light having a constant wavelength, an output light (output light a1) of laser 1, and an output of laser 2 An ultraviolet laser device including a wavelength conversion unit (conversion unit 1) that generates ultraviolet light by sum frequency generation based on light (output light b), and the laser 1 includes at least Pr as a laser medium in a core And a semiconductor laser that generates excitation light having a wavelength of 400 nm or more and 480 nm or less as an excitation light source, and a ferroelectric fluoride crystal is used for the conversion unit 1, whereby ultraviolet light (output light c) having a wavelength of 250 nm or less is used. Is an ultraviolet laser device characterized by continuously outputting.

The 400 nm-band blue semiconductor laser as the excitation light source has been developed mainly for GaN-based semiconductor lasers such as for blue DVD heads and blue laser projections, and can be obtained by appropriately selecting the wavelength and output. When a TO-CAN-shaped semiconductor laser or laser chip is used as the excitation light source, the shape of the emitted beam from the semiconductor laser is elliptical and the divergence angle varies depending on the direction. Therefore, the prism or anamorphic lens is used upstream of the optical coupling system. It is preferable to perform beam shaping. The optimum wavelength and optimum power of the excitation laser of the laser 1 cannot be determined uniquely because it varies depending on the Pr ion concentration and the resonator configuration. However, the absorption cross section of Pr ions, the concentration limit that does not quench the concentration, and are readily available Considering the excitation laser wavelength, the range of 100 mW to 10 W is most suitable in the wavelength range of 420 to 470 nm. In the case of excitation in this wavelength band, levels having a higher energy level (such as ³ P ₂ , ¹ I ₆ , ³ P ₁ , ³ P ₀ ) than the emission upper level of Pr are directly excited. Compared with the up-conversion laser, the excitation efficiency is high, and high emission intensity can be obtained.

Laser 1 needs to oscillate directly in the visible light region. As such a material, fluoride glass is suitable. As a kind of fluoride glass, Zr glass, Al glass, In glass, Ga glass, or the like can be used. By using a Pr-doped fluoride optical waveguide obtained by adding Pr to the fluoride glass as the core of the laser medium of the laser 1, visible light laser oscillation can be performed with high efficiency. If fluoride glass is used for the core portion, the cladding portion may be fluoride glass, or a material other than fluoride glass may be used. For example, an optical waveguide in which the core part is Pr-added Al-based fluoride glass and the clad part is made of different glass such as fluorophosphate glass, or the core part is Pr-added Zr-based fluoride glass and the cladding part is acrylic. A resin clad optical waveguide which is a resin of the system can be used.

As the Pr-doped optical waveguide, an optical waveguide having a Pr-doped concentration and a waveguide parameter according to the purpose is prepared. If the Pr concentration is too high, the concentration is quenched, so a concentration of 2 × 10 ²⁰ particles / cm ³ or less is preferable. For high-efficiency operation, the concentration should be adjusted to 1 × 10 ²⁰ particles / cm ³ or less. Is more preferable. On the other hand, if the Pr concentration is less than 1 × 10 ¹⁷ atoms / cm ³ , the length necessary for absorption of the excitation light becomes long, which is not preferable. In order to reduce the required optical waveguide length to about 10 m or less, it is more preferable to set the Pr concentration to 1 × 10 ¹⁸ pieces / cm ³ or more.

As the structure of the optical waveguide, the refractive index distribution in the cross section may be a stepped refractive index distribution, or a distributed refractive index type optical waveguide in which the refractive index changes gently. A so-called double clad structure having a plurality of clad layers may also be used. In the case of a double clad structure, the cross-sectional shape of the clad (first clad) adjacent to the core is preferably non-circular. As the cross-sectional shape of the first clad, for example, a D shape, a rectangle, a star shape, a petal shape, and the like are known. The excitation light is first coupled to the first clad, and gradually propagates through the first clad and gradually enters the core. Combined. As the Pr-doped optical waveguide, a Pr-doped fiber is preferable in terms of optical coupling and manufacturing efficiency.

As an optical coupling method of the excitation light to the Pr-doped optical waveguide, the light is condensed and coupled to the end of the optical waveguide with a lens, or when the Pr-doped optical waveguide is a Pr-doped optical fiber, it is coupled through the fiber. it can. When the excitation light source is equipped with a fiber pigtail, a fiber-type optical coupler or multiplexer / demultiplexer whose wavelength is dependent on the transmission characteristics can be used for the excitation light coupling, which is particularly preferable because the excitation light coupling loss can be reduced. .

At this time, it is preferable to use a non-Pr-doped optical waveguide or a non-Pr-doped glass block (hereinafter referred to as a non-Pr-doped portion) having a high photodestructive threshold at the condensing end for condensing at least the high-power excitation laser. These non-Pr-added portions can be attached only to the excitation light incident end or can be attached to both ends, but it is particularly preferable to attach to both ends from the viewpoint of preventing end face destruction. The non-Pr-added portion to be attached is preferably a silica-based optical waveguide, a silica-based optical fiber, a silica-based glass block, a dielectric multilayer film using a silica-based glass substrate, a dielectric multilayer film using a quartz-based crystallized glass substrate, or the like. . Among the silica fibers, it is particularly preferable to use a silica fiber having a pure silica core in which Ge is not added to the core. These non-Pr doped portions and the Pr doped optical waveguide as a gain medium are preferably connected by a connection method that does not use an adhesive. When the Pr-doped optical waveguide is a Pr-doped fiber and the aforementioned non-Pr-doped portion is a quartz fiber, it is particularly preferable that the connection method between the two is fusion splicing. The Pr-doped fiber thus connected to the quartz fiber is particularly preferably used by being sealed in a moisture and weather resistant package such as a metal package (hereinafter referred to as “Pr fiber module”).

