Light reabsorption and radiation trapping can noticeably distort fluorescence decay in solid-state laser gain media with a partial overlap of absorption and emission bands. In this paper, the upper-state lifetime measurements in laser materials by the method of transient gratings are discussed. A theoretical model for description of reabsorption in a thin layer is developed. It is shown that under certain conditions reabsorption has no effect on the transient time of refractive index grating and thus the true upper-state lifetime can be measured. Some experimental results confirming effectiveness of the technique are presented.
We exploit the effect of light-induced atomic desorption (LIAD) to produce high atomic densities (
n≫k3) in a rubidium vapor cell. An intense off-resonant laser is pulsed for roughly one nanosecond on a micrometer-sized sapphire-coated cell, which results in the desorption of atomic clouds from both internal surfaces. We probe the transient (LIAD-induced) atomic density by time-resolved absorption spectroscopy. With a temporal resolution of
≈1ns, we measure the broadening and line shift of the atomic resonances. This broadening and line shift is attributed to dipole-dipole interactions. As this timescale is much faster than the natural atomic lifetime, the experiment probes the dipolar interaction in a non-equilibrium situation beyond the usual steady-state, assumed in the derivation of the Lorentz-Lorenz shift. This fast switching of the atomic density and dipolar interactions could be the basis for future quantum devices based on the excitation blockade.