A broadly tunable extreme ultraviolet laser source with a 0.008 cm-1 bandwidth

A new coherent narrow bandwidth extreme ultraviolet (XUV) laser source has been developed that is broadly tunable in the range 10-17 eV with a bandwidth of 0.008 cm(-1) and intensities of 10(8) photons/pulse at 20 Hz. The source is based on two-photon resonance-enhanced sum-frequency mixing in rare gases. To demonstrate its properties, high-resolution photoionization and photoelectron spectra of argon have been recorded in the vicinity of the second, spin-orbit excited ionization threshold (Ar+2P1/2). From the analysis of the autoionization line shapes of the ns(')[1/2](J=1) and nd'[3/2](J=1) resonances, reduced linewidths Gamma (r,l)=Gamma (l)xn(*3) of 499.3(46) cm(-1) and 28.76(89)x10(3) cm(-1) have been determined for the s(') and d(') series, respectively. The results for the ns'[1/2](J=1) series confirm the conclusion reached by Klar [Z. Phys. D 23, 101 (1992)] that earlier single-photon XUV investigations have overestimated the width of these sharp resonances. The narrow bandwidth of the source is also used to accurately determine the range of principal quantum number of the high Rydberg states that are probed by selected electric field ionization sequences in pulsed-field-ionization zero-kinetic-energy photoelectron spectroscopy. (C) 2000 American Institute of Physics. [S0034-6748(00)05110-8].