Selected Topics in Laser Spectroscopy
The optical Bloch equations which incorporate the phenomenological population (T1) and dipole dephasing (T2) times have been tested recently by optical free induction decay (FID) measurements on an impurity-ion crystal Pr3+:LaF3 at 1.6°K. At low optical fields, the observed Pr3+ optical linewidth is dominated by magnetic fluctuations arising from pairs of fluorine nuclear flip-flops where the condition T1>>T2 prevails. At elevated fields, this nuclear broadening mechanism is quenched and the Bloch equations are violated with T2→T1. A microscopic theory appropriate for a low temperature impurity solid is developed which reveals the above features both for optical and radio frequencies, and a simple physical interpretation of this line narrowing phenomenon is given. Modified Bloch equations of a novel form are derived to second order and yield analytic FID solutions over the entire range of optical field strength. A discussion of the earlier NMR theories will be given pointing out similarities and differences.
KeywordsFree Induction Decay Bloch Equation Magnetic Fluctuation Simple Physical Interpretation Rare Earth Impurity
- 6.R. G. DeVoe and R. G. Brewer, Phys. Rev. A (October 1984).Google Scholar