Femtosecond relaxation kinetics of highly excited $\mathrm{M}_{\mathrm{Na}}^{**}$ states in CaF2 at 3.2 eV and 4.7 eV

Abstract

Femtosecond (fs) laser pulses at variable delay times allowed us to track the fast non-radiative transitions between the manifold of highly excited \(\mathrm{M}_{\mathrm{Na}}^{**}\) states to the lower lying fluorescent \(\mathrm{M}_{\mathrm{Na}}^{*}\) state in CaF2. Two distinct \(\mathrm{M}_{\mathrm{Na}}^{**}\) states of the manifold at 3.16 eV (\(\mathrm{M}_{\mathrm{Na}2}^{**}\)) and 4.73 eV (\(\mathrm{M}_{\mathrm{Na}3}^{**}\)) were populated using the second (SH) and third harmonics (TH) of fs laser light at 785 nm. The population kinetics of the fluorescent \(\mathrm{M}_{\mathrm{Na}}^{*}\) state in the 2 eV excitation energy range was revealed by depleting its fluorescence centered at 740 nm using fundamental near infrared (NIR) fs laser pulses. The related time constants for \(\mathrm{M}_{\mathrm{Na}2,3}^{**}{\sim}{>} \mathrm{M}_{\mathrm{Na}}^{*}\) relaxation amounted to 1.0±0.14 ps and 3.0±0.3 ps upon SH and TH excitation, respectively.