Lasers in the soft-x-ray wavelength range (0.3 30 nm) are expected to have an impact on applica-tions as revolutionary as they did in the visible and infrared wavelength range. The range of these applications is very wide as a result of the inherent properties of x-raylasers: high brilliance, short pulse duration, coherence, and short wavelength. The development of lasers in the x-ray spec-tral region is hence of fundamental importance in many fields such as holo-graphy, microscopy, interferome-try, x-ray lithography, surface analysis, atomic physics, and plasma physics.
Most of the soft-x-ray lasers demonstrated experimen-tally up to now have used the electron-colli-sio-nal excita-tion scheme in a hot, dense laser-pro-duced plasma. Reducing the very high pump energy required for saturated output remains the primary goal in x-ray laser research if these are to become a stan-dard laboratory tool. Using the novel technique of grazing-inci-dence pumping (GRIP), saturated x-ray lasing has recently been demonstrated in plasmas of Ni-like Ag, Pd, and Cd at wavelengths down to 13.2 nm, at repetition rates of up to 10 Hz, and for pump energies as low as 1 J. Simula-tions predict that sub-10-nm lasing should be feasible with 5-10 J of pump energy, and ~100 J would be required to generate an x-ray laser close to the water window (2.5-4.4 nm).
The main goals of the current project are to: i) complete the CPA (chirped-pulse ampli-fi-ca-tion) upgrade of the existing 300-GW/100-ps Nd:glass laser system and, ii) use the CPA laser system to systematically investigate and optimize x-ray lasing in the grazing-incidence pump-ing(GRIP) geometry.
The completion the CPA upgrade of the laser system is projected to result in pulse peak powers of up to 10 TW (20 J/2 ps) available for x-ray laser experiments. In a first phase, the systematic opti-mization the angle of inci-dence and prepulse configuration is planned for x-ray lasing in tar-gets of Pd, Sn, and, if possible, Ba at wavelengths of 14.7, 11.9, and9.2 nm, respec-tively. For this purpose, a new, larger vacuum chamber will be installed which will allow us to work at angles of incidence between approximately 9 and 32°.
With the CPA laser system fully operational, it should be feasible to extend the range of x-ray lasing wave-lengths accessible to the GRIP scheme into the region well below 10 nm and, eventually, into the water window below 4.4 nm. The candidates for lasing in this region will be the rare-earth elements (La, Pr, Sm, Gd, Dy, etc.), and this may require the development of novel target fabrica-tion techni-ques, as they are not amenable to simple machining from bulk material.