Gilles Cheriaux

Linear techniques of phase measurement by femtosecond spectral interferometry for applications in spectroscopy

Although nonlinear methods can provide only the amplitude and the phase of an isolated ultrashort pulse, linear techniques can yield such measurements with a much better sensitivity and reliability when a reference pulse is available. We demonstrate two such methods, dual-quadrature spectral interferometry and Fourier-transform spectral interferometry. These techniques are simple to implement, very sensitive, and provide a complete measurement of the complex electric field, E(ω), as a continuous function of frequency.

Ultra-high intensity- 300-TW laser at 0.1 Hz repetition rate.

We demonstrate the highest intensity - 300 TW laser by developing booster amplifying stage to the 50-TW-Ti:sapphire laser (HERCULES). To our knowledge this is the first multi-100TW-scale laser at 0.1 Hz repetition rate.

10 ?10 temporal contrast for femtosecond ultraintense lasers by cross-polarized wave generation

We take advantage of nonlinear properties associated with chi(3) tensor elements in BaF2 cubic crystal to improve the temporal contrast of femtosecond laser pulses. The technique presented is based on cross-polarized wave (XPW) generation. We have obtained a transmission efficiency of 10% and 10(-10) contrast with an input pulse in the millijoule range. This filter does not affect the spectral shape or the phase of the cleaned pulse. It also acts as an efficient spatial filter. In this method the contrast enhancement is limited only by the extinction ratio of the polarization discrimination device.

Aberration-free stretcher design for ultrashort-pulse amplification

A novel aberration-free pulse stretcher design is presented. This system permits the stretching of a 30-fs pulse to 300 ps and recompression to a duration of 33 fs, limited by the spectral clipping.

High-efficiency, simple setup for pulse cleaning at the millijoule level by nonlinear induced birefringence.

Nonlinear elliptical polarization rotation is used to improve the contrast of femtosecond pulses by several orders of magnitude. Using nonlinear induced birefringence in air, we produced cleaned pulses with an energy of a few hundreds of microjoules. This technique presents several major advantages, such as convenience and stability of the setup. We investigated the phase profile required for obtaining high-energy pulses. No phase distortion is observed, and the spatial quality of the beam is preserved.

Generation of 25-TW, 32-fs pulses at 10 Hz

We have developed a femtosecond laser chain that generates 25-TW pulses of less than 35 fs at 10 Hz with focused intensities higher than 5 x 10(19) W/cm(2) and an average power of 8 W. This system is optimized for a broad transmission bandwidth and includes an aberration-free stretcher compressor.

Highly efficient nonlinear filter for femtosecond pulse contrast enhancement and pulse shortening.

We propose a highly efficient scheme for temporal filters devoted to femtosecond pulse contrast enhancement. The filter is based on cross-polarized wave generation with a spatially suger-Gaussian-shaped beam. In a single nonlinear crystal scheme the energy conversion to the cross-polarized pulse can reach 28%. We demonstrate that the process enables a significant spectral broadening. For an efficiency of 23% the pulse shortening is estimated to 2.2, leading to an intensity transmission of the nonlinear filter of 50%.

A two crystal arrangement to fight efficiency saturation in cross-polarized wave generation.

We describe a method that overcomes the observed saturation effect in cross polarized wave (XPW) generation. The previously reported internal efficiencies for XPW generation are known to be limited to around 15% whatever the length of the nonlinear medium and/or the input intensity values are. At the opposite, the theoretical limit had been estimated to be close to 25%. Here we show that using two thin BaF(2) crystals separated at optimum distance the saturation level of XPW generation efficiency can be drastically increased. An internal efficiency of 30% is demonstrated experimentally using two BaF(2) crystals.

Nonlinear polarization rotation of elliptical light in cubic crystals, with application to cross-polarized wave generation

We have investigated theoretically and experimentally the nonlinear propagation of intense elliptically polarized light pulses along a fourfold axis of the cubic crystal BaF2. Third-order nonlinear optical processes generate a cross-polarized wave, an effect that presents significant possibilities for application in femtosecond pulse contrast enhancement. The experimental setup consists of an input linear polarized light that passes through a cubic crystal sandwiched between two crossed quarter-wave plates. The exit orthogonal polarization-state production amount is measured at the output of an analyzer. When the light impinging on the sample is elliptically polarized with a quarter-wave plate at 22.5 deg, the achieved efficiency reaches 15%. It is more than twice that of a conventional polarization filter based on nonlinear ellipse rotation in an isotropic medium. This device is compared with previously reported polarization filtering [J. Opt. Soc. Am. B21, 1659 (2004)], in which a linearly polarized light produced a perpendicular field component. The theoretical model describes in detail the obtained dependencies and allows the different nonlinear processes that contribute to the generation of a cross-polarized wave to be distinguished. Possible applications are discussed.

Extreme Light Infrastructure: Architecture and major challenges

Extreme Light Infrastructure (ELI), the first research facility hosting an exawatt class laser will be built with a joint international effort and form an integrated infrastructure comprised at last three branches: Attosecond Science (in Szeged, Hungary) designed to make temporal investigation at the attosecond scale of electron dynamics in atoms, molecules, plasmas and solids. High Field Science will be mainly focused on producing ultra intense and ultra short sources of electons, protons and ions, coherent and high energetic X rays (in Prague, Czech Republic) as well as laserbased nuclear physics (in Magurele, Romania). The location of the fourth pillar devoted to Extreme Field Science, which will explore laser-matter interaction up to the non linear QED limit including the investigation of vacuum structure and pair creation, will be decided after 2012. The research activities will be based on an incremental development of the light sources starting from the current high intensity lasers (APOLLON, GEMINI, Vulcan and PFS) as prototypes to achieve unprecedented peak power performance, from tens of petawatt up to a fraction of exawatt (1018 W). This last step will depend on the laser technology development in the above three sites as well as in current high intensity laser facilities.