JP2008242184A - Wavelength conversion device, ultraviolet laser device, and laser processing device - Google Patents

Abstract

An optical element for wavelength separation is disposed outside a wavelength converter for wavelength separation, and impurities and organic gas contained in the atmosphere adhere to a coating for wavelength separation deposited on the surface of the optical element for wavelength separation. In addition, the attached impurities and the like serve as an absorption center for high-energy ultraviolet laser light, solve the problem that the wavelength separation coating is damaged and deteriorated, and it is not necessary to arrange the wavelength separation optical element outside the sealed container, An object of the present invention is to obtain a wavelength conversion device capable of reducing deterioration of the wavelength separation coating.
A hermetically sealed container (3) that houses a wavelength conversion crystal (2) that converts the wavelength of incident laser light into the wavelength of ultraviolet laser light is provided. A wavelength separation coating 9 is provided on the surface of the laser emission window 5 disposed in the hermetic container 3 on the laser light incident side from the wavelength conversion crystal 2.
[Selection] Figure 1

Description

  The present invention relates to a wavelength conversion device, an ultraviolet laser device, and a laser processing device that generate ultraviolet rays using a nonlinear optical crystal.

  In a wavelength converter that converts the wavelength of the incident laser light and generates ultraviolet light, while suppressing the adhesion of impurities to the crystal end face, the impurities attached to the crystal end face serve as an absorption center for high-energy ultraviolet laser light. In order to reduce deterioration of the crystal end face in the wavelength conversion crystal due to ultraviolet light wavelength-converted inside the conversion crystal, there is a technique for maintaining the atmosphere around the wavelength conversion crystal by holding the wavelength conversion crystal in a sealed container. For example, in Patent Document 1, in order to reduce the reflection of the laser beam at the laser entrance window and the laser exit window of the sealed container, the laser entrance window is arranged at a Brewster angle with respect to the incident laser beam, and the laser exit window is set as the exit laser. A wavelength conversion device and an ultraviolet laser device having a sealed container arranged at a Brewster angle with respect to light are shown.

  In the ultraviolet laser device disclosed in Patent Document 1, since there is laser light that is not wavelength-converted by a wavelength conversion crystal, a beam splitter as an optical element for wavelength separation that is indispensable for selecting desired ultraviolet rays is a sealed container. Had been placed outside.

US Pat. No. 6,0026,977 (column 4, line 27 to column 5, line 51, FIG. 1)

  In a wavelength conversion device such as Patent Document 1, a wavelength separation optical element is disposed outside a sealed container for wavelength separation, and moisture or dust contained in an atmosphere in which the wavelength separation optical element is disposed. Influenced by organic impurities such as impurities and siloxy acid gas. Impurities and organic gases adhere to the wavelength separation coating deposited on the surface of the wavelength separation optical element, and the adhered impurities become an absorption center for high-energy ultraviolet laser light, which damages and degrades the wavelength separation coating. . As a result, there has been a problem in that the output of ultraviolet light that has been wavelength-separated to a desired wavelength is reduced, or the beam shape of the ultraviolet light is deteriorated.

  Further, in order to delay the deterioration of the wavelength separation coating of the wavelength separation optical element, the energy per unit area of the ultraviolet laser beam is lowered, that is, the wavelength diameter of the ultraviolet laser beam is widened so that the beam diameter of the ultraviolet laser beam is widened. There is a problem in that the wavelength conversion device, and hence the ultraviolet laser device, is increased in size because the optical element must be arranged apart from the optical element.

  The present invention has been made to solve the above-described problems, and it is not necessary to dispose the optical element for wavelength separation outside the sealed container, and the wavelength conversion that can reduce the deterioration of the coating for wavelength separation. The object is to obtain a device.

  The wavelength conversion device according to the present invention includes a sealed container that houses a wavelength conversion crystal that converts the wavelength of incident laser light into the wavelength of ultraviolet laser light. A wavelength separation coating is provided on the surface of the laser exit window disposed in the hermetic container located on the laser light incident side from the wavelength conversion crystal.

