JPH04196378A - Excimer laser wavelength selection element - Google Patents

Abstract

PURPOSE:To easily dissipate heat generated inside an etalon so as to enable it to be protected against deformation due to heat and to keep constant in initial optical characteristics for a long term by a method wherein heat dissipating grooves or fins are provided to the outer surface of the cylindrical etalon. CONSTITUTION:Grooves 45 or heat dissipating fins 46 are provided to the outer surface of a cylindrical etalon 4 which serves as a wavelength selection element. As mentioned above, the grooves 45 or the heat dissipating fins 46 are provided to the outer surface of the cylindrical etalon 4, whereby the etalon 4 can be enhanced in heat dissipating properties. As a result, the etalon can be prevented from deteriorating in optical characteristics due to deformation caused by heat. By this setup, the etalon 4 can be restrained from increasing in temperature, so that it can be kept constant in initial optical characteristics through a long time.

Description

DETAILED DESCRIPTION OF THE INVENTION 1. Field of Industrial Application] The present invention relates to a wavelength selection element for an excimer laser that is incorporated into a narrowband laser device.

[Prior Art] FIG. 6 shows a laser device using a conventional laser wavelength selection element (etalon) disclosed in, for example, Japanese Unexamined Patent Publication No. 62-198182. In the figure, a total reflection mirror (1)
An etalon (4) as a wavelength selection element is disposed within a cavity of an excimer laser having a resonator consisting of a laser beam and an output mirror (2).

(3) is a chamber sealed by windows (5a) and (5b), and the chamber (3) is filled with a laser medium (6) such as a mixed gas of argon and nitrogen, or krypton. It is filled with a mixture of gas and fluorine.

Next, the operation will be explained. When a discharge is performed in a chamber (3) filled with a laser medium, a total reflection mirror (1)
Laser oscillation occurs between the output mirror (2) and the output mirror (2). In case 2, since an etalon (4) is inserted between the total reflection mirror (1) and the output mirror (2), the wavelength is selected and a laser beam (L) with a narrow spectrum width is emitted.

As shown in FIG. 5, the etalon (4) consists of two synthetic quartz substrates (44a) and (41b) with a high reflection film (43) formed on one surface and an antireflection film (44) formed on the other surface. > spacers (42) so that the high reflective films (43) face each other.
wavelength selectivity is obtained by multiple reflection and interference of light between the gap between the two opposing high reflection film surfaces (43).

-Problems to be Solved by the Invention] In the conventional wavelength selection element for excimer laser as described above, the etalon is used in such a way that light enters at a slight angle with respect to the incident surface of the etalon. Therefore, in principle, some of the incident light does not resonate and deviates from the optical axis, resulting in loss.

Surfaces A and B in Figure 8 are the gear and knob surfaces of the etalon, respectively.
Alternatively, it is a highly reflective film surface (43), and C and D are the incident light and the outgoing light of the etalon l\. Light C incident from A side
After repeating multiple reflections between the gears and knobs on surfaces A and B,
Emitted from the B side. In case 2, part a is extracted as effective light, but part b does not interfere sufficiently and cannot be extracted as effective light, resulting in a loss. Furthermore, since both the high reflection film (43) and the antireflection film (44) of the etalon do not have ideal reflection and transmission surfaces, scattering of light on these surfaces also causes the light to deviate from the optical axis. It will be a loss.

Of the light incident on the etalon, the light that deviates from the optical axis of the light is unnecessary light.

In conventional etalons, some of these unnecessary lights off the optical axis are converted into heat as they are repeatedly reflected inside the etalon, raising the temperature of the etalon and causing distortion due to thermal expansion. 〉The function as 〉I!
There was a point.

The second invention was made to solve the above-mentioned problems, and was designed to provide an excimer laser wavelength that can reduce the temperature rise of the etalon and maintain its initial characteristics over a long period of time. The purpose is to obtain a selective element. Means for Solving Problem '11] The wavelength selection element for an excimer laser according to the second invention is provided with a rim on the outer cylindrical surface of the etalon, which is the wavelength selection element, or
A heat dissipation fin is installed around the outer circumference of the etalon.

