Controlled nonlinearity and the lasing effect under femtosecond filamentation in dense and supercritical Xe

摘要

We demonstrate novel approaches for femtosecond laser pulse spectral-temporal control under filamentation in a wide range of high pressures from 5 bar up to supercritical xenon. Laser induced processes, such as supercontinuum (SC) generation and pulse self-compression, can be tuned both by pressure and by energy adjustment as a result of the nonlinear refractive index alteration via pressure change. Due to the high pressure-controlled nonlinearity of xenon, a broadband (from 250 to 2500 nm) SC with a total efficiency more than 50% of the energy can be generated in the supercritical state. We showed that the filament-induced SC in the visible wavelength range is accompanied by an amplified spontaneous emission observed in the forward direction. The maximum emission efficiency (about 0.5%) was achieved at a pressure of 30 bar for the 466 nm line. It was demonstrated that the femtosecond laser pulse can be compressed in Xe in the regime of femtosecond monofilamentation by 3.5 times with an efficiency as high as 60%.