  A wavelength conversion device according to the present invention includes a wavelength separation coating for wavelength separation on a surface located on a laser light incident side from a wavelength conversion crystal in a laser emission window disposed in a sealed container that houses a wavelength conversion crystal. Therefore, it is not necessary to arrange the wavelength separation optical element outside the sealed container, and deterioration of the wavelength separation coating can be reduced.

Embodiment 1 FIG.
1 is a cross-sectional view of a wavelength conversion device according to Embodiment 1 of the present invention. In the wavelength conversion device 1, a wavelength conversion crystal 2 that converts the wavelength of incident laser light is housed in a sealed container 3. The wavelength conversion crystal 2 is, for example, a TYPE II LBO (LiO ₃ B ₅ ) crystal without an antireflection coating. The sealed container 3 includes a main body and a laser incident window 4 and a laser emission window 5 that block an opening through which laser light passes through the main body. The laser entrance window 4 and the laser exit window 5 are held by window holders 7A and 7B, and are fixed to the main body of the hermetic container 3 with the O-ring 8 interposed therebetween, so that the wavelength converter 1 is kept airtight. By doing so, the adhesion of impurities to the crystal end face of the wavelength conversion crystal 2 is suppressed, and the impurities attached to the crystal end face serve as an absorption center for high-energy ultraviolet laser light, and the wavelength inside the wavelength conversion crystal Deterioration of the crystal end face in the wavelength conversion crystal due to the converted ultraviolet light can be reduced. Here, the laser entrance window 4 and the laser exit window 5 are optical elements made of synthetic quartz or the like, and an optical surface through which the laser light passes is optically polished.

  In order to generate the third-order harmonic ultraviolet light by sum frequency generation, incident laser light 12 composed of the fundamental wave and the second-order harmonic enters from the laser incident window 4. When the wavelength of the fundamental wave oscillated from the laser light source is 1064 nm, the wavelength of the second harmonic is 532 nm and the wavelength of the third harmonic is 355 nm. The emitted laser beam 13 that is the third harmonic generated in the wavelength conversion crystal 2 is emitted from the laser emission window 5. The wavelength of the wavelength conversion crystal 2 is adjusted by the thermoelectric element 6 in order to achieve phase matching at the time of wavelength conversion. The thermoelectric element 6 for adjusting the crystal temperature is, for example, a Peltier element or a ceramic heater, and the Peltier element and the heater may be combined. When an LBO crystal is used as the wavelength conversion crystal 2, the temperature is adjusted to about 25 ° C.

  A wavelength separation coating 9 is applied to the inner surface of the wavelength conversion device 1 in the laser emission window 5, that is, the surface located on the laser light incident side from the wavelength conversion crystal 2 in the laser emission window 5. This wavelength separation coating 9 is for separating the outgoing laser beam 13 which is the third harmonic and the incident laser beam 12 which is composed of the fundamental wave and the second harmonic which remain without being wavelength-converted. Unlike the inner surface of the wavelength conversion device 1 in the laser emission window 5, no coating is applied to the outer surface of the wavelength conversion device 1 in the laser emission window 5. The laser emission window 5 has a Brewster angle with respect to the emission laser beam 13 which is a laser beam having a desired wavelength among the laser beams (incident laser beam 12 and emission laser beam 13) incident on the laser emission window 5. Has been placed.

  The wavelength separation coating 9 is a so-called multi-layer coating in which dielectric films having different refractive indexes are alternately stacked. The multi-layer coating has a narrow effective wavelength range and a large incident angle dependency. Since the incident angle of the laser beam to the laser exit window 5 is a Brewster angle, the transmittance is high for p-polarized light of 355 nm, high for s-polarized light of 532 nm and p-polarized light of 1064 nm at the incident angle of the Brewster angle. Use a multi-layer coating designed to be reflective.

  The reflected laser beam 14 composed of the fundamental wave and the second harmonic wave, which is reflected by the wavelength separation coating 9 and remains without being converted, reaches the inner surface of the main body of the sealed container 3 and is absorbed by the inner surface. In order to absorb quickly without further reflection on the inner surface of the main body of the sealed container 3, the sealed container 3 is provided with light absorbing means such as a recess 10 or a black paint. In order to prevent the temperature of the wavelength conversion device 1 from rising due to absorption of the fundamental wave and the second harmonic remaining without being wavelength-converted, the cooling vessel 11 is provided in the sealed container 3 to circulate the cooling water. In addition, the absorption effect of the reflected laser beam 14 can be enhanced by applying black paint or the like in the recess 10.

