Intense narrow-bandwidth extreme ultraviolet laser system tunable up to 20 eV

Abstract

Narrow-bandwidth, broadly tunable vacuum ultraviolet (VUV) and extreme ultraviolet (XUV) radiation has been generated up to 20 eV by resonance-enhanced four-wave mixing in argon using the five two-photon resonances of argon between 105 000 and 109 000 cm−1 corresponding to the optically accessible fine-structure components of the 3p54p electron configuration. These two-photon resonances were reached by using the output of an F2 excimer laser (157 nm) and the tripled output of a dye laser. The highest VUV/XUV intensities were obtained using the 3p54p′[1/2]0←3p6(1S0) two-photon resonance at 108 722.62 cm−1 in combination with the main excimer line. The conversion efficiency reaches an optimum for photon energies around 16 eV and slowly decreases when the photon energy rises to 20 eV. The use of the argon resonances also facilitates the generation of intense VUV laser radiation around 90 000 cm−1, a region that is not easily accessible by four-wave mixing with the commonly used two-photon resonances of krypton (202.3 and 212.5 nm) and xenon (222.6 and 249.6 nm). The bandwidth of the VUV/XUV laser radiation was measured to be less than 0.2 cm−1 over the entire range between 11 and 20 eV. The VUV/XUV laser system was used to measure the isotopic shift of the 2p54s[3/2]1←2p6(1S0) resonance in neon at 158 796 cm−1, and fully rotationally resolved photoelectron spectra of C2H2 around 92 000 cm−1 and CO2 between 140 000 and 146 000 cm−1. Improved values of the first adiabatic ionization energy of C2H2 (91 953.5±0.5 cm−1) and CO2 (111 112.3±0.8 cm−1) were determined.