Detection and pulse shaping of continuous wave and pulsed broadband light

Date of Award

2021

Degree Name

M.S. in Electro-Optics and Photonics

Department

Department of Electro-Optics and Photonics

Advisor/Chair

Imad Agha

Abstract

Ultrafast optical spectroscopy is the branch of optical science that involves the use of a femto/pico/nanosecond pump as an excitation source, with a broadband probe (either white light or a supercontinuum source) that captures the spectral signatures of dynamic events as a function of frequency/wavelength. In these methods, while the pump pulse is responsible for a physical or chemical change of the sample, the delay between the pump and the probe allows for reconstruction of the time dynamics of the ultrafast process. By sending multiple pump-probe pairs with a successive (small) delays between them, the dynamics in either the transmission or reflection spectrum can be reconstructed; however, the observed sample has to be excited multiple times with pump pulse corresponding to the time-stamp determined by the delay. Repetitive excitation of a sample can result in damaging effects for a reversible process. On the other hand, the starting conditions will not be same each time pump-probe pair hits the material or sample under study for an irreversible process where different spots on a material or different specimen are used per pulse delay. This thesis offers a new, rather simple way of achieving dynamic transmission/reflection spectral characterization using state-of-the art electronics and parallel detection on commercial detector arrays. Rather than sending single pump-single probe signals for each time stamp, a single pump multiple probe technique is proposed: In this method, we excite a sample only once and read out transmission/reflection spectrum multiple times during the window in which the physical transformation under study occurs. To achieve this, an advanced light detection and pulse shaping techniques is required to achieve the requisite detection speed for this real-time detection. In this thesis, I present the starting blocks for a complete ultrafast real-time spectrometer, with focus on the electronic subsystem, which was the main challenge during the thesis effort.

Keywords

Electrical Engineering, Physics, Engineering, Detection, APD, Avalanche Photo Diodes, Transimpedance Amplifiers, TIA, Pulse Shaping, Peak Detection, Gated Integrator, Laser Clock Generation, Spectrometer

Rights Statement

Copyright © 2021, author.

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