JP4102109B2 - Optical wavelength conversion element - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical wavelength conversion element that converts the wavelength of laser light using a nonlinear optical crystal such as a CLBO crystal.
[0002]
[Prior art]
In recent years, optical wavelength conversion elements using CLBO crystals (cesium, lithium, borate crystals) are promising as high-power laser wavelength conversion devices. This is because the CLBO crystal is a non-linear optical crystal that has high wavelength conversion efficiency and a high optical damage threshold and that can be easily grown. However, since the CLBO crystal has deliquescence, in the optical wavelength conversion element using the CLBO crystal, it is necessary to keep the CLBO crystal airtight.
[0003]
Therefore, for example, Japanese Patent Laid-Open No. 4-204923 discloses the following optical wavelength conversion element. The optical wavelength conversion element described in this publication has a transparent plate bonded to both end faces of a nonlinear optical crystal via an adhesive, and the side surfaces of the nonlinear optical crystal are covered with a cylindrical holder via an adhesive. . As a result, the nonlinear optical crystal is covered with the adhesive and blocked from the outside air.
[0004]
[Problems to be solved by the invention]
However, in the optical wavelength conversion element described in the above publication, there is a concern that the adhesive may deteriorate due to laser light irradiation. When a nonlinear optical crystal having deliquescence such as a CLBO crystal is used, the outside air There is a possibility that the nonlinear optical crystal is destroyed by the intrusion. In addition, since the nonlinear optical crystal is covered with an adhesive, when the nonlinear optical crystal generates heat due to incidence of laser light, heat radiation of the nonlinear optical crystal is hindered, and the wavelength conversion efficiency of the laser light may be reduced. . Furthermore, there is a possibility that the nonlinear optical crystal and the adhesive cause a chemical reaction, or the nonlinear optical crystal is distorted due to a difference in thermal expansion between them (particularly, the CLBO crystal is vulnerable to distortion).
[0005]
Therefore, the present invention has been made in view of such circumstances, and provides an optical wavelength conversion element capable of maintaining a nonlinear optical crystal in an airtight manner and efficiently performing heat dissipation of the nonlinear optical crystal. The purpose is to do.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, an optical wavelength conversion element according to the present invention is an optical wavelength conversion element that converts the wavelength of a laser beam by a CLBO crystal that is a nonlinear optical crystal, and has a through-hole into which the CLBO crystal is inserted. A metal holder, a pair of light transmission members that sandwich the CLBO crystal in the through-hole, and a part of which protrudes from the bottom surface of the recess formed at the end of the holder, a CLBO crystal, and a light transmission plate member And a spacer made of aluminum or an alloy mainly composed of aluminum provided with a light passage hole through which a laser beam passes at the center thereof, and a wall surface of the through hole and a side surface of the light transmitting member The opening portion on the outer side of the gap formed between the two is filled with an adhesive, and the concave portion is filled with a resin covering the side surface of the protruding portion of the light transmitting member.
[0007]
According to this optical wavelength conversion element, since the outer side opening portion of the gap formed between the wall surface of the through hole of the holder and the side surface of the light transmitting member is filled with the adhesive, The nonlinear optical crystal can be kept airtight by the transmission member and the adhesive. Then, when the laser beam is irradiated so as to pass through the through hole of the holder, the laser beam is incident on the nonlinear optical crystal through one light transmitting member, wavelength-converted by the nonlinear optical crystal, and the other light. The light is emitted through the transmission member. At this time, the nonlinear optical crystal generates heat by the incidence of the laser beam, but since the nonlinear optical crystal is inserted into the through hole of the metal holder, the heat generated by the nonlinear optical crystal is efficiently absorbed by the holder. Therefore, the heat radiation of the nonlinear optical crystal can be efficiently performed. Further, a part of the light transmitting member protrudes from the end face of the holder, and the adhesive is not applied to the end face of the light transmitting member through which the laser light passes. Therefore, the irradiation amount of the laser light to the adhesive is reduced. Therefore, it is possible to prevent the adhesive from deteriorating due to the laser light irradiation.
