<title>Determination of the electrical characteristics of the discharges in a pulsed gas laser through its current waveforms</title>

Abstract

A method of finding the time dependent resistance and inductance of the discharges in the switch system and laser chamber in pulsed gas lasers is describel in the IDresent work. According to this method the current waveioriri is digtized and the first and second derivative is calculated through a computer. For a certain time instant, substituting the value of the current and its first and second derivative into the integrodifferential equations describing the performance ofthe circuit lOOpS. we forni relationships which connect the values of the resistance and inductance for this particular time instant. Combining relationships originated from very closed adjacent time instants. the values of the resistance and inductance can be found. Scanning the entire time region of the discharge. the time history of the resistances and inductances of the discharges are revealed. Their behavior Shows for the resistances an abrupt drop while for the inductances a sharp peak. both during the formation phase. After that the above characteristic quantities fluctuate slowly around constant values. INTRODUCTIONIn pulsed gas lasers (Excimer, N2. CO. HF, Fetc) there are two electrical discharges. The first in the switch system (thyratron, spark-gap) and the second in the laser chamber. Strictly speaking, these can be symbolized in the laser electric circuit as time dependent resistance and inductance in series combination. These quantities are both considered in some cases constant [I,2] while in other cases the inductance is considered constant and the resistance is parametrized through an exponential drop during the formation phase of the discharge [3]. To date there is no method of finding the resistance and inductance by time. In this paper a method is presented where the time history of the resistance and inductance are revealed elaborating step by step the current waveform through the differential equations governing the performance of the electric circuit. The quantities which can be calculated after that, by time, are the oscillation frequencies, the damping constants, the impedance of the discharges etc. 440 ISPIE Vo/. 2502 0-8194-1860-9/95/$6.00 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/28/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx