JPH02234105A - Hollow waveguide tube for ultraviolet wavelength range laser beam - Google Patents

Abstract

PURPOSE:To prevent transmission efficiency from decreasing owing to the decrease of reflection factor by using a glass tube which has high transmissivity to ultraviolet light and superior environment resistance as the internal surface of the waveguide and forming a metallic film which has a high reflection factor to ultraviolet light at the outside of it. CONSTITUTION:The waveguide 3 is constituted by forming an aluminum film 1 on the external surface of the quartz glass tube by a CVD method, etc. Here, the optical axis 8 of the laser beam (l) is made coincident with the center axis 6 of the waveguide 3, the position of a focus 7 is on the center axis 6 of the waveguide, and the laser beam (l) is all made incident on the internal surface of the quartz glass tube 2 of the waveguide 3. The incident laser beam (l) is transmitted while being reflected by the surface of the quartz glass tube 2 and the boundary surface between the quartz glass tube 2 and aluminum film 1. Thus, the reflecting surface of the metallic film 1 contacts the external surface of the glass tube, so the reflecting surface is not brought into contact with air and its surface is not covered with an oxide film to decrease in reflection factor, so the transmission efficiency is prevented from deteriorating.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a hollow waveguide that can transmit high-power laser light in the ultraviolet wavelength range with high efficiency.

[Prior art]

Laser light having a wavelength in the ultraviolet region, such as excimer laser, has high energy, and is used in laser CVD,
Its application range is extremely wide, including surface modification and photochemical synthesis. Furthermore, in the medical field, it is used in combination with an endoscope for internal surgery, and in the industrial field, it is used for microfabrication.

In the practical application of the above-mentioned Caesar light in the industrial and medical fields,
Establishing waveguide technology that efficiently guides it to its destination is an essential requirement. Laser light with a short wavelength and high peak power, such as excimer laser, is harmful to living organisms, and there are difficult problems in safely transmitting it to a remote location. Furthermore, there has been a demand for waveguides that can easily transmit such laser light to locations where it is needed, especially from medical distribution facilities and the like.

Conventionally, methods for transmitting high-energy laser light such as a laser having a wavelength in the ultraviolet range, such as an excimer laser, include:
There were methods (1) to (3) below.

(1) Method using silica-based optical fiber As shown in Figure 6, the core 51 is made of quartz glass that has good transmittance for light in the ultraviolet region, and the cladding 5 surrounding it
2 is made of quartz glass doped with impurities such as fluorine,
This method uses a glass fiber made of two types of glasses with a refractive index smaller than that of the core 51, and transmits the light P while reflecting the laser light at the interface between the fiber 51 and the cladding 52.

Some cores are doped with hydroxyl groups to reduce absorption at specific wavelengths. Note that FIG. 6(a) is a cross-sectional view of the glass fiber, and FIG. 6(b) is a vertical cross-sectional view thereof.

(2) Method using an aluminum tube waveguide As shown in Figure 7, an aluminum tube 53 made of aluminum, which has a high reflectance for ultraviolet light, is used, and its inner surface is polished to increase the inner reflectance. Light is reflected on the inner surface of the aluminum tube 53! A method that uses a so-called hollow waveguide to transmit. Note that FIG. 7(a) is a cross-sectional view of the aluminum tube, and FIG. 7(b) is a longitudinal cross-sectional view thereof.

(3) Aluminum plate rectangular hollow path method As shown in FIG. 8, two metal flat plates 54.
54 is used as a reflector, dielectric spacers 55 are sandwiched between its lateral ends, and a waveguide is used in which the interval between the hollow paths is kept constant. is transmitted while being reflected by two flat metal plates 54, 54.

The flat metal plates 54, 54 are made of aluminum having a high reflectance for light in the ultraviolet region, and the inner surfaces of the hollow passages are polished. Additionally, Teflon is used for the dielectric spacer. Note that FIG. 8(a) is a cross-sectional view of the rectangular hollow channel of an aluminum plate, and FIG. 8(b) is a longitudinal cross-sectional view thereof.

[Problem to be solved by the invention]

However, although the conventional method (1) using a silica-based optical fiber has good transmission efficiency, the damage threshold of the input end face is low, and if the energy density of the incident light is high, the input end face will be destroyed. There was a problem. Furthermore, there are wavelengths at which light absorption occurs at wavelengths corresponding to the bond energy between atoms of the material of the core 51, resulting in extremely low transmittance. Moreover, temporal changes in the transmission rate also become large, which poses a problem. In addition, although the incident power of (2) Y type using an aluminum tube waveguide can be increased, as the diameter of the waveguide becomes smaller, it is difficult to polish the inner surface, and the reflectance of the inner surface decreases over time due to oxidation etc. There is a problem that efficiency decreases.

