Ge Xiao-Chun

Low Resistance and Long Lifetime Plasma Channel Generated by Filamentation of Femtosecond Laser Pulses in Air

An experimental investigation of the length and resistance of the laser plasma channel generated by filamentation of fs laser pulses in air was presented. It was found that the length of the plasma channel was different from that of the laser filament. This phenomenon was commensurate with a special self-guide mechanism without ionization. Through increase of the laser energy the plasma channel could be prolonged and the resistance could be reduced. To get even lower resistance, more effective control would be needed over the multi-filament. The lifetime of the plasma channel was increased by a factor of 4.5 by pulse sequences, which were generated by detuning the regenerative amplifier in the chirped pulse amplification (CPA) laser system.

Compression of Intense Laser Pulse through Filamentation in an Argon-Filled Cell

We demonstrate a pulse compression technique through filamentation in an argon-filled cell. By using a pair of chirped mirrors for dispersion compensation, we have successfully compressed the 53 fs pulse to 15 fs with good spatial qualities and good pulse stability. The total transmitted efficiency is more than 75%. The influence of the experiment parameters to the compressed pulses is also studied experimentally.

Pulse Compression by Filamentation in Argon with an Acoustic Optical Programmable Dispersive Filter for Predispersion Compensation

We have experimentally demonstrated pulses 0.4 mJ in duration smaller than 12 fs with an excellent spatial beam profile by self-guided propagation in argon. The original 52 fs pulses from the chirped pulsed amplification laser system are first precompressed to 32 fs by inserting an acoustic optical programmable dispersive filter instrument into the laser system for spectrum reshaping and dispersion compensation, and the pulse spectrum is subsequently broadened by filamentation in an argon cell. By using chirped mirrors for post-dispersion compensation, the pulses are successfully compressed to smaller than 12 fs.

Carrier-envelope phase effects on high-harmonic generation driven by mid-infrared laser field

The influence of the carrier-envelope phase on high-harmonic generation is investigated, both experimentally and theoretically, for three different interaction gas media, driven by mid-infrared, few-cycle and CEP-stabilized laser pulses. Different patterns of harmonic spectra with varying CEP for the three interaction gas media are observed. Furthermore, in comparing our experiment results to the previous works driven by near-infrared laser pulses, different phenomena are found. Through numerical simulation, we find that for the two different kinds of driving fields, i.e. mid-infrared and near-infrared laser pulses, different kinds of electron trajectories contribute to the generation of high harmonics.

Red-shift conical emission by femtosecond pulses at low input power

Red-shift conical emission (CE) is observed by femtosecond laser pulse propagating in BK7 at a low input power (compared to those input powers for generation of blue-shift CE). With the increasing input power the blue-shift CE begins to appear whereas the red-shift CE ring (902 nm in our experiment) disappears accompanied by the augment of the central white spot size synchronously. The disappearing of red-shift CE in our experiment is explained such that the increase of axial intensity is much higher than that of ring emission and the augment of the central white spot size with the increasing input laser power.

Conical Emission Patterns by Femtosecond Pulses with Different Spectral Bandwidths

Different conical emission (CE) patterns are obtained experimentally at various incident powers and beam sizes of pump laser pulses with pulse durations of 7 fs, 44 fs and 100 fs. The results show that it is the incident power but not the incident power density that determines a certain CE pattern. In addition, the critical powers for similar CE patterns are nearly the same for the laser pulses with the same spectral bandwidth. Furthermore, as far as a certain CE pattern is concerned, the wider the spectral bandwidth of pump laser pulse is, the higher the critical power is. This will hopefully provide new insights for the generation of CE pattern in optical medium.

Effect of the Initial Laser Phase on the Interaction Between Relativistic Electron and Ultra-Intense Laser Field in a Strong Uniform Magnetic Field

We investigate the influence of the initial laser phase on the interaction between relativistic electron and ultra-intense linear polarized laser field in a strong uniform magnetic field. It is found that the dynamic behaviour of the relativistic electron and the emission spectrum varies dramatically with different initial laser field phases. The effect of changing initial phase is contrary in the two parameter regions divided by the resonance condition. The phase dependence of the electron energy and velocity components are also studied. Some beat structure is found when the initial laser phase is zero and this structure is absent when the initial laser phase is a quarter of a period.