  In order to maintain the atmosphere in the wavelength conversion device 1 in a state free from impurities and organic gas, a gas sealing valve 15 is provided in the main body of the sealed container 3. As a method for maintaining the atmosphere in the wavelength converter 1 in a state free of impurities and organic gas, for example, the sealing valve 15 is opened and high-purity oxygen gas, nitrogen gas, carbon dioxide gas, rare gas, etc. are circulated for a certain period of time. Then, the wavelength conversion device 1 is once evacuated through a method of closing the sealing valve 15 or through the sealing valve 15, and then high-purity oxygen gas, nitrogen gas, carbon dioxide gas, rare gas, or the like is introduced from the sealing valve 15. There are a method of closing the post-sealing valve 15 and a method of closing the sealing valve 15 by evacuating the wavelength conversion device 1 through the sealing valve 15. Alternatively, the laser operation may be performed while circulating high-purity oxygen gas, nitrogen gas, carbon dioxide gas, rare gas, or the like with the sealing valve 15 open.

  Next, it will be explained that the wavelength separation coating 9 of the laser emission window 5 can be reduced in deterioration. Since the wavelength separation coating 9 of the wavelength conversion device 1 according to Embodiment 1 of the present invention is disposed inside the wavelength conversion device 1 in which no impurities or organic gas exists, impurities and organic gas adhere to the wavelength separation coating 9. There is nothing. Therefore, since the absorption center of the ultraviolet laser beam having high energy is not formed, the deterioration of the wavelength separation coating 9 can be suppressed. Although it is inevitable that the wavelength separation coating 9 is decomposed and deteriorated by ultraviolet rays, since the deterioration of the wavelength separation coating 9 due to adhesion of impurities or the like can be suppressed, the wavelength conversion device according to the first embodiment of the present invention. One wavelength separation coating 9 can slow down the deterioration rate and reduce the deterioration.

  In general, an optical element that transmits or reflects a laser beam has a high degradation rate by satisfying the following three conditions. (1) The coating is present, (2) the energy of the laser beam is high (ultraviolet rays are incident), and (3) impurities and organic gases in the atmosphere are included. A coating applied to an optical element such as a non-reflective coating as well as a wavelength separation coating is a thin film, and is easily deteriorated as compared with a base material of an optical element such as synthetic quartz. When all of the above three conditions are satisfied, impurities or the like adhere to the coating, and the adhered impurities or the like serve as an absorption center for high-energy ultraviolet laser light, and the coating is damaged and deteriorated.

  As in Patent Document 1, using a beam splitter (wavelength separation optical element) that reflects a desired ultraviolet ray in a state exposed to the outside air containing impurities and organic gas satisfies all the above three conditions. Degradation of the beam splitter is significant because the extent to which the separation coating is damaged and degraded is great. However, the laser emission window 5 of the wavelength conversion device 1 according to Embodiment 1 of the present invention does not touch the outside air without any coating on the outer surface of the wavelength conversion device 1 in the laser emission window 5 that contacts the outside air. By applying the wavelength separation coating 9 on the inner surface of the wavelength conversion device 1 in the laser exit window 5, the optical element for wavelength separation composed of the wavelength separation coating 9 and the laser exit window 5 is less deteriorated than before. can do.

  In the wavelength conversion device 1 according to the first embodiment, the wavelength separation coating 9 repeatedly increases and decreases in temperature so that the adhesive force between the wavelength separation coating 9 and the synthetic quartz that is the base material of the optical element causes thermal stress. In order to prevent the laser emission window 5 from being lowered by the cooling water passing through the cooling water passage 11 arranged in the vicinity of the contact portion between the main body of the sealed container 3 and the laser emission window 5, the laser emission window 5 is brought into an appropriate temperature range. So cool. Further, since the cooling water channel 11 is disposed near the light absorbing means such as the recess 10 for quickly absorbing the reflected laser light 14 composed of the fundamental wave and the second harmonic wave reflected by the laser emission window 5, The heat converted by the absorbing means is prevented from being transmitted to the laser emission window 5 as much as possible. Therefore, the wavelength conversion device 1 according to the first embodiment can reduce the temperature rise / fall in the wavelength separation coating 9 even when the laser oscillation / stop is repeated. It is possible to prevent the adhesive force with the synthetic quartz that is the base material of the element from being lowered.