[0008]
In the light wavelength conversion element according to the present invention, the end surface is a bottom surface of a recess formed at the end of the holder, and the recess is filled with resin so as to cover the side surface of the protruding portion of the light transmitting member. preferable. Since the adhesive is covered with the resin, the nonlinear optical crystal can be kept more airtight by the synergistic effect of the adhesive and the resin.
[0009]
In the optical wavelength conversion element according to the present invention, the nonlinear optical crystal is preferably a CLBO crystal. Although the CLBO crystal has deliquescence, in this optical wavelength conversion element, the CLBO crystal can be kept airtight as described above. Therefore, it is possible to effectively exhibit the characteristics of the CLBO crystal that has high wavelength conversion efficiency and a high optical damage threshold, and that crystal growth is easy.
[0010]
Furthermore, in the optical wavelength conversion element according to the present invention, the holder is preferably formed of aluminum or an alloy containing aluminum as a main component, or copper or an alloy containing copper as a main component. Since these metals are metals having high thermal conductivity, it is possible to more efficiently dissipate heat from the nonlinear optical crystal to the holder. Further, since these metals are softer than the nonlinear optical crystal, it is possible to prevent the occurrence of friction scratches due to the contact between the holder and the nonlinear optical crystal.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a preferred embodiment of an optical wavelength conversion element according to the present invention will be described in detail with reference to the drawings.
[0012]
As shown in FIGS. 1 and 2, the optical wavelength conversion element 10 has a cylindrical holder 12 formed of aluminum (or an alloy containing aluminum as a main component). Circular recesses 14 and 16 are formed on both end faces of the holder 12, and a through hole 18 having a rectangular cross section is formed between the bottom surface 14 a of the recess 14 and the bottom surface 16 a of the recess 16. . Protective caps 20 and 22 are attached to both ends of the holder 12 to prevent damage to the edge portion of the holder 12 and resin damage due to direct irradiation of laser light. A light passage hole 20 a is provided in the central portion of the protective cap 20, and similarly, a light passage hole 22 a is provided in the central portion of the protective cap 22. Laser light passes through a path formed by the light passage hole 20a of the protective cap 20, the light passage hole 22a of the protective cap 22, and the through hole 18 of the holder 12. In order to prevent reflection of laser light, the surfaces of the holder 12 and the protective caps 20 and 22 are blackened by alumite treatment or the like.
[0013]
A CLBO crystal 24 cut into a rectangular parallelepiped shape is inserted into the through hole 18 of the holder 12. The CLBO crystal 24 is formed so as to have a gap of about 0.1 to 0.2 mm between the side surface and the wall surface of the through hole 18. Thereby, the CLBO crystal 24 can be inserted into the through-hole 18, and further, the thermal expansion difference between the holder 12 and the CLBO crystal 24 can be absorbed. In addition, since the holder 12 is made of aluminum that is softer than the CLBO crystal 24, it is possible to prevent the occurrence of friction scratches due to contact between the holder 12 and the CLBO crystal 24. A relief with a radius of 0.3 to 0.5 mm may be provided at the corner of the through hole 18. As a result, it is possible to easily insert the CLBO crystal 24 into the through hole 18 while maintaining a small gap between the side surface of the CLBO crystal 24 and the wall surface of the through hole 18. Furthermore, in the cutting process of the CLBO crystal 24, the chamfering process of the edge portion of the CLBO crystal 24 can be omitted.
[0014]
Further, a spacer 26 that contacts the end surface of the CLBO crystal 24 on the concave portion 14 side and a spacer 28 that contacts the end surface of the CLBO crystal 24 on the concave portion 16 side are inserted into the through hole 18 of the holder 12. The spacers 26 and 28 are formed in a plate shape having a thickness of about 0.2 to 0.5 mm from aluminum (or an alloy containing aluminum as a main component). A light passage hole 26 a through which laser light passes is provided in the central portion of the spacer 26, and similarly, a light passage hole 28 a is also provided in the central portion of the spacer 28. In order to prevent reflection of laser light, the surfaces of the spacers 26 and 28 are also dyed black by anodizing or the like.
