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Identifier 000421542
Title Enhanced Terahertz emission from ultrafast laser ablated Gallium Arsenide devices
Alternative Title Ενισχυμένη εκπομπή THz από GaAs με φωτοαποδόμηση από υπερβραχείς παλμούς
Author Μαργιολάκης, Αθανάσιος
Thesis advisor Τσιρώνης, Γεώργιος
Abstract In this thesis research, is presented the study and development of the first photoconductive antenna for generating Terahertz (THz), made of a Gallium Arsenide (GaAs) substrate, treated with femtosecond laser pulses, demonstrating increased performance compared to non-ablated antennas. Ripples are observed on the surface of the device after the laser ablation and we assume they are responsible for the increased performance. They are studied theoretically and experimentally, in order to explain this behavior. For the first time, a theoretical model is made to study GaAs ultrafast dynamics under irradiation of femtosecond laser pulses. In this model, energy balance equations are used to explain the ultrashort time-scales and evolution of dynamics. They are resolved numerically due to their coupled non-linear complexity, while the stability of the solution is ensured. Evolution of carrier density, electron and lattice temperature are the measured variables in order to obtain the thermal response of GaAs. The optical properties with dependence to fluence and pulse duration of the laser are studied, namely reflectivity and dielectric constant. The ripple wavelength is numerically calculated from our model and compared to our experimental data. The material’s damage threshold dependence on laser pulse duration was also calculated. A parametric analysis based on the properties of the ablation laser pulse and how it affects the ripples was performed and the measured properties are the applied power intensity, the overlapping area on each spot, polarization angle and number of pulses per spot. In the last chapter, using THz-TDS setup, the laser ablated GaAs antenna is measured for its THz generation performance and compared to a non-ablated antenna. Despite higher THz efficiency the following I-V measurements of the photocurrent, return lower values. To explain this discrepancy, an Optical Pump THz Probe (OPTP) setup is used to measure the excited carrier lifetime and photoconductivity. Complementary, Fourier Transform Infrared (FTIR) measurements are performed, to confirm higher photo-absorption and Hall Effect measurements are made for measuring the level of doping, sheet concentration and carrier mobility.
Language English
Subject Ablation
Laser photoconductive
Αρσενίδιο του Γαλλίου
Κεραία υπερβραχείς
Issue date 2019-03-18
Collection   Faculty/Department--Faculty of Sciences and Engineering--Department of Physics--Doctoral theses
  Type of Work
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