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 bandwid th of 0.008 cm(-1) and intensities of 10(8) photons/pulse at 20 Hz. The sou rce is based on two-photon resonance-enhanced sum-frequency mixing in rare gases. To demonstrate its properties, high-resolution photoionization and p hotoelectron spectra of argon have been recorded in the vicinity of the sec ond, 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(') s eries, respectively. The results for the ns'[1/2](J=1) series confirm the c onclusion reached by Klar [Z. Phys. D 23, 101 (1992)] that earlier single-p hoton XUV investigations have overestimated the width of these sharp resona nces. The narrow bandwidth of the source is also used to accurately determi ne the range of principal quantum number of the high Rydberg states that ar e probed by selected electric field ionization sequences in pulsed-field-io nization zero-kinetic-energy photoelectron spectroscopy. (C) 2000 American Institute of Physics. [S0034-6748(00)05110-8].