[0015]
Further, in the through hole 18 of the holder 12, a light transmission plate (light transmission member) 30 that contacts the end surface on the concave portion 14 side of the spacer 26 and a light transmission plate (light transmission member) that contacts the end surface on the concave portion 16 side of the spacer 28. 32 is inserted. The light transmission plates 30 and 32 are formed in a rectangular parallelepiped shape from quartz glass, and are formed so as to have a gap of about 0.1 to 0.2 mm between the side surface and the wall surface of the through hole 18. Thereby, the light transmission plates 30 and 32 can be inserted into the through-hole 18, and further, the difference in thermal expansion between the holder 12 and the light transmission plates 30 and 32 can be absorbed. As described above, the spacers 26 and 28 are interposed between the CLBO crystal 24 and the light transmission plates 30 and 32 because the frictional scratches caused by the direct contact between the CLBO crystal 24 and the light transmission plates 30 and 32 and the laser light are transmitted. This is because the occurrence of interference distortion can be prevented. The material of the light transmission plates 30 and 32 is not limited to quartz glass, and may be any material that has high light transmittance with respect to incident laser light.
[0016]
The end face 30a on the outer side of the light transmission plate 30 protrudes from the bottom surface 14a of the recess 14 and is formed at the corner formed by the protruding portion of the side surface 30b of the light transmission plate 30 and the bottom surface 14a of the recess 14. Adhesive 34 is filled. On the other hand, the end face 32a on the outer side of the light transmission plate 32 protrudes from the bottom surface 16a of the recess 16, and also at the corner formed by the protruding portion of the side surface 32b of the light transmission plate 32 and the bottom surface 16a of the recess 16. Adhesive 34 is filled. The adhesive 34 has adhesiveness and airtightness. As an example, there is an adhesive (so-called vacuum adhesive) that emits very little gas during the curing process. When such a vacuum adhesive is cured by heating, hermeticity is improved as compared with the case of curing at room temperature. In addition, since the filling operation of the adhesive 34 is performed on the corner portion where the viscous material is well accommodated and can be performed near the end face of the holder 12, the adhesive 34 can be easily and surely placed at a predetermined position. Can be filled.
[0017]
The recesses 14 and 16 of the holder 12 are filled with a resin 36 by potting, and the resin 36 covers the protruding portions of the side surfaces 30b and 32b of the light transmission plates 30 and 32. As the material of the resin 36, a room temperature curable silicone resin having viscosity is used in consideration of adhesion and airtightness to the aluminum holder 12 and the quartz glass light transmission plates 30 and 32. Then, by filling the adhesive 34 and the resin 36, the outer side of the gap 38 formed between the wall surface 18a of the through hole 18 and the side surface 30b of the light transmission plate 30 as shown in FIG. The opening 38a is hermetically sealed. Similarly, the opening portion on the outer side of the gap formed between the wall surface 18a of the through hole 18 and the side surface 32b of the light transmission plate 32 is also hermetically sealed. As a material of the resin 36, a heat-curable epoxy resin having flexibility is also suitable.
[0018]
In order to confirm the moisture resistance of the optical wavelength conversion element 10 configured as described above, a humidification heating test was performed. C. T (pressure cooker test) was performed. The humidification heating test is a test in which the test object is left for 96 hours under the conditions of 85% humidity and 85 ° C. C. T is a test in which an object to be tested is left for 48 hours under conditions of 2 atm, humidity 85%, and temperature 85 ° C. Here, silica gel that changes from blue to white (color loss) upon moisture absorption was placed in the holder 12 in place of the CLBO crystal 24, and the moisture resistance was evaluated based on the degree of discoloration of the silica gel.
[0019]
As a result, the P.P. C. Even after the completion of T, no discoloration of the silica gel was observed. This is because the space formed by the holder 12, the pair of light transmission plates 30, 32, the adhesive 34, and the resin 36 (that is, the space where the CLBO crystal 24 is arranged) is extremely excellent over a long period of time. It can be maintained. Therefore, in the optical wavelength conversion element 10, the CLBO crystal 24 is kept airtight, and the CLBO crystal 24 having deliquescence is destroyed by the intrusion of outside air without particularly performing maintenance or the like for maintaining moisture resistance. Can be prevented. In the optical wavelength conversion element 10, since the gap formed around the CLBO crystal 24 is extremely small, it is not necessary to perform vacuuming or the like when packaging the CLBO crystal 24. However, in consideration of moisture resistance of the CLBO crystal 24, it is preferable to package the CLBO crystal 24 in dry air or in a nitrogen atmosphere.
