Intense-field dissociation dynamics of D2+ molecular ions using ultrafast laser pulses

The dynamics of dissociation of pre-ionized D2+ molecules using intense (10^12–10^15 W cm-2), ultrashort (50 fs), infrared (? = 790 nm) laser pulses are examined. Use of an intensity selective scan technique has allowed the deuterium energy spectrum to be measured over a broad range of intensity. It is found that the dominant emission shifts to lower energies as intensity is increased, in good agreement with corresponding wavepacket simulations. The results are consistent with an interpretation in terms of bond softening, which at high intensity (approximately >3 × 10^14 W cm-2) becomes dominated by dissociative ionization. Angular distribution measurements reveal the presence of slow molecular dissociation, an indication that vibrational trapping mechanisms occur in this molecule.

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.

Fast-beam study of H2+ ions in an intense femtosecond laser field

A fast beam of H-2(+) ions, produced from a low energy ion accelerator, has been used for the first time in intense laser field experiments. The technique has enabled neutral dissociation products to be analysed and detected for the first time in such studies. Energy spectra of neutral and ionized fragments, product yields as a function of focused laser intensity and angular distributions of neutral dissociation products have been measured. Significant differences are observed between the present results and those obtained from experiments involving neutral H-2 molecules. These differences are indicative of the precursor H-2 molecule playing an important and hitherto neglected formative role in the laser-induced fragmentation processes.

Stable GeV Ion Beam Acceleration from Thin Foils by Circularly Polarized Laser Pulses

A stable relativistic ion acceleration regime for thin foils irradiated by circularly polarized laser pulses is suggested. In this regime, the "light-sail" stage of radiation pressure acceleration for ions is smoothly connected with the initial relativistic "hole-boring" stage, and a defined relationship between laser intensity I(0), foil density n(0), and thickness l(0) should be satisfied. For foils with a wide range of n(0), the required I(0) and l(0) for the regime are theoretically estimated and verified with the particle-in-cell code ILLUMINATION. It is shown for the first time by 2D simulations that high-density monoenergetic ion beams with energy above GeV/u and divergence of 10 degrees are produced by circularly polarized lasers at intensities of 10(22) W/cm(2), which are within reach of current laser systems.

Plasma emission spectroscopy of solids irradiated by intense XUV pulses from a free electron laser

The FLASH XUV-free electron laser has been used to irradiate solid samples at intensities of the order 10(16) W cm(-2) at a wavelength of 13.5 nm. The subsequent time integrated XUV emission was observed with a grating spectrometer. The electron temperature inferred from plasma line ratios was in the range 5-8 eV with electron density in the range 10(21)-10(22) cm(-3). These results are consistent with the saturation of absorption through bleaching of the L-edge by intense photo-absorption reported in an earlier publication. (C) 2009 Elsevier B.V. All rights reserved.

Submicron ionography of nanostructures using a femtosecond-laser-driven-cluster-based source

An intense isotropic source of multicharged carbon and oxygen ions with energy above 300 keV and particle number >108 per shot was obtained by femtosecond Ti:Sa laser irradiation of submicron clusters. The source was employed for high-contrast contact ionography images with 600 nm spatial resolution. A variation in object thickness of 100 nm was well resolved for both Zr and polymer foils.