Wang S, Gong Q. Progress in femtochemistry and femtobiology. Science China Physics, Mechanics and AstronomyScience China Physics, Mechanics and Astronomy. 2011;54:2103-2108.
Propagation of intense femtosecond laser pulses (60 fs, 800 nm, 120 mJ, 6 × 1017 W/cm2 in vacuum) in supersonic (CD4)N and (D2)N cluster jets at different backing pressures was studied. Pump-probe interferometry is employed to investigate the propagation of laser beams in dense cluster jets by examining the electron density distribution of plasma channels. It was found that propagation effects, including ionization-induced defocusing and laser attenuation of incident pulses, are very different in the (CD4)N and (D2)N cluster jets. Different ionization states of CD4 and D2 molecules were observed by analyzing the transverse electron density profiles of the plasma channels and should be considered as a major reason for the differences in the propagation effects. Numerical simulations of the nonlinear propagation of femtosecond laser pulses in (CD4)N and (D2)N cluster jets were performed, and the results indicated a good reproduction of the experimental data.
Acceleration of protons by a circularly polarized laser pulse irradiating on a double-layer target is investigated by a theoretical model and particle-in-cell simulations. The target is made up of a heavy ion layer coated with a proton layer on the rear surface. The results show that when the first layer is transparent induced by the hole-boring effect, the whole proton layer is accelerated by the transmitted laser pulse to high energy with low energy spread. The quality of the proton beam generated from a double-layer target is better than that from a single-layer target. The improvement is attributed to the flat top structure of the electrostatic field caused by the electrons injected into the second layer. It is easier to control the spectrum quality by using a double-layer target rather than using a single-layer one when the radiation pressure acceleration is dominant.
This paper extends the Barro (1990) model with single aggregate government spending and one flat income tax to include public expenditures and taxes by multiple levels of government. It derives the rate of endogenous growth and, with both simulations and special examples, examines how that rate changes with respect to federal income tax, local taxes, and federal transfers. It also discusses the growth and welfare‐maximizing choices of taxes and federal transfers.