Generation and Optimization of Ultrafast Terahertz (THZ) Radiation using Femtosecond Lasers
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Abstract
Terahertz radiation occupies the electromagnetic region between the microwave and infrared bands and is widely used in time-domain spectroscopy, material characterization, imaging and ultrafast control experiments. The availability of stable femtosecond laser systems has made it possible to generate coherent single-cycle and few-cycle THz pulses through photoconductive switching, optical rectification, plasma generation and spintronic emission. However, THz output is highly sensitive to pump pulse duration, fluence, repetition rate, focusing geometry, nonlinear medium, antenna structure, phase matching, absorption and detection alignment. An analytical and parameter-sweep based research design was prepared. The optimization framework considered photoconductive antenna emission and nonlinear optical rectification as the principal source pathways, with comparative discussion of air plasma and spintronic sources. Input variables included laser wavelength, pulse duration, pump fluence, beam size, antenna bias, crystal type, crystal thickness, pulse-front tilt, collection optics and detection method. The analysis showed that femtosecond laser pulse duration and pump fluence are dominant parameters for bandwidth and output amplitude, while velocity matching and absorption determine the usable interaction length in optical rectification. Photoconductive antennas are suitable for compact broadband laboratory systems at moderate field strength, whereas tilted pulse-front lithium niobate is advantageous for high-field, lower-frequency single-cycle output.
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