JPH0423480A - Narrow band laser device - Google Patents

Abstract

PURPOSE:To realize high output by forming an obtuse angle between a surface intersecting with laser light and a surface adjacent thereto with a prism to reflect laser light outside an optical path in the optical path. CONSTITUTION:A prism 30 to reflect laser light outside an optical path 28 is put on the optical path 28 and an obtuse angle is formed between a surface 33 intersecting with laser light and a surface 34 adjacent thereto. A diffraction grating 32 is disposed at an angle which makes an incident angle and a reflection angle the same to light having a specified wavelength. Laser light which is diffracted and narrow-band processed by the diffraction grating 32 after generated at a laser excitation part 20 is directed inside the laser excitation part 20 and amplified. Meanwhile, a part of laser light which is reflected by a high reflection mirror 27 and projected from a transmitting window 21b at a specified divergence angle passing through a control member 26 is directed to the prism 30, and the rest thereof goes outside as output. Since there is scarecely any loss due to absorption and scattering in an optical part and scattered light is not included, laser light of high output can be acquired.

Description

DETAILED DESCRIPTION OF THE INVENTION [Objective of the Invention (Industrial Field of Application) The present invention relates to a narrowband laser device, and particularly to a device for obtaining high-output, narrowband laser light.

(Prior art) In transversely pumped gas laser oscillation devices such as TEACO lasers and excimer lasers, which have a relatively large discharge section cross section, an aperture is formed between the resonator mirrors in order to improve the optical characteristics of the laser beam. In the past, only the portion of the oscillation beam with good optical characteristics was passed through, and the laser oscillation was performed.

In such laser oscillation, a portion of the laser output is extracted, resulting in a low laser output.

For this reason, in addition to the laser oscillation section, a laser amplification section was provided to increase the output.

On the other hand, as the degree of integration of large-scale integrated circuits, image pickup devices, etc. becomes increasingly dense, laser light in the ultraviolet region with a short wavelength is increasingly being used in the lithography process in the semiconductor manufacturing process. In the lithography process, the condensing lens that images the mask pattern on the resist surface applied to the surface of the semiconductor substrate is made of quartz, which transmits laser light well in the ultraviolet region. Since the chromatic aberration of the optical lens is not sufficiently corrected, the monochromaticity of the laser light is increased by narrowing the wavelength band of the laser light so that the chromatic aberration does not appear in the projected pattern. Narrowband laser light suffers from energy loss during the narrowing process.
The output was reduced to about 1/20 of the original output. As a measure to reduce this output drop, the above-mentioned laser amplification section has been installed, but for example, a method called the self-amplification method introduced in "Laser Research, Vol. 17, No. 1" is known. ing. As shown in Fig. 3, this method includes a laser tube (5) that has a pair of main discharge electrodes (1) and (2) inside, and transparent windows (3) and (4) formed at both ends. On one side of the transparent window (8), this transparent window (3)
The first aperture (6
), a first etalon (7), a high reflection mirror (8) forming one of the optical resonators, and a transmission window (4) on the other side, provided coaxially facing the first aperture (6). a second aperture (9), a second etalon (10), a grating (11) tilted at a predetermined angle, and a high reflection mirror (12) facing the grating and forming the other resonator mirror; The laser beam reflected by the grating (11) and exited from the bipedal optical resonator is sent to the laser tube (5).
The beam is configured to include a folding mirror (14) which is folded back into the discharge space via a beam expander (13). In this configuration, oscillation occurs between the high reflection mirror (8) and the grating (11) to narrow the band, and the grating (11)
The laser beam (Ll) outputted from 1) enters the discharge space again by the folding mirror (14), is amplified, becomes an amplified beam (L2), and is output from the transmission window (3).

(Problems to be Solved by the Invention) The former technique in which the laser amplification section is provided has a problem in that the overall structure of the device becomes large. In addition, in the latter configuration, the discharge space is divided into a space for laser oscillation and a space for amplification, and the narrow band laser light is amplified in one pass through the discharge space, resulting in efficient use of the discharge space. do not have. Therefore, the amplification was insufficient and the output could not be increased sufficiently. An object of the present invention is to provide a narrow band laser device which has a small cross-sectional area and can obtain high-output laser light with a simple configuration in a horizontally pumped gas laser oscillation device.

