The Effects of Velocity-Changing Collisions on Two-Photon and Stepwise Absorption Spectroscopic Lineshapes,
Abstract
We report the results of an experimental study of the effects of velocity-changing collisions on two-photon and stepwise absorption lineshapes. Excitation spectra for the 3S(1/2) yields 3P(1/2) yields 4D(3/2) transitions of sodium atoms undergoing collisions with foreign gas perturbers are obtained. These spectra are obtained with two cw dye lasers. One laser, the pump laser, is tuned 1.6 GHz below the 3S(1/2) yields 3P(1/2) transition frequency and excites a nonthermal longitudinal velocity distribution of excited 3P(1/2) atoms in vapor. Absorption of the second (probe) laser is used to monitor the steady state excited state distribution which is a result of collisions with rare gas atoms. The spectra are obtained for various pressures of He, Ne, and Kr gases and are fit to a theoretical model which utilizes either the phenomenological Keilson-Stoerer or the classical hard sphere collision kernel. The theoretical model includes the effects of collisionally aided excitation of the 3P(1/2) state as well as effects due to fine-structure state-changing collisions. Although both kernels are found to predict lineshapes which are in reasonable agreement with the experimental results, the hard sphere kernel is found superior as it gives a better description of the effects of large angle scattering for heavy perturbers. Neither kernel provides a fully adequate description over the entire line profile. The experimental data is used to extract effective hard-sphere collision cross sections for collisions between sodium 3P(1/2) atoms and helium, neon and krypton perturbers. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 1979
- Accession Number
- ADA076100
Entities
People
- J. E. Bjorkholm
- P. R. Berman
- Peicheng Liao
Organizations
- New York University