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Flexible control of nonlinear processes under femtosecond filamentation using adjustable high-pressure gases and supercritical fluids

We demonstrate a novel approach of femtosecond laser pulse spectral-temporal control under filamentation in a wide range of pressures from 5 bar up to supercritical state. We showed that laser-induced processes such as supercontinuum generation and pulse self-compression could be tuned both by pressure and by energy adjustment due to the nonlinear refractive index alteration via pressure change. Thanks to the high pressure-controlled nonlinearity, a broadband (from 250 to 2500nm) supercontinuum with total efficiency more than 50% of energy can be generated in supercritical Xe and CO2. It was also demonstrated that the femtosecond laser pulse can be compressed in Xe in the femtosecond monofilamentation mode by 3.5 times with efficiency as high as 60%.