The resonator configuration of the laser 1 may be any type, such as a Fabry-Perot resonator, a ring resonator, a multistage cascade connection, a parallel connection using a multiplexing / demultiplexing coupler, and an amplifier connection type, as long as the laser can be oscillated. The laser 1 needs to have a wavelength adjusting function for adjusting the laser wavelength inside or outside the resonator so that an output can be obtained in a desired laser wavelength tuning range. Wavelength adjustment function includes diffraction grating angle adjustment, folding mirror angle adjustment, etalon adjustment, sub-resonator adjustment, injection laser wavelength adjustment, laser loss adjustment by resonator loss adjustment, fiber grating temperature adjustment, Laser oscillation wavelength adjustment by tension adjustment is known, and any method capable of changing the wavelength may be used.

In addition, the oscillation wavelength of an ArF laser that is particularly important for use as an excimer laser is around 193.3 nm, and a CW laser tuned to this wavelength is particularly important in practice, and has a wavelength tunable characteristic in this wavelength region. If obtained, it can be used for optical component inspection and stepper performance tests, which is very important. When the oscillation wavelength of the laser 1 is 700 nm to 715 nm and the oscillation wavelength of the laser 2 is a fixed wavelength in the range of more than 250 nm to 300 nm, the ultraviolet light output is selected from a wavelength range of 184.2 nm to 211.3 nm. Ultraviolet light can be obtained. This configuration has an advantage that the output can be increased because the fundamental wavelength output of the wavelength tunable laser is used as it is.

The laser 2 is a solid-state laser having a laser wavelength in the range of more than 250 nm and not more than 300 nm. The laser 2 can be a direct fourth harmonic of a semiconductor laser or a fourth harmonic of a solid-state laser. For example, a high-power laser having a wavelength of about 266 nm or about 257 nm is commercially available at a relatively low price due to the fourth harmonic of an Nd: YAG laser or a Yb: fiber laser, which is preferable. When the fourth harmonic of an Nd: YAG laser having a wavelength of 266 nm is used for the laser 2, by adjusting the wavelength of the laser 1 to 707.3 nm ± 0.5 nm, an ultraviolet light output in the 193.3 nm band can be obtained by the sum frequency. can get.

Further, the laser 1 has a laser oscillation wavelength in the range of 598 nm or more and 715 nm or less, a laser having a wavelength in the range of 400 nm or more and 550 nm or less is used as the laser 2, and the output light is further transmitted between the laser 1 and the conversion unit 1. In the case where the wavelength conversion unit (conversion unit 2) that converts the wavelength of a1 is provided and ultraviolet light is generated by sum frequency generation based on the output light (output light a2) whose wavelength is converted and the output light b, the output light a2 A laser having a wavelength of 299 nm or more and 357.5 nm or less is obtained. When the output light a2 and the output light b from the laser 2 are sum-frequency generated in the converter 1, ultraviolet light having a wavelength in the range of 171.1 nm to 216.7 nm can be obtained.

The oscillation wavelength of the laser 1 is particularly preferably in the wavelength range of 598 to 645 nm and 700 to 715 nm because laser oscillation is easy. High power operation is possible in these wavelength ranges, and it is suitable for improving the ultraviolet output. When the laser 1 in this range is used, in combination with the laser 2, an ultraviolet light wavelength range of 171.1 nm or more and 203.3 nm or less and an ultraviolet wavelength range selected from two ranges of wavelengths of 186.7 nm or more and 216.7 nm or less. Light can be obtained.

Laser 2 is a solid-state laser having a laser wavelength in the range of oscillation wavelength of 400 nm or more and 550 nm or less. The laser 2 can be a direct second harmonic of a semiconductor laser or a second harmonic of a solid-state laser. For example, lasers such as 407.5, 480, and 488 nm are commercially available with second harmonics of high-power semiconductor lasers such as 915, 960, and 976 nm. Also, lasers of 532 nm and 515 nm can be obtained by the second harmonic of Nd: YAG laser and Yb: fiber laser, and high power and relatively inexpensive lasers are commercially available. Use these lasers. Is preferred. Alternatively, when the second harmonic of an Nd: YAG laser with a wavelength of 532 nm is used for the laser 2, the wavelength of the laser 1 is adjusted to 607.2 nm ± 0.5 nm, thereby outputting an ultraviolet light with a wavelength of 193.3 nm. Can be obtained. Alternatively, when the second harmonic of a semiconductor laser having a wavelength of 488 nm is used for the laser 2, an ultraviolet light output of a wavelength of 193.3 nm band is obtained by adjusting the wavelength of the laser 1 to 640.2 nm ± 0.5 nm. be able to.

In addition to this, a laser of a laser power amplifier (MOPA) type using a combination of a low-power and high-quality seed light and an amplifier can be used for the laser 2. For the low-power seed, a laser having excellent mode controllability such as a Yb-doped YVO4 microchip laser or a DFB semiconductor laser is used, and a rare-earth doped fiber such as a Yb-doped fiber or a Yb-doped crystal or a rare earth doped By using a crystal, it is possible to obtain a laser beam having a single mode and a high light collecting property even at a high output. It is desirable to insert non-reciprocal means such as an optical isolator between the low-power seed light and the amplifying unit so that strong light amplified by the seed light generating unit does not return.

