Measurement Of Two-Photon Absorption Cross Sections In Atomic 0 At 226 nm: Single-Frequency Versus Multimode Lasers

Abstract

Absolute atomic bound-bound two-photon cross sections have been measured using a single-frequency laser, eliminating the usual uncertainties about unresolved temporal fluctuations. The cross sections were measured using the technique of two-photon excited fluorescence. For the 3p3 P2,1,0+2P3P2 transition in atomic oxygen at 226 nm the integrated cross section (obtained by s6afining the laser frequency through the two-photon resonance) is 1.87 ±0.60 x 10-35 cm4. Relative fine structure cross sections and energy spacings have been measured by Doppler-free spectroscopy. Absolute and relative two-photon cross sections agree well with ab initio calculations. Comparison with similar measurements carried out with multimode lasers yields information about multimode laser photon statistics. The experimental integrated cross section is shown to be proportional to the product of the atomic cross section and G(2)(0) the second-order intensity correlation at time zero of the laser field. It is assumed that G(2)(0)=1.0 for the single-frequency laser source. Five other laser 226 configurations have values of G(2)(0) ranging from 0.8 ±0.2 Until multimode lasers are well enough understood to allow predictions of G2) (0 (especially after frequency conversion processes such as doubling and Raman shifting), single-frequency lasers will be the best source of reliable multiphoton cross section measurements.© (1988) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.