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Development of Ytterbium Laser-based Terahertz Sources and Enhancing the Terahertz Emission of GaAs-based Photoconductive Antennas via the Nanodecoration of Their Surfaces by Pulsed-Laser-Deposited Gold Nanoparticles.


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Isgandarov, Elchin (2023). Development of Ytterbium Laser-based Terahertz Sources and Enhancing the Terahertz Emission of GaAs-based Photoconductive Antennas via the Nanodecoration of Their Surfaces by Pulsed-Laser-Deposited Gold Nanoparticles. Thèse. Québec, Doctorat en sciences de l'énergie et des matériaux, Université du Québec, Institut national de la recherche scientifique, 160 p.

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The science and technology of terahertz (THz) electromagnetic radiation has witnessed significant advances over the past few decades. For most of the 20th century, this part of the electromagnetic spectrum was modest due to the lack of tunable high-power sources and fast, sensitive detectors, thus dubbed the THz gap. Nowadays, we can count various techniques for the generation and detection of THz radiation. Among these techniques, photoconductive antennas (PCAs) are widely used devices for THz wave generation and detection. With their unique characteristics such as good shot-to-shot pulse stability of the radiated THz pulses, compactness, and relatively higher optical-to-THz conversion efficiency while pumping the lower optical pump power, PCAs have been used for a wide range of applications. The THz sources have become increasingly advanced over the past few decades, due to the increasing availability and commercialization of ultrafast Ti:Sapphire lasers generating femtosecond pulses at the central wavelength of 800 nm. Today, we can count many efficient THz sources and detectors that can be operated at the fundamental and secondary harmonic (SH) wavelengths of Ti:Sapphire laser. Recently, Ytterbium (Yb)-doped femtosecond lasers have become the main promising alternative to Ti:Sapphire light sources due to their obvious advantages of stability, compactness, and achieving higher average power levels with higher pulse repetition rates. In addition, relatively low cost, free maintenance, and higher heat transfer from the active medium to air make Yb lasers very attractive compared to Ti:Sapphire lasers. The latter advantages make Yb-lasers very attractive light sources for applications in THz technology. From this perspective, in this thesis, we explored the implementation of various THz sources driven by a femtosecond Yb laser oscillator delivered optical pulses at the fundamental and SH wavelengths of 1045 and 522 nm, respectively. Specifically, we first performed a series of comparative studies on two optical rectification THz sources excited by the fundamental pulses of the Yb laser at 1045. Then, the fabrication and characterization of the THz photoconductive sources were studied using the SHG of the Yb laser at 522 nm. In addition, considering one of the current limitations of the optical-THz conversion efficiency in conventional photoconductive sources, we presented a new method to improve their radiation efficiency. To this end, a systematic study of the THz radiation performance of photoconductive antennas (PCAs) decorated with various concentrations of NPs has been implemented under the excitation of 522 nm laser pulses. The novel pulsed laser deposition (PLD) method presented for the decoration of PCAs allows the density of the deposited NPs to be progressively adjusted over the excitation area, thus controlling the efficiency of the emitted THz pulses from the antenna. Therefore, the dependence of the THz radiation amplification of SI-GaAs PCAs on the variation of the Au-NPs concentration in the active excitation region has been demonstrated. Another advantage of PLD is its ability to direct the deposition of high-quality NPs in a large excitation area, which could be a novel solution to overcome the current limitations of generating higher-intensity THz pulses from large-aperture photoconductive antennas (LAPCAs). Furthermore, a new experimental approach for the generation of intense quasi-half-cycle THz pulses with variable polarization has been presented in this thesis. This experimental approach consists of using different thicknesses of phase masks on interdigitated large aperture photoconductive antennas (ILAPCA) having a specific design with alternating vertical and horizontal electrodes. Therefore, by changing the thickness of the phase mask, we can tune the polarization state of the radiated THz pulses from linear to quasi-circular on demand.

Type de document: Thèse Thèse
Directeur de mémoire/thèse: Ozaki, Tsuneyuki
Mots-clés libres: énergie; matériaux
Centre: Centre Énergie Matériaux Télécommunications
Date de dépôt: 31 août 2023 13:55
Dernière modification: 10 mars 2024 05:00
URI: https://espace.inrs.ca/id/eprint/13545

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