Showing papers by "Gerard Mourou published in 2006"

Optics in the relativistic regime

Abstract: The advent of ultraintense laser pulses generated by the technique of chirped pulse amplification (CPA) along with the development of high-fluence laser materials has opened up an entirely new field of optics. The electromagnetic field intensities produced by these techniques, in excess of ${10}^{18}\phantom{\rule{0.3em}{0ex}}\mathrm{W}∕{\mathrm{cm}}^{2}$, lead to relativistic electron motion in the laser field. The CPA method is reviewed and the future growth of laser technique is discussed, including the prospect of generating the ultimate power of a zettawatt. A number of consequences of relativistic-strength optical fields are surveyed. In contrast to the nonrelativistic regime, these laser fields are capable of moving matter more effectively, including motion in the direction of laser propagation. One of the consequences of this is wakefield generation, a relativistic version of optical rectification, in which longitudinal field effects could be as large as the transverse ones. In addition to this, other effects may occur, including relativistic focusing, relativistic transparency, nonlinear modulation and multiple harmonic generation, and strong coupling to matter and other fields (such as high-frequency radiation). A proper utilization of these phenomena and effects leads to the new technology of relativistic engineering, in which light-matter interactions in the relativistic regime drives the development of laser-driven accelerator science. A number of significant applications are reviewed, including the fast ignition of an inertially confined fusion target by short-pulsed laser energy and potential sources of energetic particles (electrons, protons, other ions, positrons, pions, etc.). The coupling of an intense laser field to matter also has implications for the study of the highest energies in astrophysics, such as ultrahigh-energy cosmic rays, with energies in excess of ${10}^{20}\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. The laser fields can be so intense as to make the accelerating field large enough for general relativistic effects (via the equivalence principle) to be examined in the laboratory. It will also enable one to access the nonlinear regime of quantum electrodynamics, where the effects of radiative damping are no longer negligible. Furthermore, when the fields are close to the Schwinger value, the vacuum can behave like a nonlinear medium in much the same way as ordinary dielectric matter expanded to laser radiation in the early days of laser research.

Generation of high-fidelity, down-chirped sub-10 fs mJ pulses through filamentation for driving relativistic laser-matter interactions at 1 kHz

Abstract: The authors present a simple add on for multicycle, multimJ Ti:sapphire-based amplifier systems to efficiently generate 9.5fs pulses with 1.8mJ. Filamentary propagation yields spectrally broadened pulses carrying an unexpected large group-delay dispersion of −500fs2 which allows linear propagation of the few-cycle pulses towards target areas without need of any sophisticated dispersion control. Pulse compression could easily be achieved by transmission through a combination of different glass substrates. The pulse wave front, the low energy fluctuations, and the good temporal contrast make this source well suited for relativistic laser-solid experiments with intense few-cycle pulses at kilohertz repetition rate.

Hard X-ray generation from solids driven by relativistic intensity in the lambda-cubed regime

Abstract: Interaction of relativistic intensity laser pulses encompassed at focus by a volume of a few wavelengths cubed with solids is examined. Spectroscopy of hard X-rays of several metallic targets, including Cu, Ge, Mo, Ag, and Sn, irradiated in this regime at a high repetition rate (0.4 kHz), has been experimentally studied. The Kα and Kβ peaks of all targets were obtained. Averaged electron temperatures of several tens of keV and total X-ray conversion efficiencies up to 0.02% are calculated. The X-ray source size is measured to be ∼10 micron with varying elliptical shape.

The Road to High Peak Power and High Average Power Lasers: Coherent‐Amplification‐Network (CAN)

Abstract: A new amplifying laser concept based on Coherent Amplification Network (CAN) is proposed to solve the high‐peak high‐average‐power quandary. The amplification network is based on identical telecommunication diode‐pumped fiber lasers. The philosophy behind the approach is to build the amplifying system from numerous small but identical parts as opposed to larger but non‐identical components like in the laser Megajoule in France or NIF in the USA. The basic amplification scheme is in‐fiber Chirped Pulse Amplification. Besides the possibility to simultaneously provide high peak and high average power, the technique gives independent control of the output beam spatial and temporal coherence, as well as the pupilary distribution. In addition to being rugged, CAN offers the additional benefit of being inexpensive and low maintenance. A conceptual design based on CAN is presented that offers an alternative to the next CERN Linear Collider (CLIC).

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

Abstract: 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.

Demonstration of fiber-laser-produced plasma source and application to efficient extreme UV light generation

Abstract: Efficient generation of extreme UV (EUV) light at lambda = 13.5 nm from a bulk Sn target has been demonstrated by using a fiber laser. The conversion efficiency from the 1064 nm IR to the EUV was measured to be around 0.9% into 2pi steradians within a 2% bandwidth. To the best of our knowledge, this is the first time an all-fiber system was used to generate EUV or soft x rays.