The conversion unit 2 may be any nonlinear optical crystal that generates a second harmonic with respect to a fundamental wavelength of 598 nm or more and 715 nm or less and can output in a wavelength range of 299 nm or more and 357.5 nm or less. . As such crystals, many crystals such as LiNbO ₃ (LN), LiTaO ₃ (LT), and β-BaB ₂ O ₄ (β-BBO) are known. These crystals may be used as a bulk shape with a specific orientation, or may be processed into a polarization inversion element capable of quasi phase matching (QPM). In addition, waveguide-type elements are also commercially available as QPM elements, and are particularly preferable for applications where importance is placed on efficiency. Since the laser 1 is a fiber output, the conversion unit 2 is particularly preferably a fiber device connected by a fiber pigtail. Since the conversion wavelength of the conversion unit 2 changes according to the wavelength adjustment of the laser 1, it is preferable to follow the laser 1 by changing the crystal angle, the crystal temperature, and the like. It is particularly preferable that the adjustment function is linked.

Further, in the present invention, the composition in which the ferroelectric fluoride crystal of the converter 1 is represented by XMgF ₄ , XZnF ₄ , XAlF ₅ , Na ₂ MgAlF ₇ , or Na ₂ ZnAlF ₇ (where X is Ca, Sr, 1 represents an element selected from any one of Ba.), An ultraviolet laser device.

The converter 1 generates a sum frequency based on the output light (output light a2) from the converter 2 or the output light (output light a1) of the laser 1 and the purple to green output light (output light b) of the laser 2. A ferroelectric fluoride optical crystal that can output ultraviolet light having a wavelength of 171.3 nm to 216.7 nm and has high transparency in the ultraviolet region is suitable. The oxide crystal has a large loss at a wavelength of 300 nm or less and is opaque at a wavelength of 200 nm or less, and thus is easily damaged by high-power ultraviolet light. In contrast, fluoride crystals are highly transparent even at 200 nm or less and are not easily damaged by light. As is well known, since a second-order nonlinear optical effect can be obtained if the crystal has no central symmetry, there is no central symmetry, and a fluorine compound that can ensure the necessary transparency in the required wavelength range. Any crystal can be used. As the crystal composition, the absorption in the ultraviolet wavelength region is an electron transition, so that the absorption is specific to the element or ion. For this reason, compounds containing some elements of transition metals and lanthanides are not suitable. Specifically, fluorine compound crystals containing Fe, Ni, Co, Cu, Cr, Mn, Ce, Pr, Nd, Er, Tm, etc. are not suitable. On the other hand, fluorine compounds such as Rb, Cs, Sr, Ba, Zn, Pb, Ga, Zr, Hf, Nb, Ta, Y, La, Gd, and Lu are highly transparent and have a high electron density even in the ultraviolet wavelength region. Therefore, the non-linear optical characteristics of the fluorine compound crystal containing these improve.

An example of a suitable fluorine compound crystal for the converter 1 is ABF ₄ (A: at least one element selected from A, Ca, Sr, Ba, B: Mg, Zn, Sn belonging to the crystal point group “mm2” _−. At least one element selected) and C ₂ BDF ₇ (C: at least one element selected from Na, K, Rb, Cs, B: the same as above, D: at least one element selected from Al, Ga) ADF ₅ whose crystal point group belongs to “4” (both A and D are described above), CLnF ₄ whose crystal point group belongs to “32” (C is the above, Ln is selected from Y, La, Gd, Lu) One kind of element).

Among them, a series of compositions represented by XMgF _4, XZnF ₄ or XAlF ₅ (where X is at least one element selected from Ca, Sr, Ba), Na ₂ MgAlF ₇ or Na ₂ ZnAlF _7, etc. Manufacture is relatively easy and practical. As the fluorine compound crystal, BaMgF4, BaZnF4, and SrAlF5 having a relatively high refractive index and high transparency up to the ultraviolet wavelength region are particularly suitable. In particular, BaMgF4 can be processed by a QPM element and is suitable for high-efficiency conversion. Further, Na ₂ MgAlF ₇ and Na ₂ ZnAlF ₇ can form a waveguide relatively easily in addition to QPM processing, and are suitable for wavelength conversion using optical confinement.

Further, since the wavelength of the output light a1 is variable, the ultraviolet laser device of the present invention can output by adjusting the crystal orientation of the converter 1 and the crystal orientation of the converter 2 when the converter 2 is present. The wavelength of the light c can be adjusted in the range of 171.3 nm to 216.7 nm.

Next, an optimal configuration example of the laser 1 in which the resonator is a ring resonator and a Pr-doped fluoride fiber is used as a laser medium will be described with reference to FIG. Although this example shows a case where the wavelength is changed from 620 to 640 nm, the same configuration is preferable as the configuration, except that the optical characteristics of the components used are different in other wavelength bands.

As the laser medium, a single mode Pr-doped fluoride fiber 1 having a core of ZBLAN fluoride glass containing 3000 ppm by mass of Pr was used. The core diameter of the fiber is 3.4 μm, the numerical aperture is 0.13, the cutoff wavelength is 570 nm, and the fiber length is 25 cm. Silica fibers (quartz fiber 3 and quartz fiber 4) having similar fiber parameters are fused and connected to both ends of the fiber, and sealed in a weatherproof package 2 made of stainless steel to form a fiber module (module 1). . From the module 1, the quartz fiber 3 and the quartz fiber 4 are projected. Since fiber parameters such as Pr concentration, fiber length, and core diameter vary depending on pumping laser characteristics, target laser oscillation wavelength, optical characteristics of optical components such as resonators, etc., this example is always optimal. Is not limited.

As an excitation light source, a product in which the output light of the semiconductor laser 5 having a wavelength of 440 nm was coupled to a quartz fiber having a core diameter of 2.2 μm, a numerical aperture of 0.13, and a cutoff wavelength of 375 nm was prepared. The fiber end output of this excitation light source is a maximum of 150 mW.

