Abstract

Excitation of xenon near the two-photon resonance between the ground state and the 6p(1/2,0) state produces forward conical emission at a wavelength close to the 828-nm 6p(1/2,0)—6s(3/ 2,1) excited-state transition. We describe experimental features of this process as excited by 600-ps pulses of 250-nm radiation from a frequency-doubled dye laser with intensity up to 1.3 × 10⁸ W/ cm² in xenon at pressures of 1-20 Torr. The conical emission occurs most prominently when the driving field is a few gigahertz above the frequency at which spontaneous emission from the excited 6p state peaks. The cone angle increases with xenon pressure in the 1-10-Torr range. The dependence appears consistent with the predictions based on noncollinearly phase-matched four-wave mixing. In this interpretation, the fourth wave would be near resonance with the 146.9-nm first resonance transition of xenon and detuned to the low-frequency side. The conical emission co-exists (and may compete with) an axial stimulated process which may be either two-photon driven amplified spontaneous emission or stimulated hyper-Raman scattering. The different tuning characteristics for the two processes make the extent of their competition unclear.

© 1987 Optical Society of America