Leng Yuxin

Active–passive mode-locking using Cr4+:YAG crystal as saturable absorber

Abstract Cr 4+ : YAG crystal was used as a saturable absorber in an active–passive mode-locked Ndxa0:xa0YAG laser. The stable and complete mode-locked pulse train was achieved at 1064 nm . The duration of a single pulse was obtained from 0.8 to 2.4 ns by changing the Cr 4+ : YAG crystal with different initial transmission, when there was the shortest pulse width. The mode-locking dynamic process of Cr 4+ : YAG crystal was analyzed by the rate equations to explain the experimental result, and the effect of excited-state absorption was considered.

Generation of an isolated sub-100 attosecond pulse in the water-window spectral region

We propose a scheme to generate isolated attosecond pulses in the water-window spectral region. Based on the numerical solutions of the single active electron model, we investigate high-order harmonic generation in helium atoms driven by a multi-cycle two-colour optical field synthesized by an intense 2000 nm, 20 fs pulse and its frequency-doubled pulse. When the latter is slightly detuned and properly phase shifted with respect to the fundamental laser pulse, an ultra-broad extreme ultraviolet supercontinuum with a spectral width of 130 eV can be generated in the 270–400 eV spectral regions. A supercontinuum from 280–340 eV in the water window can be selected to yield an isolated 67 attosecond pulse without employing any phase compensation. This water window coherent x-ray pulse with less than 100 attosecond duration is a potential tool for studying the ultrafast electronic dynamics of biological samples in water.