As the multiplexing / demultiplexing element 11 for introducing the excitation light into the module 1, a melt-stretching coupler can be used. For example, a melt-drawn coupler has a signal light introduction port (quartz fiber 6) in the 635 nm band and an excitation light introduction port (quartz fiber 8) having a wavelength of 440 nm, and the other side is combined with the excitation light and the signal light to be emitted. It consists of a port (quartz fiber 7) and a blank port (quartz fiber 9) with almost no light output. Regarding the propagation loss of light of the melt-drawn coupler, for example, the propagation loss from the pumping light introduction port having a wavelength of 440 nm to the common port is 1.2 dB, and the propagation loss from the signal light introduction port in the 635 nm band to the common port is 1.3 dB. It is. The excitation light source quartz fiber is fused and connected to the excitation light introduction port (quartz fiber 8) of the multiplexing / demultiplexing element 11. The quartz fiber 3 coming out of the fiber module is fusion-connected to the common port (quartz fiber 7). The tip of the blank port (quartz fiber 9) is cut obliquely at an angle of 8 ° so that Fresnel reflection with air does not return, and silicone with an adhesive having a refractive index of 1.45, which is substantially the same as the core refractive index of the fiber 3. It is fixed in the tube (beam damper 10).

A part of the excitation light is absorbed in the Pr-doped fluoride fiber 1 and emits fluorescence. The generated fluorescence is amplified while propagating through the Pr-doped fluoride fiber 1 and is emitted from the quartz fiber 4 side as enhanced light. This radiation finally oscillates by passing through the ring-shaped resonator. On the other hand, the fluorescence is also emitted from the quartz fiber 3 in the reverse direction, which will be described later.

A decoupler (multiplexing / demultiplexing element 11 ') having the same configuration as that of the multiplexing / demultiplexing element 11 is prepared, and the common port (quartz fiber 7') and the silica fiber 4 of the fiber module are fusion-connected. The light in the 620 nm to 640 nm band which is the laser oscillation wavelength is directed to the signal light port (quartz fiber 6 '), and the excitation light having a wavelength of 440 nm is separated into the drop port (quartz fiber 8'). The tip of the drop port is cleaved at an angle of 8 ° and is fixed in the silicone tube with an adhesive having a refractive index of 1.45, which is almost the same as the core refractive index of the fiber 3 (beam damper 10 ″). The tip of the blank port (quartz fiber 9 ') is similarly cleaved and fixed in the silicone tube with the same adhesive (beam damper 10').

The signal light port (quartz fiber 6 ′) of the decoupler (multiplexing / demultiplexing element 11 ′) is fused and connected to a fiber-type polarization controller (polarization controller 12) made of fiber to adjust the polarization state. The polarization controller 12 is also used for adjusting the output coupling ratio, as will be described later.
The input / output end 13 of the polarization controller 12 was fixed to a zirconia ferrule and polished flat, and a non-reflective coating of a dielectric multilayer film was applied. The reflectance of the input / output end 13 at a wavelength of 620 to 640 nm is 0.5% or less.

The radiation from the input / output end 13 is collimated by the collimating lens 14 and polarized by the polarization beam splitter 15. One separated output light 23 is taken out as output light of the laser 1. The ratio of the output light 23 to the optical power in the resonator can be adjusted depending on the polarization state, and is used for fine adjustment of the output by controlling the polarization controller 12 to change the output ratio.

The light transmitted through the polarization beam splitter 15 is rotated by 45 ° by the Faraday rotator 16. The polarization-rotated light is introduced into the dispersion prism 17 at a Brewster angle and dispersed with low loss. The dispersion prism 17 converts the wavelength difference into the angle difference. The dispersed light is folded back by the wavelength selection broadband mirror 18. The reflectance of the broadband mirror 18 at a wavelength of 620 to 640 nm is 99% or more, and the angle dependency of the reflectance at an incident angle of 0 ° ± 10 ° is 0.5% or less. When the broadband mirror 18 is rotated, the loss increases except for the light in the direction in which the resonator can be configured. Therefore, by combining with the function of the dispersion prism 17, it operates as a wavelength selection element.

The light reflected by the broadband mirror 18 passes through the dispersion prism 17 again, passes through the Faraday rotator 16, and rotates by 45 °. Further, the light bent by the polarization beam splitter 15 passes through the optical isolator 19 for visible light, and is collected by the condenser lens 20 onto the incident / exit end 21 of the quartz fiber 6. Although the reflection mirror 22 is illustrated as an example of the bending optical system in FIG. 1, it is not always necessary. The entrance / exit end 21 is polished and coated with non-reflective coating similarly to the entrance / exit end 13. Only light of a specific incident angle that is favorably collected at the input / output end 21, that is, light of a specific wavelength selected by the dispersion prism 17 and the broadband mirror 18 within the specific angle is coupled to the core of the fiber. A selection is made.

The light of a specific wavelength coupled to the input / output end 21 returns to the Pr-doped fluoride fiber 1 through the coupler (multiplexing / demultiplexing element 11) and is amplified. When the amplification factor exceeds the total loss of the optical system, laser oscillation is started, and output light 23 is extracted as output light of the laser 1 having a predetermined wavelength.

Here, the fluorescence from the quartz fiber 3 side of the fiber module will be described. The fluorescence from the quartz fiber 3 is transmitted to the signal light port (quartz fiber 6) of the coupler (multiplexing / demultiplexing element 11) and radiated in the reverse direction from the incident / exit end 21. The emitted light is collimated by the condenser lens 20, blocked or angularly deflected by the optical isolator 19 for visible light, and excluded from the resonator system.

The Faraday rotator 16 and the optical isolator 19 are transparent to visible light and require nonreciprocal operation. For this reason, lead flint glass has been known as a material for a long time, but recently, rare earth-doped glass such as high-concentration Tb-doped glass, Tb ₃ Ga ₅ O ₁₂ (TGG) crystal has been used. Wavelength variable characteristics are realized.