Femtosecond microscopy of radial energy transport in a micrometer-scale aluminum plasma excited at relativistic intensity.

Abstract: Using femtosecond microscopy, we observe subpicosecond transport of thermal energy radially outward from a micrometer-sized spot of an aluminum target following P-polarized excitation at >1018 W/cm2 with a 24 fs pulse. The rapid expansion coincides with the onset of nonlocal energy transport dominated by radiation and hot electrons.

All-reflective high fringe contrast autocorrelator for measurement of ultrabroadband optical pulses

Abstract: We describe an all-reflective interferometric autocorrelator designed to measure ultrabroadband optical pulses in the UV through IR spectral regions. By carefully choosing the device geometry we are able to obtain approximations for the nonlinear autocorrelation functions that reduce computation times to values acceptable for use in iterative pulse reconstruction schemes. We describe the optical design, autocorrelation functions, and present proof-of-principle experimental results measuring 20.6 fs pulses with a transform limit of 9.6 fs.

Carrier-envelope phase stabilization of high-contrast femtosecond laser pulses with a relativistic intensity

Abstract: We report on the generation of carrier-envelope phase (CEP)-stabilized pulses with a relativistic intensity and a high-contrast ratio. The CEP stabilization is achieved with a jitter of 0.95rad from a 0.5kHz femtosecond laser pulses with a focal intensity of 2.6×1018W∕cm2 and a picosecond contrast of 2.5×10−9. CEP noise analysis shows that the beam pointing at the pulse compressor is a dominant factor of the CEP fluctuation with our laser system.

Distinctive physical effects and applications approaching the relativistic lambda-cubed regime

Abstract: Using small amounts of optical energy, it is possible to drive matter with relativistic intensity. We show unique energy transport properties, X-ray production, and efficient attosecond phenomena coming from microscopic plasmas driven by precisely focused ultrashort pulses of light.

Generation and characterization of quasi-monoenergetic electron beams from laser wakefield

Abstract: In the interaction of a 30 fs, 40 TW Ti:sapphire Hercules laser focused to the intensity of 10 19 W/cm 2 onto a supersonic He gas jet, we observed quasi-monoenergetic electron beams with energy up to 300 MeV and an angular divergence of 10 mrad. We found that the initial plasma density significantly affects the resultant electron beam. For plasma densities ranging between 2 x 10 19 to 3.5 x 10 19 cm -3 , quasi-monoenergetic electrons with energies from 80 to 160 MeV and a total charge of about 0.5 nC were produced. Lower plasma densities around 1.5 x 10 19 cm -3 produced quasi-monoenergetic electron beams with higher energy, up to 320 ± 50 MeV, but with a decrease of the total charge to about 5 pC. Characterization of the electron beam in terms of the electron's maximum energy, beam divergence and pointing stability is presented. The performed 2D PIC simulations show the evolution of the laser pulse in the plasma, electron injection, and the specifics of electron acceleration.

Demonstration of spatial coherence with a compact and ultrafast X-ray source

Abstract: We used Fresnel diffraction from knife-edges to demonstrate spatial coherence of tabletop and ultrafast X-ray sources produced by laser-plasma interaction, and show that source size is limited by the spatial spread of absorbed laser energy.

Characterization of a minute hard x-ray source driven by a relativistic wavelength-cubed laser

Abstract: Tightly focused ultrashort-pulse light efficiently drives a hard x-ray source (eta=0.08%) with 9-mum size enabling imaging of small features using indigenous electrons in Mo and Au/Si. In-plane and out-of-plane angular distribution of x-rays is measured.

Simple and robust solution for high-intensity laser adaptive optic correction on a tightly focused beam using third-harmonic signal generated at an interface

Abstract: The wavefront of a KHz TW laser was corrected by maximizing a third-harmonic signal via a genetic algorithm. This method optimizes the whole beam and is well suited for high numerical aperture focusing optics.

Dispersion-frre interferometric autocorrelator for measurement of ultra-broadband pulses

Abstract: We demonstrate a dispersion-free split mirror interferometric autocorrelator suitable for measuring pulses with durations from hundreds of attoseconds to tens of femtoseconds and spectral content from the near-UV to near-IR.

Caractérisation du seuil de dommage dans les cristaux de saphir dopé au titane avec des impulsions de durée nanoseconde, picoseconde et femtoseconde

Abstract: Le verrou principal pour le developpement des systemes femtoseconde robustes et rentables est l'incertitude du seuil de dommages du cristal de Ti: Saphir. Nous avons d'abord caracterise le seuil dielectrique de dommages du Ti: Saphir.

Acceleration of quasi-monochromatic electron beams in laser wakefield to 300 Mev and initiation of photonuclear reactions

Abstract: We observed quasi-monoenergetic electron beams with energy up to 300 MeV from the laser wakefield. The resultant electron beams have been used to perform efficiently gamma-neutron activation of 12C and 63Cu and photo-fission of 238U.