Broadly tunable vacuum-ultraviolet/extreme-ultraviolet radiation generated by resonant third-order frequency conversion in krypton

Abstract

Resonant third-order sum- and difference-frequency conversion (ωuv = 2ωR ± ωT) of pulsed-dye-laser radiation is investigated in the rare gas, Kr. The frequency ωR(λR = 216.6 nm) is resonant with the Kr two-photon transition 4p–5p[5/2, 2]. On tuning ωT in the range λT = 219–364 nm, the sum frequency generates light in the extreme ultraviolet (XUV) (λxuv = 72.5–83.5 nm). In agreement with theoretical predictions, the conversion efficiency η is almost constant within this spectral range. At input powers PR = 14 kW and PT = 400 kW, the pulse power of the XUV exceeded Pxuv = 20 W. However, absorptions in the Kr gas reduced the power of the detected XUV light to about 5 W (effective efficiency, η = 1.2 × 10−5). With laser light at λT = 272–737 nm, the difference frequency generates continuously tunable radiation in the vacuum ultraviolet (VUV) (λvuv = 127–180 nm). In this range, the conversion efficiency increases with wavelength by more than 1 order of magnitude. At λvuv = 135 nm, for example, input powers PR = 0.2 MW and PT = 1.2 MW generate VUV light with Pvuv = 250 W (n = 1.8 × 10−4). At λvuv = 175 nm, a lower input (PR = 80 kW, PT = 560 kW) produced VUV light pulses of Pvuv = 1.8 kW (η = 2.8 × 10−3). This spectral variation of η is in agreement with the calculated wavelength dependence of the nonlinear susceptibility and of the gas pressure required for optimum VUV output.