The polarization controller 12, the Faraday rotator 16, and the optical isolator 19 measure in advance the wavelength, the magnetic field applied to the Faraday rotator and the visible light isolator, the target output, and the optimum state of the polarization controller, and store them in the memory. And is automatically driven by the program. All optical systems are controlled at a constant temperature in a temperature-controlled heat bath. All fibers and parts are fixed in a case with a seismic isolation function.

FIG. 2 shows an optimum configuration example of a laser 1 in which the resonator is a Fabry-Perot resonator, Pr 1 -added fluoride glass is used as a gain medium, and a conversion unit 2 is installed in the resonator. explain.

As the laser medium, a single-mode Pr-doped fluoride fiber 34 having an Al-based fluoride glass containing 3000 ppm by weight of Pr as a core is used. The core diameter of the Pr-doped fluoride fiber 34 is 2.4 μm, the numerical aperture is 0.16, the cutoff wavelength is 500 nm, and the fiber length is 40 cm. Quartz fibers (quartz fiber 35, quartz fiber 35 ') having similar fiber parameters were fused and connected to both ends of this fiber, and sealed in a weatherproof package 36 made of stainless steel. The tip (input / output end 37) of the quartz fiber 35 is polished to a flat surface, and an AR coating that is non-reflective in the excitation light wavelength and the laser oscillation wavelength band is applied to introduce the excitation light. The end face (input / output end 39) of the quartz fiber 35 'is polished into a flat surface, and AR coating is applied which is non-reflective in the laser oscillation wavelength band.

The excitation GaN-based semiconductor laser (semiconductor laser 31) has an oscillation wavelength of 450 nm, and is fixed to a heat radiating stand held at a constant temperature by a Peltier element. The excitation light emitted from the semiconductor laser 31 is shaped into a perfect circle by the anamorphic prism pair 32, and then passes through the condensing lens 33 and the concave dichroic reflector (the dichroic concave mirror 38 for laser resonators) to the end of the quartz fiber ( The light is condensed at the input / output end 37) and coupled to the core of the quartz fiber 35. The concave dichroic reflector (laser resonator dichroic concave mirror 38) has a characteristic of transmitting excitation light and totally reflecting the laser oscillation wavelength of the laser 1, and constitutes one end of the resonator. The concave dichroic reflecting mirror is a spherical mirror, and is adjusted to a position where the laser beam of the laser 1 emitted from the input / output end 37 is reflected and turned back to the core of the input / output end 37.

The coupled excitation light is absorbed by the Pr-doped fluoride fiber 34 and emits fluorescence. The generated fluorescence is amplified while propagating through the Pr-added fluoride fiber 34 and is emitted from the input / output end 39 as enhanced light. On the other hand, the fluorescent light traveling in the reverse direction is radiated from the input / output end 37, folded back by the concave dichroic reflecting mirror (laser resonator dichroic concave mirror 38), amplified again when passing through the Pr-doped fluoride fiber 34, and input / output end 39. Radiated from. Fluorescence emitted from the input / output end 39 is collimated by the collimating lens 40 and decomposed into orthogonal polarization components by the polarization beam splitter 41. One polarized light (polarization power component 43) is incident on the dispersion prism 45 at an angle near the minimum deflection angle, and only the fluorescence in the direction of a specific dispersion angle is folded by the wavelength selection mirror (broadband mirror 46). The light that has been selected and turned back is condensed at the input / output end 39 through the polarization beam splitter 41 and the collimating lens 40, and the resonator is completed.

On the other hand, the component (polarization power component 42) orthogonal to the polarization component (polarization power component 43) passes through the condensing lens 47 and the dichroic concave mirror 51, and is the core of the waveguide-type periodically poled LN crystal (PPLN) (nonlinear crystal 48). The light is condensed and wavelength-converted. PPLN (nonlinear crystal 48) is mounted on a temperature adjustment bench with a Peltier element attached so that the optimum conversion wavelength can be tracked when the wavelength of laser 1 (fundamental wave) is changed. The wavelength-converted light is output as output light a2 through the dichroic concave mirror 50 (laser output light 49). The dichroic concave mirror 50 transmits the output light (output light a2) wavelength-converted by PPLN (nonlinear crystal 48), and totally reflects the wavelength of the laser 1.

On the contrary, the dichroic concave mirror 51 totally reflects the wavelength-converted output (output light a2) and transmits the wavelength of the laser 1. The wavelength of the laser 1 reflected by the dichroic concave mirror 50 passes through the PPLN (nonlinear crystal 48) again, passes through the condenser lens 47, the polarization beam splitter 41, and the collimator lens 40, and is condensed at the input / output end 39. It constitutes a part of the resonator of the laser 1. The output light a2 reflected by the dichroic concave mirror 51 passes through the PPLN element, passes through the dichroic concave mirror 50, and is output (laser output light 49). In this configuration, there are a resonator formed by two dichroic concave mirrors (a dichroic concave mirror 38 for laser resonators and a dichroic concave mirror 50), and a resonator composed of a dichroic concave mirror (dichroic concave mirror 38 for laser resonators) and a wavelength selection mirror 46. The polarization state must be controlled by the polarization controller 44 so that the latter is dominant.

In this configuration, since the remaining fundamental wave that has not been used for wavelength conversion can be collected in the resonator, it is possible to increase the apparent wavelength conversion efficiency. In addition, since no isolator is required, there are few members having large wavelength dependence, and it is suitable for broadband wavelength tuning. In order to provide a broadband wavelength variable characteristic exceeding 5 nm, it is better not to use a waveguide type PPLN for the wavelength conversion crystal, but to adjust the crystal orientation by using a bulk shape or a flat plate QPM element.

Hereinafter, the present invention will be described in detail by the following specific examples. However, the present invention is not limited to these examples.

