JP2011158838A - Waveguide-type beam homogenizer and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a waveguide-type beam homogenizer which can suppress transmission loss and polarization dependence is improved in the uniformity of intensity distribution of an emitted laser beam, and is made compact, and is very durable optically and thermally even with respect to high-output laser beam, inexpensive, is mechanically firm, and has superior durability. <P>SOLUTION: In the waveguide-type beam homogenizer 1, where a dielectric thin film 14 is formed on the metal inner wall surface 13 of a hollow metal member 10 having a space 12 rectangular in cross section where a laser beam is propagated, the film thickness d of the dielectric thin film 14 is set between a film thickness da obtained when arithmetic mean reflectance of the reflectance in an S-polarized wave and the reflectance in a P-polarized wave of the laser beam that is incident on the dielectric thin film 14 at the deepest angle becomes a maximum, and film thickness db obtained when the reflectance in S-polarized wave, and the reflectance in P-polarized wave existing nearest the film thickness da become equal to each other. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a waveguide beam homogenizer that makes uniform the laser light intensity distribution on an irradiation surface when performing laser processing such as marking or surface treatment, or laser treatment such as ablation or hair removal.

  In general, the intensity distribution of light emitted from a laser light source is a Gaussian distribution having the strongest intensity in the central portion or a non-uniform distribution having several localized intensity peaks. When laser light with such a non-uniform intensity distribution is irradiated to a specific range, for example, laser marking causes visual shading, and surface treatment of metals, resin materials, etc. is not only visually but also unsatisfactory. Uniform mechanical strength distribution and structural defects may occur. Also in laser treatment, when a laser beam having such a non-uniform intensity distribution is irradiated to a specific range, there is a risk that normal tissue is destroyed or inflamed by local excessive irradiation.

  In order to improve the non-uniformity of the intensity distribution of the laser beam and to uniformly process a wide range of areas, for example, the laser beam is narrowed to a small spot diameter that can ignore the non-uniformity of the intensity distribution. Can be scanned over a large area to make the irradiation effect (intensity distribution) uniform. However, in such a method, it takes a long time to scan the laser beam, and since it has a movable part, it is difficult to reduce the size of the irradiation device, and the optical axis is easily changed due to vibration. There is also a problem.

  A beam homogenizer is known as an optical element that solves such a problem and makes a non-uniform light intensity distribution unique to laser light uniform, and various types of beam homogenizers have been proposed so far. By using a beam homogenizer, it is possible to uniformly process a wide area in a short time, which is particularly useful in the field of industrial processing such as marking and surface treatment, or in the field of laser treatment such as azalea and hair removal. It is.

  Examples of the beam homogenizer include a transmission beam homogenizer, a reflection beam homogenizer, and a waveguide beam homogenizer.

  As a transmission beam homogenizer, a so-called fly-eye lens in which minute lenses divided into a grid pattern are integrated into a two-dimensional array, or minute irregularities in units of microns are formed on a transparent substrate, There is a diffractive beam homogenizer that uses the diffraction phenomenon of laser light to achieve uniformity (Patent Document 1).

  Further, as a reflection beam homogenizer, there is one that once divides a beam incident thereon by a subdivided segment mirror and superimposes it again while collecting it to obtain a uniform beam (Patent Document 2).

  Furthermore, as a waveguide type beam homogenizer, a rectangular hollow propagation region is formed by combining opposing reflectors, and the intensity distribution is made uniform while reflecting the laser beam on the inner wall surface of this hollow propagation region. A beam homogenizer having a waveguide structure (also called a kaleidoscope) has been proposed (Patent Documents 3 to 7).

JP 2007-101844 A JP-A-8-94812 JP-A-5-285684 JP-A-7-171223 JP 2004-170484 A JP 2008-147463 A JP 2009-122614 A

  However, the beam homogenizer described above has the following problems.

First, a transmission-type beam homogenizer using a fly-eye lens or a diffraction phenomenon uses a transparent material in the wavelength band of the laser beam, and if an appropriate optical system is constructed, the laser beam can be made uniform with low loss. . However, since it is necessary to join a large number of microlenses or to finely process a diffraction grating on a transparent substrate, there is a problem that the manufacturing process is complicated and the cost is high. In particular, quartz glass cannot be used as a substrate material for laser processing of metals or resins, or for CO ₂ laser light that is effective for medical laser treatment. In the case of glass materials, lens processing and microfabrication of diffraction gratings are relatively easy, but in general, crystalline materials such as zinc selenide and germanium, which are transparent optical materials for CO ₂ laser light, are used for bonding and micron units. Therefore, even if a transmission beam homogenizer can be manufactured using these materials, it becomes very expensive.

