EXCIMER LASER SYSTEMS WITH A RING CAVITY STRUCTURE

Abstract

The present disclosure provides an excimer laser system. A master oscillator chamber may generate laser pulses with a narrowed line width and a small energy by means of a line width narrowing module, as a seed light. The seed light is refracted by a master oscillator wavefront engineering box and then incident into a power amplifier chamber through a beam splitting system. The beam splitting system, a first high reflectance mirror, a second high reflectance mirror and a third high reflectance mirror may constitute a quadrilateral annular optical path, The power amplifier chamber may have a first pair of Brewster windows and a second pair of Brewster windows, wherein the first pair of Brewster windows is located in a first optical path of the annular optical path along with a discharging electrode of the power amplifier chamber, and the second pair of Brewster windows is located in a second optical path of annular optical path which is parallel to a first amplification optical path. The present disclosure reduces the length of a ring cavity of an excimer laser system with a ring cavity structure, increasing the amplification times and achieving a deeper gain saturation amplification than a traditional structure, thereby improving the output characteristic of the excimer laser system.

Claims

1. An excimer laser system, comprising: a master oscillator chamber (MO), a power amplifier chamber (PA), a line width narrowing module (LNM), a line width analysis module (LAM), a master oscillator wavefront engineering box (MO WEB), an optical pulse stretcher (OPS), an auto shutter, a partial reflectance mirror (PR), a beam splitting system (Splitter), a first high reflectance mirror (HR1), a second high reflectance mirror (HR2) and a third high reflectance mirror (HR3), the master oscillator chamber (MO) generates laser pulses with a narrowed line width and a small energy by means of the line width narrowing module (LNM) as a seed light, wherein the seed light is refracted by the master oscillator wavefront engineering box (MO WEB) and then injected into the power amplifier chamber (PA) through the beam splitting system (Splitter), the beam splitting system (Splitter), the first high reflectance mirror (HR1), the second high reflectance mirror (HR2) and the third high reflectance mirror (HR3) constitute a quadrilateral annular optical path, the power amplifier chamber (PA) has a first pair of Brewster windows (B1, B1) and a second pair of Brewster windows (B2, B2), wherein the first pair of Brewster windows (B1, B1) is located in a first optical path of the annular optical path along with a discharging electrode of the power amplifier chamber (PA), and the second pair of Brewster windows (B2, B2) is located in a second optical path of annular optical path which is parallel to the first amplification optical path.

2. The excimer laser system of claim 1, wherein the power amplifier chamber (PA) has two parallel discharging electrodes, and the first optical path and the second optical path in the annular optical path pass through the two discharging electrodes, respectively.

3. The excimer laser system of claim 1, wherein each of the first high reflectance mirror (HR1), the second high reflectance mirror (HR2) and the third high reflectance mirror (HR3) is a reflectance mirror with an angle of 45.

4. The excimer laser system of claim 2, wherein each of the first high reflectance mirror (HR1), the second high reflectance mirror (HR2) and the third high reflectance mirror (HR3) is a reflectance mirror with an angle of 45.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 is a schematic diagram illustrating a structure of an excimer laser system with a dual-cavity MORRA structure in prior art;

[0015] FIG. 2 is a schematic diagram illustrating a structure of an excimer laser system with a single-electrode dual-cavity MORRA structure according to an embodiment of the present disclosure; and

[0016] FIG. 3 is a schematic diagram illustrating a structure of an excimer laser system with a dual-electrode dual-cavity MORRA structure according to another embodiment of the present disclosure.

DETAILED DESCRIPTION

[0017] In view of the problem that the ring cavity length of the excimer laser cannot be reduced without limit due to its physical size, the present disclosure proposes a design of disposing the entire ring structure inside the power amplifier chamber, rather than disposing a part of the ring cavity outside the chamber as the prior art, which can reduce the cavity length of the ring structure and increasing the amplification times, thereby further enhancing the stability of the output.

[0018] The present disclosure positions the part outside the ring cavity of a traditional excimer laser into the amplification chamber, reducing the length of the ring cavity significantly. Since the amplification times N=c.Math.t/L, wherein L indicates for the length of the ring cavity, c is the speed of light, and At indicates for the pulse width. A decrease of L can lead to an increase of the amplification times N. Therefore, the amplification times N can be increased by reducing the length of the ring cavity, thereby obtaining a more stable laser output. At the same time, positioning the annular optical path into the amplification chamber can reduce adverse effects of external instable factors on beam propagation.

[0019] To make the objectives, solutions, and advantages of the present disclosure clearer, the present disclosure is further described in detail below with reference to specific embodiments in combination with the accompanying drawings.

[0020] FIG. 2 is a schematic diagram illustrating a structure of an excimer laser system with a single-electrode dual-cavity MORRA structure according to an embodiment of the present disclosure. As shown in FIG. 2, the laser system may comprise a master oscillator chamber MO, a power amplifier chamber PA, a line width narrowing module LNM, a line width analysis module LAM, a master oscillator wavefront engineering box MO WEB, an optical pulse stretcher OPS, an auto shutter Auto Shutter and a beam splitting system Splitter.

[0021] The master oscillator chamber MO may generate laser pulses with a narrowed line width and a small energy by means of the line width narrowing module LNM, as a seed light, which is refracted by the master oscillator wavefront engineering box MO WEB and then incident into the power amplifier chamber PA through the beam splitting system Splitter. Three high reflectance mirror HR1, HR2, HR3, each of which has an incident angle of 45, act as mirrors of the power amplifier chamber PA, so as to form a multi-path amplification system for the seed light along with the beam splitting system Splitter. The beam splitting system (Splitter), the first high reflectance mirror (HR1), the second high reflectance mirror (HR2) and the third high reflectance mirror (HR3) constitute a quadrilateral annular optical path. That is, the ring amplification optical path structure of the system may be in a form of a quadrilateral, in which the optical path between discharging electrodes of the discharging cavity may have an effect of amplifying on the seed light.

[0022] In contrast to the structure as shown in FIG. 1, the power amplifier cavity PA according to this embodiment has two pairs of Brewster windows (upper and lower). Herein, the two Brewster windows in the same optical path with the discharging electrode are referred to as a first pair of Brewster windows (indicated by B1, B1), and the other two Brewster windows located on another optical path within the discharge cavity which is in parallel with the amplification optical path are referred to as a second pair of Brewster windows (indicated by B2, B2).

[0023] The first pair of Brewster windows (B1, B1) is located in a first optical path of the annular optical path along with a discharging electrode of the power amplifier chamber PA, and the second pair of Brewster windows (B2, B2) is located in a second optical path of annular optical path which is parallel to a first amplification optical path.

[0024] As shown in FIG. 2, the laser light emitted from one Brewster window B1 of the first pair of Brewster windows B1, B1 is incident into the Brewster window B2 of the second pair of Brewster windows B2, B2 after being reflected by the second and third high reflectance mirrors HR2, HR3, so as to emit into the power amplifier chamber PA, wherein the Brewster window B2 is located on the same side of the power amplifier chamber PA as the Brewster window B1. Then, the light is emitted from the other Brewster window B2 of the second pair of Brewster windows B2, B2. In addition, compared with the conventional structure, the power amplifier chamber PA having two pairs of Brewster windows shown in FIG. 2 can improve the polarization degree of the P light, so as to obtain a laser light with more superior laser polarization characteristics. Since the optical path parallel to the discharging optical path is disposed in the discharging cavity, the remaining two optical paths perpendicular to the discharging optical path are no longer limited by the size of the discharging cavity, thereby reducing the length of the annular amplification chamber.

[0025] In the structure according to this embodiment, the amplification chamber is a single-electrode structure. Compared with the conventional dual-cavity MORRA structure, the length of the ring cavity can be effectively reduced, which is beneficial for multi-path amplification to achieve a deep-gain saturation amplification. Compared with the conventional structure, an output with more stable index can be obtained.

[0026] FIG. 3 is a schematic diagram illustrating a structure of an excimer laser system with a dual-electrode dual-cavity MORRA structure according to another embodiment of the present disclosure.

[0027] Different from the embodiment as shown in FIG. 2, the power amplifier chamber PA in FIG. 3 may have two parallel discharging electrodes. The first optical path and the second optical path of the annular optical path may both have an amplification effect on the seed light through the two discharging electrodes. It can be seen that in this embodiment, not only the length of the ring cavity is effectively reduced, but also the magnification is twice as that of the single electrode. That is, if the same seed light is injected into the amplification cavities discussed above, the structure according to this embodiment may output with a higher energy. In addition, the increase of magnification times enables the amplification occur in a state of deeper gain saturation, which makes the output beam obtained by this structure more stable.

[0028] In summary, the present disclosure is directed to an improvement on a power amplification mechanism in a ring cavity of an excimer laser system in terms of its structure and performance. Through a design of single (dual)-electrode structure, the low amplification due to the limit of cavity length can be solved, which may further improve the efficiency for gain utilization in the cavity, thereby ensuring an effective output of the system. The present disclosure is intended to increase the amplification capability by means of multi-path cavity transition. Meanwhile, the ring cavity structure may also reduce the influence of external unfavorable factors, such as passing through the atmosphere.

[0029] The above specific embodiments are used to further describe the objectives, technical solutions and advantages of the present disclosure in detail. It should be understood that the above description is only specific embodiments of the present disclosure and not intended to limit the present disclosure. Any modifications, equivalent substitutions and improvements made within the spirit and principle of the present disclosure should be included in the scope of the present disclosure.