The overall configuration is shown in FIG. As the laser 64 (laser 1), a laser having a configuration based on the configuration example shown in FIG. 1 is used. However, in the ring laser of FIG. 1, a fiber-coupled wavelength variable shortcut wavelength selection filter is further provided between the input / output end 21 and the signal light port (quartz fiber 6) of the multiplexing / demultiplexing element 11, and the wavelength variable shortcut filter. And a wavelength variable long cut wavelength selection filter is inserted between the signal light port (quartz fiber 6) of the multiplexer / demultiplexer 11 to limit the pass wavelength band of the ring resonator, and the transmission center wavelength is the wavelength selection mirror ( It is tuned to the selected wavelength of the broadband mirror 18).

The laser medium used (Pr-doped fluoride fiber 1) has a glass composition of 32.8AlF ₃ -15YF ₃ -4.7LaF ₃ -9.4MgF ₂ -7.4CaF ₂ -5.4SrF ₂ -20BaF. represented by ₂ -5BaCl ₂ -0.3PrF _3, the cladding is represented by _{32.8AlF 3 -15YF 3 -5LaF 3 -9.4MgF 2} -8.4CaF 2 -7.4SrF 2 -17BaF 2 -5BaCl 2 Al-based fluoride fiber is used. The core diameter is 4 μm and the fiber diameter is 125 μm. The numerical aperture of this fiber was 0.1. The fiber length is 10 cm. Both end surfaces were polished at an angle of 8 °, and a broadband non-reflective coating in the visible light range was applied. The reflectance is 2% or less over the entire visible light wavelength range.

This output light (output light a 1) was focused by the condenser lens 52 and input to the LiNbO ₃ nonlinear optical crystal 53. The wavelength-converted light and the fundamental wave are emitted from the opposite side of the LN crystal. The output from the LiNbO ₃ nonlinear optical crystal 53 is collimated by the collimating lens 54 and irradiated to the dichroic mirror 55. The dichroic mirror 55 reflects the fundamental wave in the 600 nm band and transmits the double wave (output light a2) in the 300 nm band.

As the laser 56 (laser 2), an Nd: YAG laser double wave (output light b) having a wavelength of 532 nm is used. The magnification of the output light of the laser 2 was adjusted by the concave lens 57 and the convex lens 58 in order to match the laser beam diameter of the laser 1. After controlling the beam diameter, the light is reflected by a 90-degree folding mirror (right angle mirror 59), is further bent and reflected by 90 degrees on the dichroic mirror 55, and is combined with the output light of the laser 1.

The synthesized laser light is incident on the BaMgF ₄ pseudo phase matching element 61 (QPMC) by the achromatic condenser lens 60. By the achromatic condenser lens 60, the output light a2 and the output light b having different wavelengths are condensed on the BaMgF ₄ pseudo phase matching element 61 at the same focal length, and the sum frequency conversion efficiency can be kept at the maximum. In the BaMgF ₄ pseudo phase matching element 61, the sum frequency of the output light of the laser 1 and the laser 2 is generated. The ultraviolet light emitted from the QPMC is collimated by the collimating lens 62, the dichroic mirror 63 cuts the second harmonic wave of the laser 1 and the output of the laser 2, and only the ultraviolet light (output light c) passes and is output. .

FIG. 4 shows the relationship between the ultraviolet light output wavelength and the laser 1 output wavelength when the wavelength of the laser 1 is changed from 602 nm to 612 nm and from 630 nm to 638 nm. It can be seen that the ultraviolet light output changes linearly according to the wavelength of the laser 1. An example of the output spectrum obtained by measuring the ultraviolet light output with a spectroscope and a photomultiplier for ultraviolet light is shown in FIG. The resolution is 0.02 nm. As can be seen from FIG. 5, the full width at half maximum of the laser oscillation line is about 0.05 nm, indicating that it is a narrow band. The state of continuous output of ultraviolet light is shown in FIG. 6 as the change with time of the relative intensity of the ultraviolet light output. It can be seen that a continuous stable output is obtained. When the total input power including the cooling system was 500 W in total, the ultraviolet light output was 100 mW, which was a practical efficiency.

7 is the same as in the first embodiment, but in the configuration of FIG. 7, a laser having a configuration based on the configuration example of FIG. However, in order to prevent laser oscillation at multiple wavelengths, in FIG. 2, a Fabry-Perot wavelength tunable filter with a fiber is provided between the polarization controller 44 and the input / output end 39, and the Fabry-Perot wavelength tunable filter is further input / output. A narrow band tunable filter with a fiber is attached between the ends 39. The tuning range of these filters is 580 nm to 680 nm, the finesse of the Fabry-Perot tunable filter is 2000, and the band interval of the narrow-band tunable filter is 200 GHz.

Further, as a gain medium (Pr-added fluoride fiber 34) of the laser 65 to be used, the glass composition of the core portion is 53ZrF ₄ -18.5BaF ₂ -2.7LaF ₃ -4YF ₃ -3AlF ₃ -18.5NaF-0. A fluoride fiber made of Zr-based fluoride glass (3000 ppm) represented by 3PrF ₃ and having a clad of 26ZrF ₄ -24HfF ₄ -21BaF ₂ -3LaF ₃ -2YF ₃ -4AlF ₃ -20NaF is used. The core diameter is 3 μm and the fiber diameter is 125 μm. The numerical aperture of this fiber was 0.16. The fiber length is 25 cm.