Transmission beam homogenizer that for the fly-eye lens or a diffractive type is limited to laser light follows a near-infrared wavelength band to which the application can be used mainly quartz glass or other optical glass,, CO ₂ laser beam It is not widespread for use.

  Since the laser beam with a uniform intensity distribution after passing through the beam homogenizer has a larger spread angle than the laser beam from the light source, the beam homogenizer is generally installed at a position closer to the irradiated object side than the light source side. The Therefore, the beam homogenizer is often exposed to a poor environment in which dust or transpiration from the irradiated object flies and is likely to be contaminated.

  In the transmission beam homogenizer, once these contaminants adhere to the surface of the element, the contaminants are further stuck by the irradiation of the laser beam and the defects are expanded, not only the transmittance is lowered, but also the lifetime of the element is greatly reduced. End up.

In particular, in the case of CO ₂ laser processing that handles kW-class power used in metal processing, once the contaminants adhere, the device itself is easily destroyed, so the beam homogenizer that has progressed contamination is discontinued. And should be replaced with new ones. However, as described above, such a beam homogenizer is very expensive, and it is economically difficult to replace it frequently.

  In addition, a transmission beam homogenizer is a beam homogenizer that spreads a certain amount of laser light in order to achieve uniformity in the intensity distribution of the laser light or to prevent the power density of the laser light from exceeding the destruction threshold of the element. It is necessary to make the light incident on. For this reason, it is difficult to make the laser beam incident at a position where the light is focused on the minute spot and has a high power density. As a result, although the thickness of the element of the beam homogenizer can be reduced, the light receiving area cannot be sufficiently reduced. As described above, since the transmission beam homogenizer requires a certain light receiving area, it is difficult to accommodate the transmission beam homogenizer in a handpiece portion attached to the tip of the laser treatment device, for example.

  Next, the reflection type beam homogenizer using a segment mirror has a relatively high durability against the adhesion of contaminants, and although the transmission efficiency of laser light is reduced to some extent depending on the contamination state, the threshold value for damage is high. However, a reflective beam homogenizer using such a segment mirror generally has a shallow focal depth at the focal point where a uniform distribution of laser light intensity can be obtained, and is constructed by folding the optical axis of the laser light. There is a problem that the optical system becomes complicated and large. Furthermore, since a large number of segment mirrors are attached to the concave plate and used, the reflective beam homogenizer is also very expensive.

  Next, in the beam homogenizer having the rectangular hollow waveguide structure, the propagation region of the laser light is a hollow region, and the laser light is propagated while being repeatedly reflected on the inner wall surface of the rectangular hollow waveguide. Therefore, the risk of destruction due to high power density or destruction due to the adhesion of contaminants is smaller than that of the transmission beam homogenizer.

  However, in a beam homogenizer having a rectangular hollow waveguide structure, since the laser light is repeatedly reflected on the inner wall surface of the rectangular hollow waveguide, overall reflection loss becomes a problem.

  Further, in the beam homogenizer having the rectangular hollow waveguide structure, the laser light is incident on the inner wall surface of the rectangular hollow waveguide at a shallow angle, so that the reflectance generally depends on the polarization state of the laser light.

  In the reflection beam homogenizer using the segment mirror described above, the laser beam is incident substantially perpendicular to the mirror surface and is reflected only once, so that the reflection loss is small, and the reflectance is in the polarization state of the incident laser beam. However, the beam homogenizer having the rectangular hollow waveguide structure has a large transmission loss as a whole, and the transmission efficiency through the beam homogenizer depends on the polarization state of the laser light.

  Further, in a beam homogenizer having a rectangular hollow waveguide structure, since the beam homogenizer itself generates heat due to transmission loss that occurs when passing through the beam homogenizer, heat dissipation (heat conductivity of the beam homogenizer) is also important. In Patent Documents 5 and 7, a waveguide type beam homogenizer configured by covering a glass material with a smooth inner wall surface with a metal film has been proposed. However, in terms of thermal conductivity, a glass material is not necessarily suitable. I can not say.