[0020]
By the way, a humidification heating test was carried out on the resin 36 not filled with the adhesive 34 alone, and after the humidification heating test, P.I. C. T was performed. In this case, the P.P. C. After the completion of T, discoloration of silica gel was observed. C. In T, no discoloration of the silica gel was observed until after 24 hours. This indicates that a material filled only with the adhesive 34 without being filled with the resin 36 also has excellent airtightness and can be effectively used practically as a light wavelength conversion element.
[0021]
The optical wavelength conversion element 10 described above can be used, for example, as a high-power laser wavelength conversion device that converts the wavelength of a laser beam having a wavelength of 532 nm into a laser beam having a wavelength of 266 nm in an ultraviolet laser processing apparatus. That is, when a laser beam having a wavelength of 532 nm is irradiated so as to pass through the light passage hole 20 a of the protective cap 20, the laser beam having a wavelength of 532 nm passes through the light transmission plate 30 and passes through the light passage hole 26 a of the spacer 26. 24 is incident. The laser beam having a wavelength of 532 nm incident on the CLBO crystal 24 is converted into a laser beam having a wavelength of 266 nm by the CLBO crystal 24. The laser beam having a wavelength of 266 nm passes through the light passage hole 28 a of the spacer 28, passes through the light transmission plate 32, and is emitted from the light passage hole 22 a of the protective cap 22.
[0022]
At this time, although the CLBO crystal 24 generates heat due to the incidence of the laser light, since the CLBO crystal 24 is inserted into the through hole 18 of the aluminum holder 12, the heat generated by the CLBO crystal 24 is efficiently absorbed by the holder 12. Is done. Therefore, the heat dissipation of the CLBO crystal 24 can be efficiently performed, and the temperature of the CLBO crystal 24 can be prevented from rising and the wavelength conversion efficiency of the laser light from being lowered. Further, since the adhesive 34 is not applied to the end surface 30a of the light transmitting plate 30 through which the laser light passes and the end surface 32a of the light transmitting plate 32, the irradiation amount of the laser light to the adhesive 34 when the laser light passes through. Is reduced. Therefore, it is possible to prevent the adhesive 34 from deteriorating due to the laser light irradiation.
[0023]
Here, a wavelength conversion characteristic comparison experiment will be described with reference to FIG. In FIG. 4, the horizontal axis represents energy per pulse of incident light (laser light having a wavelength of 532 nm), and the vertical axis represents energy per pulse of emitted light (laser light having a wavelength of 266 nm). The incident light is a laser light having a wavelength of 1064 nm emitted from a lamp-pumped Q-switch Nd: YAG laser (Powerlite 8000EP, pulse width 10 ns, repetition frequency 10 Hz) and converted into a laser light having a wavelength of 532 nm by a Type II SHG-CLBO device. It is converted.
[0024]
In this wavelength conversion characteristic comparison experiment, the optical wavelength conversion elements 10a and 10b according to the present embodiment, CLBO crystals arranged in a vacuum space in a vacuum package (hereinafter referred to as “vacuum package”), and A CLBO crystal exposed in the air without packaging (hereinafter referred to as “reference”) was prepared. As a result, as shown in FIG. 4, the optical wavelength conversion elements 10a and 10b exhibited better wavelength conversion characteristics than the reference. This is because the optical wavelength conversion elements 10a and 10b, in which the CLBO crystal 24 is radiated to the holder 12 made of aluminum, are more radiant than the reference in which the heat of the CLBO crystal is radiated to the air. Because. The vacuum package exhibited a wavelength conversion characteristic worse than that of the reference because there was no heat transfer medium around the CLBO crystal.