Pigtail quartz fibers (quartz fiber 35, quartz fiber 35 ') were selected by fusion splicing with fibers having the same core diameter and numerical aperture. Both end faces (input / output end 37, input / output end 39) of these quartz fibers were obliquely polished by 8 °, and a broadband non-reflective coating in the visible light region was applied. The reflectance is 2% or less over the entire visible light wavelength range. The fundamental wave in the 600 nm band is confined in the resonator, converted to the 300 nm band by the bulk LN nonlinear crystal (nonlinear crystal 48) of the converter 2 installed in the resonator, and output from the output mirror (dichroic concave mirror 50). Radiated as light a2 (laser output 49). The LN crystal is controlled so that the crystal orientation is automatically adjusted in conjunction with the wavelength variable mirror (broadband mirror 46), and the power of the output light a2 is maximized.

The output light (output light a2) of the laser having a wavelength of 300 nm (laser 65) passes through the dichroic mirror 66 and is combined with the output light (output light b) of the laser 67 (laser 2) whose mode diameter is adjusted. The As the laser 2, a second harmonic wave of a high-power semiconductor laser having a wavelength of 980 nm was used. The laser wavelength is 490 nm and the output is 600 mW. The output of the laser 2 (laser 67) is adjusted by the concave lens 68 and the convex lens 69 so as to coincide with the mode diameter of the 300 nm band laser (laser 65), folded back by the right angle mirror 70, and 300 nm band laser (laser) by the dichroic mirror 66. 65). The dichroic mirror 66 is coated with a non-reflective broadband in the 300 nm band and a total reflection in the 450 to 500 nm band.

The combined laser light passes through the dichroic mirror 71 and is focused and incident on the QPM-SrAlF ₅ crystal (fluorine compound crystal 73) by the achromatic condenser lens 72. The QPM-SrAlF ₅ crystal (fluorine compound crystal 73) is attached to a temperature control bench capable of controlling the crystal temperature, and the optimum conversion wavelength is controlled by temperature control. The dichroic mirror 71 is coated with no reflection in the 300 nm to 500 nm band and total reflection in the 190 nm band. The ultraviolet light generated by the sum frequency in the QPM-SrAlF ₅ crystal (fluorine compound crystal 73) and the original output light a2 and output light b are collimated by the achromatic collimating lens 74 and enter the dichroic mirror 75. The ultraviolet light output passes through the dichroic mirror 75 and is extracted as a laser output.

On the other hand, the output light a2 and the output light b, which are the sources of the sum frequency, are reflected and condensed again in the QPM-SrAlF ₅ crystal (fluorine compound crystal 73) by the achromatic collimating lens 74 and reused for generating the sum frequency. Is done. The ultraviolet light generated at this time is collimated by the achromatic condenser lens 72, reflected by the dichroic mirror 71, achromatic condenser lens 72, a QPM-SrAlF ₅ crystal (fluorine compound crystal 73), an achromatic collimator lens 74, The light is output through the dichroic mirror 75.

When the oscillation wavelength of the laser 1 was adjusted to 638.5 nm, the wavelength of the output ultraviolet light (output light c) was 193.3 nm. When the output of laser 1 (laser 65) was 500 W and the output of laser 2 (laser 67) was 600 mW, the output of ultraviolet light (output light c) was 40 mW at the maximum.

The overall structure is shown in FIG. As the laser 65, a laser having a configuration based on the configuration example shown in FIG. 1 is used. However, the laser 65 includes a fiber-coupled wavelength variable shortcut wavelength selection filter between the input / output end 21 and the signal light port (quartz fiber 6) of FIG. A wavelength variable long cut wavelength selection filter is inserted between the signal light ports (quartz fiber 6) of the multiplexing / demultiplexing element 11 to limit the pass wavelength band of the ring resonator, and the transmission center wavelength is the wavelength selection mirror ( It is tuned to a wavelength range of 700 nm to 715 nm, which is a selected wavelength of the broadband mirror 18).

The gain medium (Pr-doped fluoride fiber 1) used has a glass composition of 32.8AlF ₃ -15YF ₃ -4.7LaF ₃ -9.4MgF ₂ -7.4CaF ₂ -5.4SrF ₂ -20BaF. represented by ₂ -5BaCl ₂ -0.3PrF _3, the cladding is represented by _{32.8AlF 3 -15YF 3 -5LaF 3 -9.4MgF 2} -8.4CaF 2 -7.4SrF 2 -17BaF 2 -5BaCl 2 Al-based fluoride fiber is used. The core diameter is 4 μm and the fiber diameter is 125 μm. The numerical aperture of this fiber was 0.1. The fiber length is 20 cm. Both end surfaces were polished at an angle of 8 °, and a broadband non-reflective coating in the visible light range was applied. The reflectance is 2% or less over the entire visible light wavelength range.

The output light (output light a1) of the laser 1 (laser 65) passes through the dichroic mirror 66 and is combined with the output light (output light b) of the laser 2 (laser 67) whose mode diameter is adjusted. As the laser 2 (laser 67), a fourth harmonic wave of a high output Nd: YAG laser having a wavelength of 1064 nm was used. The laser wavelength is 266 nm and the output is 400 mW. The output of the laser 2 (laser 67) is adjusted by the concave lens 68 and the convex lens 69 so as to coincide with the mode diameter of the laser 1 (laser 65), folded back by the right angle mirror 70, and laser 1 (laser 65) by the dichroic mirror 66. Is combined with the output of. The dichroic mirror 66 is coated with a broadband non-reflection in the 700 to 715 nm band and total reflection in the 266 nm band.

The combined laser light passes through the dichroic mirror 71 and is focused and incident on the QPM-BaMgF ₄ crystal (fluorine compound crystal 73) by the achromatic condenser lens 72. The QPM-BaMgF ₄ crystal (fluorine compound crystal 73) is attached to a temperature control bench capable of controlling the crystal temperature, and the optimum conversion wavelength is controlled by temperature control. The dichroic mirror 71 is provided with a non-reflective broadband non-reflective in the 250 nm to 750 nm band and a total reflection ultraviolet reflective dichroic coating in the 190 nm band. The ultraviolet light generated by the sum frequency in the QPM-BaMgF ₄ crystal (fluorine compound crystal 73) and the original output light a1 and output light b are collimated by the collimator lens 74 and enter the dichroic mirror 75. The ultraviolet light output passes through the dichroic mirror 75 and is extracted as a laser output.

