Pulse distortion, energy extraction, and ASE in an HF amplifier with angular multiplexing

It has been proposed that 1 ns pulses can be efficiently extracted from the e-beam initiated HF laser by angular multiplexing, i.e., filling the amplifier with the 1 ns pulses, 1 ns apart in time, each pulse at a slightly different angle; each pulse has an input intensity of 1 W/cm2 per line and almost fills the amplifier. We have treated this in a one dimensional model, neglecting transverse amplified spontaneous emission. We conclude that the scheme is efficient, and that most of the pulses are amplified but not distorted. The first few pulses are distorted by transient effects and the last pulse has an enhanced tail. The ratio of peak pulse intensity to forward ASE at the output is 104. We then include transverse ASE and find a drastically different situation. ASE saturates the inversion after a short time depending on pulse intensity (4 ns at I/sub o/ = 1 W/cm2, 7 ns at I/sub o/ = 100 W/cm2). The saturation time is only weakly dependent on the transverse reflection coefficient. Calculations were done on an amplifier system designed for 10 KJ output. At an incident peak pulse intensity of 104 W/cm2-line (.77 MW/cm2 for 77 lines) 2.5 KJ was obtained in amplified pulse energy, i.e., only 6 pulses of the 24 pulse train were fully amplified. The calculations indicate that double passing the pulse train through the amplifier would enhance the energy extracted