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.

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.

Photodissociation of D-3(+) in an intense, femtosecond laser field

H-3(+) is the simplest triatomic molecule and plays an important role in laboratory and astrophysical plasmas. It is very stable both in terms of its electronic and nuclear degrees of freedom but is difficult to study in depth in the laboratory due to its ionic nature. In this communication, experimental results are presented for the strong field dissociation of the isotopic analogue D-3(+), using 30 fs, 800 nm laser pulses with intensities up to 10(16) W cm(-2). By employing a novel experimental set-up, ions were confined in an electrostatic ion trap so that dissociation of the molecule could be studied as it radiatively cools. It was determined that dissociation could only be observed for molecules in ro-vibrational states relatively close to the dissociation limit, while more tightly bound states demonstrated remarkable stability in even the strongest fields.

Development of XUV lasers at the RAL central laser facility

Recent progress in the development of XUV lasers by research teams using high-power and ultrashort-pulse Nd:glass and KrF laser facilities at the Rutherford Appleton Laboratory is reviewed. Injector-amplifier operation and prepulse enhanced output of the Ge XXIII collisional laser driven by a kilojoule glass laser, enhanced gain in CVI recombination with picosecond CPA drive pulses from a glass laser, and optical field ionization and XUV harmonic generation with a KrF CPA laser are described.

High-energy electron beam production by femtosecond laser interactions with exploding-foil plasmas

The interaction of an ultraintense, 30-fs laser pulse with a preformed plasma was investigated as a method of producing a beam of high-energy electrons. We used thin foil targets that are exploded by the laser amplified spontaneous emission preceding the main pulse. Optical diagnostics show that the main pulse interacts with a plasma whose density is well below the critical density. By varying the foil thickness, we were able to obtain a substantial emission of electrons in a narrow cone along the laser direction with a typical energy well above the laser ponderomotive potential. These results are explained in terms of wake-field acceleration.

Fragmentation of Neutral Amino Acids and Small Peptides by Intense, Femtosecond Laser Pulses

High power femtosecond laser pulses have unique properties that could lead to their application as ionization or activation sources in mass spectrometry. By concentrating many photons into pulse lengths approaching the timescales associated with atomic motion, very strong electric field strengths are generated, which can efficiently ionize and fragment molecules without the need for resonant absorption. However, the complex interaction between these pulses and biomolecular species is not well understood. To address this issue, we have studied the interaction of intense, femtosecond pulses with a number of amino acids and small peptides. Unlike previous studies, we have used neutral forms of these molecular targets, which allowed us to investigate dissociation of radical cations without the spectra being complicated by the action of mobile protons. We found fragmentation was dominated by fast, radical-initiated dissociation close to the charge site generated by the initial ionization or from subsequent ultrafast migration of this charge. Fragments with lower yields, which are useful for structural determinations, were also observed and attributed to radical migration caused by hydrogen atom transfer within the molecule.

Direct Photodetachment of F‾ by mid-infrared few-cycle femtosecond laser pulses

The recent adiabatic saddle-point approach of Shearer et al. [ Phys. Rev. A 84 033409 (2011)] is extended to multiphoton detachment of negative ions with outer p-state electrons. This theory is applied to investigate the strong-field photodetachment dynamics of F- ions exposed to few-cycle femtosecond laser pulses, without taking into account the rescattering mechanism. Numerical calculations are considered for mid-infrared laser wavelengths of 1300 and 1800 nm at laser intensities of 7.7 × 1012, 1.1 × 1013, and 1.3 × 1013 W/cm2. Two-dimensional momenta saddle-point spectra exhibit a distinct distribution in the shape of a “smile” in the complex-time plane. Electron momentum distribution maps of direct electrons are investigated. These produce a distinct pattern of above-threshold detachment (ATD) concentric rings due to constructive and destructive quantum interference of electrons detached from their parent ions. Probability detachment distributions presented, capturing the influence of saturation effects that are found to become more significant with increasing laser intensity at a fixed wavelength. ATD photoangular distributions as functions of laser intensity and wavelength near channel closings are also investigated and found to be sensitive to initial-state symmetry. Nonmonotonic structures observed in the ejected photoelectron energy spectra are attributed to interference effects from coherent electronic wave packets. Additionally the profiles of all the photoelectron emission spectra show strong dependence on the carrier-envelope phase, indicating that it is a reliable parameter for characterizing the wave form of the pulse.

Femtosecond-laser assisted cataract surgery: a review.

Introduced in 2008, the femtosecond laser is a promising new technological advance which plays an ever increasing role in cataract surgery where it automates the three main surgical steps: corneal incision, capsulotomy and lens fragmentation. The proven advantages over manual surgery are: a better quality of incision with reduced induced astigmatism; increased reliability and reproducibility of the capsulotomy with increased stability of the implanted lens; a reduction in the use of ultrasound. Regarding refractive results or safety, however, no prospective randomized study to date has shown significant superiority compared with standard manual technique. The significant extra cost generated by this laser, undertaken by the patient, is a limiting factor for both its use and study. This review outlines the potential benefits of femtosecond-laser-assisted cataract surgery due to the automation of key steps and the safety of this new technology.

Investigation of femtosecond laser technology for the fabrication of drug nanocrystals in suspension

La technique du laser femtoseconde (fs) a été précédemment utilisée pour la production de nanoparticules d'or dans un environnement aqueux biologiquement compatible. Au cours de ce travail de maîtrise, cette méthode a été investiguée en vue d'une application pour la fabrication de nanocristaux de médicament en utilisant le paclitaxel comme modèle. Deux procédés distincts de cette technologie à savoir l'ablation et la fragmentation ont été étudiés. L'influence de la puissance du laser, de point de focalisation, et de la durée du traitement sur la distribution de taille des particules obtenues ainsi que leur intégrité chimique a été évaluée. Les paramètres ont ainsi été optimisés pour la fabrication des nanoparticules. L’évaluation morphologique et chimique a été réalisée par microscopie électronique et spectroscopie infrarouge respectivement. L'état cristallin des nanoparticules de paclitaxel a été caractérisé par calorimétrie differentielle et diffraction des rayons X. L'optimisation du procédé de production de nanoparticules par laser fs a permis d'obtenir des nanocristaux de taille moyenne (400 nm, polydispersité ≤ 0,3). Cependant une dégradation non négligeable a été observée. La cristallinité du médicament a été maintenue durant la procédure de réduction de taille, mais le paclitaxel anhydre a été transformé en une forme hydratée. Les résultats de cette étude suggèrent que le laser fs peut générer des nanocristaux de principe actif. Cependant cette technique peut se révéler problématique pour des médicaments sensibles à la dégradation. Grâce à sa facilité d'utilisation et la possibilité de travailler avec des quantités restreintes de produit, le laser fs pourrait représenter une alternative valable pour la production de nanoparticules de médicaments peu solubles lors des phases initiales de développement préclinique. Mots-clés: paclitaxel, nanocristaux, laser femtoseconde, ablation, fragmentation