  If the laser beam is incident on the inner wall surface at a shallower angle to increase the reflectance, and the length of the rectangular hollow waveguide is limited, and the number of reflections is limited, the transmission loss can be suppressed to some extent, The uniformity of the intensity distribution of the emitted laser light is inferior. In order to achieve both suppression of transmission loss and uniformity of the intensity distribution of the emitted laser beam, there is also means for averaging the laser beam irradiation intensity over time by vibrating the beam homogenizer itself or the laser beam incident thereon. It has been devised (Patent Documents 3, 6, and 7). However, an optical system having such a movable part has a complicated vibration mechanism, and is not particularly suitable for a small beam homogenizer that is mounted in a handpiece part of a laser treatment device. Even without such a mechanism, there is a need for a beam homogenizer that suppresses transmission loss, suppresses the polarization dependence of laser light, and achieves uniform laser light.

  Therefore, the object of the present invention is to solve the above-mentioned problems of transmission loss and polarization dependency, have sufficient optical and thermal durability against high-power laser light, and are inexpensive and mechanical. Is to provide a highly robust waveguide beam homogenizer. It is another object of the present invention to provide a waveguide beam homogenizer having a shape that can be installed in a small member such as a handpiece attached to the tip of a transmission system of a laser treatment device, and a method for manufacturing the same.

  The present invention was devised to achieve the above object, and is a waveguide beam homogenizer in which a dielectric thin film is formed on a metal inner wall surface of a hollow metal member having a rectangular space in which a laser beam propagates. When a polarized wave whose electric field of the laser light incident on the dielectric thin film is perpendicular to the incident surface is an S-polarized wave, and a polarized wave parallel to the incident surface is a P-polarized wave, the dielectric thin film The film thickness d is the film thickness da when the arithmetic mean reflectance of the reflectance of the S-polarized wave and the reflectance of the P-polarized wave of the laser light incident at the deepest angle on the dielectric thin film is maximized. A waveguide beam homogenizer set so as to be between the film thickness db when the reflectance of the S-polarized wave existing closest to the film thickness da and the reflectance of the P-polarized wave are equal. is there.

  More preferably, the hollow metal member is formed by joining four metal members so that the outer cross-sectional shape is circular, and the cross-sectional rectangular space is defined by the metal inner wall surface at the center thereof, and The cross-sectional shapes of the metal members facing each other at least across the rectangular cross-sectional space are the same.

  More preferably, the rectangular space in cross section is connected to a shape converting portion having a conical side surface shape whose diameter increases toward a circular entrance through which the laser beam is incident.

  More preferably, the hollow metal member is made of oxygen-free copper, and the dielectric thin film is made of any of germanium, zinc selenide, zinc sulfide, calcium fluoride, copper oxide, copper iodide, or quartz. did.

  The present invention also provides a method for manufacturing a waveguide homogenizer in which a dielectric thin film having a predetermined film thickness is formed on a metal inner wall surface of a hollow metal member having a rectangular space in which a laser beam propagates. When the polarized wave in which the electric field of the laser beam incident on the thin film is perpendicular to the incident surface is an S-polarized wave and the polarized wave parallel to the incident surface is a P-polarized wave, The film thickness da is obtained when the arithmetic mean reflectance of the reflectance of the S-polarized wave and the reflectance of the P-polarized wave of the laser light incident at a deep angle is maximized, and is present at a position closest to the film thickness da. After obtaining the film thickness db when the reflectance in the S-polarized wave and the reflectance in the P-polarized wave are equal, the film thickness d of the dielectric thin film is set to the thickness da and the film thickness db. Waveguide set to be between It is a manufacturing method of the type homogenizer.

  According to the present invention, transmission loss is small, and the polarization dependence of incident laser light can be suppressed. In addition, it is possible to provide a waveguide beam homogenizer that is sufficiently optically and thermally durable to high-power laser light, that is small, inexpensive, and mechanically strong, and a method for manufacturing the same.