2 Effects] In the present invention, by providing grooves or semi-radiating fins on the outer circumferential cylindrical surface of the etalon, the heat radiation effect is enhanced and deterioration of optical characteristics due to thermal distortion is prevented.

[Embodiment] FIGS. 1 and 2 show an embodiment of the present invention. In the figures, (45) is a synthetic quartz substrate (41a), (41b)
) are the same parts on the right as in FIG. 7 with the same reference numerals.

With the above configuration, synthetic quartz substrates (41a), (4
In the wavelength selection element (4) in which the heat radiation 1 (45) is provided on the outer cylindrical surface of 1b), it is possible to easily dissipate the heat generated inside the etalon, suppress the temperature rise of the etalon, and reduce thermal distortion. It can be reduced.

Laser devices, especially etalons for short wavelength lasers such as excimer lasers, control light on the order of pm (picometers), so the distance between the gaps on the substrate and the surface accuracy of the gap surfaces must be extremely accurate. is required.

According to this embodiment, it is possible to reduce thermal strain, which is a factor in reducing precision, and to improve the performance of the etalon and, by extension, the performance of the laser device.

Table 1 shows the experimental results in this example.

Table 1 shows how the etalon was treated with KrF excimer (wavelength 248 mm, 20]1z, 10 mJ/cm:)
This figure shows the temperature rise of the etalon when operated for 30 minutes, and the wavelength shift caused by thermal strain caused by the temperature rise. From Table 1, it can be seen that the performance of the etalon according to the present invention is improved compared to the conventional etalon. The above shows an example of the application of the present invention to an air cap type etalon.The present invention can also improve the performance of the two parallel plate type and solid type etalons as well as the air gap type.

Further, the direction of the heat dissipation groove (45) may be any vertical, horizontal, or diagonal direction.

Figures 3 and 4 show heat dissipation with solid etalon (45)
shows another embodiment in which the direction is vertical. The same reference numerals as in FIG. 1 indicate the same parts.

The above configuration provides the same effects as the previous embodiment.

Furthermore, instead of directly processing the heat dissipation grooves on the synthetic quartz substrate (41), heat dissipation fins made of a material with high thermal conductivity, such as aluminum, can be mounted on the circumferential surface of the conventional etalon. good. An example thereof is shown in FIG. In the figure, (46) is a post-installed heat dissipation fin.

With the above configuration, the scattered light inside the etalon will not be emitted in the direction of the cylindrical surface, and there will be no reaction with the etalon holder (not shown), which is made of some material or organic matter, so the etalon will not be contaminated and will be stable and clean for a long time. Another effect is that a good surface condition can be obtained.

Note that as means for controlling the wavelength selected by the etalon, any of the following methods can be used: changing the distance between the gaps, or changing the angle between the optical axis of the laser beam and the etalon.

[Effect of the invention j As described above, according to the second invention, by providing heat radiation grooves or radiation fins on the outer cylindrical surface of the etalon, it is possible to easily dissipate the heat generated inside the etalon and reduce thermal distortion of the etalon. However, it has the effect of maintaining initial optical characteristics for a long period of time.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of one embodiment of the invention, FIG. 2 is a longitudinal sectional view, FIG. 3 is a perspective view of another embodiment, FIG. 4 is a longitudinal sectional view, and FIG. Perspective view of another embodiment, No. 6
7 is a side view of a conventional excimer laser etalon, and FIG. 8 is an optical path diagram of the one shown in FIG. 7. (4) Etalon (wavelength selection element), (45)
- Heat radiation groove, (46)... Heat radiation fin. In each figure, the same reference numerals indicate the same or corresponding parts. Agents: Soga, Michiharu PF,
Figure 1 Original Figure 2 ′'''8 Pl-) Figure 3 Onion Figure 4 W) Figure 6

Claims (1)

[Claims] 1. A wavelength selection element for an excimer laser disposed in a laser resonator, the wavelength selection element for an excimer laser being characterized in that either a heat radiation groove or a heat radiation fin is provided on an outer circumferential cylindrical surface.