Génération d'ondes TeraHertz par Différence de Fréquence

THz-waves extend from the far InfraRed (15 μm – 20 THz) to radio waves (3000 μm – 0.1 THz). Current sources based on thermal (Mercury lamps…), electronics (Gunn diode...) or optics (laser, antennas…) technologies can’t cover this wide spectral range for applications in spectroscopy and imaging. An alternative is provided by parametric nonlinear optics, which leads to the generation of THz waves from Difference Frequency Generation (DFG) by injecting one or two lasers in a nonlinear crystal. To better cover the wide THz domain, it is necessary to determine nonlinear crystals with optical properties leading to the generation of such waves with high conversion efficiencies.This PhD thesis is devoted to the study of these properties for a panel of nonlinear crystals, along with experimental results of THz generation from DFG between two monochromatic lasers in the nanosecond and picosecond regimes, or between two Fourier components within a femtosecond laser. We selected twenty new crystals never studied before in the THz domain, along with the organic crystal of BNA. We measured their transmission spectra from visible to THz, and their nonlinear properties including phase-matching conditions and conversion efficiency.Le domaine des ondes TeraHertz (THz) s’étend de l’infrarouge lointain (15 μm / 20 THz) aux ondes radios (3000 μm / 0.1 THz). La couverture spectrale des sources actuelles, qu’elles soient thermique (lampes à mercure…), électronique (diode Gunn…) ou optique (laser, antennes…), ne permet pas de répondre à l’ensemble des applications en spectroscopie et en imagerie. Une alternative à ces sources est l’optique non linéaire paramétrique, qui permet de générer des ondes THz à partir du processus de Différence de Fréquences (DFG), et qui consiste à injecter un ou deux lasers dans un cristal non linéaire. Afin de couvrir au mieux le très large domaine THz, il est nécessaire de déterminer un ensemble de cristaux dont les propriétés optiques permettent de générer ces ondes avec de forts rendements de conversion.Le travail présenté dans ce manuscrit de thèse décrit l’étude de ces propriétés pour un ensemble de cristaux non linéaires, ainsi que des résultats expérimentaux de génération THz à partir de la DFG entre deux lasers monochromatiques en régime nanoseconde et picoseconde, ou entre deux composantes de Fourier au sein d’une impulsion laser femtoseconde. Nous avons sélectionné vingt nouveaux cristaux jamais étudiés dans le domaine THz auparavant, ainsi que le nouveau cristal organique de BNA. Nous avons mesuré leurs spectres de transmission du visible au THz, ainsi que les propriétés optiques non linéaires incluant les conditions d’accord de phase et le rendement de conversion

TeraHertz Waves Generation from Difference Frequency Generation

Le domaine des ondes TeraHertz (THz) s’étend de l’infrarouge lointain (15 μm / 20 THz) aux ondes radios (3000 μm / 0.1 THz). La couverture spectrale des sources actuelles, qu’elles soient thermique (lampes à mercure…), électronique (diode Gunn…) ou optique (laser, antennes…), ne permet pas de répondre à l’ensemble des applications en spectroscopie et en imagerie. Une alternative à ces sources est l’optique non linéaire paramétrique, qui permet de générer des ondes THz à partir du processus de Différence de Fréquences (DFG), et qui consiste à injecter un ou deux lasers dans un cristal non linéaire. Afin de couvrir au mieux le très large domaine THz, il est nécessaire de déterminer un ensemble de cristaux dont les propriétés optiques permettent de générer ces ondes avec de forts rendements de conversion.Le travail présenté dans ce manuscrit de thèse décrit l’étude de ces propriétés pour un ensemble de cristaux non linéaires, ainsi que des résultats expérimentaux de génération THz à partir de la DFG entre deux lasers monochromatiques en régime nanoseconde et picoseconde, ou entre deux composantes de Fourier au sein d’une impulsion laser femtoseconde. Nous avons sélectionné vingt nouveaux cristaux jamais étudiés dans le domaine THz auparavant, ainsi que le nouveau cristal organique de BNA. Nous avons mesuré leurs spectres de transmission du visible au THz, ainsi que les propriétés optiques non linéaires incluant les conditions d’accord de phase et le rendement de conversion.THz-waves extend from the far InfraRed (15 μm – 20 THz) to radio waves (3000 μm – 0.1 THz). Current sources based on thermal (Mercury lamps…), electronics (Gunn diode...) or optics (laser, antennas…) technologies can’t cover this wide spectral range for applications in spectroscopy and imaging. An alternative is provided by parametric nonlinear optics, which leads to the generation of THz waves from Difference Frequency Generation (DFG) by injecting one or two lasers in a nonlinear crystal. To better cover the wide THz domain, it is necessary to determine nonlinear crystals with optical properties leading to the generation of such waves with high conversion efficiencies.This PhD thesis is devoted to the study of these properties for a panel of nonlinear crystals, along with experimental results of THz generation from DFG between two monochromatic lasers in the nanosecond and picosecond regimes, or between two Fourier components within a femtosecond laser. We selected twenty new crystals never studied before in the THz domain, along with the organic crystal of BNA. We measured their transmission spectra from visible to THz, and their nonlinear properties including phase-matching conditions and conversion efficiency

