Generation of sub-20-fs deep-ultraviolet pulses by using chirped-pulse four-wave mixing in CaF2 plate

Sub-20-fs deep ultraviolet (DUV) pulses are generated by using nondegenerate, chirped-pulse four-wave mixing of the fundamental and second-harmonic pulses from a commercial Ti:sapphire amplifier in a CaF(2) plate. The energy of the DUV pulses is 3.8 μJ, with a conversion efficiency from total pump energy to DUV of ~3.8%. The DUV pulse is compressed using a pre-chirp, introduced via a fused silica window in the fundamental beam. The central wavelength of the DUV spectrum can be tuned from 257 to 277 nm by adjusting the cross angle between the two pump beams. The spectrum can reach a width of 16.8 nm, which can support a pulse duration of 8.7 fs.