Yuxin Song

Underwater giant enhancement of broadband diffraction efficiency of surface diffraction gratings fabricated by femtosecond laser

In this study, a simple approach is proposed to improve the diffraction efficiency of surface diffraction gratings on fused silica fabricated by femtosecond laser. Effects of grating period, pulse energy, scanning speed and wavelength on the total diffraction efficiency are also investigated. In addition, the mechanism of the diffraction efficiencys giant enhancement is discussed by finite difference time domain (FDTD) and optical phase shift structure calculation. It is revealed that: (1) Compared with the diffraction efficiency obtained in air, the underwater image via diffraction grating is clearer than that in air and diffraction pattern in water is much brighter; (2) The diffraction efficiency increases with an increase in wavelength and scanning speed, whereas it decreases while the laser pulse energy is high; and (3) This giant enhancement is attributed to the degree of Mie scattering and refraction, which is effectively reduced for the existence of water.

Pulse train dependence of electron dynamics during resonant femtosecond laser nonlinear ionization of a Na4 cluster

In this study, a real-time and real-space time-dependent density functional theory (TDDFT) is applied to describe nonlinear electron–photon interactions during a resonant femtosecond laser pulse train photoionization of a Na4 cluster. The effects of key pulse train parameters, such as the spatial/temporal pulse energy distribution, pulse number per train, pulse separation and pulse phase on resonant absorption, are discussed. The calculations show that the resonant effect and the nonlinear electron dynamics, including energy absorption, electron emission, dipole response and ionization probability, can be controlled by shaping the ultrafast laser pulse train.