It is a figure which shows the waveguide type beam homogenizer which concerns on one embodiment of this invention, (a) is the front view seen from the incident side, (b) is the side view. It is a longitudinal cross-sectional schematic diagram for demonstrating the polarization | polarized-light and reflection of the laser beam which divides the cross-sectional rectangular space of the waveguide type beam homogenizer in this invention, and injects into the metal inner wall surface in which the dielectric thin film was formed. Reflectance of S-polarized wave (Rs) and reflection of P-polarized wave with respect to film thickness d of germanium thin film when CO ₂ laser light having a wavelength of 10.6 μm is incident on a reflective surface having a germanium thin film formed on a copper wall surface FIG. 3 is a diagram showing a rate (Rp) and an arithmetic average reflectance (Ra), in which (a) is an angle θ of an incident angle shown in FIG. 2, and (b) is an angle. (c) is a figure which shows the case where angle (theta) is 10 degrees. Reflectance (Rs) of S-polarized wave with respect to film thickness d of zinc selenide thin film when CO ₂ laser light having a wavelength of 10.6 μm is incident on a reflective surface having a zinc selenide thin film formed on a copper wall surface, P It is a figure which shows the reflectance (Rp) of a polarized wave, and the reflectance (Ra) of the arithmetic mean, (a) is the angle (theta) which is the remainder of the incident angle shown in FIG. (b) is a figure which shows the case where angle (theta) is 5 degrees, (c) is a case where angle (theta) is 10 degrees. It is the front view seen from the incident side direction which shows the waveguide type beam homogenizer which concerns on another embodiment of this invention. It is a figure which shows the waveguide type beam homogenizer which concerns on another embodiment of this invention, (a) is the front view seen from the incident side direction, (b) is the side view.

  Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

  1A and 1B are diagrams showing a waveguide beam homogenizer according to the present embodiment, in which FIG. 1A is a front view seen from the laser beam incident side, and FIG. 1B is a side view.

  The waveguide type beam homogenizer 1 includes a hollow metal member 10 in which four metal members 11a to 11d having substantially the same sectional fan shape are assembled to face each other, and a rectangular space 12 is formed in the center thereof. And a dielectric thin film 14 formed on the metal inner wall surface 13 of the hollow metal member 10.

  In the present embodiment, oxygen-free copper that has good thermal conductivity and can obtain a large reflectance is used as the material of the metal members 11a to 11d.

  Further, germanium was used as a material of the dielectric thin film 14 and was formed on the metal inner wall surface 13 by a sputtering method.

At an oscillation wavelength of 10.6 μm of CO ₂ laser light, the complex refractive index of copper is 14.1-j64.5, and the refractive index of germanium is 4. The extinction coefficient of germanium (imaginary part of the complex refractive index) is almost negligible, that is, germanium is regarded as a transparent dielectric in the wavelength band of CO ₂ laser light.

  Further, in this embodiment, four metal members 11a to 11d having the same shape are joined, the outer cross section forms a circle having a diameter of 6 mm, and the cross sectional rectangular space 12 in the center has a square cross section having a side of 1.5 mm. The length of the waveguide type homogenizer 1 was 10 cm. The four metal members 11a to 11d are fixed and integrated by screwing bolts (not shown) into the screw holes 15, but they may be integrated by adhesion or welding.

  The metal inner wall surface 13 that defines the rectangular space 12 is polished to a mirror surface in order to increase the reflectance of the laser beam. As the region to be polished and the region where the dielectric thin film 14 is formed, only the region that divides the rectangular space 12 through which the laser beam propagates is optically sufficient. You may give over the whole surface of metal member 11a-11d containing an area | region.

  Laser light is incident on the rectangular rectangular space 12 of the waveguide beam homogenizer 1 and propagates in the longitudinal direction while being repeatedly reflected at various angles not only on the upper and lower inner wall surfaces but also on the left and right inner wall surfaces with respect to the traveling axis. As a result, the spatial intensity distribution of the laser light is made uniform. At this time, the rectangular space 12 is sectioned, and the laser light in various polarization states is mixed and propagates on the metal inner wall surface 13 on which the dielectric thin film is formed while repeating reflection.

  FIG. 2 is a schematic vertical cross-sectional view of a rectangular cross-sectional space 12 defined by a metal inner wall surface 13 on which a dielectric thin film 14 is formed. The laser beam is reflected by the boundary surface between the rectangular space 12 and the dielectric thin film 14 and the metal inner wall surface 13. A polarized wave in which the electric field of the laser light 21 incident on each reflecting surface is perpendicular to the incident surface is called an S-polarized wave, and a polarized wave parallel to the incident surface is called a P-polarized wave. The reflectance of the laser beam 21 on the reflecting surface depends on the polarization state of the incident laser beam 21 and the thickness of the dielectric thin film 14.

