Collisional optical-field ionization soft x-ray lasers

ABSTRACT We report recent investigations on collisional Optical-Field Ionization soft-x ray lasers. The amplifying medium is generated by focussing a high energy circularly polarized, 35 fs 10 Hz Ti: sapphire laser system in a few mm cell filledwith gas (xenon or krypton). Using xenon, a gain of 67 cm1 on the 4d95p-4d95d transition at 41.8 nm in Pd-like xenon and a gain-length product of 15 have been inferred at saturation. This source delivers about 5 i09 photons per pulse. Using krypton, a large amplification of the 3d94d-3d94p line at 32.8 nm as been observed for the first time. The influence of thepumping energy and the laser polarization on the lasing output are also presented.Keywords : OFI, saturation, collisional x-ray lasers 1.INTRODUCTION Since the last decade there has been much interest in developing Optical-Field Ionization (OFT) soft-x ray lasers ( XRL). The main motivation is to reduce dramatically the size ofXRL systems and to increase repetition rates. The basis isto optical-field ionize a moderate density gas by a high intensity short laser pulse to create a non equilibrium plasma inwhich population inversion between excited states of specific ionic species can be obtained. The electron distribution and