[0025]
Such a difference in optical wavelength conversion characteristics becomes more prominent as the intensity of incident light increases. This is because when the intensity of incident light increases, the calorific value of the CLBO crystal increases, so that the difference in heat dissipation of the CLBO crystal greatly affects. As described above, since the optical wavelength conversion element 10 according to the present embodiment can maintain the wavelength conversion efficiency of the CLBO crystal 24 well even in the wavelength conversion of high-power laser light, as a high-power laser wavelength conversion device. It can be used suitably.
[0026]
By the way, in the said wavelength conversion characteristic comparison experiment, although the holder 12 of the optical wavelength conversion elements 10a and 10b was formed with aluminum, you may form the holder 12 with the alloy which has copper or a copper as a main component. This is because copper or an alloy containing copper as a main component is also a metal having high thermal conductivity. Further, if an indium wheel (foil) is inserted into the gap between the wall surface of the through hole 18 of the holder 12 and the side surface of the CLBO crystal 24, the heat dissipation of the CLBO crystal 24 can be further improved. And a constriction may be provided in the outer peripheral side surface of the holder 12, or a heat radiating fin may be provided. Thereby, since the surface area of the outer peripheral side surface of the holder 12 increases, the heat dissipation from the holder 12 to the outside of the holder 12 (for example, a refrigerant) can be improved, and the heat dissipation of the CLBO crystal 24 is further stabilized. Is possible. Even if the holder 12 is made of another metal, the CLBO crystal 24 can be radiated more efficiently than the vacuum package or reference in the wavelength conversion characteristic comparison experiment.
[0027]
The preferred embodiment of the present invention has been described in detail above. However, the present invention is not limited to the optical wavelength conversion element using the CLBO crystal, but the optical wavelength conversion using various nonlinear optical crystals such as BBO and LBO. Applicable to devices.
[0028]
【The invention's effect】
As described above, the optical wavelength conversion element according to the present invention is an optical wavelength conversion element that converts the wavelength of laser light by a nonlinear optical crystal, and is a metal holder having a through hole in which the nonlinear optical crystal is inserted. And a pair of light transmitting members that sandwich the nonlinear optical crystal in the through hole and partly protrude from the end surface of the holder, and are formed between the wall surface of the through hole and the side surface of the light transmitting member Since the opening portion on the outer side of the gap is filled with an adhesive, the nonlinear optical crystal can be kept airtight, and heat radiation of the nonlinear optical crystal can be efficiently performed. it can.
[Brief description of the drawings]
FIG. 1 is a perspective view of an optical wavelength conversion element according to an embodiment.
FIG. 2 is a longitudinal sectional view of the optical wavelength conversion element shown in FIG.
3 is an enlarged cross-sectional view showing a main part of the optical wavelength conversion element shown in FIG. 1. FIG.
FIG. 4 is a diagram illustrating wavelength conversion characteristics of laser light.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Optical wavelength conversion element, 12 ... Holder, 14, 16 ... Recess, 14a, 16a ... Bottom surface (end surface of holder), 18 ... Through-hole, 18a ... Wall surface, 24 ... CLBO crystal (nonlinear optical crystal), 30, 32 ... light transmission plate (light transmission member), 30b, 32b ... side surface, 34 ... adhesive, 36 ... resin, 38 ... gap, 38a ... opening.

Claims (3)

An optical wavelength conversion element that converts the wavelength of laser light by a CLBO crystal that is a nonlinear optical crystal,
A metal holder having a through-hole into which the CLBO crystal is inserted;
A pair of light transmitting members that sandwich the CLBO crystal in the through hole and that partially protrude from the bottom surface of the recess formed in the end of the holder;
A spacer made of aluminum or an alloy containing aluminum as a main component, which is interposed between the CLBO crystal and the light transmitting plate member, and has a light passage hole through which a laser beam passes in the center.
The opening portion on the outer side of the gap formed between the wall surface of the through hole and the side surface of the light transmitting member is filled with an adhesive,
The light wavelength conversion element, wherein the concave portion is filled with a resin so as to cover a side surface of the protruding portion of the light transmitting member.   The optical wavelength conversion element according to claim 1, wherein the holder is made of aluminum or an alloy containing aluminum as a main component.   The optical wavelength conversion element according to claim 1, wherein the holder is made of copper or an alloy containing copper as a main component.

Images