Double-pulse non-normal incidence pumping geometry for transient collisionally excited short-wavelength x-ray lasers

On the way to reaching shorter wavelength x-ray lasers (XRL) great progress was achieved towards lowering the necessary high pump laser energy required for the preparation of the lasing medium. For this, two pulses in two independent beam-lines with different duration and at different angles of incidence were applied. This is a non-trivial complication, since the delivery of highenergy pulses require the use of large beam diameters. With the concept presented here, the set-up is simplified tremendously. Since the double pumping pulse scheme uses only one beam-line to generate the x-ray laser gain medium, numerous advantages i.e. improved stability, reproducibility and not least cost decrease are apparent. In the front-end of the driving chirped pulse amplification (CPA) laser system, the double pumping pulse is generated in a standard Mach-Zehnder type set-up. The stretched pulse is distributed into the two arms with an adjustable energy ratio. One of the arms incorporates a delay line adjustable between 0 and 3 nanoseconds delay. The two pulses are then amplified through the chain of the CPA system which includes regenerative Ti:Sapphire and Nd:Glass amplifiers. After compression, the two short pulses are sent to the experiment chamber [1]. For this experiment an additional adjustable compressor is installed in the pre-pulse arm, which allows to produce a pre-pulse duration between 100 and 200 picoseconds.