In addition, the method (3) using an aluminum plate rectangular hollow channel allows the incident power to be increased and the inner surface of the reflector to be easily polished, as in (2) above, but the method is similar to (2) above. products) are difficult to produce.Also,
Similar to (2) above, there is a problem in that the reflectance of the inner surface decreases due to oxidation and the like, resulting in a decrease in transmission efficiency.

The present invention has been made in view of the above-mentioned points, and eliminates the above-mentioned problems, and eliminates the need for difficult processes such as internal polishing, and reduces transmission efficiency due to reduction in reflectance due to absorption and oxidation of the reflective surface. It is an object of the present invention to provide a hollow waveguide for laser light in the ultraviolet wavelength range that does not deteriorate.

[Means to solve the problem]

In order to solve the above problems, the present invention uses a glass tube made of a glass material such as quartz that has high transmittance to ultraviolet light and has excellent environmental resistance as the inner surface of the waveguide, and has a The present invention is characterized in that a metal film with a high reflectance is formed in the glass tube, and the laser light in the ultraviolet wavelength range is transmitted while being reflected on the inner surface of the glass tube and the interface between the glass tube and the gold-plated film.

Another feature is that a laser beam in the ultraviolet wavelength range is transmitted while flowing a material fluid with high ultraviolet light transmittance through the space inside the glass tube.

[Effect]

With the above configuration, since the glass tube is used, the laser beam is incident on the inner surface of the waveguide, and the incident area is large, so the damage threshold per unit area is the same as the end face in the case of (1) above. Even so, the damage threshold of the incident energy becomes larger in total.

In addition, since a metal film is formed on the outer surface of the glass tube, the surface roughness of the metal film becomes the surface roughness of the outer surface of the glass tube, and since this surface roughness is about several tenths of a micrometer, methods such as decomposition polishing are used. An excellent reflective surface with a polished surface roughness of less than a few μm/J% can be easily obtained.

Further, since the reflective surface of the metal film is in close contact with the outer surface of the glass tube, the reflective surface does not come into contact with air, and the surface is not covered with an oxide film and the reflectance is not reduced.

In addition, a material fluid with high ultraviolet light transmittance can be flowed into the waveguide interior space, improving transmission efficiency and reducing the temporal decrease in transmission rate due to the cooling effect.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a cross-sectional view of a hollow waveguide for ultraviolet wavelength laser light according to the present invention. As shown in the figure, the waveguide 3 has a structure in which an aluminum film 1 is formed on the outer surface of a quartz glass tube 2 by an appropriate method such as CVD, PVD, or vacuum evaporation.

FIG. 2 is a diagram for explaining how a laser beam is transmitted through the quartz glass tube 2 of the waveguide 3 having the above configuration.As shown in the figure, the incident laser beam! is transmitted while being reflected on the surface of the quartz glass tube 2 and the interface between the quartz glass tube 2 and the aluminum film 1.

FIG. 4 is a diagram for explaining how the laser beam P is incident on the waveguide 3. The laser beam 2 coming out of the laser device 5 is focused by the focusing lens 4 and is inside the waveguide 3. Guided by
Transmission is carried out through the waveguide 3 as described above.

Figure 4 shows a focused laser beam! is a diagram showing the positional relationship between the focal point 7 and the waveguide 3, where the optical axis 8 of the laser beam and the central axis 6 of the waveguide 3 are aligned, and the position of the focal point 7 is aligned with the central axis 6 of the waveguide.
above, so that all the laser light P enters the inner surface of the quartz glass tube 2 of the waveguide 3. As a result, the incident laser beam is transmitted while being reflected at the surface of the quartz glass tube 2 and the interface between the quartz glass tube 2 and the aluminum film 1, as shown in FIG. By configuring the waveguide 3 as shown in Fig. 1, silica glass has a high transmittance to ultraviolet light and is a glass with excellent environmental resistance, and aluminum has a high reflectance to ultraviolet light. , the incident laser beam e hits the surface of the quartz glass tube 2 and the quartz glass tube 2 and the aluminum film 1.
The attenuation during transmission while being reflected at the interface with is extremely small.

Further, since the quartz glass tube 2 is used and the laser beam P is incident on the inner surface of the quartz glass tube 2, the incident area is large, so that the damage threshold of the incident energy becomes large in total.

In addition, aluminum is coated on the outer surface of the quartz glass tube 2 by CVD,
Since the aluminum film 1 is formed by an appropriate method such as PVD or vacuum evaporation, the surface roughness of the aluminum film 1 is the same as that of the outer surface of the quartz glass tube 2, and the surface roughness is about several tenths of a μm. Therefore, it is possible to easily obtain an excellent surface with a polished surface roughness of less than several μm by a method such as electrolytic polishing.