On the other hand, the output light a1 and the output light b, which are the sources of the sum frequency, are reflected and condensed again in the QPM-BaMgF ₄ crystal (fluorine compound crystal 73) by the collimating lens 74 and reused for generating the sum frequency. . The ultraviolet light generated at this time is collimated by the achromatic condenser lens 72, reflected by the dichroic mirror 71, and achromatic condenser lens 72, the QPM-BaMgF ₄ crystal (fluorine compound crystal 73), the collimator lens 74, and the dichroic mirror. 75 is output.

When the oscillation wavelength of laser 1 was adjusted to 707.3 nm, the output ultraviolet light (output light c) wavelength was 193.3 nm. When the output of laser 1 (laser 65) was 500 W and the output of laser 2 (laser 67) was 400 mW, the output of ultraviolet light (output light c) was 25 mW at the maximum.

The ultraviolet laser device of the present invention can be used for optical design, inspection, verification, assembly process, etc. of equipment using an existing excimer laser, and the measurement result is more accurate and simple than conventional non-laser inspection light sources. It can be expected to be obtained. Further, since the wavelength of the ultraviolet laser device of the present invention is variable, it can be used for inspection of wavelength response and dispersion of optical components in the ultraviolet region, selection of the optimum wavelength for a processing target, selective molecular reaction, and the like.

Furthermore, design, inspection and assembly of semiconductor manufacturing equipment, semiconductor manufacturing equipment and optical systems, surface shape measurement, interference measurement, processing and marking of metals, ceramics, glass, crystals, polymers, etc., decomposition and synthesis of organic compounds, selection It can also be applied to a wide range of fields such as chemical molecular cleavage, selective molecular bonding, application to pharmaceutical synthesis including chemicals and intermediates, and modification of specific molecules such as DNA.

DESCRIPTION OF SYMBOLS 1 Pr addition fluoride fiber 2,36 Weatherproof package 3,4 Quartz fiber 5 Semiconductor laser 6,7,8,9 Quartz fiber 10,10 ', 10''Beam damper 11,11' Multiplexing / demultiplexing element 12 Polarization controller DESCRIPTION OF SYMBOLS 13 Input / output end 14 Collimate lens 15 Polarization beam splitter 16 Faraday rotator 17 Dispersion prism 18 Broadband mirror 19 Optical isolator 20 Condensing lens 21 Input / output end 22 Polarization beam splitter 23 Output light (output light a1)
31 Laser Diode 32 Anamorphic Prism Pair 33 Condensing Lens 34 Pr- Doped Fluoride Fiber 35, 35 ′ Quartz Fiber 37, 39 Input / Output End 38 Dichroic Concave Mirror for Laser Resonator 40 Collimating Lens 41 Polarizing Beam Splitter 42, 43 Polarizing Power Component 44 Polarization controller 45 Dispersion prism 46 Broadband mirror 47 Condensing lens 48 Nonlinear crystal 49 Laser output power (output light a2)
50, 51 Dichroic concave mirror 52 Condensing lens 53 LiNbO ₃ nonlinear optical crystal 54 Collimating lens 55 Dichroic mirror 56 Laser (Laser 2)
57 Concave lens 58 Convex lens 59 Right angle mirror 60 Achromatic condenser lens 61 BaMgF ₄ quasi phase matching element (QPMC)
62 Collimating lens 63 Dichroic mirror 64 Laser (Laser 1)
65 Laser 66 Dichroic mirror 67 Laser (Laser 2)
68 Concave lens 69 Convex lens 70 Right angle mirror 71,75 Dichroic mirror 72 Achromatic condenser lens 73 Fluorine compound crystal 74 Achromatic collimating lens

Claims (4)

1. A visible laser oscillation unit (laser 1) having a variable wavelength, a laser (laser 2) that generates laser light having a constant wavelength, an output light (output light a1) of laser 1, and an output light (output light) of laser 2 In a laser apparatus including a wavelength converter (converter 1) that generates ultraviolet light by sum frequency generation based on b), the laser 1 includes an optical waveguide containing at least Pr as a laser medium in the core, and an excitation light source By providing a semiconductor laser that generates excitation light having a wavelength of 400 nm or more and 480 nm or less, and using a ferroelectric fluoride crystal for the conversion unit 1, ultraviolet light (output light c) having a wavelength of 250 nm or less is continuously output. An ultraviolet laser device.
2. The laser oscillation wavelength of the laser 1 is in a range of 700 nm or more and 715 nm or less, and a laser having a wavelength in the range of more than 250 nm and 300 nm or less is used as the laser 2. Ultraviolet laser device.
3. A laser oscillation wavelength of the laser 1 is in a range of 598 nm or more and 715 nm or less, a laser having a wavelength in a range of 400 nm or more and 550 nm or less is used as the laser 2, and further, between the laser 1 and the conversion unit 1 A wavelength conversion unit (conversion unit 2) for converting the wavelength of the output light a1 is provided, and ultraviolet light is generated by sum frequency generation based on the output light (output light a2) whose wavelength is converted and the output light b. The ultraviolet laser device according to claim 1.
4. The ferroelectric fluoride crystal is a composition represented by XMgF ₄ , XZnF ₄ , XAlF ₅ , Na ₂ MgAlF ₇ , or Na ₂ ZnAlF ₇ (where X is one selected from Ca, Sr, and Ba) The ultraviolet laser device according to any one of claims 1 to 3, wherein two elements are represented.).

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