FIG. 3 shows a reflection surface in which a germanium thin film (dielectric thin film 14) is formed on a copper wall surface (metal inner wall surface 13). When CO ₂ laser light having a wavelength of 10.6 μm is incident at 10 ° and 10 °, the reflectance of the S-polarized wave (Rs), the reflectance of the P-polarized wave (Rp), and the phase of the film thickness d of the germanium thin film The average reflectance (Ra) is shown. 3A to 3C, the reflectance (Rs) of the S-polarized wave is indicated by a solid line, the reflectance (Rp) of the P-polarized wave is indicated by a broken line, and the average reflectance (Ra) is indicated by a one-dot chain line. ing.

  The reflectance of S-polarized wave (Rs) and the reflectance of P-polarized wave (Rp) are the basics of optical transmission issued by Shoshodo Co., Ltd. (Miyanobu Mitsunobu, first published on May 27, 1991) ), Pages 122 to 128.

  As can be seen from FIG. 3, in general, when the dielectric thin film 14 is not formed (d = 0), the reflectance at the metal inner wall surface 13 is the reflectance of the S-polarized wave when the angle θ is shallow (small). (Rs) is a value close to 100%, while the reflectance (Rp) of the P-polarized wave is very small. As the angle θ becomes deeper (larger), the reflectivity (Rs) of the S-polarized wave decreases and the reflectivity (Rp) of the P-polarized wave increases, and when θ = 90 ° (incident angle 0 °), the reflection occurs. Since the direction of polarized light with respect to the surface does not make sense, both agree, and the theoretical reflectance at that time is 98.7%.

  That is, the reflectivity of the normal incidence copper mirror can be obtained in this way, but when the laser beam is incident at a shallow angle with respect to the reflection surface as in the waveguide beam homogenizer of the present invention. The reflectivity varies greatly depending on the polarization state of incident light.

  In general, as shown in FIG. 3, the reflectance with respect to the metal surface is such that the reflectance (Rs) of the S-polarized wave is larger than the reflectance (Rp) of the P-polarized wave, and the laser beam is at a shallow angle to the reflecting surface. The difference is large in the incident range.

  When the dielectric thin film 14 is formed on the metal inner wall surface 13, the reflectance (Rs) of the S-polarized wave is slightly reduced, but the reflectance (Rp) of the P-polarized wave can be greatly increased. Moreover, there exists a film thickness of the dielectric thin film 14 in which the reflectances of the two coincide with each other, and the reflectances of both are reversed when the film thickness is further increased.

  When the dielectric thin film 14 is formed on such a metal inner wall surface 13, the reflectance of each polarized wave depends on the film thickness of the dielectric thin film 14, and periodically changes as the film thickness increases.

  In the waveguide beam homogenizer 1 of the present invention, since the propagation region of the laser light is the rectangular space 12, even if the S-polarized laser light is incident on one wall surface, P-polarized laser light is incident. As the number of reflections is increased in order to make the beam intensity uniform, the polarization state of the laser light is mixed, and the ratio of the laser light of the S-polarized wave and the P-polarized wave is averaged.

  Therefore, in order to minimize transmission loss, in the present invention, the thickness of the dielectric thin film 14 provided therein is set to the average reflectance (Ra) of the reflectance of the S-polarized wave (Rs) and the reflectance of the P-polarized wave (Rp). ) Is set to the maximum.

  When a germanium thin film is used as the dielectric thin film 14, the average reflectance (Ra) of the reflectance (Rs) of the S-polarized wave and the reflectance (Rp) of the P-polarized wave is maximized as shown in FIG. The film thickness da is 0.46 μm and 0.86 μm when the angle θ is 1 °, 0.45 μm and 0.87 μm when the angle θ is 5 °, and 0.41 μm and 0 when the angle θ is 10 °. The film thickness da having the maximum average reflectance (Ra) appears periodically even in a region where the film thickness is .91 μm and the film thickness is thicker.

