Pulses with a tunable central wavelength from 278-310 nm reaching <27 fs duration and >1 \mu J energy are generated by non-collinear four-wave mixing in a 0.5-mm CaF2 crystal.

The chirp effect in supercontinuum (SC) generation in photonic crystal fibers (PCFs) is researched carefully in experiment. Using an acoustic-optics programmable dispersive filter (AOPDF), the 1-4 order dispersions of the pulses from femtosecond oscillator can be accurately controlled. The experimental results show the SC generation in PCF is sensitive to the chirp of incident pulse, and the output spectrum and conversion efficiency can be tuned by changing the initial dispersion state. With different group delay dispersion (GDD) brought to the incident pulse, we find that positive chirp can enhance the energy conversion to long wavelength, and negative chirp can enhance the conversion to short wavelength. Specially, an optimal negative chirp can maximize the conversion to the shortest one at about 625 nm. The effect of the third-order dispersion (TOD) also has been investigated, and we find that the same value of the positive and negative TOD has the similar effect on the SC.

We describe a Ti:sapphire multi-pass amplifier with high efficiency at the repetition rate of 1 kHz. In the amplifier, the incident pulse is 0.66 mJ with the pulse duration about 90 ps. The incident pulse is amplified to 7.2 mJ when the pump energy is 23 mJ. The energy efficiency in the amplifier is nearly 30% with extracting efficiency larger than 40% when considering about 25% static reflecting loss in the amplifier. After compressed in the compressor, 5.4-mJ, 36-fs pulses with peak power larger than 0.1 TW are obtained.

The effects of gain narrowing and high order dispersions on the pulse duration in our kilohertz chirped-pulse amplification system have been compensated experimentally. Using an acousto-optic programmable dispersive filter (AOPDF), the spectral full-width at half-maximum (FWHM) is expanded from 30 to 50 nm. Stable laser pulses with the duration of 30 fs (FWHM), which is 1.07 times Fourier-transform-limitation, have been acquired by pre-compensating the high order phase distortions using the phase measured by spectral phase interferometry for direct electric-field reconstruction (SPIDER).