Carrier-envelope phase dependence of molecular harmonic spectral minima induced by mid-infrared laser pulses.

The spectral minima in harmonic spectra of H2+ induced by mid-infrared laser pulses are numerically investigated based on two models of Born-Oppenheimer (BO) and non-Born-Oppenheimer (NBO) approximations. The simulation results show that, with the variation of the mid-infrared laser's carrier-envelope phase (CEP), the spectral minima positions (SMPs) are fixed for the BO model, while oscillate periodically for the NBO model. This can be understood by the two-center-destructive-interference theory via the detailed investigation to several physical quantities for each CEP case, such as SMPs, effective potential, internuclear separation and the electron's de Broglie wavelength at the time for interference occurring. The fittings to these quantities' CEP-dependent curves demonstrate that they follow a variation law in the form of a sine function.

Equivalent-nanocircuit-theory-based design to infrared broad band-stop filters.

We theoretically introduced a design paradigm and tool by extending the circuit functionalities from radio frequency to near infrared domain, and a broad band-stop filter, is successfully demonstrated by cascading triple layers of nano-square arrays. The feasibility is confirmed by its consistency with the rigorous FDTD calculation. Moreover, such a third-order Butterworth filter is not only insensitive to the incident angle and but also to input light's polarization. The new paradigm forms a theoretical foundation for designing optical devices and also enriches the classic circuit operations at the optical frequency region.

Theoretical analysis and design of a near-infrared broadband absorber based on EC model.

We theoretically introduced a design paradigm and tool by extending the circuit functionalities from radio frequency to near infrared domain, and its first usage to design a broadband near-infrared (1.5µm~3.5µm) absorber, is successfully demonstrated. After extracting the equivalent circuit (EC) model of the absorber structure, the formerly relatively complicated frequency response can be evaluated relatively easily based on classic circuit formulas. The feasibility is confirmed by its consistency with the rigorous FDTD calculation. The absorber is an array of truncated metal-dielectric multilayer composited pyramid unit structure, and the gradually modified square patch design makes the absorber be not sensitive to the incident angle and polarization of light.

Above-threshold ionization by few-cycle phase jump pulses.

We theoretically investigate the above-threshold ionization of hydrogen atoms driven by few-cycle phase jump laser pulses. By numerically solving the three-dimensional time-dependent Schrödinger equation, we demonstrate that the phase jump plays an important role in the ionization process. The cutoff of the photoelectron energy spectrum can extend to a range of very high energy, and the yield of the photoelectrons can be dramatically enhanced by choosing proper phase jump times. Both the classical simulations and Fourier transform method are used to understand the spectra features found in our investigation.