  In the vicinity of the film thickness da of the dielectric thin film 14 at which the average reflectivity (Ra) is maximum, the change in the average reflectivity (Ra) is insensitive to the film thickness d of the dielectric thin film 14, but S-polarized light. The reflectance of the wave (Rs) and the reflectance of the P-polarized wave (Rp) do not match. When the germanium thin film is used as the dielectric thin film 14, the thickness db of the dielectric thin film 14 having the same reflectivity does not substantially depend on the angle θ as shown in FIG. 3, and is 0.56 μm and 0.76 μm. It was found to exist. The film thickness db in which the reflectance (Rs) of the S-polarized wave and the reflectance (Rp) of the P-polarized wave coincide with each other also periodically appears in a thicker region.

  The film thickness d of the dielectric thin film 14 is the film thickness da when the average reflectance (Ra) of the S-polarized wave and the P-polarized wave is the largest, and the S-polarized wave existing closest to the film thickness da. With the film thickness db when the reflectivity (Rs) and the reflectivity (Rp) in the P-polarized wave become equal, if the value falls outside this range, the reflectivity rapidly decreases, or the S-polarized wave and the P-polarized wave. The difference in wave reflectance becomes larger.

  Therefore, in the present invention, as an allowable range of the film thickness d of the dielectric thin film 14, the reflectance (Rs) of the S-polarized wave of the laser light incident at the deepest angle θ on the metal inner wall surface 13 on which the dielectric thin film 14 is formed. The film thickness da when the average reflectivity (Ra) of the reflectivity (Rp) in the P-polarized wave is the largest, and the reflectivity (Rs) and P in the S-polarized wave that is closest to the film thickness da It was set to be in a range between the film thickness db when the reflectance (Rp) in the polarized wave is equal (when da <db, da ≦ d ≦ db, and when da> db, db ≦ d ≦ da). With this setting, high reflectivity is maintained regardless of the polarization state, and when the polarization state of the laser light incident on the homogenizer fluctuates, for example, a laser transmission system such as a laser treatment device can be used as a human Even in the case of arbitrary movement by hand, fluctuations in the laser output can be suppressed.

  In a specific embodiment of the present invention, a laser beam having a beam diameter of 10 mm is collected by a condenser lens having a focal length of 28 mm and is incident on the waveguide beam homogenizer 1 in FIG. At this time, the angle θ of the laser beam incident at the deepest angle on the metal inner wall surface 13 on which the dielectric thin film 14 is formed is approximately 10 °. That is, in the example of the present invention, the film thickness range of the germanium to be incorporated is set to be 0.41 μm or more and 0.56 μm or less.

  In the present embodiment, the waveguide beam homogenizer 1 also propagates the laser light incident on the metal inner wall surface 13 on which the dielectric thin film 14 is formed at a shallower angle as a low-order mode. As can be seen from FIG. 3, in the germanium film thickness range of 0.41 μm to 0.56 μm, the angle θ is smaller, that is, a laser incident at a shallow angle with respect to the metal inner wall surface 13 on which the dielectric thin film 14 is formed. The reflectance is higher as light is applied, and the difference in reflectance due to the difference in polarization is also smaller. Therefore, if the allowable film thickness range of the dielectric thin film 14 is set with respect to the laser beam incident at the deepest angle on the metal inner wall surface 13 on which the dielectric thin film 14 is formed, the allowable film thickness range is shallower. A high reflectance can be maintained even for laser light incident at an angle, and the polarization dependence of the reflectance can be suppressed.

  The effective film thickness range according to the present invention also exists in a region where the film thickness is larger, but in a specific embodiment of the present invention, the film thickness range of the dielectric thin film is the thinnest film thickness tolerance range (0. 41 μm or more and 0.56 μm or less). Even if the allowable range is set in a region where the film thickness is thicker, that is, the film thickness of germanium is set to be 0.76 μm or more and 0.91 μm or less, the effect of the present invention is exhibited. However, in general, as the film thickness increases, problems such as uniformity of film thickness distribution, film surface roughness, and film absorption loss may occur, which may adversely affect the propagation characteristics of the light beam. Thus, the film thickness range of the dielectric thin film 14 is preferably set to the thinnest allowable film thickness range.

  In the above embodiment of the present invention, germanium is used as the dielectric thin film 14, but as another embodiment, FIG. 4 shows a case where zinc selenide is used as the dielectric thin film 14.

