Weijun Ling

Spatial evolution of multiple filaments in air induced by femtosecond laser pulses.

The spatial evolution of plasma filaments in air induced by femtosecond laser pulses is investigated experimentally. Several major filaments and small scaled additional filaments are detected in the plasma channel. The complicated interaction process of filaments as splitting, fusion and spreading is observed. The major filaments propagate stably, and the small scaled additional filaments can be attracted to the major filaments and merged with them. The major filaments are formed due to the perturbation of initial beam profile and the small scaled filaments are mainly caused by the transverse modulational instability.

Effective fast electron acceleration along the target surface

The dependence of angular distributions of fast electrons generated in the interaction of p-polarized femtosecond laser pulses with foil targets on laser intensities is investigated. A novel fast electron beam along the front target surface is observed for high laser intensity. It is found that the electron acceleration along the target surface is more efficient than those in other directions.

High-energy picosecond near-vacuum ultraviolet pulses generated by sum-frequency mixing of an amplified Ti: Sapphire laser

We demonstrate high-energy picosecond near-vacuum ultraviolet laser pulse generation. Frequency quadrupling is achieved by noncollinear sum-frequency mixing of the fundamental and the third harmonic of a two-stage Ti:sapphire amplifier in beta-BaB(2)O(4) crystal. UV pulses with energies of approximately 10 mJ tunable from 195 to 210 nm at a 10 Hz repetition rate are obtained.

A compact 355TW femtosecod Ti:sapphire laser facility and trend to high contrast ratio

A Ti:sapphire laser facility is established based on the chirped pulse amplification technology. For the first time we generate laser peak power of multi-100TW with three stages of amplifiers. In the final amplifier a 100J frequency-doubled Nd:glass laser is used as the pump source. To suppress the parasitic lasing (PL), we design the Ti:sapphire crystal with V groove cutting shape and use polymer thermoplastic cladding to absorb the reflection at the Ti:sapphhire interface. With the optimized alignment under 60J pump energy, laser peak power of 355TW is obtained at 31fs average pulse duration. The repetition rate is about 20min between two shots. Although the multi-100TW laser will enable us to open new applications on ultra-intense physics, the contrast ratio play more important role for the laser-matter interaction. To pursue a higher contrast ratio, new design on doubled CPA and ring regenerative amplifier are introduced. By further improving the amplification efficiency, our analysis shows that it should be possible to obtain peak power of high than 500TW with contrast ratio of about 1010.

Low-threshold self-starting femtosecond Ti:sapphire laser.

A low-threshold self-starting Kerr-lens mode-locked Ti:sapphire laser is demonstrated that uses a tight-focusing cavity design in conjunction with a semiconductor saturable-absorber mirror (SESAM). With 3% and 12% output couplers, we achieve mode-locking thresholds as low as 390 and 600 mW, respectively. Stable femtosecond laser pulses with average power of 114 mW are generated at a pump power of 1.2 W, which corresponds to a typical duration of 17 fs and bandwidth of 47 nm. Mode-locking operation is achieved in a pump power range of 600 mW to 4.8 W at an output coupling of 12%; the advantages of using a SESAM for low-power mode-locking operation are demonstrated.

High Energy Picosecond Optical Parametric Amplifier Pumped by the Second Harmonic of a Two-Stage Ti:sapphire Laser

We demonstrate a high energy picosecond optical parametric generation and amplification (OPA) system in the visible range based on two type-I phase matched β-barium borate crystals, in a walk-off compensating geometry. The second harmonic of a two-stage 60 ps Ti:sapphire laser amplifier at 10 Hz repetition rate serves as the pump. The signal is continuously tunable from 460 to 750 nm, which covers most of the visible range. The corresponding tuning range in the idler branch is from 0.86 to 3.07 μm. At a pumping energy of 110 mJ per pulse, the signal pulse energy is at 20 mJ class for most of the tuning wavelength in the OPA stage, and reaches a maximum of 33 mJ at 710 nm, corresponding to a conversion efficiency of ~ 30%.

Kerr-lens mode-locked polycrystalline Cr:ZnS femtosecond laser pumped by a monolithic Er:YAG laser*

We demonstrated a Kerr-lens mode-locked polycrystalline Cr:ZnS laser pumped by a narrow-linewidth linear-polarised monolithic Er:YAG nonplanar ring oscillator operated at 1645 nm. With a 5-mm-thick sapphire plate for intracavity dispersion compensation, a compact and stable Kerr-lens mode-locking operation was realised. The oscillator delivered 125-fs pulses at 2347 nm with an average power of 80 mW. Owing to the special polycrystalline structure of the Cr:ZnS crystal, the second to fourth harmonic generation was observed by random quasi-phase-matching.

High energy optical parametric amplifier pumped by 400nm picosecond Ti:sapphire laser

We present a picosecond optical parametric amplifier pumped by a 360 mJ frequency-doubled Ti:sapphire laser at 60 ps duration. Tunable signal wavelength from 460 nm to 750 nm was realized, maximum output energy up to 30 mJ.

Amplification Ti:sapphire laser to 355TW with a compact design

A new Ti:sapphire chirped pulse amplification system was established with three stage amplifiers. Pumping the final amplifier with a 100 J doubled-frequency Nd:glass laser, we generated stable 355 TW laser pulses at duration of 31 f s.

A 355 TW femtosecond Ti:Sapphire laser facility with three stage amplifiers

A compact femtosecond Ti:sapphire laser facility with three stage amplifiers was developed. By eliminating ASE and shaping spectrum, we generated 11 J laser pulse at duration of 31 fs, which corresponds to peak power of about 355 TW.