Zhaoyang Li

Spatial asymmetry of optical parametric fluorescence with a divergent pump beam and potential applications

The spatial distribution of the optical parametric fluorescence generated in a negative uniaxial nonlinear crystal is asymmetric with respect to the pump when the pump beam has a slight divergence angle. The formation mechanism of this phenomenon and the influence of parameters were analyzed and discussed from a theoretical standpoint. Moreover, two potential applications of this phenomenon were experimentally demonstrated, showing the temporal contrast improvement of ultra-intense lasers and the intensity enhancement of special light sources induced by the optical parametric generation.

Investigation of optical parametric fluorescence suppression with a quencher pulse in an optical parametric chirped-pulse amplification laser

The mechanism of suppressing optical parametric fluorescence (OPF) with a quencher pulse in an optical parametric chirped-pulse amplification (OPCPA) laser is investigated. A simplified theoretical model of this phenomenon is presented, and numerical simulations and experimental demonstrations are performed for explanation and verification. The results show that, although the improvement of the temporal contrast usually is limited, the generation and amplification of the OPF in an OPCPA process does be suppressed by the injection of a quencher pulse, and the suppression capability can be slightly enhanced by increasing the quencher-pulse energy. We believe that this work will be helpful in designing high-peak-power lasers with high temporal contrast.

Scattering pulse-induced temporal contrast degradation in chirped-pulse amplification lasers

Herein, a theory for modeling the problem of scattering pulse-induced temporal contrast degradation in chirped-pulse amplification (CPA) lasers is introduced. Using this model, the temporal evolutions of the scattering and signal pulses were simulated, the temporal contrasts for different cases were compared, and finally the theoretical prediction was verified by an experimental demonstration. The result shows that the picosecond and the nanosecond temporal contrast is mainly determined by the scattering pulses generated in the stretcher and the compressor, respectively. In addition, the B-integral accumulation will further degrade the temporal contrast, especially the picosecond temporal contrast. We believe it is helpful for solving the problem of the picosecond pedestal contrast (i.e., noise limit). With reference to these results, some suggestions for the temporal contrast improvement are presented.

Degradation of femtosecond petawatt laser beams: Spatio-temporal/spectral coupling induced by wavefront errors of compression gratings

Recently, several petawatt (PW, 1015 W) lasers with pulse duration of ~20–30 fs have been introduced throughout the world, pushing the upper limit on laser peak power. However, besides well-known spatio-temporal coupling effects, such as residual spatial/angular chirps and pulsefront tilt/curvature, the spatio-temporal/spectral coupling in compressors induced by wavefront errors of gratings, which could dramatically distort ultra-intense pulses, has been neglected. In this work, for the first time we analyzed this phenomenon and the peak power/intensity degradation induced by it. Our results suggest that the actual performance of femtosecond PW lasers may be worse than previously estimated.

Theoretical method for generating regular spatiotemporal pulsed-beam with controlled transverse-spatiotemporal dispersion

Abstract Herein we theoretically report a method that generates a transverse-spatiotemporal dispersion, which is distinct from previous spatial, temporal, and longitudinal-spatiotemporal dispersions. By modulating the transverse-spatiotemporal dispersion, two not yet reported spatiotemporally structured beams, i.e., the honeycomb beam and the picket-fence beam, can be generated in the space–time domain. The generated spatiotemporally structured beams have novel and tunable periodic distributions. The transverse-spatiotemporal dispersion, spatiotemporally structured beams and their inner relationship are analyzed and introduced. We believe that this method might open a path towards new optical beams for potential applications, such as ultrafast optical fabrication and detection.

Cone-angle tunable second-harmonic generation at the edge of a cube uniaxial nonlinear crystal

A simple method to generate second-harmonic conical waves with tunable cone angles (apex angles) only using a cube uniaxial nonlinear crystal is proposed. The formation mechanism is based on the birefringence phase-matching among a plane fundamental wave, a spherical fundamental wave, and a conical second-harmonic wave. The cone angle in our demonstration of the method could be continuously adjusted from 0 to 30° by just rotating the crystal, which is the largest reported tunable range. Moreover, a tunable range of 0–68° could be achieved by using several crystals with different cut angles. The polarization and the longitudinal distribution of the generated second-harmonic wave are theoretically analyzed. The measured conversion efficiency was around 7%, and it decreased with the increasing of the cone angle.

Direction-dependent waist-shift-difference of Gaussian beam in a multiple-pass zigzag slab amplifier and geometrical optics compensation method

Zigzag and non-zigzag beam waist shifts in a multiple-pass zigzag slab amplifier are investigated based on the propagation of a Gaussian beam. Different incident angles in the zigzag and non-zigzag planes would introduce a direction-dependent waist-shift-difference, which distorts the beam quality in both the near- and far-fields. The theoretical model and analytical expressions of this phenomenon are presented, and intensity distributions in the two orthogonal planes are simulated and compared. A geometrical optics compensation method by a beam with 90° rotation is proposed, which not only could correct the direction-dependent waist-shift-difference but also possibly average the traditional thermally induced wavefront-distortion-difference between the horizontal and vertical beam directions.