Spectral Broadening of Chirped Laser Pulse Caused by Four-Wave Mixing in BaWO4 Crystals

The spectral broadening of a chirped, temporally stretched (up to 200 ps) Ti:sapphire laser pulse propagating together with a broadband low-power seed pulse through BaWO4 crystals was experimentally and numerically studied. Our analysis demonstrated that self-phase modulation could not have affected the pulse spectrum under the experimental conditions. The spectral broadening of the Ti:sapphire laser pulse was found to be due to four-wave mixing, which resulted in transferring the power of the central wavelength to the spectral wings. To the best of our knowledge, this is the first demonstration of such origin of laser pulse spectral broadening in crystals.