We investigated femtosecond pump-repump depletion excitation in biological fluorescent molecules (tryptophan and flavins) in solutions and in organic fluorescent interferents such as polycyclic hydrocarbons (naphthalene, diesel fuel). If the repump pulse induces in both flavins and Trp a depletion of the excited state, populated by the pump pulse, which leads to a drastic decrease of the fluorescence, such mechanism is ineffective in organic fluorescent interferents. The repump induced depletion is still observed for bacteria containing solutions. This opens interesting perspectives to discriminate biological from non-biological fluorescent particles in air.
The propagation of ultrashort, ultra-intense laser pulses gives rise to strongly nonlinear processes. In particular, filamentation is observed, yielding an ionized, conducting plasma channel where white-light supercontinuum due to self-phase modulation occurs. This supercontinuum, extending from the UV to the IR, is a suitable "white laser" source for atmospheric remote sensing, and especially Lidar (Light Detection and Ranging). Recent significant results in this regard are presented, as well as lightning control using ultrashort laser pulses. The application of ultrashort-pulse lidar to aerosol monitoring is also discussed.