Gas discharge laser with means for removing gas impurities

Details Gas discharge laser with means for removing gas impurities Gas discharge laser with means for removing gas impurities

2002-06-12

2004-05-11

Ip, Paul (Department: 2828)

Coherent light generators

Particular active media

Gas

C372S057000

Reexamination Certificate

active

06735233

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to gas discharge lasers, in particular excimer lasers or molecular fluorine lasers, which emit laser radiation in the UV range or in the VUV range of the electromagnetic spectrum.
Such lasers contain suitable gas mixtures in the gas discharge space.
2. Description of Related Art
The problem of contamination of the gas mixture has been known for a long time. Impurities in the laser gas have negative effects on the gas lifetime, the laser pulse energy, the stability and other properties of the laser. The impurities can both influence the laser process itself and, in particular, have negative effects owing to build-ups on components of the laser, for example in the form of deposits on optical surfaces or on the windows of the gas discharge chamber.
It is, for example, known in the prior art to remove impurities from the laser gas by using so-called cold traps.
DE 198 26 701 A1 addresses the problem of water (H
2
O), which is also known as a detrimental impurity, in the laser gas. The gas mixtures in excimer lasers are usually made up from commercially available gases and gas mixtures. In this case, commercially available gases are generally contaminated with H
2
O at a level of 1-2 ppm. This means that H
2
O is re-introduced into the gas discharge space every time the gas is changed. Even at this concentration, water has a negative effect on the properties of the laser, in particular the working life. Water can also enter the gas discharge space from the outside, or may alternatively become desorbed from the surfaces of the walls of the chamber or of optical components. The remarks above concerning H
2
O likewise apply to other substances as well, for example N
2
and O
2
, which are also considered as detrimental impurities.
DE 198 26 701 proposes the use of a hygroscopically active medium in order to remove H
2
O from the laser gas.
BRIEF SUMMARY OF THE INVENTION
It is an object of the invention to provide another effective means for the removal of impurities from laser gas, which removes not only H
2
O but also other impurities.


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