Comptes Rendus de l'Académie des Sciences - Series IV - Physics-Astrophysics最新文献

We review recent advances, both experimental and theoretical, that have furthered our understanding of many-body effects in laser excited semiconductors and their heterostructures. They manifest themselves in two classes of phenomena. The first are observed in the coherently driven electron–hole pair system generated during and immediately after laser excitation before dissipation is turned on. The second are the effects electron–phonon and electron–electron scattering that drive the non-Markovian behavior of relaxation processes seen following laser excitation.

Traditional optics and nonlinear optics are related to laser–matter interaction with eV characteristic energy. Recent progresses in ultrahigh intensity makes it possible to drive electrons with relativistic energy opening up the field of relativistic nonlinear optics. In the last decade, lasers have undergone orders-of-magnitude jumps in peak power, with the invention of the technique of chirped pulse amplification (CPA) and the refinements of femtosecond techniques. Modern CPA lasers can produce intensities greater than 10²¹ W/cm², one million times greater than previously possible. These ultraintense lasers give researchers a tool to produce unprecedented pressures (terabars), magnetic fields (gigagauss), temperatures (10¹⁰ K), and accelerations (10²⁵ g) with applications in fusion energy, nuclear physics (fast ignition), high-energy physics, astrophysics, and cosmology. They promote the optics field from the eV to the GeV.

Application of time-resolved femtosecond spectroscopy to the investigation of the ultrafast electron kinetics in metallic materials is reviewed. The main experimental techniques are presented and the results obtained on electron scattering processes discussed in bulk metals and nanoparticles, focusing on the energy redistribution processes (electron–electron and electron–phonon coupling) and electronic transport. Application of the femtosecond techniques to the investigation of the acoustic vibrations of metal films and nanoparticles is also presented.

We propose a combination of 4Pi and Theta microscopies to improve the resolution of fluorescence microscopy by using six microscope objectives in a configuration we call Multiple Objective Microscopy (MOM). A resolution in the 100 nm range is obtained in the three dimensions using low numerical aperture, long working distance objectives. The obtained results not only show that high resolution is not restricted to high numerical aperture objectives, but also open the possibility of exploring large volumes with a very good resolution.

The complete characterization of a short light pulse requires the measurement of the value of the electric field as a function of time, or conversely, as a function of the optical frequency. Many different techniques have been demonstrated for this purpose. They fall in two main categories, whether a known reference pulse whose spectrum encompasses that of the unknown pulse is available or not. In the first case, linear techniques such as time-domain or frequency-domain interferometry can be directly used, with the advantage of a high sensitivity. In the latter case, non-stationary filters can be implemented using optical non-linearities, in techniques such as Frequency Resolved Optical Gating (FROG) or Spectral Phase Interferometry for Direct Electric-field Reconstruction (SPIDER).

Femtosecond X-ray science is a new frontier in ultrafast research in which time-resolved measurement techniques are applied with X-ray pulses to investigate structural dynamics at the atomic scale on the fundamental time scale of an atomic vibrational period (∼100 fs). This new research area depends critically on the development of suitable femtosecond X-ray sources with the appropriate flux (ph/(s·0.1% BW)), brightness (ph/(s·mm²·mrad²·0.1% BW)), and tunability for demanding optical/X-ray pump probe experiments. In this paper we review recently demonstrated techniques for generating femtosecond X-rays via interaction between femtosecond laser pulses and relativistic electron beams. We give an overview of a novel femtosecond X-ray source that is proposed based on a linear accelerator combined with X-ray pulse compression.