Plasma ion evolution in the wake of a high-intensity ultrashort laser pulse

Experimental investigations of the late-time ion structures formed in the wake of an ultrashort, intense laser pulse propagating in a tenuous plasma have been performed using the proton imaging technique. The pattern found in the wake of the laser pulse shows unexpectedly regular modulations inside a long, finite width channel. On the basis of extensive particle in cell simulations of the plasma evolution in the wake of the pulse, we interpret this pattern as due to ion modulations developed during a two-stream instability excited by the return electric current generated by the wakefield.

Self-focusing and envelope pulse generation in nonlinear magnetic metamaterials

The self-modulation of waves propagating in nonlinear magnetic metamaterials is investigated. Considering the propagation of a modulated amplitude magnetic field in such a medium, we show that the self-modulation of the carrier wave leads to a spontaneous energy localization via the generation of localized envelope structures (envelope solitons), whose form and properties are discussed. These results are also supported by numerical calculations.

Dissociation of H2+ from a short, intense, infrared laser pulse: proton emission spectra and pulse calibration

The proton energy spectrum from photodissociation of the hydrogen molecular ion by short intense pulses of infrared light is calculated. The time-dependent Schrödinger equation is discretized and integrated. For few-cycle pulses one can resolve vibrational structure, arising from the experimental preparation of the molecular ion. We calculate the corresponding energy spectrum and analyse the dependence on the pulse time delay, pulse length and intensity of the laser for ? ~ 790 nm. We conclude that the proton spectrum is a sensitive probe of both the vibrational populations and phases, and allows us to distinguish between adiabatic and nonadiabatic dissociation. Furthermore, the sensitivity of the proton spectrum from H2+ is a practical means of calibrating the pulse. Our results are compared with recent measurements of the proton spectrum for 65 fs pulses using a Ti:Sapphire laser (? ~ 790 nm) including molecular orientation and focal-volume averaging. Integrating over the laser focal volume, for the intensity I ~ 3 × 1015 W cm-2, we find our results are in excellent agreement with these experiments.

Short pulse laser interaction with positive ions

The viability of using beams of molecular ions as a target for strong field fragmentation studies using intense ultra-short laser pulses is demonstrated. In this way the production mechanism for multiply charged ions in strong fields may be elucidated.

Resonance Raman and DFT studies of tetra-tert-butyl porphine: Assignment of strongly enhanced distortion modes in a ruffled porphyrin

The free-base form of tetra-tert-butyl porphine (TtBP), which has extremely bulky meso substituents, is severely distorted from planarity, with a ruffling angle of 65.5degrees. The resonance Raman spectrum of TtBP (lambda(ex) = 457.9 nm) and its d(2), d(8), and d(10) isotopomers have been recorded, and while the spectra show high-frequency bands similar to those observed for planar meso-substituted porphyrins, there are several additional intense bands in the low-frequency region. Density functional calculations at the B3-LYP/6-31G(d) level were carried out for all four isotopomers, and calculated frequencies were scaled using a single factor of 0.98. The single factor scaling approach was validated on free base porphine where the RMS error was found to be 14.9 cm(-1). All the assigned bands in the high-frequency (> 1000 cm(-1)) region of TtBP were found to be due to vibrations similar in character to the in-plane skeletal modes of conventional planar porphyrins. In the low-frequency region, two of the bands, assigned as nu(8) (ca. 330 cm(-1)) and nu(16) (ca. 540 cm(-1)), are also found in planar porphyrins such as tetra-phenyl porphine (TPP) and tetra-iso-propyl porphine (IPP). Of the remaining three very strong bands, the lowest frequency band was assigned as gamma(12) (pyr swivel, obsd 415 cm(-1), calcd 407 cm(-1) in do). The next band, observed at 589 cm-1 in the do compound (calcd 583 cm(-1)), was assigned as a mode whose composition is a mixture of modes that were previously labeled gamma(13) (gamma(CmCaHmCa)) andy gamma(11) (pyr fold(asym)) in NiOEP. The final strong band, observed at 744 cm(-1) (calcd 746 cm(-1)), was assigned to a mode whose composition is again a mixture of gamma(11) and gamma(13), although here it is gamma(11) rather than gamma(13) which predominates. These bands have characters and positions similar to those of three of the four porphyrin ring-based, weak bands that have previously been observed for NiTPP. In addition there are several weaker bands in the TtBP spectra that are also