Phase-Matching Conditions and Refined Sellmeier equations up to the near-infrared for THz generation in BNA

International audienc

DFT calculations of Ti-based molecules clustering with Ar for laser-based enrichment of stable isotopes

Within PRISMAP, the European medical radionuclides program, we are investigating the possible enrichment of titanium and calcium stable isotopes by means of Separation of Isotopes by Laser Assisted Retardation of Condensation (SILARC). Titanium or calcium-containing molecules are injected in a gas cell containing argon as a buffer gas and released via a nozzle creating a supersonic jet. The temperature drops to ∼15K, at which point argon atoms cluster around the molecules. If an isotopomer can be selectively excited by an infrared laser, the clusterization can be prevented and the molecule experiences a drag force through the jet, physically separating it from the clusters. As a first step in this development, Density Functional Theory (DFT) calculations have been performed on titanium-containing molecules, to determine the ground-state configuration of the molecules (geometry and spin state), their interaction with Ar, and to calculate the frequencies of their vibrational modes as a function of Ti isotope. Isotope-selective transitions were identified, mostly in the mid-infrared region. In this contribution, the results from those calculations for simple molecules (TiFx (x=1−4)) and complex molecules (Ti[OEt]4, Ti[OPr]4, C10H2TiF12O4) are reported

Phase-Matching Conditions and Refined Sellmeier equations up to the near-infrared for THz generation in BNA

International audienc

Design and characterisation of Photoswitches for picosecond electric pulses generation at very low temperature

International audienc

Refined Sellmeier equations up to the near-infrared in the organic N-benzyl-2-methyl-4-nitroaniline (BNA) crystal

International audienc

Quadratic nonlinear optical properties of the organic N-benzyl-2-methyl-4-nitroaniline (BNA) biaxial crystal

International audienc

In‐Source High‐Resolution Spectroscopy Using an Integrated Tunable Raman Laser

Tunable single-frequency lasers are the most prominent tool for high-resolution spectroscopy, allowing for the study and exploitation of the electronic structure of atoms. A significant milestone relies on the demonstration of integrated laser technology for performing such a task. The device presented here is composed of a compact Fabry–Perot monolithic resonator capable of producing tunable and Fourier-limited nanosecond pulses with a MHz-class frequency stability without active cavity stabilization elements. It also has the remarkable capability of exploiting the Raman effect to funnel efficiently the broad spectrum of an input laser to a spectrally-bright Stokes pulse at hard-to-access wavelength ranges. The targeted atom for the demonstrations is 152Sm, released as an atomic vapor in a hot cavity environment. Here, the Stokes field is tuned to a wavelength of 433.9 nm, while a crossed-beams spectroscopy setup is used to minimize the Doppler broadened spectral features of the atoms. With this work, the suitability of integrated diamond Raman lasers as a high-resolution in-source spectroscopy tool is demonstrated, enabling many applications in atomic and nuclear physics. The integrated form-factor and inherent simplicity makes such a laser an interesting prospect for quantum-technology based sensing systems and related applications

Génération THz par différence de fréquences optiques en accord de phase

National audienc