Asymmetry of the photoionization rate of H atoms by a sequence of one-cycle laser pulses

Using an unperturbed scattering theory, the characteristics of H atom photoionization are studied respectively by a linearly- and by a circularly- polarized one-cycle laser pulse sequence. The asymmetry for photoelectrons in two directions opposite to each other is investigated. It is found that the asymmetry degree varies with the carrier-envelope (CE) phase, laser intensity, as well as the kinetic energy of photoelectrons. For the linear polarization, the maximal ionization rate varies with the CE phase, and the asymmetry degree varies with the CE phase in a sine-like pattern. For the circular polarization, the maximal ionization rate keeps constant for various CE phases, but the variation of asymmetry degree is still in a sine-like pattern.

Adaptive image sequence coding based on global and local compensability analysis

Our study of a novel technique for adaptive image sequence coding is reported. The number of reference frames and the intervals between them are adjusted to improve the temporal compensability of the input video. The bits are distributed more efficiently on different frame types according to temporal and spatial complexity of the image scene. Experimental results show that this dynamic group-of-picture (GOP) structure coding scheme is not only feasible but also better than the conventional fixed GOP method in terms of perceptual quality and SNR. (C) 1996 Society of Photo-Optical Instrumentation Engineers.