X-ray lasing upon two-pulse irradiation of targets on the picosecond SOKOL-P facility

The results of experimental studies of the X-ray lasing on the 3p–3s transitions of neon-like titanium ions are presented. The laser radiation at 1.054 μm was focused to a ~30-μm wide line of length from 2 to 8 mm. Plane polished titanium plates were successively irradiated by two pulses: a 400-ps prepulse and a 4-ps main pump pulse delayed by 1.5 ns relative to the prepulse. The total laser energy was 8–10 J. The nanosecond-to-picosecond pulse energy ratio was maintained constant and was equal to 1:3. For a short target length (from 2 to 4 mm), the 326-Å line intensity was experimentally observed to grow exponentially with length. The small-signal gain for the X-ray laser radiation is estimated at approximately 30 cm^-1. The X-ray laser beam divergence was equal to about 9 mrad.