Spontaneous Raman scattering as a high-resolution XUV radiation source

The paper describes a new type of high-resolution XUV radiation source which is based upon spontaneous anti-Stokes scattering of tunable incident laser radiation from atoms excited to metastable levels. The theory of the source is summarized and two sets of experiments using He (
1s2s
)
¹
S atoms, produced in a CW hollow cathode and in a pulsed high-power microwave discharge, are discussed. The radiation source is used to examine transitions originating from the 3p
⁶
shell of potassium. The observed features include four previously unreported absorption lines and several sharp interferences of closely spaced autoionizing lines. A source linewidth of about 1.9 cm
^-1
at 185 000 cm
^-1
is demonstrated.