Transient collisionally excited x-ray laser in nickel-like zirconium at PHELIX laser facility

A transient collisionally pumped X-ray laser (XRL) driven by the infrared pulses from the PHELIX laser preamplifier at GSI has successfully been put into operation. Strong lasing at 22 nm has been observed in nickel-like zirconium. Experimental data from the optimization of the XRL energy output support the conclusion that inverse Bremsstrahlung plays a key role in the pumping mechanism. Laser induced fluorescence spectroscopy in lithium-like heavy ions can be performed using narrow bandwidth light pulses with a few μJ of energy in the XUV spectral region [1]. Such pulses are routinely produced in the scheme of transient collisional excitation (TCE) x-ray laser , which was first demonstrated by Nickles et al. [2]. In this scheme, saturated output can be obtained with a few J of pulse energy from the pumping laser (see e.g. [3]). A laser pulse with an energy of a few J and ns duration is focused to a line onto a solid target, creating a line-shaped plasma with a high abundance of nickel-like ions. A high intensity short (∼ ps) infrared laser pulse produced by the technique of ,,chirped pulse amplification” (CPA) heats the plasma rapidly to a high temperature which leads to a short lived (transient) population inversion. A bright, partly coherent XUV-pulse is emitted from the end of the plasma column by amplified spontaneous emission. Due to the short life time of the transient gain [4], the pumped region has to travel with the amplified radiation, which is achieved by so called travelling wave excitation [5]. At GSI, a high intensity/high energy laser system (PHELIX) is under construction [6]. The CPA front-end together with the preamplifier and pulse compressor are well suited for pumping a TCE XRL. The front-end delivers stretched pulses of > 50 mJ with a bandwidth of ∼ 7 nm. The preamplifier consists of three flashlamp pumped Nd:Glass rods (with 2x 19 mm and 45 mm diameter) which amplify the pulses further to an energy of several J. The pulse compressor, in a double folded single grating arrangement, is entirely housed in a vacuum chamber and is designed to compress pulses of up to 15 J to durations below 400 fs. Pulses up to 10 TW peak power have been achieved. Without the use of adaptive optics for the wave front correction the repetition rate is limited by the cooling time of the three heads to one shot