Abstract

We report new observations of a fast fluorescence process on 6p—6s transitions in xenon (0.01-5 Torr). A 600-ps pulse (λ~ 250 nm, Δν~ 3 GHz) from a frequency-doubled dye laser populates a single 6p state by two-photon coupling. The ensuing fluorescence (823 nm < λ < 993 nm) is collected by f/1 optics, detected by a photomultiplier or microchannel plate phototube, and displayed on an oscilloscope (1-GHz bandwidth) or digitized and recorded for statistical analysis. We previously characterized the emission process as amplified spontaneous emission (ASE) based on emission rate (> 10× spontaneous), high directionality, existence of threshold, and other time-independent characteristics.¹ New time-resolved observations with the microchannel plate detector (500-ps overall rise time) showed that far above threshold the fluorescence pulses temporally reproduced the excitation pulses and occurred simultaneously. Pulses near threshold showed widths up to 3 ns and delays up to 3.5 ns. Ringing or multiple-pulse emission also occurred. When the emission was spontaneous, fluorescence energy yields showed the quadratic dependence expected of two-photon excitation and decreased monotonically when N₂ was added to the xenon. ASE-dominated yields were linear in excitation energy and increased when N₂ was introduced. ASE yields were smaller than predictions based on work of Raymond et al.² Mechanisms for these results are discussed.

© 1985 Optical Society of America