Coherent light generators – Particular active media – Gas
Reexamination Certificate
2000-02-22
2004-08-24
Ip, Paul (Department: 2828)
Coherent light generators
Particular active media
Gas
C372S051000, C372S055000, C372S059000, C372S081000, C372S082000, C372S087000
Reexamination Certificate
active
06782029
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to gas lasers. The present invention also relates to dedusting units for the laser optical elements of gas lasers and to methods for assembling dedusting units for laser optical elements in gas lasers.
Lasers have recently been applied to a large variety of technical areas, such as optical measurement techniques, material processing, medicine, etc.
Thus, there is a big demand on providing near diffraction limited lasers, i.e. lasers generating laser beams having a short wavelength.
The excimer laser, such as the one disclosed in U.S. Pat. No. 5,771,258, serves well as a laser for generating coherent light.
The excimer laser described in U.S. Pat. No. 5,771,258 is a pulsed laser. Pulsing a is required in excimer lasers to allow sufficient time between pulses to replace the laser gas within the discharge region with fresh gas and allow the gas used for generating the previous pulse to recover before being used again for another gas discharge. In the discharge region (i.e., discharge gap), which in an excimer laser is typically defined between an elongated high voltage electrode and an elongated ground electrode which are spaced apart from each other, a pulsed high voltage occurs, thereby initializing emissions of photons which form the laser beam.
The laser beam is emitted along the extended ground electrode in a longitudinal direction of the laser tube. The laser beam leaves the tube through a window of the tube.
Unfortunately dust within the laser tube deteriorates the optical performance of the optical elements within the tube, for example the windows and/or mirrors in the tube that define the laser resonator.
There have been made several efforts to solve this problem.
For example, Japanese Patent No. 6 237 034 discloses a discharge excited gas laser device with negative electrodes having holes, through which the laser beam can pass. The negative electrodes are mounted to the optical window sections in the laser tube. Negative voltage is applied to the electrodes by a negative power supply to thereby charge the surface of the optical windows, which would normally be brought into contact with dust in the laser tube, with a negative charge. As a result, negatively charged dust particles in the tube are prevented from adhering to the optical windows.
Furthermore, Japanese Patent No. 5 067 823 discloses a discharge excitation pulse gas laser apparatus with a static gas chamber provided near an optical window at the end section of the laser tube. The static gas chamber includes a space that is designed to ensure no gas flow occurs within the chamber due to the gas circulation in the rest of the laser, thus making it hard for the metallic dust particles to reach the surface of the window even if the gas is agitated by a gas circulation means, such as a fan, in the laser tube.
German Patent Application DE 198 400 35 discloses an excimer laser with a pair of electrodes in the region of the windows. A high voltage is applied to the electrodes to control a plasma gas flow through the output window. The electrodes located in the region of the windows thus generate a directed gas flow. Further, a series of slots in the electrodes are electrostatically charged to attract dust particles. In the laser tube, a main electrode arrangement is provided for creating a gas discharge. In addition, a gas cleaning unit is provided.
The laser tubes according to the state of the art as mentioned above use a technology, in which the optical system itself or the limiter of the reduced flow area is charged. This leads to a large surface to be charged and thus, high-energy losses occur with only low field gradients of the electrical field being generated. The charged elements push off precharged metallic dust particles. Another disadvantage of the devices described above is their rather complex construction, which makes them expensive and susceptible to malfunctions.
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 Discharge
Claus Strowitzki
Feb. 22,
09/510,539
Unit
and Hans Kodeda
2000
249/301
A Gas Laser and a
Hans Kodeda,
Feb. 22,
09/511,649
Dedusting Unit
Helmut Frowein,
2000
Thereof
Claus Strowitzki,
and Alexander
Hohla
249/303
Shadow Device for
Claus Strowitzki
Feb. 22,
09/510,017
A Gas Laser
and Hans Kodeda
2000
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 for
Helmut Frowein,
2000
an Optical Element
Claus Strowitzki,
of a Gas Laser
and Alexander
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
A first object of the invention is to provide a dedusting unit for a laser optical element with improved properties, especially with reference to the complexity of construction.
To achieve the first object, a dedusting unit for a laser optical element is provided, which comprises a high-voltage duct comprising a high-voltage conducting core having a first end and a second end and an insulator element disposed around the core, the first end of the core being connectable to a high voltage power supply, and a wire loop electrically connected to the second end of the high-voltage core.
The optical element to be protected by the dedusting unit may be any of the optical elements used in a gas laser. As a result, the optical element to be protected may be a fully reflective mirror, a partially transparent, partially reflective mirror, or a fully transparent window.
Thus, the present invention provides a very simple device for preventing dust from reaching an optical element of the laser tube, especially the output window, through which the laser light is emitted, or the 100% reflecting mirror providing resonant laser light. Because the construction is very simple and small, the dedusting unit according to the invention may be readily mounted in front of the mirrors and windows in the tube.
Furthermore, the dedusting unit according to the invention may easily be detached from its mounting. A further advantage of the device is that an electrical field with very high field gradients is generated by the wire loop when the dedusting unit is connected to a high voltage power supply, thereby significantly improving the dedusting effect compared with the devices according to the state of the art.
The wire loop may have any loop form. Preferably, however, the wire loop has a substantially circular form having a diameter that is sufficient to allow the resonating laser light within the tube to pass through the wire loop without being obstructed.
A second object of the invention is to provide a gas laser comprising a laser optical element with an improved dedusting unit, especially with reference to the complexity of the construction of the dedusting unit.
To achieve the second object of the invention, a gas laser is provided comprising a tube having a first end wall at one end and a second end wall at the other end and defining a cavity for containing a laser gas. 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. The ground electrode extends parallel to the high voltage electrode and is spaced apart from the high voltage electrode to thereby define a gas discharge gap therebetween. A laser resonating path is also provided in axial alignment with the gas discharge gap. A first laser optical element is disposed in the laser resonating path and has a side exposed to the cavity formed by the tube. And a dedusting unit is mounted to the laser tube. The dedusting unit comprises (1) a high-voltage d
Flores-Ruiz Delma R.
Ip Paul
Mintz Levin Cohn Ferris Glovsky and Popeo P.C.
TuiLaser AG
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