In addition, although aluminum is a metal with a high reflectance for ultraviolet light, it is a metal that is easily oxidized, and if it is placed in the air, the surface will immediately become coated with aluminum oxide as its main component, which will immediately reduce the laser beam reflection efficiency. covered in. However, in this embodiment, the aluminum film 1 is formed by CVD, PV
The process is carried out in a high vacuum atmosphere such as D or vacuum evaporation, and the reflective surface that reflects the laser beam is formed in close contact with the outer surface of the quartz glass tube 2, so it never comes into contact with air and the surface is coated with an oxide film. It will not be covered and the reflectance will not decrease.

FIG. 5 is a diagram showing a schematic configuration of an apparatus for transmitting laser light by flowing nitrogen gas N through a waveguide.

A gas inlet 10 is provided in the fixture 9 to which the focusing lens 4 is attached. While flowing nitrogen gas N from this gas inlet 10 into the quartz glass tube 2 of the waveguide 3, a laser beam is generated!
When entering the waveguide 3 (see Figure 4), since nitrogen gas is a substance with good ultraviolet light transmittance, it not only suppresses the attenuation of the transmittance due to ultraviolet light absorption, but also allows the waveguide 3 to be exposed to light from the outside. It functions to prevent the inflow of substances and to cool the waveguide 3. In the above embodiment, the quartz glass tube 2 was used as the glass tube of the waveguide 3, but any glass that has high transmittance to ultraviolet light and excellent environmental resistance may be used. It's not something you can do.

Further, although the aluminum film 1 was used as the metal film on the outer surface of the glass tube, the metal of this film is not limited to aluminum as long as it has a high reflectance to ultraviolet light. In addition, nitrogen gas was used as the substance flowing into the waveguide 3, but
The fluid is not limited to nitrogen gas as long as it is made of a substance with good ultraviolet light transmittance.

〔Effect of the invention〕

As explained above, according to the present invention, the following excellent effects can be obtained. (1) Since a glass tube is used as the inner surface of the waveguide, the incident surface of the laser beam is the inner surface of the glass tube, and since the incident area is large, the damage threshold of the incident energy becomes large in total. <<2>> Since a metal film is formed on the outer surface of the glass tube, the surface roughness of the metal film becomes the surface roughness of the outer surface of the glass tube, and since this surface roughness is about a few tenths of a micrometer, methods such as electrolytic polishing can be used. An excellent reflective surface with a polished surface roughness of less than a few μm can be easily obtained.

(3) Since the reflective surface of the metal film is in close contact with the outer surface of the glass tube, the reflective surface does not come into contact with air during or after formation, and the surface is not covered with an oxide film and the reflectance does not decrease. (4) By flowing a material fluid with good ultraviolet light transmittance into the waveguide interior space, transmission efficiency is improved, and its cooling effect reduces the temporal decrease in transmission rate.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a hollow waveguide for laser light in the ultraviolet wavelength range according to the present invention, Figure 2 is a diagram for explaining how laser light is transmitted through the waveguide, and Figure 3 is Figure 4 is a diagram to explain how the laser beam is incident on the waveguide. Figure 4 is a diagram showing the positional relationship between the focal point of the laser beam and the waveguide. Figure 5 is a diagram showing how nitrogen gas is introduced into the waveguide. FIG. 6, FIG. 7, and FIG. 8 are diagrams each showing a schematic configuration of a device for transmitting conventional high-energy laser light. In the figure, 1...aluminum film, 2...quartz glass tube, 3...waveguide, 4...focusing lens, 5...
...Laser device, 6.. Central axis, 7.. Focus, 8.. Optical axis, 9.. Equipment, 10.. Gas inlet. Figure 1 Applicant Sakaki←←Kaiho Co., Ltd. (1 other person) Agent Patent attorney Takashi Kumagai (1 other person) Figure 2 Figure 5 Figure [L: Lノ (b No. 6 Figure 7) Figure 8 Figure t

Claims (2)

[Claims] (1) The inner surface of the waveguide is a glass tube made of a glass material that has high transmittance to ultraviolet light and excellent environmental resistance, and a metal film with high reflectance to ultraviolet light is formed on the outside. A hollow waveguide for laser light in the ultraviolet wavelength range, characterized in that the laser light in the ultraviolet wavelength range is transmitted while being reflected at the inner surface of the glass tube and the interface between the glass tube and the metal film. (2) A hollow waveguide for ultraviolet wavelength laser light according to claim (1), characterized in that the ultraviolet wavelength laser beam is transmitted while flowing a material fluid with good ultraviolet light transmittance through the space inside the glass tube. tube.