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Etude théorique et expérimentale des lasers solides bi-fréquences dans les domaines GHz à THz, en régime continu ou impulsionnel. Applications opto-microondes

Abstract : We explored some new features of single- and dual-frequency solid-state lasers oscillating in continuous-wave or pulsed regimes.
Firstly, we have developed some techniques to optimise the characteristics of pulsed lasers. (i) A weak modulation of the pump power made it possible to obtain a stable repetition rate with a relative stability of 10-6. (ii) The pulse duration was continuously controlled from ten nanoseconds to a few hundreds nanoseconds by three different methods : adjustment of the laser beam diameter in the absorber, adjustment of the pump beam diameter in the active medium, and, in particular, the use of forked eigenstates in a two-axis laser. Moreover, the forked eigenstates allows (iii) to increase the pulse energy by coherent addition of the pulses.
A compact two-frequency Nd:YAG−Cr:YAG laser with a beat note frequency continuously adjustable up to 2,7 GHz was demonstrated. The two-frequency pulses are ideal sources to meet various needs of applications such as the Doppler lidar-radar. Moreover, we show that two-frequency pulses at 1,55 μm can be obtained by using a new c-cut Co:ASL saturable absorber in an Er-Yb:glass laser. These pulses are perfectly adapted to free-space detection systems requiring eye safety. The coherence time of the beat note in these lasers was also studied : it is limited by the pulse duration. A new technique of modulating the pump power of a solid-state laser at frequencies close to its relaxation oscillation frequency was studied and made it possible to generate a beat note coherence from pulse to pulse.
Frequency conversion techniques using the nonlinear optical effects make it possible to obtain tunable two-frequency sources in the visible spectrum. Green and red two-frequency pulses were obtained by using different conversion techniques, intracavity or extracavity. A two-frequency THz source in the red spectrum was also obtained by doubling the frequencies of a two-frequency THz Er-Yb:glass laser using a mixed fan-out PPLN crystal. Applications to the generation of microwaves and submillimeter waves using these two-frequency sources in the visible spectrum are discussed.
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https://tel.archives-ouvertes.fr/tel-00410958
Contributor : Ngoc Diep Lai <>
Submitted on : Tuesday, August 25, 2009 - 12:40:53 PM
Last modification on : Tuesday, June 16, 2020 - 5:04:02 PM
Long-term archiving on: : Saturday, November 26, 2016 - 11:34:01 AM

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  • HAL Id : tel-00410958, version 1

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Ngoc Diep Lai. Etude théorique et expérimentale des lasers solides bi-fréquences dans les domaines GHz à THz, en régime continu ou impulsionnel. Applications opto-microondes. Physique Atomique [physics.atom-ph]. Université Rennes 1, 2003. Français. ⟨tel-00410958⟩

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