Génération, caractérisation et applications d’impulsions lasers intenses de quelques cycles optiques du visible jusqu'à l’infrarouge moyen
|Abstract:||The topic of this thesis lies in the field of the ultrafast intense laser science and technology. An historical review of this vast field is presented as an introduction. The carrier-envelope phase stabilized Ti:sapphire laser system of Professor Witzel's laboratory is then explained in details. The optical parametric amplifier and the difference frequency generation module reaching the mid-infrared are also presented. The first chapter of original scientific content presents in great details a variable gate width polarization gating technique that was developed in the laboratory. Four birefringent quartz wedges were used together with an achromatic quarter wave plate to produce polarization gated few cycle laser pulses. The central part of each pulse is linearly polarized and the wings are circularly polarized. This technique was used to study resonant multiphoton ionization of xenon. We show that it is possible to excite the Rydberg 5g state of xenon with an effective pulse that is shorter than one optical cycle. Electric dipole quantum selection rules confine the excitation process to the polarization gate duration. The three following chapters are mainly about the design of setups to characterize and optimally compress few cycle laser pulses. We first present the second harmonic frequency-resolved optical gating (SHG-FROG) setup that was developed to retrieve the intensity profiles and the spectral and temporal phases of few cycle Ti:sapphire laser pulses. The white light interferometer that was built to measure the dispersion of several optical components is then exposed. Its main purpose is to characterize the chirped mirrors used to compress few cycle pulses. The reverse engineering of commercial chirped mirrors that led us to the development, the production and the characterization of our own designs is then presented. A systematic method to optimally compress femtosecond laser pulses with the optimization of the angle of incidence of chirped mirrors is then presented. This method was inspired by the realizations of the three previous chapters. An ongoing project in our research group is the production of intense mid-infrared laser pulses to generate coherent high-order harmonics in the X-ray regime. A general method to characterize arbitrary complex infrared pulses was thus developed. It is based on four-wave mixing between a Ti:sapphire few cycle pulse and an infrared pulse. The resulting signal is close to the second harmonic band of the Ti:sapphire pulse and it is proportional to the intensity of the infrared pulse. An heterodyne version of this technique was also tried, but the results were disappointing mainly because the shot-to-shot carrier-envelope phase stabilization of the infrared source is insufficient over the duration of the measurement. The last chapter of this thesis thus investigates the absolute phase stability of our infrared sources. Most specifically, we found a strong coupling between the pulse energy and the measured phase from a f-2f nonlinear interferometer relying on supercontinuum generation in sapphire. We present the measured energy-phase coupling coefficients from 800 to 1940 nm.|
|Document Type:||Thèse de doctorat|
|Open Access Date:||20 April 2018|
|Collection:||Thèses et mémoires|
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