  Further, in the wavelength conversion device 1 according to the first embodiment, the laser exit window 5 is installed so as to have a Brewster angle with respect to the optical axis of the incident laser light, so that the beam area of the third harmonic is provided. Becomes larger than that when the light is incident perpendicularly, and the beam intensity per unit area is lowered. Therefore, the deterioration rate of the wavelength separation coating 9 can be further reduced. Further, even if there is no non-reflective coating on the outer surface of the sealed container 3 in the laser exit window 5, the third harmonic reflection loss on the outer surface of the sealed container 3 in the laser exit window 5 can be eliminated. it can. Therefore, the wavelength conversion device 1 according to the first embodiment can reduce the deterioration rate of the wavelength separation coating 9 and obtain ultraviolet laser light with little energy loss.

  As described above, the wavelength conversion device 1 of the first embodiment is for wavelength separation on the surface located on the laser light incident side from the wavelength conversion crystal 2 in the laser emission window 5 of the sealed container 3 that houses the wavelength conversion crystal 2. Since the wavelength separation coating 9 is provided, it is not necessary to dispose the wavelength separation optical element outside the sealed container, and deterioration of the wavelength separation coating 9 can be reduced.

  FIG. 2 is a cross-sectional view of another wavelength converter according to Embodiment 1 of the present invention. 1 differs from the wavelength conversion device shown in FIG. 1 in that a cooling water channel 11 is provided in the window holder 7B of the laser emission window 5. By doing in this way, the laser emission window 5 can be cooled by the contact part in the laser emission window 5 which contact | connects the window holder 7B rather than the wavelength converter of FIG. Therefore, since the temperature rise / fall in the wavelength separation coating 9 can be further reduced, it is possible to prevent the adhesive force between the wavelength separation coating 9 and the synthetic quartz which is the base material of the optical element from being lowered. it can.

  In addition, although the laser emission window 5 provided with the wavelength separation coating 9 has been described in the case where it is installed so as to have a Brewster angle with respect to the optical axis of the incident laser light, the light of the laser light incident on the laser emission window 5 is described. It may be perpendicular to the axis. By doing so, there is a merit that the wavelength conversion device can be downsized by arranging the laser emission window 5 without being inclined even if the energy loss of the ultraviolet laser beam is somewhat increased. Here, the wavelength separation coating 9 is a multi-layer coating designed to have a high transmittance with respect to 355 nm of p-polarized light and a high reflectance with respect to 532 nm of s-polarized light and 1064 nm of p-polarized light at a normal incident angle. use.

  Further, since the laser incident light is not ultraviolet rays, the laser incident window 4 may be provided with a non-reflective coating on the laser incident side and the emission side surfaces of the laser incident window 4. By doing in this way, reflection with respect to incident laser light can be reduced. As a result, a large amount of incident laser light can be incident on the wavelength conversion device 1, so that the generation efficiency of ultraviolet rays can be increased.

Moreover, although the LBO crystal was taken as an example as the wavelength conversion crystal 2, BBO (β-BaB ₂ O ₄ ), KDP (KH ₂ PO ₄ ), KTP (KTiOPO ₄ ) CLBO (CsLiB ₆ O ₁₀ ), CBO (CsB ₃ O ₅ ) or the like can be used.

Embodiment 2. FIG.
FIG. 3 is a diagram showing the configuration of the ultraviolet laser apparatus according to Embodiment 2 of the present invention. A fundamental wave is generated in a fundamental wave generator 17 which is a laser light source of the ultraviolet laser device 16. As the fundamental wave generator 17, for example, a Q-switch Nd: YAG laser oscillator is used, the polarization is linearly polarized, and the oscillation wavelength is 1064 nm. This laser oscillator may have a configuration using an amplifier to obtain an output. In addition to the above Nd: YAG, the fundamental wave generation unit 17 is a laser crystal such as Nd: YVO ₄ (oscillation wavelength 1064 nm), Nd: YLF (oscillation wavelength 1047 nm), Nd: GdVO ₄ (oscillation wavelength 1063 nm), or the like. It may be a laser using a laser or a fiber laser using a fiber laser medium.

