Experimental demonstration of dyed water aerosol fluorescence stimulated by femtosecond laser postfilaments propagating in air.

We present the fluorescence spectra of single millimeter water droplets and micron-sized dyed water aerosol (rhodamine 6G) stimulated by a high-intensity femtosecond Ti:sapphire-laser pulse (carrier wavelength 792 nm) upon its nonlinear propagation in air. The distinctive feature of our experimental measurements is that the droplet fluorescence is obtained in the area of plasma-free pulse propagation after the pulse filamentation has already been terminated (postfilamentation region). Our results significantly expand the working area of femtosecond laser-induced fluorescence spectroscopy for remote diagnostics of atmospheric aerosols.

Broadband emission spectrum dynamics of large water droplets exposed to intense ultrashort laser radiation.

We report on experiments on the interaction of a gigawatt femtosecond laser pulse train with hanging isolated millimeter-sized water droplets. A transparent droplet experienced explosive boiling-up and emitted light in the visible spectrum as a result of laser-induced plasma formed inside the droplet volume. The droplet emission spectra showed remarkable broadening, depending on the laser power. The role of pulse self-phase modulation in measured spectral broadening when the pulse propagates through the droplet is discussed.