JPH0342887A - Laser resonator - Google Patents

Abstract

PURPOSE:To obtain output light having large cross-sectional areas and relieve the deviation of an output distribution on a cross section by amplifying rays of laser light which is generated in a high gain region after reflecting the rays of laser light to a low gain region through a reflecting means, besides, dispersing the above rays which are reflected through an expanding means so that the rays of laser light pass through the low gain region in parallel to an optical axis. CONSTITUTION:Discharge electrodes 1 which are formed into respective semi-column shapes and are facing each other at given intervals form gain regions where laser gas is excited by discharge. As electric discharge, in such a case, is concentrated in the neighborhood of a central axis where a distance between electrodes becomes short, a high gain region including the central axis is formed. Being corresponding to the high gain region, laser resonators ate formed at a total reflection mirror 2 and at the part of the central half mirror of a corner cube type reflecting mirror 4. Further, a beam expander consisting of concave and convex lenses 5 and 6 in which a rectangular opening is formed is provided at a central part corresponding to the high gain region and the width of laser light that is reflected by the reflected mirror 4 is expanded by a factor of 4 and is allowed to pass through a low gain region. In this way, energy is taken out even from the low gain region to improve laser efficiency and gain of each resonator is averaged as well.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a laser resonator suitable for application to a transverse discharge type gas laser device, such as a discharge type excimer laser device.

[Prior Art] Lateral discharge type gas laser devices have been developed for various applications and are already used in many fields. ,
There is a strong demand for stable output.

FIG. 5 shows a schematic configuration of a numerically lateral discharge type gas laser device. Here, a discharge region 11 of laser gas (formed by a pair of discharge electrodes (not shown) facing each other in a direction perpendicular to the paper surface) A total reflection mirror 12 and a laser output half mirror 13 face each other with the mirror 12 in between to form a laser resonator. When the laser gas is excited in the discharge region 11, the emitted light of the laser gas enters a resonance state between the total reflection mirror 12 and the half mirror 13, and a portion of the light is emitted from the half mirror 13 side as a laser output.

However, there were problems when applying this laser resonator to a discharge type excimer laser device. In the discharge type excimer laser device, due to the electrode structure and the special characteristics of the laser gas, the discharge region 11 in which the laser gas molecules are excited is concentrated in a narrow region along the longitudinal direction of the opposing discharge electrodes.
The gain distribution in the cross section of the laser resonator is not -like.

When the intensity distribution of the laser beam in the cross section of the laser beam is measured, it is almost negative in the discharge direction, but in the width direction perpendicular to the discharge direction, it shows a distribution close to a Gaussian distribution as shown in FIG. In other words, between the opposing discharge electrodes of a discharge-type excimer laser device, there is a high gain region where resonance is likely to occur in a thin plate-shaped region that includes the optical axis of the laser resonator, and a high-gain region on both sides of this plate-shaped region sandwiching this plate-shaped region. A low gain region was formed in which the gain decreases as the distance from the optical axis increases.

Therefore, in a discharge-type excimer laser device, in a laser resonance state, high-intensity output light can be obtained in a portion several millimeters wide related to the high gain region, but in a portion related to the low gain region, a limited output light near the high gain region is obtained. The resonance state was maintained only in some parts, and the efficiency of extracting laser light was low.

[Problems to be Solved by the Invention] Discharge-type excimer laser devices have different resonance-related gains around the central axis and outside the central axis, and the cross-sectional distribution of output light intensity is also greatly biased. In this case, a complicated optical system was required at the subsequent stage to smooth the cross-sectional intensity distribution of the output light. Furthermore, when a band narrowing element such as an etalon is inserted into the resonator in order to narrow the wavelength band of the output light, the band narrowing element reduces the total gain of the resonator by its own optical path loss. The area where laser oscillation is possible on the cross section has become even narrower. As a result, the beam cross-sectional area became smaller and the efficiency of the device also decreased significantly.

[Means for Solving the Problems] A laser resonator according to the present invention has a pair of electrodes forming a high gain region on a central axis passing between a pair of mirrors facing each other and a low gain region on the outside. In a laser resonator that resonates discharge light on the axis, there is a reflecting means that returns the laser light in the high gain region toward the low gain region, and a reflection means that allows the reflected laser light to pass through the low gain region parallel to the central axis. , and a magnifying means for dispersing the folded laser beam.

[Function] In the laser resonator according to the present invention, a laser medium in a space surrounded by a pair of mirrors and a pair of electrodes forms an excited gain region. Here, a high gain region is formed on the central axis passing between the pair of mirrors, and a low gain region is formed on the outer circumferential side sandwiching this region.

Therefore, the main resonance that forms the output light occurs on the central axis.

In the laser resonator according to the present invention, the reflecting means returns the laser light generated in the high gain region toward the low gain region, so that the laser light passes through the gain region again and is amplified.

Further, the enlarging means enlarges the cross-sectional area of the folded laser beam, so that a wider range of the low gain region is involved in the laser beam output. At this time, the laser beam whose cross-sectional area has been expanded by the expansion means passes through the low gain region in parallel to the central axis.

In the present invention, the reflecting means and enlarging means inserted into the laser optical path also have optical path loss, but since the laser light passing through the low gain region is a high-intensity laser light oscillated in the high gain region, the conventional example Output light with a larger cross-sectional area than the laser resonator described above can be obtained, and the bias in the output distribution on the cross-section is also alleviated.

