PubMed Health⌕ Search

Biomedical subjects

G Mourou

Publications and source records attributed to G Mourou.

12 recordsLinked to original sources
PubMed2006

Adaptive correction of a tightly focused, high-intensity laser beam by use of a third-harmonic signal generated at an interface.

By using the third-harmonic signal generated at an air-dielectric interface, we demonstrate a novel way of correcting wavefront aberrations induced by high-numerical-aperture optics. The third harmonic is used as the input physical parameter of a genetic algorithm working in closed loop with a 37-actuator deformable mirror. This method is simple and reliable and can be used to correct aberrations of tightly focused beams, a regime where other methods have limitations. Improvement of the third-harmonic signal generated with an f/1.2 parabolic mirror by 1 order of magnitude is demonstrated.

Journal Article↗
PubMed2004

Attosecond electron bunches.

Electron bunches of attosecond duration may coherently interact with laser beams. We show how p-polarized ultraintense laser pulses interacting with sharp boundaries of overdense plasmas can produce such bunches. Particle-in-cell simulations demonstrate attosecond bunch generation during pulse propagation through a thin channel or in the course of grazing incidence on a plasma layer. In the plasma, due to the self-intersection of electron trajectories, electron concentration is abruptly peaked. A group of counterstream electrons is pushed away from the plasma through nulls in the electromagnetic field, having inherited a peaked electron density distribution and forming relativistic ultrashort bunches in vacuum.

Journal Article↗
PubMed2004

[Femtosecond laser: a micromachining system for corneal surgery].

INTRODUCTION: The authors present the diode-pumped, all-solid state, neodymium:glass femtosecond laser from the Laboratory of Ocular Biotechnology, Hotel-Dieu Hospital. MATERIALS AND METHODS: We worked with a 1,065-nm wavelength infrared laser. This laser is composed of an oscillator and amplification glass matrix mixed with neodymium. Its stretching and compression system is capable of producing pulses lasting a few hundred femtoseconds. The repetition rate is adjustable, ranging from 1 to 10 kHz, and can reach energies up to 60 microJ. The delivery system was set up on an optical table, with human corneal samples fixed to an anterior chamber system, which can be moved over the X-Y-Z axis by a computer-guided translation motor with micrometric precision. We analyzed the biological effects of laser impacts in human corneal tissue, obtained from the French Eye Bank. RESULTS: The femtosecond laser provides automated corneal cutting with a high level of precision, which can be verified on the corneal surface regularity by scanning electron microscopy analysis. Silicon samples can also be cut and can be used for calibration testing of the laser. CONCLUSION: The set-up composed of the femtosecond laser and the described delivery system enable precise corneal cutting and offer the opportunity to study its characteristics.

Calibration↗
PubMed2003

Electron acceleration by few-cycle laser pulses with single-wavelength spot size.

Generation of relativistic electrons from the interaction of a laser pulse with a high density plasma foil, accompanied by an underdense preplasma in front of it, has been studied with two-dimensional particle-in-cell (PIC) simulations for pulse durations comparable to a single cycle and for single-wavelength spot size. The electrons are accelerated predominantly in forward direction for a preplasma longer than the pulse length. Otherwise, both forward and backward electron accelerations occur. The primary mechanism responsible for electron acceleration is identified. Simulations show that the energy of the accelerated electrons has a maximum versus the pulse duration for relativistic laser intensities. The most effective electron acceleration takes place when the preplasma scale length is comparable to the pulse duration. Electron distribution functions have been found from PIC simulations. Their tails are well approximated by Maxwellian distributions with a hot temperature in the MeV range.

Journal Article↗
PubMed1999

Self-focusing, channel formation, and high-energy ion generation in interaction of an intense short laser pulse with a He jet.

Using interferometry, we investigate the dynamics of interaction of a relativistically intense 4-TW, 400-fs laser pulse with a He gas jet. We observe a stable plasma channel 1 mm long and less than 30 microm in diameter, with a radial gradient of electron density approximately 5 x 10(22) cm(-4) and with an on-axis electron density approximately ten times less than its maximum value of 8 x 10(19) cm(-3). A high radial velocity of the surrounding gas ionization of approximately 3.8 x 10(8) cm/s has been observed after the channel formation, and it is attributed to the fast ions expelled from the laser channel and propagating radially outward. We developed a kinetic model which describes the plasma channel formation and the subsequent ambient gas excitation and ionization. Comparing the model predictions with the interferometric data, we reconstructed the axial profile of laser channel and on-axis laser intensity. The estimated maximum energy of accelerated ions is about 500 keV, and the total energy of the fast ions is 5% of the laser pulse energy.

Journal Article↗
PubMed1996

Nonlinear Optics in Relativistic Plasmas and Laser Wake Field Acceleration of Electrons

When a terawatt-peak-power laser beam is focused into a gas jet, an electron plasma wave, driven by forward Raman scattering, is observed to accelerate a naturally collimated beam of electrons to relativistic energies (up to 10(9) total electrons, with an energy distribution maximizing at 2 megaelectron volts, a transverse emittance as low as 1 millimeter-milliradian, and a field gradient of up to 2 gigaelectron volts per centimeter). Electron acceleration and the appearance of high-frequency modulations in the transmitted light spectrum were both found to have sharp thresholds in laser power and plasma density. A hole in the center of the electron beam may indicate that plasma electrons were expelled radially.

Journal Article↗