Zhengquan Zhang

Multiterawatt laser system based on optical parametric chirped pulse amplification

A compact multiterawatt laser system based on optical parametric chirped pulse amplification is demonstrated. Chirped pulses are amplified from 20 pJ to 900 mJ by two lithium triborate optical parametric preamplifiers and a final KDP optical parametric power amplifier with a pump energy of 5 J at 532 nm from Nd:YAG-Nd:glass hybrid amplifiers. After compression, we obtained a final output of 570-mJ-155-fs pulses with a peak power of 3.67 TW, which is the highest output power from an optical parametric chirped pulse amplification laser, to the best of our knowledge.

A reproducible route to p-ZnO films and their application in light-emitting devices

Although great efforts have been made, reproducible p-type doping is still one of the largest hurdles that hinders the optoelectronic applications of ZnO. In this Letter, a reproducible route to p-type ZnO films employing lithium-nitrogen as a dual-acceptor dopant has been demonstrated, and p-i-n structured light-emitting devices (LEDs) have been constructed. Obvious purple emissions have been observed from the LEDs, confirming the applicability of the p-type ZnO films in optoelectronic devices. The results reported in this Letter provide a reproducible route to p-type ZnO films, and thus may lay a solid ground for future optoelectronic applications of ZnO.

Regenerative amplifier with continuously variable pulse duration used in an optical parametric chirped-pulse amplification laser system for synchronous pumping

A Nd:glass regenerative amplifier has been set up to generate the pumping pulse with variable pulse width for an optical parametric chirped-pulse amplification (OPCPA) laser system. Each pulse of the pulse train from a cw self-mode-locking femtosecond Ti:sapphire oscillator is stretched to approximate to300 ps at 1062 nm to be split equally and injected into a nonlinear crystal and the Nd:glass regenerative amplifier, as the chirped signal pulse train and the seed pulse train of the pumping laser system, respectively. By adjusting the cavity length of the regenerative amplifier directly, the width of amplified pulse could be varied continuously from approximate to300 ps to approximate to3 ns. The chirped signal pulse for the OPCPA laser system and the seed pulse for the pumping laser system come from the same oscillator, so that the time jitter between the signal pulse and the pumping pulse in optical parametric amplification stages could be <10 ps

Broadband high-gain optical parametric chirped- pulse amplification near 780 nm with LBO-I near-degenerate near-collinear phase match

Near-degenerative near-collinear phase-match geometry for broadband optical parametric chirped-pulse amplification (OPCPA) at approximate to 780 nm is calculated in comparison with nondegenerate noncollinear phase-match geometry. In an experiment on LBO-I near-degenerate near-collinear OPCPA, high gain with broad gain bandwidth (approximate to 71 nm, FWHM) at approximate to 780 nm is achieved by using an approximate to 390-nm pumping pulse. The stretched broadband chirped signal pulse near 780 nm is amplified to approximate to 412 mu J with a pumping energy of approximate to 15 mJ, and the total gain is > 3.7 X 10(6), which agrees well with the calculation. For a broadband (covering approximate to 100 nm) chirped signal pulse, the theoretical gain bandwidth has been attained experimentally for the first time. (c) 2005 Society of Photo-Optical Instrumentation Engineers.

Spatial uniformity and its time evolution of linear laser plasmas

The effect of laser illumination conditions on the uniformity of the linear laser plasmas produced is investigated with time-integrated and time-resolved soft x-ray diagnostics. Evident nonuniformities along the line focus resulting from nonuniform laser intensity distributions have been observed with a conventional simple line-focusing technique. Specifically, the nonuniformity of higher charge-state ions is more remarkable than that of lower ones. A uniform linear plasma can be obtained with a new line-focusing technique that produces uniform laser illumination. Nonuniformities under uniform laser illumination are found to occur primarily in the laser heating period. Further development of time-matched and spatial uniform line-focused laser illumination will produce more uniform linear plasmas.

A multi‐terawatt OPCPA laser system

The novel optical parametric chirped pulse amplification (OPCPA) scheme is promising for generating ultra‐intense and ultra‐short laser pulse. Based on the OPCPA technique, a compact 3.67TW tabletop laser system was developed with an output of the 570mJ/155fs per‐pulse, which is the highest power output in the existing laser systems based on OPCPA, to the best of our knowledge.

Direct experimental evidence of influence of ionizations on high-order harmonic generation

Abstract The influence of laser focusing conditions on high-order harmonic generation in neon gas was investigated with a 45 fs Ti:sapphire laser by adjusting the incident laser beam diameter. For the first time by observing the spectral line of Ne + : 3s–2p, the effect of the free electrons was also studied. Our experimental results suggested that more intense harmonics could be generated under weakly focused field than under tightly focused one, and the electrons free from atoms have a detrimental effect on harmonic generation.

Development of high-power OPCPA laser at 1064 and 780 nm

A compact 10-TW/100-fs level ultrashort-pulse and ultra-intense laser system at 1064 nm based on optical parametric chirped pulse amplification (OPCPA) scheme is described, at which the pump and seed for the optical parametric amplification (OPA) process is optically synchronized. We investigated the output stability and the conversion efficiency of the system. Moreover, a design toward higher peak power output is given and an optically synchronized amplifier based on the concept of OPCPA at 800 nm is preliminarily explored.

ON THE GAIN MEDIA UNIFORMITY IN CONTROLLED EXPANSION COOLED HIGH GAIN RECOMBINATION X-RAY LASERS

We investigate the uniformity of the plasma column produced on a multifin target which is designed for implementing a high gain recombination x-ray laser based on the controlled adiabatic expansion cooling scheme. It is shown that a plasma column, which is as uniform as that produced on a flat slab target, can be generated on a segmented target under an appropriate laser irradiation condition, and an enhancement of the on-axis emission of lasing lines is observed simultaneously, which can be attributed to an increase in laser gain. For the Li-like Al 4f-3d laser system, an increase of gain from 1.8 to 2.4 cm−1 was evaluated by comparing the on-axis emission from the multifin target with that from the flat-slab target. However, a large nonuniformity is also observed when the laser condition is so changed that strong ion collisions between the neighboring plasmas appear. The extension of this target design to the shorter wavelength laser regime appears to be promising provided that both the target parameter...

Spectral imaging of a flat-field grating spectrograph

The general expression of the optical path function and the focusing conditions of a variable line-spacing concave grating with a spherical surface are given. The spectral imaging of our flat-field grating spectrograph with a HITACHI flat-field grating was investigated and the typical experimental results of the two modes of the spectrograph (that is, the astigmatic mode and the stigmatic mode) are presented.