Photo-triggering and secondary electron produced ionization in electric discharge ArF* excimer lasers

Abstract

Electric discharge excimer lasers are sustained in multi-atmosphere attaching gas mixtures that are typically preionized to enable a reproducible, uniform glow, which maximizes optical quality and gain. This preionization is often accomplished using UV light produced by a corona discharge within the plasma cavity. To quantify the relationship between corona discharge properties and those of the laser discharge, the triggering of electron avalanche by preionizing UV light in an electric dischargepumped ArF* excimer laser was numerically investigated using a two-dimensional model. The preionizing UV fluxes were generated by a corona-bar discharge driven by the same voltage pulse as the main discharge sustained in a multi-atmospheric Ne/Ar/Xe/F 2 gas mixture. The resulting peak photoelectron density in the inter-electrode spacing is around 10 8 cm À3 , and its distribution is biased toward the UV source. The preionization density increases with increasing dielectric constant and capacitance of the corona bar. The symmetry and uniformity of the discharge are, however, improved significantly once the main avalanche develops. In addition to bulk electron impact ionization, the ionization generated by sheath accelerated secondary electrons was found to be important in sustaining the discharge current at experimentally observed values. At peak current, the magnitude of the ionization by sheath accelerated electrons is comparable to that from bulk electron impact in the vicinity of the cathode.

Effects of tunable circuit parameters on pulsed discharge and input-output characteristics of a XeCl excimer laser

“…In the cavity of XeCl excimer laser, the main discharge electrodes include a powered cathode and a grounded anode, resulting in discharge dimensions of 1.5 cm × 3.5 cm × 100 cm (width × distance × length). In order to improve the pump efficiency and the laser quality, it is necessary to provide adequate initial electron density n e,0 , typically 10 8 -10 9 cm −3 , through pre-ionizing the gas mixture [31][32][33]. Thus, the discharge volume is assumed to be uniformly pre-ionized by a UV spark, producing a sufficient electron density n e,0 = 10 9 cm −3 at t = 0.…”

Repetitively pulsed streamer discharge with laser-induced surface trapped electron desorption to exploit residual charges in situ

“…The bigger primary streamer around the needle tip is probably caused by the higher availability of free electrons released from charge surface by the pulsed laser. A uniform discharge plasma could be expected, which is crucial for the pre-ionization source of the excimer laser [4,72]. The prolonged secondary streamer and the easier streamerto-spark transition is possibly caused by the higher deposited energy and higher reduced electric field without the additional reversed electric field from residual surface charges.…”

“…Both the discharge appearance and the discharge regime are crucial and fundamental plasma characteristics. On the one hand, complicated and sometimes unexpected discharge appearances and discharge regime transitions due to plasma instabilities under repetitive pulses are undesired because consistencies of the chemically active particles and ultraviolet emission outflux [4] are compromised. On the other hand, the discharge regime transition towards the high energy density state (e.g.…”

Numerical investigation of discharge evolution and breakdown characteristics of ArF excimer lasers

“…Research encompassing both pre-ionization and the main discharge coupling processes remains exceptionally scarce. Only Xiong and Mark J Kushner's work has ventured into investigating the complete pre-ionization [34] and discharge process [35] of ArF excimer lasers (2D) first of all. They discussed the pre-avalanche photo-generated electron density is about 10 8 cm −3 , and the critical role of sheath-accelerated secondary electrons in ArF excimer Lasers.…”