Gas laser and a dedusting unit thereof

Details Gas laser and a dedusting unit thereof Gas laser and a dedusting unit thereof

2000-02-22

2003-08-05

Leung, Quyen (Department: 2828)

Coherent light generators

Particular active media

Gas

C372S061000, C372S055000, C372S057000, C372S060000, C372S081000, C372S082000, C372S087000

Reexamination Certificate

active

06603790

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to a gas laser and a dedusting unit thereof for removing dust particles generated during normal laser operation from a gas mixture within the gas laser containing a laser gas and a buffer gas.
Gas lasers are generally known in the art wherein a laser gas is excited by an electrical power source to generate a longitudinal discharge of light. In a typical structure, the laser gas is contained within a tube having a laser discharge zone defined therein between a pair of laser electrodes. The laser gas is excited by applying a relatively high voltage, resulting in the generation of light that can be directed by appropriate optic elements to provide a laser beam. The laser is normally operated or fired in a pulsed manner by connecting a main electrode circuit to the electrical power source at a selected operating frequency. A circulation fan is commonly provided within the laser tube for circulation of the gas mixture through the laser discharge zone.
During laser operation, dust particles are generated within the tube, particularly in an excimer laser. These dust particles are produced by a combination of erosion of metal and insulator material components such as the electrodes in the laser discharge zone, and chemical corrosion of said components by the aggressive laser gas. Dust within the gas has to be avoided since it diffuses the light resonating in the gas discharge gap between the electrodes, thereby lowering the laser light output power significantly. Moreover, the dust particles can accumulate on the optic elements, resulting in potentially significant reduction in the power of the light beam discharged from the tube.
A variety of dust particle filtration systems have been proposed in an effort to reduce the impact of dust particle generation on laser operation. From DE-C-32 12 928 a gas laser is known, in which an external electrical dedusting device is mounted to remove dust particles from the laser gas. Such systems, however, are relatively complex with respect to the assembly of structural components and related circulation of the laser gas to and from the laser housing. U.S. Pat. No. 5,319,663 describes a gas laser including an electrostatic dedusting device directly mounted within the laser housing for flow-through gas circulation during laser operation. However, these devices have not been highly efficient in operation, typically collecting only a small proportion of the generated dust entrained within the gas flow stream during each pass therethrough. Moreover, since the whole gas flow circulating within the tube has to pass through this electrostatic dedusting unit, undesired turbulences are generated within the gas flow. Further, U.S. Pat. No. 5,729,564 discloses a gas discharge laser within a housing that accommodates an electrostatic precipitator for flow-through passage of the laser gas circulated by a fan. However, since the entire flow passes the precipitator, turbulences are generated within the gas flow during the laser operation. Additionally, the precipitator has a large sized structure and, therefore, requires too much space within the housing.
RELATED APPLICATIONS
The present invention may be used in conjunction with the inventions described in the patent applications identified below and which are being filed simultaneously with the present application:
Docket
Filing
Serial or
No.
Title
Inventors
Date
Patent No.
249/300
Gas Laser
Claus Strowitzki
Feb. 22,
09/510,539
Discharge Unit
and Hans Kodeda
2000
249/302
Dedusting Unit
Claus Strowitzki
Feb. 22,
09/510,667
for a Laser Optical
2000
Element of a Gas
Laser and Method
for Assembling
249/303
Shadow Device for
Claus Strowitzki
Feb. 22,
09/510,017
A Gas Laser
And
2000
Hans Kodeda
249/304
Modular Gas Laser
Claus Strowitzki
Feb. 22,
09/510,538
Discharge Unit
and Hans Kodeda
2000
250/001
Adjustable
Hans Kodeda,
Feb. 22,
09/511,648
Mounting Unit
Helmut Frowein,
2000
for an Optical
Claus Strowitzki
Element of a Gas
and Alexander
Laser
Hohla
250/002
An Optical Element
Hans Kodeda and
Feb. 22,
09/510,666
Holding and
Helmut Frowein
2000
Extraction
Device
All of the foregoing applications are incorporated by reference as if fully set forth herein.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a gas laser and a dedusting unit thereof wherein a continuous circulation of the gas flow within the gas laser is achieved while the gas laser has a reduced, very compact size.
According to the present invention, the gas laser comprises a tube containing a gas mixture including a laser gas and possibly a buffer gas. The tube preferably comprises a cylindrical inner wall. An elongated high voltage electrode is disposed within the tube and extends parallel to the longitudinal axis of the tube. An elongated ground electrode is also disposed within the tube and extends parallel to the high voltage electrode. The ground electrode is spaced apart from the high voltage electrode to thereby define a gas discharge gap therebetween. A circulation means, such as a fan, is positioned within the tube for generating a gas flow within the tube that passes between the electrodes. And, a dedusting unit is mounted along the inner cylindrical wall of the tube in such a manner that a bypass flow which is a part of the gas flow within the tube passes through the dedusting unit.
The elongated high voltage electrode and ground electrode are preferably mounted on the same electrode plate to thereby form a modular discharge unit. The discharge unit may then be removably inserted into the tube.
By passing only a portion of the gas flow within the laser tube through the dedusting unit, turbulences within the circulating gas are avoided, resulting in a continuous gas circulation within the tube during the laser operation. Therefore, the electrical gas discharge gap between the two electrodes is provided with a continuous gas flow to achieve an effective ionization of the laser gas.
Additionally, since the dedusting unit is mounted along the inner cylindrical wall of the tube, the structural size of the gas laser may be reduced over prior art designs. In a particular preferred embodiment of the present invention, the dedusting unit is directly mounted to and integrated within the tube to provide a compact and operationally efficient gas laser. The centrifugal force of the bypass gas flow towards the inner cylindrical tube wall adjacent to the dedusting unit, helps to effectively dispose the dust particles at this cylindrical wall portion, without deflecting this flow in an undesired direction. Because the dedusting unit charges the dust particles electrostatically, they remain adhered to the cylindrical wall portion of the tube.
Preferably, the inner cylindrical wall of the tube is circular in cross section. This allows the gas flow to efficiently circulate within the tube during the laser operation at a uniform velocity of gas flow.
In a preferred embodiment of the invention, the dedusting unit comprises a partition wall that has a substantially circular middle section extending substantially parallel to the inner cylindrical wall. The arrangement and design of the partition wall enables the gas flow to exactly control the bypass flow between the partition wall and the inner cylindrical wall for dedusting the bypass flow. For effective dedusting, it is sufficient if only a minor part of the whole gas flow is directed through the dedusting unit.
The bypass flow is directed through a mouth portion having a substantially constant cross section and a defined orientation with respect to the partition wall and the inner cylindrical wall, so that an efficient and uniform dedusting of the bypass flow is secured. The remaining, or main, gas flow is guided along the side of the partition wall facing away from the inner cylindrical wall. This main gas flow is continuously supplied together with the joining dedusted bypass flow to the circulation means. The circulation means again circulates the gas through the discharge gap and then through the dedusting unit where it is once again di

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