Filamentation of 100-fs Pulses from a Ti:Sapphire Laser in Gases to Generate a Signal Wave of a Difference Frequency Generator

In order to increase the energy of a signal wave for a difference frequency generator, a spectral broadening of 100-fs pulses from a Ti:sapphire laser (center wavelength of 950 nm) is experimentally studied during their filamentation in five different gases: N₂, NH₃, He, CO₂, and CO. The greatest broadening and the highest energy in the Stokes region of the spectrum are observed for CO₂. Variation in the CO₂ pressure in the gas cell shows that for a Ti:sapphire laser with a pulse energy of several mJ, the highest radiation energy in the Stokes wing with a shift of ∼1000 cm^–1 is achieved at a pressure of 1 bar. Also, for each of the studied gases, the nonlinear refractive index is estimated at a pressure of 1 bar.