29 research outputs found
Effect of input pulse chirp on nonlinear energy deposition and plasma excitation in water
We analyze numerically and experimentally the effect of the input pulse chirp
on the nonlinear energy deposition from J fs-pulses at nm to
water. Numerical results are also shown for pulses at nm, where linear
losses are minimized, and for different focusing geometries. Input chirp is
found to have a big impact on the deposited energy and on the plasma
distribution around focus, thus providing a simple and effective mechanism to
tune the electron density and energy deposition. We identify three relevant
ways in which plasma features may be tuned.Comment: 9 pages, 7 figure
Patterning enhanced tetragonality in BiFeO3 thin films with effective negative pressure by helium implantation
Helium implantation in epitaxial thin films is a way to control the out-of-plane deformation independentlyfrom the in-plane strain controlled by epitaxy. In particular, implantation by means of a helium microscopeallows for local implantation and patterning down to the nanometer resolution, which is of interest for deviceapplications. We present here a study of bismuth ferrite (BiFeO3) films where strain was patterned locally byhelium implantation. Our combined Raman, x-ray diffraction, and transmission electron microscopy (TEM)study shows that the implantation causes an elongation of the BiFeO3unit cell and ultimately a transition towardsthe so-called supertetragonal polymorph via states with mixed phases. In addition, TEM reveals the onset ofamorphization at a threshold dose that does not seem to impede the overall increase in tetragonality. The phasetransition from the R-like to T-like BiFeO3appears as first-order in character, with regions of phase coexistenceand abrupt changes in lattice parameters
Filamentation and Pulse Self-compression in the Anomalous Dispersion Region of Glasses
International audienceThe propagation of near-infrared ultra-short laser pulses in the regime of anomalous dispersion of transparent solids is associated with a host of self-induced effects including a significant spectral broadening extending from the ultraviolet into the infrared region, pulse self-compression down to few-cycle pulse durations, free and driven third harmonic generation, conical emission and the formation of stable filaments over several cm showing the emergence of conical light bullets. We review measurements performed in different experimental conditions and results of numerical simulations of unidirectional propagation models showing that the interpretation of all these phenomena proceed from the formation of non-spreading conical light bullets during filamentation
Dynamics Of Plasma Gratings In Atomic And Molecular Gases
The decay of the plasma grating formed at the intersection of two femtosecond filaments is measured in several molecular and atomic gases. The grating evolution is ruled by ambipolar diffusion in atomic gases and by a combination of ambipolar diffusion and collision-assisted free electron recombination in molecular gases. Electron diffusion and recombination coefficients are extracted for Ne, Ar, Kr, Xe, N 2, O 2, CO 2, and air at 1 bar. © 2012 American Physical Society
Self-Cleaning Properties Of A Filament Conjugate Mirror
Two counter propagating filaments can create a phase conjugate mirror in air. This mirror can efficiently clean a femtosecond laser pulse. © 2013 OSA
Spatio-Temporal Cleaning Of A Femtosecond Laser Pulse By A Filament Conjugate Mirror
Optical phase conjugation is well known for its time reversal properties [1]. A phase conjugate mirror is formed when two laser beams of same frequency w meet from opposite directions in a transparent nonlinear medium. When a probe beam is retro-reflected by an optical phase conjugate mirror, wavefront distortions induced by a phase object are removed after re-crossing this object [2, 3]. In this presentation, we use two counter-propagating filaments to create a conjugate mirror with air as a non linear medium [4]. We demonstrate that it operates differently from a usual conjugate mirror. With a filament conjugate mirror, the reflected signal has essentially a perfect spatial mode independent of the initial probe beam profile. © 2013 IEEE
Spatio-Temporal Cleaning Of A Femtosecond Laser Pulse By A Filament Conjugate Mirror
Optical phase conjugation is well known for its time reversal properties [1]. A phase conjugate mirror is formed when two laser beams of same frequency w meet from opposite directions in a transparent nonlinear medium. When a probe beam is retro-reflected by an optical phase conjugate mirror, wavefront distortions induced by a phase object are removed after re-crossing this object [2, 3]. In this presentation, we use two counter-propagating filaments to create a conjugate mirror with air as a non linear medium [4]. We demonstrate that it operates differently from a usual conjugate mirror. With a filament conjugate mirror, the reflected signal has essentially a perfect spatial mode independent of the initial probe beam profile. © 2013 IEEE
Study Of Laser Induced Plasma Grating Dynamics In Gases
The relaxation of a plasma grating resulting from the interference of two crossing laser filaments in molecular and atomic gases is studied experimentally. Dissipation of the grating fringes is dominated by ambipolar diffusion in atomic gases and by a combination of ambipolar diffusion and collision-assisted free electron recombination in molecular gases. A theoretical model of the grating evolution is developed and compared to experimental results. Good agreement with simulations allows extracting plasma properties such as electron density, diffusion and recombination coefficients in Ne, Ar, Kr, Xe, N2, O2, CO2 and air at atmospheric pressure. © 2013 Elsevier B.V