[Configuration of the Invention (Means and Effects for Solving the Problems) A laser excitation section, a high reflection mirror provided at one end of the laser excitation section and forming one of the optical resonators, and the other end of the laser excitation section. A prism is provided, a part of which is inserted into the optical path of the laser beam on the side, and is provided so as to refract the laser beam incident on the inserted part out of the optical path, and a prism that narrows a part of the refracted laser beam. the prism is configured such that the angle between the surface that intersects with the laser beam in the optical path and the surface adjacent to this surface is set to be an obtuse angle, so that the spectral width is expanded. It is an object of the present invention to provide a narrowband laser device that can achieve high output without causing any damage.

(Example) EMBODIMENT OF THE INVENTION Hereinafter, the present invention will be described based on drawings showing examples.

That is, in FIG. 1, (20) is a laser excitation unit such as an excimer laser, and transmission windows (21) are provided at both ends.
a) and (21b) are airtightly installed and a gas laser medium is sealed at a predetermined pressure in an airtight container (22), and inside this airtight container, the main discharge electrodes are provided facing each other in a direction perpendicular to the plane of the drawing. It has a cathode (23) and an anode (24). These cathode (23) and anode (24) are connected to a power source (not shown) so that pulse discharge is controlled. A high reflection mirror (27) is arranged on one end side facing one of the transmission windows (21a) via a regulating member (26) in which a slit (25) is formed. At the other end facing the other transmission window (21b), a square prism (30) with one of its interior angles at a right angle is partially inserted into the reflected optical path (28) from the high reflection mirror (27). It is provided. Further, facing the refracted optical path (31) refracted by the prism (30), a diffraction grating (32), which is a band narrowing element and forms an optical resonator with the high reflection mirror (27), is sequentially installed. It is provided. In the above insertion, as shown in FIG. 2, the prism (30) is placed at the Brewster angle (56, 5
It is tilted so as to intersect the passing optical path (28) at the incident optical path (28), and in this incident optical path, the incident surface (3
The angle θl between 3) and the adjacent surface (34) is 146.
The angle θ2 between the surface (84) and the adjacent surface (35) is set to 67°.

The laser beam generated in the laser excitation section (20) passes through a prism (
30), the beam is refracted and expanded, and enters the diffraction grating (32). This diffraction grating (32) is arranged at an angle where the angle of incidence and angle of reflection are equal for light of a predetermined wavelength. As a result, the laser light generated in the laser excitation section (20) and then diffracted by the diffraction grating (32) to have a narrow band enters the laser excitation section (20) and is amplified.

On the other hand, it is reflected by the high reflection mirror (27) and the regulation member (
26) and the other transmission window (21) at a predetermined divergence angle.
Only a part of the laser beam emitted from b) passes through the prism (
30), and the rest is taken out as an output.

In the above embodiment, the angle between the surfaces (33) and (34) was 14B, 5°, but the angle is not limited to this, and may be any angle of 90° or more. In addition, the means for narrowing the band is not limited to a diffraction grating, and a combination of an etalon and a reflecting mirror may be used.

[Effect of the invention] As explained above, the laser beam is narrow-banded and then reflected by the high-reflection mirror (27) to be extracted to the outside (outside the optical path of the optical resonator) and reflected by other engineering components. Since the laser beam does not pass through the laser beam, there is almost no loss due to absorption or scattering by optical components, and the output laser beam does not include scattered light. In addition, since the narrow band laser light is amplified in the same optical path as the laser light generated in the laser excitation section (20), the discharge space is fully utilized and there is no need to increase the volume of the excitation section for amplification. , it was possible to downsize the device. Furthermore, the - part of the prism (30) inserted into the laser beam no longer has a pointed shape and has an increased volume, so the temperature of the inserted part decreases and the overall heat distribution improves. Equalized. Therefore, it was possible to prevent the spectrum width from expanding due to heat.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing one embodiment of the present invention, and FIG.
FIG. 3, which is an enlarged view of part A in the figure, is a sectional view showing a conventional example. (20)... Laser excitation part (27)... High reflection mirror (30)... Prism (32)... Diffraction grating

Claims (1)

[Claims] A laser excitation section, a high reflection mirror provided at one end of the laser excitation section and forming one of the optical resonators, and a portion of which is inserted into the optical path of the laser beam at the other end of the laser excitation section. a prism provided to refract a laser beam incident on a portion of the refracted laser beam out of the optical path; and a means for narrowing a part of the refracted laser beam and returning it to the high reflection mirror. 2. A narrow band laser device, characterized in that an angle between a surface intersecting the laser beam in the optical path and a surface adjacent to this surface is set to be an obtuse angle.