Fast-iterative technique for the calculation of frequency-dependent gain in excimer laser amplifiers

摘要

Abstract: The motivation in initiating these calculations is to allow observation of the frequency evolution of a laser pulse as it propagates through an amplifier and then through a sequence of amplifiers. The question this paper tries to answer is what pulse shape must be produced out of a front-end oscillator so that after it propagates through the whole Aurora KrF fusion amplifier chain it will result in high energy, broad-band laser fields of a given bandwidth that can be focused onto a fusion target. The propagation of single frequency source through an amplifier with distributed loss was considered by Rigrod and was significantly expanded by Hunter and Hunter. The latter included amplified spontaneous emission $LB@ASE$RB considerations both in the direction of and transverse to the coherent field. Analytic solutions that include forward and backward propagating fields and ASE were derived which were transcendental in nature but allowed for fairly easy computer calculations. Transverse ASE were calculated using the saturated gain resulting from longitudinal fields and were used to compare this with the longitudinal fields. Thus, the influence of the transverse ASE were not folded back into the longitudinal field equations. Large computer programs are now available at LANL which include the influence of transverse ASE on the longitudinal fields. However, none of these considerations have worried about the changes in the frequency characteristics of the propagating field or of how each of the frequency field components contributes to the saturation of the gain. The inclusion of full frequency characteristics to the analytic solutions of Hunter and Hunter proved impossible at least for this author and a new calculation technique was developed and is the subject of this talk.!