The generated fundamental wave is condensed on the wavelength conversion crystal 19 by the condensing lens 18A, the wavelength is converted by the wavelength conversion crystal 19, and a harmonic (wavelength conversion laser light) is generated. The wavelength conversion crystal 19 is, for example, a TYPEI LBO (LiO ₃ B ₅ ) crystal that is not coated with an antireflection coating, that is, without an antireflection coating. By not applying the antireflective coating to the wavelength conversion crystal 19, it is possible to prevent lowering of the harmonic output due to deterioration or damage of the antireflective coating due to the generated harmonics. The harmonics generated here are second harmonics, and the wavelength is 532 nm. The wavelength conversion crystal 19 is exemplified by LBO. Besides, BBO (β-BaB ₂ O ₄ ), KDP (KH ₂ PO ₄ ), KTP (KTiOPO ₄ ) CLBO (CsLiB ₆ O ₁₀ ), CBO (CsB ₃ O ₅ ) or the like can be used.

The laser beam that has passed through the wavelength conversion crystal 19, that is, the second harmonic generated in the wavelength conversion crystal 19 and the fundamental wave that has not been wavelength-converted are arranged in the wavelength conversion device 1 using the condenser lens 18 </ b> B. Condensed on the wavelength conversion crystal. When the condensed laser light is incident on the wavelength conversion crystal 2, a third harmonic (wavelength 355 nm) is generated by sum frequency generation. Thus, the third harmonic (wavelength 355 nm) which is ultraviolet light can be generated. As the wavelength conversion crystal, for example, a TYPE II LBO (LiO ₃ B ₅ ) crystal without an antireflection coating is used.

  As described above, the ultraviolet laser device 16 according to the second embodiment is capable of performing wavelength separation on the surface located on the laser light incident side from the wavelength conversion crystal 2 in the laser emission window 5 of the sealed container 3 that houses the wavelength conversion crystal 2. Since the wavelength conversion device 1 provided with the wavelength separation coating 9 is used, the distance between the wavelength separation optical element conventionally arranged outside the sealed container and the wavelength conversion crystal in the sealed container must be increased. Unlike the conventional one, there is no need to arrange the wavelength separation optical element outside the sealed container. Therefore, the ultraviolet laser device can be reduced in size.

  Since the wavelength conversion crystal 19 that is the second harmonic generation crystal of the ultraviolet laser device 16 has a slower deterioration rate than the wavelength conversion crystal 2 that is the third harmonic generation crystal, the sealed container 3 However, the same sealed container 3 may be used when it is used under conditions where the light collecting intensity is strong. Thereby, deterioration of the wavelength conversion crystal 19 can be reduced. In this case, since the fundamental wave and the second harmonic are output, it is not necessary to apply a wavelength separation coating to the laser emission window.

Embodiment 3 FIG.
FIG. 4 is a diagram showing an optical system of the laser machining apparatus according to Embodiment 3 of the present invention. In FIG. 4, 16 is the ultraviolet laser device described in the second embodiment, 20 is a collimator lens, 21 is a mask changer, 22 is a bend mirror, 23 is a galvano scanner, 24 is a scan lens, 25 is a processing table, and 26 is a processing table. It is a work such as a printed circuit board arranged on a table.

  The ultraviolet laser light emitted from the ultraviolet laser device 16 is irradiated onto a mask having a predetermined beam spot shape or the like on the mask changer 21 after the beam diameter is optimized by the collimator lens 20. A part of the ultraviolet laser light irradiated to the mask passes through the mask, is guided to a predetermined position by the galvano scanner 23 via the bend mirror 22, and is condensed through the scan lens 24. The work is processed by irradiating the condensed ultraviolet laser light onto the work fixed on the work table 25. After the processing is completed, the laser beam of the ultraviolet laser device 16 is stopped, and the workpiece is replaced with another workpiece by a transport device (not shown).

