The post-compression technique based on self-phase modulation of high-energy pulses leads to an increase in achievable peak power and intensity. Typically, the pulses considered in experiments have been less than 100 fs in duration. Here, the method is applied to the ELFIE laser system at the LULI facility, for a pulse of 7 J energy and an initial measured duration of 350 fs. A 5-mm-thick fused silica window and a 2 mm cyclic-olefin polymer were used as optical nonlinear materials. The 9 cm diameter beam was spectrally broadened to a bandwidth corresponding to 124 fs Fourier-limited pulse duration, and then it was partly post-compressed to 200 fs. After measuring the spatial spectra of the beam fluence, a uniform gain factor of 4 increase in the fluctuations over the studied range of frequencies is observed, due to small-scale self-focusing.

Spectral-broadening of the APOLLON PW-class laser pulses using a thin-film compression technique within the long-focal-area interaction chamber of the APOLLON laser facility is reported, demonstrating the delivery of the full energy pulse to the target interaction area. The laser pulse at 7 J passing through large aperture, thin glass wafers is spectrally broadened to a bandwidth that is compatible with a 15-fs pulse, indicating also the possibility to achieve sub-10-fs pulses using 14 J. Placing the post-compressor near the interaction makes for an economical method to produce the shortest pulses by limiting the need for high damage, broadband optics close to the final target rather than throughout the entire laser transport system.

The interaction of a relativistic short laser pulse with thin foil is studied using 3D PIC simulations in the context of optimized high-energy proton generation for nuclear medicine and pharmacy. As an example, we analyze the Tc-99m yield from the Mo-100(p,2n)Tc-99m reaction with the International Coherent Amplification Network (ICAN) concept defined by a 10 J pulse energy and 10 kHz repetition rate. Based on 3D PIC simulation it has been demonstrated that normally incident 100 fs laser pulse with maximum intensity of 5 × 1021 W/cm2 is able to generate 1011 protons with energy upto 45 MeV from thin semi-transparent CH2 target. Such laser-produced proton beam after 6 hours bombardment of the thick metallic Mo-100 target gives around 300 Gbq activities of Tc-99m isotope. This gives reason to believe that laser technology for producing technetium is possible with ICAN concept to replace the traditional scheme through the fission of weapons-grade uranium.

Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.

Experimental spectra of hot dense plasmas of aluminium produced by the interaction of a subpicosecond laser with solid targets at 1016 and 5 × 1017 W/cm2 are analyzed and discussed. A detailed analysis of the K-shell spectra is given through time-dependent calculations of atomic physics postprocessed to Fokker-Planck calculations of the laser-matter interaction. The non-Maxwellian character of the electron distribution function is shown. An evaluation of the electronic density and of the ion temperature 7i will be presented through Stark line broadening calculations. An X-ray spectrum from a Tantalum target also will be presented along with a preliminary interpretation.

Extended abstract of a paper presented at Microscopy and Microanalysis 2005 in Honolulu, Hawaii, USA, July 31--August 4, 2005

Transmission and High Resolution Electron Microscopy have been used to study the dramatic changes in crystalline quality which occur in As-rich In0.52Al0.48As/InP layers when the growth temperature is lowered. We have found that for temperatures as low as 200°C and for a flux ratio of 20, the layers can be of high quality. For the lowest growth temperature of 150°C, pyramidal defects as well as hexagonal As grains are found which are characteristic of the breakdown of the monocrystalline growth in these layers. A mechanism for the formation of these defects is proposed based on their crystallographic structure. The fast photo response previously observed in these layers must be related to the presence of these defects.

The ultrafast carrier dynamics in GaAs, In0.52Al0 48As on InP, and In0.53Ga0.47As on InP, grown by molecular-beam-epitaxy (MBE) at low substrate temperatures, are investigated. A reduction in the carrier lifetime is observed with decreasing growth temperatures. The shortest carrier lifetimes of typically a picosecond (ps) are obtained at the lowest growth temperature range of 150 – 200 'C. Femtosecond optical absorption and reflectance measurements have been used to verify the sub-picosecond carrier lifetimes. Photoconductive switching measurements on these materials, measured using the technique of electro-optic sampling have further confirmed the sub-picosecond carrier lifetimes, and have also resulted in the generation of subpicosecond electrical signals. These short electrical pulses have been used for a variety of ultrafast optoelectronic applications.

We report on the generation of 825 V electrical pulses with 1.4 ps rise time and 4 ps Full-Width-at-Half-Maximum using pulse biased Low-Temperature-grown GaAs photoconductive switch triggered by submicrojoule, 150 fs laser pulses. Dependence of the temporal pulse shape on both the electric field and the optical energy is observed and discussed.

The effect of growth conditions on the properties of GaAs grown by molecular beam epitaxy at low substrate temperatures has been studied. It has been found that the response time to 100 fsec 830nm light pulses is a function of substrate temperature and arsenic flux. The reason for variation of optical response with growth conditions is related to the nature of the incorporation of excess arsenic. A recent model proposed by Warren and others is invoked to explain the change in optical response with growth conditions. Further substantiation of this model comes from experiments on the annealing of low substrate temperature GaAs which has been doped with silicon.

The technique of picosecond electron diffraction is used to time resolve the laser-induced melting of thin aluminum films. It is observed that under rapid heating conditions, the long range order of the lattice subsists for lattice temperatures well above the equilibrium point, indicative of superheating. This superheating can be verified by directly measuring the lattice temperature. The collapse time of the long range order is measured and found to vary from 20 ps to several nanoseconds according to the degree of superheating. Two interpretations of the delayed melting are offered, based on the conventional nucleation and point defect theories. While the nucleation theory provides an initial nucleus size and concentration for melting to occur, the point defect theory offers a possible explanation for how the nuclei are originally formed.