Stimulated Raman X waves in ultrashort optical pulse filamentation.

We demonstrate that ultrashort pulse filamentation in liquids with strong Raman gain leads to the spontaneous formation of nonlinear X waves at a Raman-shifted wavelength. We measured as much as 75% energy conversion efficiency into a Raman X wave in ethanol starting from 1 ps pulses due to the group velocity matching between the pump and Raman X pulses. Large Raman gain of a weak seed signal was observed in water, associated with a strong spatiotemporal transformation of the seed into an X wave.

High localization, focal depth and contrast by means of nonlinear Bessel beams.

We show an experimental and computational comparison between the resolution power, the contrast and the focal depth of a nonlinearly propagated diffraction-free beam and of other beams (a linear and a nonlinearly propagated Gaussian pulse): launching a nondiffractive Bessel pulse in a solution of Coumarine 120 in methanol creates a high contrast, 40 mm long, 10 microm width fluorescence channel excited by 3-photon absorption process. This fluorescence channel exhibits the same contrast and resolution of a tightly focused Gaussian pulse, but reaches a focal depth that outclasses by orders of magnitude that reached by an equivalent Gaussian pulse.