[Embodiments of the invention] Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a schematic configuration of a laser resonator in an excimer laser device according to a first embodiment of the present invention. In the first embodiment, semi-cylindrical discharge electrodes 1 with a length of 50 cm facing each other at an interval of 2 cm in the height direction perpendicular to the plane of the drawing (however, only the electrode on the back side is shown and the near side is not shown) are used to discharge laser gas. A discharge excited gain region is formed. Here, the discharge direction is the height direction perpendicular to the plane of the paper, and since the discharge is concentrated near the central axis where the distance between the electrodes is shortened, the height including the central axis is 20
A high gain region having a width of about 1'fiI11 and a width of about 2m111 is formed.

Corresponding to this high gain region, a rectangular (height 20 mm x width 2 m 111) total reflection mirror 2 is placed on the laser pre-extraction side.
However, on the opposite side, a corner cube reflecting mirror 4 consisting of two elongated right-angled prisms with a hypotenuse length of 2 mal is arranged. Here, a 2 mm wide portion at the center of the corner cube reflecting mirror 4 corresponding to the high gain region is a half mirror using surface reflection of a dielectric multilayer film or glass material. That is, the total reflection mirror 2 and a portion of the central half mirror of the corner cube reflection mirror 4 constitute a laser resonator.

On the other hand, the reflecting means has a configuration in which the laser beam that has passed through a portion of the half mirror of the corner cube reflecting mirror 4 is reflected by two sides of the right angle prism that sandwich the right angle, and is returned to the low gain region. In addition, as an enlarging means, a rectangle (height 20 mm x width 2 m +
A beam expander consisting of a cylindrical concave lens 5 and a convex lens 6 each having an aperture of (o) is provided.

The beam expander expands the width of the laser beam reflected by the corner cube reflector 4 by four times and allows it to pass through the low gain region. This improves laser efficiency by extracting energy from the low-gain region, which has not conventionally been involved in laser output, and also averages the resonator gain related to each beam of laser output light (in the high-gain region). (The center is folded back to the outer edge of the low gain area, and the outer edge of the high gain area is folded back to the inner edge of the low gain area.) Therefore, the output laser light that has passed through the low gain area has a practical level output value over a wider area. becomes.

FIG. 3 shows the output distribution in the width direction perpendicular to the discharge direction of the excimer laser device of the first embodiment. Although there is a depression in the center corresponding to the shadow of the total reflection mirror 2, it can be seen that the output from the low gain region is improved compared to the conventional output distribution in Figure 2, and a wide range of highly uniform laser output light can be obtained. .

FIG. 4 shows a schematic configuration of a laser resonator in an excimer laser device according to a second embodiment of the present invention, where:
Members having the same configuration and functions as those in the first embodiment are given the same reference numerals.

The corner cube reflection mirror 4b of the second embodiment does not have a half mirror portion like the corner cube reflection &R4 of the first embodiment, but has a total reflection mirror 2 facing across the gain region.
and the half mirror 3 constitute a laser resonator. In other words, a laser resonator is configured in which a high gain region and a low gain region are connected in series with the corner cube reflection fi4b as a turning point, and the gains related to each light beam in the laser resonant state are averaged. Similarly to the first embodiment, a wide range of highly uniform laser output light can be obtained.

In the second embodiment, the total reflection mirror 2 and the half mirror 3 are made into independent separate members, but they may also be made into one component by integrally forming a part of the total reflection mirror in the central part of the half mirror 3. It is possible.

In each of the above embodiments, even when a wavelength selection element such as an etalon is inserted into the laser resonator, the region where the gain is low enough to stop laser resonance is extremely small compared to the conventional laser resonator. The decrease in the cross-sectional area of the laser output light can be kept small. Furthermore, the laser output light is stable and highly efficient operation is possible.

[Effects of the Invention] In the laser resonator according to the present invention, energy is effectively extracted even from the low gain region that could not contribute to the laser output light conventionally, so the efficiency of the laser resonator is improved and the laser output is stabilized. In addition, since laser output light of sufficient intensity can be obtained even from the low gain region, the degree of design freedom is increased when inserting functional elements such as etalons into the laser resonator, and the cross-sectional area is wider than before. It is possible to obtain laser output light with reduced bias in the intensity distribution on the cross section while maintaining the same characteristics.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the general configuration of a laser resonator in a discharge type excimer laser device according to a first embodiment of the present invention. FIG. 2 is a diagram showing the intensity distribution in the width direction of laser output light of a conventional discharge type excimer laser. FIG. 3 is a diagram showing the intensity distribution in the width direction of the laser output light of the discharge type excimer laser according to the first embodiment of the present invention. FIG. 4 is a schematic diagram showing the general configuration of a laser resonator in a discharge type excimer laser device according to a second embodiment of the present invention. FIG. 5 is a schematic diagram showing the general configuration of a laser resonator in a conventional discharge type excimer laser device. [Explanation of symbols of main parts] 1...Discharge electrode 2...Total reflection mirror 4...Corner cube reflector 5...Concave lens 6...Convex lens

Claims (1)

[Claims] It has a pair of electrodes forming a high gain region on a central axis passing between a pair of opposing mirrors and a low gain region outside the high gain region, and emits discharge light on the central axis. In the laser resonator for resonating, a reflecting means for folding back the laser light in the high gain region toward the low gain region; a laser resonator, further comprising a magnifying means for dispersing the laser beam.