A practical femtosecond polarization-maintaining Yb-doped fiber amplifier enabling 153 fs transform-limited pulse duration with 32 μJ pulse energy at 1 MHz repetition rate corresponding to a peak power of 0.21 GW is demonstrated. The laser system based on chirped-pulse amplification (CPA) technique is seeded by a dispersion managed, nonlinear polarization evolution (NPE) mode-locked oscillator with spectrum bandwidth of 31 nm at 1040 nm and amplified by three fiber pre-amplifying stages and a rod type fiber main amplifying stage. The laser works with beam quality of M<sup>2</sup> of 1.3 and power stability of ∼0.63% (root mean square, RMS) over 24 hours will be stable sources for industrial micromachining, medical therapy and scientific research.
A white light continuum of octave spanning was produced by self-phase modulation in a hollow-core fiber filled with
noble gases at high pressure and subsequently compressed by a set of ultra-broadband chirped mirrors. Pulses as short as
5.1 fs with energy up to 400 μJ at a 1 kHz repetition rate were obtained. Based on the carrier-envelope phase (CEP)
locking of the femtosecond oscillator and the spectral interference of the white light continuum between the white
fundamental wave and the harmonic wave at the same wavelength, the CEP of 5.1 fs pulse can be further locked by
modulating the pump laser through a slow loop. The intense, few-cycle laser pulses with a stable CEP will enable us to
produce high-order harmonic X-ray laser by the interaction with a rare gas target, this may drive the individual
attosecond pulse generation.
We have constructed two kinds of table-top femtosecond terawatt (TW) Ti:sapphire laser systems based on the chirped-pulse
amplification (CPA). With a compact design using only two-stage amplifiers, output energies of 36mJ and 640mJ at 10hz
repetition rates were obtained with recompressed pulse duration of 25 fs, and 31 fs respectively, corresponding to peak
powers of about 1.4 TW and 20 TW. The total pump energy for the last stage is 260 mJ and 2.8 J at wavelength of 532 nm.
These results represent a significant efficiency in amplification and a compact configuration in size. By using an adaptive
optical system to correct the wave-front distortion of the 20TW laser. we further demonstrated the improvement of beam
quality br higher focusable laser intensity.
Effects of laser polarization were studied on behaviors of fast electrons produced from an aluminum target irradiated by obliquely incident laser pulses at 8x10<SUP>15</SUP> W/cm<SUP>2</SUP>. Jet emission of outgoing fast electrons collimated in the polarization direction was observed for the s-polarized laser irradiation, whereas for the p-polarized irradiation, very directional emission of outgoing fast electrons was found close to the normal direction of the target. The behaviors of in-going fast electrons into the target for s- and p-polarized irradiation were also investigated by observing x-ray Bremsstrahlung radiation at the backside of the target.