Dependence of quasistatic Wakefield and high harmonic generation on the pulse-shape of an ultrashort, intense, few-cycle laser in the reflected radiation from a thin dense plasma layer is investigated. The pulse envelopes considered are Gaussian, Lorentzian, and hyperbolic secant having identical full width at half maximum of intensity. The reflected radiation from the strongly driven surface plasma layer embodies a quasistatic Wakefield, which exists after the main pulse is passed over. A phase modulation is also experienced by the laser light upon reflection from plasma surface motion. As a result harmonics of center carrier frequency of the laser-pulse are generated in the reflected signal. Intensity of the laser harmonics and magnitude of the Wakefield in the reflected radiation are found to depend on the pulse-shape, number of cycles, carrier envelope phase difference, plasma density, angle of incidence, and intensity of the incident pulse.

The propagation of intense few-cycle laser beams in plasma media is considered when the quiver velocity of the electron approaches the velocity of light c. The modifications in the spatio-temporal profile of the initial Gaussian beam are found to depend on the combined effect of relativistic plasma frequency and diffraction. The results of the variation of the temporal profile of the envelope at points on the axis as well away from the axis are presented. The results so obtained are compared with those of vacuum propagation. Pulses get broadened and frequency gets chirped as a result of diffraction, phase dispersion and relativistic mass correction. The effect of the plasma on the group velocity dispersion including curvatures of pulse and phase fronts in pulsed Gaussian beam is numerically investigated.

Analytical and numerical investigation of the reflection and transmission of a counter-propagating relativistically strong laser pulse from a relativistically flying dense plasma double-sided mirror is studied. We assume that the incident laser pulse is short, so that we can neglect the slow ion dynamics and consider the electron motion only. Numerical results of the amplitudes of the reflected/transmitted electric fields from a uniformly moving mirror, accelerated mirror, and oscillating mirror are obtained. Fourier spectrum of the reflected intensity from the moving mirror shows that the intensity decreases with increase in the frequency. The reflected pulse has an up-shifted frequency and increased intensity. It is seen that the first few cycles of the reflected radiation exhibit presence of high harmonics, while the later cycles are compressed together with harmonics in comparison with the earlier cycles. The variation of the reflection coefficient for a uniformly moving mirror as a function of the thin foil plasma-density parameter is numerically studied.

No abstract

The effect of temporal pulse-shape on the characterization of the longitudinal electric field resulting from the tight-focusing of an ultrashort few-cycle TM 01 laser beam in free space is investigated analytically and numerically. The longitudinal field is found to be sensitive to the pulse-shape of the driving field. The temporal pulse-shapes considered are Gaussian, Lorentzian, and hyperbolic secant having identical full width at half maximum of intensity. Analytical calculations are made beyond the paraxial and slowly varying envelope approximations. From the numerical results we find that due to finite duration of the signal, the evolution of the pulse envelope before the waist is faster (negative time-delay) but slowed down (positive time-delay) after the waist. This time-delay, for single-cycle pulses of wavelength λ 0 , and for spot-size w 0f in the range 0.6λ 0 > w 0f > 0.25λ 0 , is pulse-shape dependent. The time delay is maximum for the Gaussian pulse and minimum for the Lorentzian pulse. The carrier frequency shift depends on the temporal profile of the pulse, beam spot size, axial propagating distance and also on the number of cycles in a pulse. In addition, a comparative study of the variation of the corrected axial Gouy-phase of the longitudinal electric field of single-cycle pulse (spot size w 0f = 0.5λ 0 ) with normalized retarded time shows that the phase variation is maximum for Gaussian and minimum for the Lorentzian pulse shape.