Generation of intense terahertz radiation using optical rectification through lithium niobate and its nonlinear spectroscopy

Abstract

Terahertz phenomenology occurs in many crucial areas of Science. With photon energy in the meV range, THz radiation strikes a fine balance by having sufficient penetrating power while being non-destructive, making it superior in detection and spectroscopic techniques.

The objective of this thesis is hence to construct and demonstrate the efficiency of a Terahertz Time Domain Spectroscopy using a laser system with nominal center wavelength of 800nm and pulse duration of 35 femtosecond at 1kHz repetition rate. For the emission of Terahertz radiation, optical rectification through Lithium Niobate crystal using the tilted-pulse-front technique was employed. Free-Space Electro-Optic Sampling with ZnTe as the detection crystal was utilized to measure the THz radiation.

The peak electric field measured was approximately 70 times greater than an optimized setup which used a large aperture ZnTe Crystal as the emission crystal, hence showing the unparalleled optical-to-Terahertz conversion efficiency of optical rectification through Lithium Niobate.

Additionally, the Fabry Perot effect was eliminated by shortening the time window of the scan. Measurements were then zero-padded to improve the resolution of the corresponding Fourier spectrum. Finally, nonlinear spectroscopy was performed on two silicon wafers with different resistance. The measurements were then processed and the optical properties, such as the dielectric constants, were accurately determined.