Zhang Wen-Qi

5.4-TW/46-fs 10-Hz Ti: sapphire laser system

We have developed a compact Ti: sapphire laser system which can generate 5.4-TW pulses at 10-Hz repetition rate. Chirped-pulses are amplified to 450 mJ by a regenerative amplifier, a 4pass amplifier and a 3-pass amplifier. After compression, 250-mJ, 46-fs pulses are obtained

Theoretical Manifestation of the Broadening Effect on Photoelectron Angular Distributions

The broadening effect in photoelectron angular distributions (PADs) observed by Freeman et al. is studied theoretically. Using a nonperturbative scattering theory developed for multiphoton ionization with the inclusion of spontaneous emission, we calculate the PADs for above-threshold ionization (ATI) peaks. The numerical calculations from our theory reproduce the kinetic-energy dependence and the laser-intensity dependence of PADs of ATI peaks observed by Freeman et al., [Phys. Rev. Lett. 57 (1986) 3156] and provide an evidence for the existence of the ponderomotive momentum of intense laser fields.

Influence of atomic motion on a microlaser in an optical standing-wave cavity

We study the microlaser in an optical standing-wave cavity injected with two-level atoms. The results have shown the obvious influence of atomic centre-of-mass motion on the microlaser, such as the photon distribution, the linewidth and the frequency shift. It was found that when the momentum of atoms is comparable to that of photons, the influence of atomic motion is dominated and the number of photons in the microlaser can be greatly enhanced, owing to part of the atomic kinetic energy being transferred to the resonator. This work provides a comparison of the related studies on the atomic motion under special assumptions.

Dynamics of Interaction of H2+ with Intense Ultrashort Laser Pulse

The dynamic process of H2+ in intense ultrashort laser pulses with intensities of 1014 ~ 1015 W/cm2, wavelength of 532 nm and duration of 22 fs is theoretically investigated by using collinear model and numerically solving the time-dependent Schr?dinger equation. The results show that: (1) the dissociation and dissociative ionization compete each other in the case of intensities between 2.5 ? 1014 and 4.0 ? 1014 W/cm2; (2) both the dissociation and the dissociative ionization are much smaller and appear at about 5 cycles (?9 fs) later than the ionization. In addition, we estimate the spectrum of high harmonic generation and find that the well-known cutoff rule is invalid for the ultrashort laser pulse (e.g. the duration???25 fs), because the shorter pulse can produce higher order harmonics than the longer one.

High-order harmonic generation in Ar and Ne with a 45fs intense laser field

Experimental results of high-order harmonic generation (HHG) in Ar and Ne gas driven with a 45fs Ti: sapphire laser are presented. The shortest-wavelength harmonic emission corresponding to the 91st order harmonic (8.63nm) is observed in argon. In neon, the harmonics up to order 131 (5.99nm) is also observed. The effects of gas density, laser intensity, free electron and the focusing geometry parameters of the laser beam on the process of harmonic generation are investigated. The direct experimental evidence that an increased electron density causes a degenerated harmonic radiation is obtained.