Coherent light generators – Particular pumping means – Electrical
Reexamination Certificate
2000-02-22
2003-02-18
Ip, Paul (Department: 2828)
Coherent light generators
Particular pumping means
Electrical
C372S055000, C372S061000, C372S051000, C372S087000, C372S059000, C372S060000, C372S082000, C372S081000
Reexamination Certificate
active
06522679
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to gas lasers, and more particularly to a discharge unit for a gas laser, wherein a high voltage is supplied to two discharge electrodes.
2. Background Of The Invention
Excimer lasers provide high intensity laser radiation in the ultraviolet spectral range. This makes them important tools especially for medical and surgical applications as well as for other industrial applications.
Excimer lasers are gas discharge lasers that use a rare gas such as argon and a halide gas such as fluor (for example ArF excimer laser) or a gas containing a halide (for example F
2
) as the laser gas.
Generally, in an excimer laser a gas mixture containing the active component and other gases is steadily provided to a discharge gap between a pair of elongated electrodes inside the laser tube by means of a fan or the like. A high voltage applied between the two electrodes causes a gas discharge in said discharge gap, whereby, from the active component of the gas, short-lived excited-state molecules are generated, whose dissociation generates ultraviolet radiation constituting the laser radiation. To increase the homogeneity of the gas discharge, in present excimer lasers a pre-ionization of the laser gas by pre-ionizers is used. As the used laser gas needs to regenerate before it can be re-used, excimer lasers are generally operated in a pulsed operation mode, wherein the laser gas in the discharge gap is being steadily replaced by fresh or regenerated laser gas provided by the fan.
The discharge electrodes for an excimer laser are usually located inside the laser tube.
The housing of an excimer laser generally consists of a metal tube having openings in a cylindrical wall on the upper side thereof. An insulating plate covers the open upper side. The metal tube and one of the discharge electrodes are grounded. A high voltage is applied to the second discharge electrode via a HV duct extending through the insulating plate.
One main problem of excimer lasers, which is still not satisfactorily solved, is the contamination of the laser gas due to the corrosive effect of the active components of the laser gas on many insulating materials which are widely used as insulators, especially on materials containing carbon molecular structures, such as many plastic materials, for example TEFLON®. Due to this contamination the lifetime of the laser gas is reduced, which makes a frequent exchange of the laser gas necessary. To overcome this problem, U.S. Pat. No. 4,891,818 utilizes high-purity aluminum oxide (Al
2
O
3
) as insulator, on which the corrosive effect of the active components of the laser gas is by far reduced as compared to plastic materials.
Another, even more corrosion resistant, class of materials that can be used as insulators is fluorides.
Directly related to the above problem is the problem, that exchanging of the gas and maintenance works are expensive and time-consuming. Moreover, they are hazardous activities, as the laser gases for excimer lasers are, besides their corrosive nature, highly toxic.
A further problem is to provide an excimer laser with a high pulse repetition rate. U.S. Pat. No. 5,771,258 discloses an aerodynamic chamber design for an excimer laser to provide a high pulse repetition rate. A high repetition rate also requires a high frequency voltage to be efficiently applied to the electrodes, which becomes more difficult with increasing frequency of the voltage.
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:
Serial or
Docket No.
Title
Inventors
Filing Date
Pat. No.
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
249/302
Dedusting Unit for a
Claus Strowitzki
Feb. 22,
09/510,667
Laser Optical Element
2000
of a Gas Laser and
Method for
Assembling
249/303
Shadow Device for A
Claus Strowitzki
Feb. 22,
09/510,017
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 Mounting
Hans Kodeda,
Feb. 22,
09/511,648
Unit for an Optical
Helmut Frowein,
2000
Element of a Gas
Claus Strowitzki,
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
One object of the present invention is to provide a laser discharge unit for a gas laser and in particular for an excimer laser, which minimizes contamination of the laser gas and thus increases the lifetime of the laser gas.
A further object of the invention is to provide a laser discharge unit for a gas laser that allows a high frequency voltage to be efficiently applied to the discharge electrodes.
Another object of the present invention is to provide a laser discharge unit for a gas laser and in particular for an excimer laser which is easy to handle and yet powerful.
The above and further objects of the invention are achieved by a laser discharge unit with an elongated electrode plate made of an electrically conductive material, such as metal, a plurality of waveguide-like coaxial high voltage ducts extending through said electrode plate and comprising respectively a central conductive core and an insulator element made of an insulator, such as a ceramic insulator, and being arranged around said core and electrically insulating said core from said electrode plate, an elongated high voltage electrode and an elongated ground electrode, said high voltage electrode being electrically connected to said cores of said ducts and said ground electrode being electrically connected to said electrode plate, wherein said ducts are arranged spaced apart from each other.
The tube of the laser is preferably electrically connected to the ground electrode, and both are preferably grounded.
The electrode plate of the discharge unit of the present invention comprises a metal plate, preferably a pure metal plate. An advantage of this is that the laser gas does not corrode the electrode plate to the same extent as it would corrode if it were made from an insulator material such as ceramic; thus contamination of the laser gas is reduced.
The electrode plate comprises a plurality of holes, through each of which one of the high voltage ducts is guided. As the electrode plate is grounded, an insulator is required between the conductive cores of the HV ducts and the electrode plate. The number of high voltage ducts (and holes) depends on the size of the laser, in particular on the length of the electrodes. For example, for a typical excimer laser, three high voltage ducts should be used. For a larger laser with longer electrodes more than three ducts should be provided. For smaller lasers with shorter electrodes only one or two ducts may be provided.
According to the invention, the conductive cores of the ducts are respectively surrounded by an insulator element. By this construction, as compared to a whole plate made of an insulator, only a small amount of insulator material is in contact with the laser gas. Thus the contamination of the laser gas is clearly reduced.
The conductive cores of the ducts and the electrode plate form a coaxial waveguide-like structure, which facilitates the effective coupling of high frequency pulses for pulsed operation mode of the laser to the high voltage electrode.
The insulator elements of the ducts are preferably made of an insulating material, such as aluminum oxide (Al
2
O
3
). Alternatively, the insulator elements can be made from a fluoride material. In this regard, the more expensive fluoride materials, which are more resistant against corrosion by the excimer laser gas, can be used since the amount of insulator material has been reduced to a minimum according to the invention.
In principle the insul
Kodeda Hans
Strowitzki Claus
Elrifi Ivor R.
Flores Ruiz Delma R.
Marenberg Barry J.
Mintz Levin Cohn Ferris Glovsky and Popeo P.C.
TuiLaser
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