Yinghui Zheng

Experimental demonstration of phase locking of a two-dimensional fiber laser array using a self-imaging resonator

Phase locking of a two-dimensional fiber laser array is experimentally demonstrated by using a self-imaging resonator and a spatial filter. The stable beam profiles of in-phase mode and out-of-phase mode are observed by controlling the position of spatial filter. The phase locking fiber array with in-phase mode has produced 26 W coherent output. An antisymmetric eigenmode is also observed in our experiments. The phase locking is not sensitive to power variations among the pump beams and the configuration has the ability to repair a missing element

Tunable phase-stabilized infrared optical parametric amplifier for high order harmonic generation

We demonstrate what we believe to be a novel tunable IR optical parametric amplifier (OPA) with the passively stabilized carrier-envelope phase (CEP), in which a hollow fiber is used to improve the output beam quality and to overcome the spatial chirp issue. Pumped by an 800 nm pump source, the output pulses are tunable from 1.2 to 2.4 microm with the CEP stabilization. The maximum output average energy can reach approximately (1.2 W/40 fs)/1 kHz with the total of (6.8 W/40 fs)/1 kHz pump energy. Further, the high-order harmonic generation driven by the tunable phase-stabilized OPA has been demonstrated.

Enhancement and broadening of extreme-ultraviolet supercontinuum in a relative phase controlled two-color laser field

We experimentally demonstrate the generation of an extreme-ultraviolet (XUV) supercontinuum in argon with a two-color laser field consisting of an intense 7 fs pulse at 800 nm and a relatively weak 37 fs pulse at 400 nm. By controlling the relative time delay between the two laser pulses, we observe enhanced high-order harmonic generation as well as spectral broadening of the supercontinuum. A method to produce isolated attosecond pulses with variable width and intensity is proposed.

All-Solid-State Continuous-Wave Frequency Doubling Nd:YLF/LBO Laser with 2.15 W Output Power at 526 nm

An efficient and compact green laser at 526 nm generated by intracavity frequency doubling of a continuous wave (CW) laser operation of a diode pumped Nd:YLF laser at 1053 nm under the condition of suppression the high gain transition at 1047 nm. With 19.5 W diode pump power and a frequency doubling crystal LBO, as high as 2.15 W of CW output power at 526 nm is achieved, corresponding to an optical-to-optical conversion efficiency of 11.2% and the output power stability in 8 h is better than 2.87%. To the best of our knowledge, this it the highest watt-level laser at 526 nm generated by intracavity frequency doubling of a diode pumped Nd:YLF laser at 1053 nm.

Nonadiabatic propagation effect for generating isolated sub-100 as pulses in the high-order harmonic plateau

A robust scheme is proposed to generate an isolated sub-100 as pulse by using a 5fs/800nm driving pulse in combination with a macroscopic propagation effect. We demonstrate that one of the generated attosecond bursts in the high-order harmonic plateau can be efficiently dominant only when both the gas pressure and the gas cell length are properly chosen. We also show that this method can relax the dependence on the stabilization of the carrier-envelope phase (CEP) of the driving pulse. A single sub-100as pulse with only 10as duration variation can be produced even for about 50% fluctuation of the CEP. Under optimized conditions, an isolated 60as pulse can be directly generated without any additional phase compensation.

Chirped polarization-gating technique for isolated attosecond pulse generation

We propose a scheme to generate broadband high harmonic supercontinuum and single attosecond pulse emission in time domain by employing a chirped polarization-gating laser field. It is shown that this scheme can significantly extend the high harmonic cutoff to higher energy region, and the produced isolated attosecond pulse is shorter than 100 attoseconds after proper dispersion compensation, when a 7 fs driving laser pulse is used.

Selective generation of an intense single harmonic from a long gas cell with loosely focusing optics based on a three-color laser field

The selective generation of an intense single harmonic has been experimentally achieved in argon from a long gas cell with loosely focusing optics using a three-color laser field. When compared with the single harmonic emission from a continuous gas jet, both the intensity and the purity of the selected single harmonic emission from the long gas cell show dramatic improvements; the peak intensity is more intense by as much as 1–2 orders of magnitude, while the contrast ratio (i.e., the spectral purity) is simultaneously increased by several times. The underlying physics of this enhancement can be explained using the strong field approximation model with the propagation effect.

Attosecond pulse generation driven by a synthesized laser field with two pulses of controlled related phase

High-order harmonic and attosecond pulse generation driven by a synthesized laser field with two laser pulses of controlled related phase is reviewed. High-order harmonic generation (HHG) is a strongly nonlinear response of a medium to the driving laser field. By controlling the laser field on subcycle timescale carefully, the motion of the electron can be accurately steered to generate the isolated attosecond pulse, to enhance the conversion efficiency of HHG, to adjust the phase of the harmonic emission spectra and so on.

Single sub-100 attosecond pulse generation in a two-colour time-gating laser field

We theoretically propose a method of generating a single sub-100 attosecond (as) pulse with a two-colour time-gating laser field. The field is synthesized by an 8 fs/800 nm (three optical cycles) pulse and a 24 fs/2400 nm (three optical cycles) pulse with an optimal time delay between them. In our simulation, we obtain a supercontinuum with an extremely broad spectrum of 150 eV and generate an isolated attosecond pulse with 96 as pulse duration without any dispersion compensation.

Effect of nuclear motion on spectral broadening of high-order harmonic generation.

High-order harmonic generation (HHG) in molecular targets is experimentally investigated in order to reveal the role of the nuclear motion played in the harmonic generation process. An obvious broadening in the harmonic spectrum from the H2 molecule is observed in comparison with the harmonic spectrum generated from other molecules with relatively heavy nuclei. We also find that the harmonic yield from the H2 molecule is much weaker than the yield from those gas targets with the similar ionization potentials, such as Ar atom and N2 molecule. The yield suppression and the spectrum broadening of HHG can be attributed to the vibrational motion of nuclear induced by the driving laser pulse. Moreover, the one-dimensional (1D) time-dependent Schrödinger equation (TDSE) with the non-Born-Oppenheimer (NBO) treatment is numerically solved to provide a theoretical support to our explanation.