Proposal for a Raman X-ray Free Electron Laser

22 pagesA scheme for an X-ray free electron laser is proposed, based on a Raman process occurring during the interaction between a moderately relativistic bunch of free electrons, and twin intense short pulse lasers interfering to form a transverse standing wave along the electron trajectories. In the high intensity regime of the Kapitza-Dirac effect, the laser ponderomotive potential forces the electrons into a lateral oscillatory motion, resulting in a Raman scattering process. I show how a parametric process is triggered, resulting in the amplification of the Stokes component of the Raman-scattered photons. Experimental operating parameters and implementations, based both on LINAC and Laser Wakefield Acceleration techniques, are discussed

X-ray amplification from a Raman Free Electron Laser

accepted for publication in Phys. Rev. Lett. 03/11/2012We demonstrate that a mm-scale free electron laser can operate in the X-ray range, in the interaction between a moderately relativistic electron bunch, and a transverse high intensity optical lattice. The corrugated light-induced ponderomotive potential acts simultaneously as a guide and as a low-frequency wiggler, triggering stimulated Raman scattering. The gain law in the small signal regime is derived in a fluid approach, and confirmed from Particle-In-Cell simulations. We describe the nature of bunching, and discuss the saturation properties. The resulting all-optical Raman X-ray laser opens perspectives for ultra-compact coherent light sources up to the hard X-ray range

Oscillateurs picosecondes de forte puissance moyenne à faibles bruits

Pour des applications médicales ou en histoire de l'art, un système compact de production de rayonnement X monochromatique à haut flux par effet Compton nécessite de disposer d une source laser impulsionnelle de forte puissance moyenne avec des durées de quelques picosecondes. Pour atteindre un haut flux de rayonnement X, le laser devra être injecté dans une cavité Fabry-Perot de haute finesse afin d atteindre les puissances laser moyennes requises. Par conséquent, le laser devra avoir une bonne qualité de mode et de faibles bruits. Afin d atteindre ces objectifs, nous avons étudié la réalisation d oscillateurs à blocage de modes passif délivrant des puissances moyennes de plus de 10 W avec des impulsions d une durée entre 10 et 20 ps. Au cours de ce travail, deux oscillateurs de haute puissance moyenne ont été conçus et réalisés : l un à pompage radial avec Nd:YAG comme milieu de gain et l autre à pompage longitudinal avec comme milieu de gain Nd:YVO4. Le développement du second oscillateur a donné lieu à une étude expérimentale de la réduction de la durée des impulsions qui nous permet d ajuster la durée entre 46 ps et 12 ps en régime de blocage de modes passif. Les résultats expérimentaux ont été expliqués à l aide d une simulation numérique et une solution analytique a été trouvée pour prédire la durée des impulsions. Enfin, une étude des caractéristiques des bruits de l oscillateur Nd:YVO4 a été réalisée. Ces mesures ont permis de mettre en évidence qu un oscillateur de forte puissance moyenne a les capacités pour être aussi peu bruyant que des oscillateurs de faible puissance et à faibles bruits. En résumé nous avons développé un oscillateur puissant (20W), à une longueur d onde de 1064 nm, avec des durées d impulsions courtes (15 ps), une bonne qualité de faisceau (M2<1,2) et de faibles bruits (gigue temporelle <1,2 ps RMS 100Hz-1MHz non asservi). Par conséquent, notre oscillateur puissant est un excellent candidat pour faire partie de la machine compacte de rayonnement X monochromatique et à haut flux.For medical or cultural heritage applications, a compact, monochromatic, Compton x-ray source system needs a powerful, few picosecond laser source. To obtain high-x-ray-flux, the laser should be coupled to a high-finesse Fabry-Perot cavity to reach the required laser power. Therefore, the laser should have a good beam quality and low noises. In order to reach theses requirements, we have studied passive mode-locking oscillators delivering more than 10 W average power and between 10 and 20 ps pulse duration.Two high-power oscillators have been designed and implemented: a side-pumped Nd:YAG and an end-pumped Nd:YVO4 oscillator. With the second oscillator, we have studied the experimental reduction of pulse duration. We obtained a decrease from 46 ps to 12 ps in the continuous-wave mode-locked regime. Those experimental results have been explained by a numerical simulation and furthermore, we have developed an analytical solution to predict the pulse duration of such oscillator. Finally, we studied the noise characteristics of the Nd:YVO4 oscillator. Our measurements have shown that a high-power oscillator might be as low-noise as other low-power, low-noise oscillators. In conclusion, we have developed a powerful (20W), 1064nm-wavelength, short-pulses (15ps), good-beam-quality (M2<1.2) and low-noise free-running oscillator (timing jitter <1.2 ps RMS 100Hz-1MHz). Therefore, our high-power oscillator is an excellent candidate to be part of a compact, high-flux, monochromatic x-ray source.BORDEAUX1-Bib.electronique (335229901) / SudocSudocFranceF

Quantum-path analysis and phase matching of high-order harmonic generation and high-order frequency mixing processes in strong laser fields

We study phase-matching conditions for high-order harmonic generation as well as high-order sum- and difference-frequency mixing processes in strong laser fields, using a graphical approach described in Balcou et al (1997 Phys. Rev. A 55 3204-10). This method is based on the analysis of the different quantum paths that contribute, with different phase properties, to the single-atom response. We propose a simple numerical method to disentangle the quantum paths contributing to the generation process. We present graphical maps of the phase matching around the laser focus, which allow one to predict the geometries that optimize the conversion efficiency of the process considered. The method is applied to the study of sum- and difference-frequency mixing processes. The qualitative predictions of the graphical phase-matching approach are confirmed by numerical propagation calculations

Injection of a relativistic electron beam into a high intensity optical lattice

We present a numerical study of the injection and trapping process of a bunch of relativistic free electrons into a transverse high intensity optical lattice. We unravel different injection regimes depending on the characteristic length scale of the onset of the optical lattice , and explore how the characteristics of the electron beam and of the high intensity lattice affect the trapping rate. The average transverse kinetic energy , and the induced longitudinal energy broadening are studied. The analysis of the transverse phase space exhibits a complex behavior , leading to inhomogeneities that may affect the amplification dynamics of X-ray Free Electron Laser

Design and characterization of extreme-ultraviolet broadband mirrors for attosecond science

International audienceA novel multilayer mirror was designed and fabricated based on a recently developed three-material technology aimed both at reaching reflectivities of about 20% and at controlling dispersion over a bandwidth covering photon energies between 35 and 50 eV. The spectral phase upon reflection was retrieved by measuring interferences in a two-color ionization process using high-order harmonics produced from a titanium: sapphire laser. We demonstrate the feasibility of designing and characterizing phase-controlled broadband optics in the extreme-ultraviolet domain, which should facilitate the manipulation of attosecond pulses for applications

Intrinsic chirp of attosecond pulses: Single-atom model versus experiment

International audienceWe demonstrate and evaluate the importance of an intrinsic chirp inherent to attosecond pulse creation accompanying high-order harmonic generation in recently published experimental data by Dinu et al. [Phys. Rev. Lett. 91, 063901 (2003)]. We present an analytical model, from which the atomic origin of the harmonic chirp is clearly understood. Moreover, the behavior of the chirp as a function of experimental parameters such as laser intensity is inferred. The comparison between our model and the experimental data provides us with useful information about the conditions in which the high-order harmonics is generated