Two-step excitation of He/K mixture for producing coherent XUV radiation

Abstract

Recently, there has been great interest in the two-step excitation for the generation of coherent XUV radiation with low pump threshold. The two-step excitation process is as follows: the energy is first stored in a metastable level, and subsequently converted into coherent XUV radiation by stimulated resonant anti-Stokes Raman scattering (SRASRS). The He/K mixture two-step pumping system was first proposed by V.O. Panpanyan et al., in 1983. The main kinetic process is that the He * (2 3 S) state is produced in a discharge. It makes use of strong collisional energy transfer from He * (2 3 S) to populate potassium high lying quartet metastables K (3p 5 3d4s 4 P 5/2 ). By using 1.209 micrometers and 498 nm laser as the second step excitation, from the quartet state and through SRASRS the 64.3 nm and 59.8 nm coherent XUV radiation is obtained. This paper discusses several physical problems of the system.