Liu Jingru

Deposition of Diamond-Like Carbon Films with Femtosecond KrF Laser Pulses

Hydrogen-free diamond-like carbon (DLC) films with the optical band gaps of 2.0-2.7 eV and the microhardness of 40-55 GPa are deposited by femtosecond KrF laser pulses. The film microstructure of nanometer spheroid is observed. The film microhardness is improved with the increase of ion kinetic energy of plasma plume from 300 to 600 eV. The characteristics of DLC film deposition with fs pulses is discussed.

Effect of characteristics of plasma plume on the diamond-like film deposition

Pulsed KrF lasers of two different durations (30 ns, 500 fs) are used to deposit DLC films. By optical emission spectroscopy and ion probe, the composite species of laser generated plasma plume are identified, the average kinetic energy of ions, the plume flux and their variation with laser energy density, and the distance from the target are investigated. The relation of the properties of deposited films with the plasma characteristics is studied.

High-Order Temporal Corrected Fields of Ultra-Short Laser Pulses and Laser-Driven Acceleration

Up to third-order temporal correction in terms of a small dimensionless temporal parameter e = 1/(ω0t0) (ω0 = ck0 the central oscillatory frequency, t0 the pulse duration of half period), the field expressions of ultra-short focused laser pulses are explicitly presented. To evaluate the correction efficacy, electric amplitudes of zeroth-order and higher-order corrected fields are compared for different pulse durations. Furthermore, electron interaction with ultra-short laser pulses is simulated using both the zeroth-order and higher-order corrected field equations. Our simulation results show that the third-order correction terms should be considered for investigating the interaction if the laser pulse duration decreases to a few optical periods.

Observation of Atomic Emission Enhancement by fs-ns Dual-Pulse Laser-Induced Breakdown Spectroscopy

An experiment of a 500-fs KrF laser pulse incident upon a high density supersonic O2 gas jet synchronously with an ns frequency-doubled Nd:YAG laser pulse is performed in orthogonal configuration. Significant atomic emission enhancement of over forty-fold is observed with an optical multi-channel analyser. The enhancement effect is probably attributed to the different ionization mechanisms between fs and ns laser pulses.

Time-Resolved Investigation of Ionization of Clusters Irradiated by a Strong Laser

Ionization dynamics of clusters irradiated by chirped femtosecond lasers is investigated by using a linearly chirped pulse spectral interferometry with a time resolution of less than 100 fs. The production of an average charged ~Xe18+ and ~Kr9+ ions indicates a strong energy coupling between laser and cluster. Ultrafast depletion of the probing laser is observed to be strictly coincident with the ionization front as seen in other experiments. Moreover, a two-step ionization process for Xe and Kr clusters irradiated by high-intensity lasers has been observed, which implies the role of resonance enhancement during the cluster explosion.