We report on near-GeV electron beam generation from an all-optical cascaded laser wakefield accelerator (LWFA). Electron injection and acceleration are successfully separated and controlled in different LWFA stages by employing two gas cells filled with a He/O2 mixture and pure He gas, respectively. Electrons with a Maxwellian spectrum, generated from the first LWFA assisted by ionization-induced injection, were seeded into the second LWFA with a 3-mm-thick gas cell and accelerated to be a 0.8-GeV quasimonoenergetic electron beam, corresponding to an acceleration gradient of 187  GV/m. The demonstrated scheme paves the way towards the multi-GeV laser accelerators.

Abstract:We report on a 2.0 PW femtosecond laser system at 800 nm based on the scheme of chirped pulse amplification using Ti:sapphire crystals, which is the highest peak power ever achieved from a femtosecond laser system. Combining the index-matching cladding technique and the precise control of the time delay between the input seed pulse and pump pulses, the parasitic lasing in the final booster amplifier is effectively suppressed at the pump energy of 140 J at 527 nm. The maximum output energy from the final amplifier is 72.6 J, corresponding to a conversion efficiency of 47.2% from the pump energy to the output laser energy. The measured spectral width of the amplified output pulse from the final amplifier is 60.8 nm for the full width at half-maximum (FWHM) by controlling the spectral evolution in the amplifier chain, and the recompressed pulse duration is 26.0 fs. The technology of cross-polarized wave (XPW) is applied in a broadband front-end, and the pulse contrast is improved to ~1.5 × 10 −11 (−100 ps before the main pulse) which is measured at 83 TW power level with a repetition rate of 5 HZ. , 963-965 (1999). 13. F. Ple, M. Pittman, G. Jamelot, and J.-P. Chambaret, "Design and demonstration of a high-energy booster amplifier for a high-repetition rate petawatt class laser system," Opt. Lett. 32(3), 238-240 (2007). 14. V. Chvykov and K. Krushelnick, "Large aperture multi-pass amplifiers for high peak power lasers," Opt.Commun. 285(8), 2134-2136 (2012). 15. http://www.cargille.com. 16. D. C. Brown, S. D. Jacobs, and N. Nee, "Parasitic oscillations, absorption, stored energy density and heat density in active-mirror and disk amplifiers," Appl. Opt. 17(2), 211-224 (1978). 17. Y. Xu, X. Guo, X. Zou, Y. Li, X. Lu, C. Wang, Y. Liu, X. Liang, Y. Leng, R. Li, and Z. Xu, "Pulse temporal quality improvement in a petawatt Ti:sapphire laser based on cross-polarized wave generation," Opt.

New parasitic lasing suppression techniques are developed and high gain amplification is demonstrated in a petawatt level Ti:sapphire amplifier based on the chirped pulse amplification (CPA) scheme. Cladding the large aperture Ti:sapphire with refractive-index matched liquid doped with absorber suppresses the transverse lasing. The acousto-optic programmable dispersive filter (AOPDF) is used to realize side-lobe suppression in the temporal profile of the compressed pulse. The 800 nm laser output with peak power of 0.89 PW and pulse width of 29.0 fs is demonstrated.

In this paper, we report the recent progress on the $1~\text{PW}/0.1~\text{Hz}$ laser beamline of Shanghai Superintense Ultrafast Laser Facility (SULF). The SULF-1 PW laser beamline is based on the double chirped pulse amplification (CPA) scheme, which can generate laser pulses of 50.8 J at 0.1 Hz after the final amplifier; the shot-to-shot energy fluctuation of the amplified pulse is as low as 1.2% (std). After compression, the pulse duration of 29.6 fs is achieved, which can support a maximal peak power of 1 PW. The contrast ratio at $-80~\text{ps}$ before main pulse is measured to be $2.5\times 10^{-11}$ . The focused peak intensity is improved by optimizing the angular dispersion in the grating compressor. The maximal focused peak intensity can reach $2.7\times 10^{19}~\text{W}/\text{cm}^{2}$ even with an $f/26.5$ off-axis parabolic mirror. The horizontal and vertical angular pointing fluctuations in 1 h are measured to be 1.89 and $2.45~\unicode[STIX]{x03BC}\text{rad}$ , respectively. The moderate repetition rate and the good stability are desirable characteristics for laser–matter interactions. The SULF-1 PW laser beamline is now in the phase of commissioning, and preliminary experiments of particle acceleration and secondary radiation under 300–400 TW/0.1 Hz laser condition have been implemented. The progress on the experiments and the daily stable operation of the laser demonstrate the availability of the SULF-1 PW beamline.

We report on the generation of 192.3 J centered at 800 nm wavelength from a chirped-pulse amplification (CPA) Ti:sapphire laser system. The experimental results demonstrate that parasitic lasing can be suppressed successfully in the final amplifier based on a Ti:sapphire crystal of 150 mm in diameter. An over 50% pump-to-signal conversion efficiency was measured for the final amplifier by optimizing the time delay of two pump pulses and enhancing the injected seed energy. With 72% compressor throughput efficiency and 27 fs long compressed pulse duration obtained at a lower energy level, this laser could potentially support a compressed laser pulse of 5.13 PW peak power. The experimental results represent notable progress regarding the CPA laser.