Toward a full optimization of a highly saturated soft-X-ray laser beam produced in extremely long capillary discharge amplifiers

We report a substantial improvement of the output characteristics of a capillary discharge single-pass 46.9 nm Ne-like Ar soft-X-ray laser obtained by increasing the length of laser amplifier from 20 up to 45 cm. The longest plasma amplifier is characterized by an aspect ratio well exceeding 1000:1. The plasma columns are pumped by long 180 ns half-cycle duration, low amplitude 17-20 kA current pulses inside 3 mm in diameter alumina capillary channels filled with Ar at pressures of 0.25-0.55 Torr. Through the elongation of the plasma we produce a highly saturated regime of operation, where the plasma medium is three times the saturation length, the output pulse energy is of 300 μJ and the pulse duration of 1.7 ns. The far-field intensity distribution, reaching value <1 mrad and the coherence properties of the laser, both have been also shown to improve with the increase of the capillary length. The stable operation of the laser has been produced at pulse repetition rate up to 0.1 Hz. © 2003 Elsevier B.V. All rights reserved.