FIG. 4 shows a reflection type surface in which a zinc selenide thin film (dielectric thin film 14) is formed on a copper wall surface (metal inner wall surface 13) using a waveguide beam homogenizer 1 using the same incident lens system as described above. CO ₂ laser light having a wavelength of 10.6 μm is incident at an angle θ (incident angle of incident angle) of 5 ° (FIG. 4A), 5 ° (FIG. 4B), and 10 ° (FIG. 4C). Shows the reflectivity (Rs) of the S-polarized wave, the reflectivity (Rp) of the P-polarized wave, and the arithmetic average reflectivity (Ra) with respect to the film thickness d of the zinc selenide thin film. . Also in this case, since the angle θ of the laser beam incident at the deepest angle on the metal inner wall surface 13 on which the dielectric thin film 14 is formed is about 10 °, the allowable thickness range of the zinc selenide thin film is shown in FIG. As shown in c), it is 0.73 μm or more and 0.91 μm or less.

  Zinc selenide has a refractive index of 2.4 at a wavelength of 10.6 μm, which is smaller than that of germanium, and a higher reflectance can be obtained. Further, since the increase in absorption loss due to thermal runaway is small, it is suitable mainly for kW class laser processing. On the other hand, since germanium is a non-toxic material, it is useful as a waveguide beam homogenizer attached to the handpiece part of a medical laser treatment device.

  In the waveguide type beam homogenizer for infrared laser, zinc sulfide, calcium fluoride, copper oxide, copper iodide, etc. are transparent in the infrared wavelength band in addition to the above-described germanium and zinc selenide. Is demonstrated. For lasers in the near-infrared wavelength band, the quartz material is transparent and effective.

  These dielectric thin films 14 are formed by sputtering or vapor deposition. When using copper oxide or copper iodide, which is a copper compound, as the dielectric thin film 14, the metal inner wall surface 13 made of a copper material is used. The surface may be oxidized or iodinated to form a dielectric thin film 14 (copper oxide or copper iodide).

  The rectangular rectangular space 12 of the waveguide beam homogenizer 1 in FIG. 1 has a square cross-sectional structure, but regardless of this, for example, a rectangular cross-sectional structure as shown in FIG. 5 may be used.

  In the waveguide beam homogenizer 1 according to the present invention, the four metal members constituting the waveguide member are the same in all four cross-sectional shapes as shown in FIG. 1, or at least in the cross-sectional rectangular space 52 as shown in FIG. The cross-sectional shapes of the members are assumed to be the same. As a result, the manufacturing cost can be reduced because it is possible to manufacture at the same time or fewer processing steps when polishing the wall surface of each member forming the rectangular space of the cross section or forming a desired dielectric thin film on the wall surface. .

  In addition, since the waveguide beam homogenizer 1 formed by assembling four metal members has a circular outer cross section, for example, when mounted on the handpiece portion of a laser treatment device, The structure can be easily held.

  Further, FIG. 6 shows a waveguide beam homogenizer 6 which is another embodiment of the present invention, (a) is a front view seen from the incident side of laser light, and (b) is a side view. FIG.

  The incident side of the laser beam has a circular incident port 65, and the space in which the laser beam propagates smoothly from the circular cross-sectional space to the rectangular cross-sectional space 62 having one side smaller than the diameter of the incident port 65 in the longitudinal direction. In other words, the rectangular rectangular space 62 is connected to a cross-sectional shape converting portion 67 having a conical side surface shape whose diameter increases toward a circular incident port 65 into which laser light is incident. .

  With such a structure, laser light from a laser light source can be directly incident without using a condenser lens. In addition, it is preferable that the inner wall surface of the cross-sectional shape converting portion 67 having a conical side surface shape on the incident side is also smooth by polishing and a dielectric thin film is formed. The film thickness of the dielectric thin film formed on the wall surface is formed to be equal to the film thickness of the dielectric thin film 14 formed in the rectangular space 62 in cross section.

  1, 5 and 6, oxygen-free copper was used for the four metal members (hollow metal members 10, 50 and 60) constituting the waveguide beam homogenizer. Oxygen-free copper is the most suitable material for the waveguide beam homogenizer of the present invention in terms of thermal conductivity, reflectance, and cost. Although the polished oxygen-free copper surface is active and easily altered, long-term stable characteristics can be obtained by coating the dielectric thin film.