  By using the ultraviolet laser device 16 shown in the second embodiment as a laser processing device, the degradation of the wavelength separation coating 9 can be reduced, thereby significantly reducing the device downtime due to the replacement of the components of the wavelength separation optical element. can do. Further, the ultraviolet laser device 16 does not require the wavelength separation optical element to be disposed outside the hermetic container 3 in the wavelength conversion device, and can be miniaturized. Therefore, the degree of freedom in installing the ultraviolet laser device 16 in the laser processing device is increased. The degree of freedom in the layout design of the optical system can be increased.

  In a laser processing apparatus using an ultraviolet laser device equipped with a conventional wavelength conversion device in which the wavelength separation optical element is outside the sealed container, the distance between the wavelength conversion crystal in the sealed container and the wavelength separation optical element is long. Therefore, there has been a problem that the direction deviation of the laser radiation from the sealed container becomes large in the wavelength separating optical element. However, the laser processing apparatus according to the third embodiment of the present invention shortens the distance between the wavelength conversion crystal 2 and the wavelength separation optical element configured by the wavelength separation coating 9 and the laser emission window 5 in the wavelength conversion apparatus 1. Thus, the deviation of the laser beam in the wavelength separation optical element is reduced, so that the fluctuation of the laser beam irradiation point on the workpiece 26, that is, the pointing fluctuation can be reduced. Thereby, the precision of laser processing can be improved.

  As described above, the laser processing apparatus according to Embodiment 3 uses the wavelength conversion apparatus 1 in which the wavelength separation coating 9 is applied to the inner surface of the wavelength conversion apparatus 1 in the laser emission window 5 as the wavelength conversion apparatus. The apparatus stop time due to the replacement of the components of the optical element can be greatly reduced.

It is sectional drawing of the wavelength converter in Embodiment 1 of this invention. FIG. 5 is a cross-sectional view of another wavelength conversion device in the first embodiment. It is a figure which shows the structure of the ultraviolet laser device in Embodiment 2 of this invention. It is a figure which shows the optical system of the laser processing apparatus in Embodiment 3 of this invention.

Explanation of symbols

  1 wavelength conversion device, 2 wavelength conversion crystal, 3 sealed container, 4 laser entrance window, 5 laser exit window, 6 thermoelectric element, 9 wavelength separation coating, 10 indentation, 11 cooling channel, 17 fundamental wave generation unit, 25 processing table, 26 Work.

Claims (6)

A wavelength conversion crystal for converting the wavelength of incident laser light;
A thermoelectric element for adjusting the temperature of the wavelength conversion crystal;
A sealed container for housing the wavelength conversion element and the thermoelectric element;
A laser incident window installed in the sealed container and passing the incident laser light;
A laser emission window installed in the sealed container and emitting ultraviolet laser light wavelength-converted by the wavelength conversion crystal to the outside of the sealed container;
A wavelength conversion device, wherein a wavelength separation coating is provided on a surface located on a laser light incident side from the wavelength conversion crystal in the laser emission window. The sealed container includes a main body, a laser incident window, and a laser emission window,
2. The wavelength conversion device according to claim 1, wherein cooling means for cooling the laser emission window is disposed in the vicinity of a contact portion between the main body and the laser emission window. 3. The wavelength conversion device according to claim 1, wherein the laser emission window is installed at a Brewster angle with respect to an optical axis of laser light wavelength-converted by the wavelength conversion crystal. The wavelength converter according to any one of claims 1 to 3, wherein an absorption means for absorbing the laser light reflected by the laser emission window is provided on the inner surface of the sealed container. A laser light source and a wavelength converter;
5. An ultraviolet laser device that generates ultraviolet laser light by converting the wavelength of light emitted from the laser light source, wherein the wavelength conversion device is the wavelength conversion device according to claim 1. Ultraviolet laser device. 6. A laser processing apparatus for processing a workpiece by irradiating a workpiece fixed on a processing table with an ultraviolet laser beam obtained by collecting the ultraviolet laser beam generated from the ultraviolet laser device according to claim 5.

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