Corona Preionizer For High Repetition Rate TEA Gas Lasers

Abstract

A corona preionization system for a high repetition gas laser is described. The system has been applied to a 200Hz repetition rate TEA CO2 laser with a 1.5x1.5x40cm3 discharge volume. Because the self inductance of the laser head can be kept at a very low value, short excitation pulses and fast rising discharge voltages are possible. Since the preionizer is incorporated in the main circuit and consumes only a small fraction of the total excitation energy, high overall efficiencies can be obtained.High repetition rate transversely excited high pressure gas lasers are found in an increasing number of applications in the fields of material processing, laser radar, optical pumping of dye lasers and far infrared lasers.In order to increase the life time of the laser gas it is important that the preionization source has little or no contribution to the contamination of the gas. X -ray sources are very suitable as a preionizer because they are outside the laser chambre and can produce a very homogeneous density of preionization electrons. However they are relative complex and demand a relative high power. As an alternative UV radiation produced by a corona discharge can also be considered as a preionization source for high repetition rate high pressure gas lasers. The advantages of a corona preionizer are the possibility of making it an integral part of the electrical circuit of the main discharge and its relative low power consumption.In general a self terminating surface discharge is initiated due to a rapidly rising electric field at the surface of a suitable dielectric. The resulting displacement current has an amplitude proportional to the ratio of dielectric constant and thickness of the plate and the applied voltage gradient. Electrons, pulled out of the electrode and the surface of the dielectricum by the high electric field, will be accelerated in the gas and will produce a plasma which travels along the dielectric plate from one electrode to the other. By adjusting the length of the path between the electrodes and the field strength the surface discharge can be made self terminating due to the high electron losses because of recombination near the surface. It has been found experimentally, [1], that the production of UV radiation and therefore the electron density in the main discharge region increases with the magnitude of the displacement current. Also, the wavelength of the emitted UV radiation can be influenced by the energy of the corona discharge electrons. A higher electric field has been observed to produce shorter wave length W radiation and higher electron density in the main discharge region [1].The polarity and geometry of the electrodes can influence the preionizer significantly, especially at a large degree of assymmetry of the system [1,2]. Abstract A corona preionization system for a high repetition gas laser is described. The system has been applied to a 200Hz repetition rate TEA CO laser with a