Coherent light generators – Particular active media – Gas
Reexamination Certificate
2000-02-22
2004-10-12
Ip, Paul (Department: 2828)
Coherent light generators
Particular active media
Gas
C372S057000, C372S061000, C372S062000, C372S065000, C372S107000, C372S063000, C372S064000, C372S099000, C372S101000, C372S108000
Reexamination Certificate
active
06804284
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to gas lasers. More particularly the invention relates to holding and extraction devices for the optical elements of gas lasers.
BACKGROUND OF THE INVENTION
Lasers have recently been applied to a large variety of technical areas, such as optical measurement techniques, material processing, medicine, etc.
Due to the special chemical, ablative, spectroscopic or diffractive properties of UV light, there is a big demand for lasers that generate laser beams having a short wavelength in the UV range.
Excimer lasers, such as the ones disclosed in U.S. Pat. Nos. 5,771,258 and 5,438,587, serve well as a laser for generating coherent, high intensity pulsed beams of light in the UV wavelength range.
The excimer lasers described in U.S. Pat. Nos. 5,771,258 and 5,438,587, are pulsed lasers. Pulsing 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. To achieve the desired amplification by stimulated emission of radiation, a resonator comprising a reflecting and a partially reflecting optical element disposed at opposite ends of the discharge gap is required. The laser beam leaves the tube through the latter.
If the reflective optical elements are provided outside the gas laser tube, a fully transparent window is provided in alignment with the discharge gap at each end of the tube to seal the tube, as can be seen in U.S. Pat. No. 5,438,587, for example. A mirror or other reflective optical element is then provided in axial alignment with one of the windows and its reflective side facing the window. A partially transparent, partially reflective mirror is positioned outside the tube so that it is aligned with and facing the other window. As a result, the faces of the two reflective optical elements are opposing one another and define a laser light resonator.
If the reflective optical elements are used to seal the tube, the mirror and the partially transparent, partially reflective mirror are integrated into the end walls of the tube at opposite ends of the discharge gap. As a result, no extra windows are required. For lasers emitting light in the ultraviolet range of the electromagnetic spectrum, extra windows have the disadvantage of significantly reducing the efficiency and increasing the operating costs, as the special window materials employed are expensive and deteriorate with use and time and need to be occasionally changed. In addition, the transparent windows closing the tube form extra optical elements resulting in extra losses and reflections on the surfaces. The latter can be removed by inclining the window at Brewster's angle as taught by U.S. Pat. No. 4,746,201, but invariably the laser output is reduced. Deterioration of the optical elements also cannot be entirely avoided, reducing output and giving rise to the need to replace the rather expensive optical elements after a certain time.
Within the laser's resonator, the laser light resonates between the fully reflective mirror and the partially transmissive, partially reflective mirror to amplify the laser effect. In addition, a portion of the resonating light is emitted through the partially transmissive, partially reflective mirror at the target.
The reflective optical elements that form the resonator must be precisely positioned relative to one another to ensure optimal laser light output power, laser efficiency, and the quality of the laser beam. This is especially true with respect to the angular alignment of the reflective optical elements, not only with respect to each other, but also with respect to the laser tube. However, maintaining the appropriate angular alignment of the reflective optical elements is difficult in view of changes in the operating conditions, such as pressure or temperature of the gas and the temperature of the tube, the optical elements, and their supporting units. In addition, mechanical vibrations or shock to the laser may also affect the angular alignment of the reflective optical elements forming the laser resonator.
As is known in the art, the reflective optical elements forming the resonator may be provided inside or outside the laser tube. Regardless of whether the reflective optical elements are positioned inside or outside the laser tube, however, an optical element of some sort must be mounted to the laser tube to seal the laser tube while allowing laser light to be transmitted out of the laser tube. Thus, when the reflective optical elements are used to seal the tube, they are integrated into the end walls of the tube at opposite ends of the discharge gap and thus are used to seal the tube. On the other hand, if the reflective optical elements forming the resonator are provided outside the laser tube, then fully transparent windows are provided at opposite ends of the tube to seal the tube. It is known that these optical elements, both reflective and transmissive, may be secured to the laser tube by means of a flange fixed by screws. This known securing mechanism, however, has many disadvantages. These disadvantages include:
1. The central portion of the optical element is blackened on its internal side, i.e. on the laser side of the window. This results in the central portion of the optical element quickly deteriorating.
2. When the optical element is detached from the laser, for cleaning for example, the optical element frequently falls out of the securing device in which the optical element is inserted during normal operation and is thereby permanently damaged.
3. Further, because the optical element is typically fixed with screws to the end of the laser tube, it has not been possible or practical to turn the window in the securing mechanism. However, a securing mechanism that would allow the optical element to be rotated about its central axis would be desirable, for instance to allow the laser beam to pass through a portion of the optical element that is not blackened.
4. In smaller gas lasers it has been especially difficult to extract the optical element from the end of the laser tube, as there is very little space for obtaining access to the edge of the optical element without damaging it. This problem is further exacerbated by the fact that the optical element frequently adheres to an O-ring provided on the end wall of the laser tube, and which provides a gas-tight seal between the end wall of the tube and the optical element.
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
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
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 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
All of the foregoing applications are incorporated by reference as if fully set forth herein.
SUMMARY OF THE
Frowein Helmut
Kodeda Hans
Flores-Ruiz Delma R.
Ip Paul
Mintz Levin Cohn Ferris Glovsky and Popeo P.C.
TuiLaser AG
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