  Oxygen-free copper is excellent in heat conduction and is advantageous in releasing heat generated by loss of laser light. Especially, the cooling effect by water-cooling metal members is great, and kW-class laser light such as surface treatment of various metals. Can also be handled.

Although the embodiment of the waveguide beam homogenizer of the present invention has been described for the CO ₂ laser as described above, other infrared lasers such as other CO lasers, Er-YAG lasers, free electron lasers, quantum cascade lasers, etc. Even in a laser having a wavelength band below the near infrared, the effect of the present invention is exhibited by using a transparent dielectric material in each wavelength band.

  As described above, according to the present invention, it is possible to provide a waveguide type homogenizer that is sufficiently optically and thermally durable to a high-power laser beam and that is inexpensive and mechanically strong. Can do. Further, the transmission loss of the waveguide beam homogenizer and the polarization dependence of the laser beam can be suppressed to a very small level. Furthermore, it can be sized so that it can be easily stored in a small member of the handpiece attached to the tip of the transmission path of the laser treatment device, so that it can be held in the hand like a pen and operated with laser light. Is also easy. Alternatively, it is possible to provide a stable waveguide beam homogenizer with a high breakdown threshold even for a high-power laser beam of kW class that enables metal surface treatment.

1, 5, 6 Waveguide type homogenizer 10, 50, 60 Hollow metal member 11a, 11b, 11c, 11d, 51a, 51b, 51c, 51d, 61a, 61b, 61c, 61d Metal member 12, 52, 62 Cross section rectangle Space 13, 53, 63 Metal inner wall surface 14, 54, 64 Dielectric thin film 15 Screw hole 21 Laser beam

Claims (5)

  In a waveguide beam homogenizer in which a dielectric thin film is formed on a metal inner wall surface of a hollow metal member having a rectangular cross-sectional space through which laser light propagates, the electric field of the laser light incident on the dielectric thin film is relative to the incident surface When a polarized wave that is perpendicular is an S-polarized wave and a polarized wave that is parallel to the incident surface is a P-polarized wave, the thickness d of the dielectric thin film is incident on the dielectric thin film at the deepest angle. The film thickness da when the reflectance of the S-polarized wave of the laser light and the reflectance of the P-polarized wave are the largest, and the reflection of the S-polarized wave that is closest to the film thickness da The waveguide type beam homogenizer is set so as to be between the refractive index and the film thickness db when the reflectance in the P-polarized wave is equal.   The hollow metal member is formed by joining four metal members so that the outer cross-sectional shape is circular, and the cross-sectional rectangular space is defined by the metal inner wall surface at the center, and the cross-sectional rectangular space is sandwiched between the hollow metal members. 2. The waveguide type beam homogenizer according to claim 1, wherein at least the metal members facing each other have the same cross-sectional shape.   3. The waveguide type according to claim 1, wherein the rectangular cross-sectional space is connected to a shape converting portion having a conical side surface shape whose diameter increases toward a circular incident port into which the laser light is incident. Beam homogenizer.   The hollow metal member is made of oxygen-free copper, and the dielectric thin film is made of germanium, zinc selenide, zinc sulfide, calcium fluoride, copper oxide, copper iodide, or quartz. Item 4. The waveguide beam homogenizer according to any one of Items 1 to 3. In a method for manufacturing a waveguide homogenizer in which a dielectric thin film having a predetermined film thickness is formed on a metal inner wall surface of a hollow metal member having a rectangular space in which a laser beam propagates,
When a polarized wave in which the electric field of the laser beam incident on the dielectric thin film is perpendicular to the incident surface is an S-polarized wave, and a polarized wave parallel to the incident surface is a P-polarized wave,
Determining the film thickness da when the arithmetic mean reflectance of the reflectance of the S-polarized wave and the reflectance of the P-polarized wave of the laser light incident at the deepest angle on the dielectric thin film is maximized;
After determining the film thickness db when the reflectance in the S-polarized wave and the reflectance in the P-polarized wave existing closest to the film thickness da are equal,
A method of manufacturing a waveguide beam homogenizer, characterized in that a film thickness d of the dielectric thin film is set to be between the film thickness da and the film thickness db.

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