Date of Award
2021
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Physics and Astronomy
Committee Chair
Lingze Duan
Committee Member
Don A. Gregory
Committee Member
Seyed Sadeghi
Committee Member
Patrick John Reardon
Committee Member
Gang Wang
Research Advisor
Lingze Duan
Subject(s)
Ultrashort laser pulses, Optical spectroscopy, Optical fiber detectors, Time-wavelength optical sampling (TWOS) spectroscopy
Abstract
Real-time optical spectroscopy capable of tracking fast and rare events has attracted considerable interest in recent years due to its potential to significantly impact the study of chemical and biological reaction dynamics. However, the development of such capabilities faces major challenges in terms of instrument response time, spectral resolution, and power sensitivity. In this dissertation, a new spectroscopy method called time-wavelength optical sampling (TWOS) spectroscopy is proposed, analyzed, and experimentally demonstrated. This method combines the advantages of time-stretch spectroscopy (TSS) and ultrafast optical sampling, and offers several key benefits over conventional TSS based on direct power measurement. By developing a comprehensive set of analytical tools and experimental apparatus, this work demonstrates, both theoretically and experimentally, that TWOS is a promising technique for achieving real-time spectroscopy with high spectral resolution and enhanced power sensitivity. From a theoretical perspective, the effects of fiber dispersion and nonlinearity on linear pulse stretching are investigated. Numerical solutions of the nonlinear Schrödinger equation (NSE) are used to evaluate the impact of third-order dispersion and self-phase modulation. These results guide experimental design to ensure a linear wavelength-to-time mapping. Experimentally, a TWOS spectrometer based on optical sampling by cavity tuning (OSCAT) is constructed from the ground up, and its performance is systematically optimized. Ultimately, a sub-GHz (714 MHz) spectral resolution at 1550 nm, a 2 kHz update rate, and a 10–15 dB improvement in power sensitivity over conventional TSS are achieved. These capabilities make TWOS a highly promising approach for high-resolution, real-time spectroscopy.
Recommended Citation
Soundararajan, Srikamal Jaganraj, "Time wavelength optical sampling spectroscopy" (2021). Dissertations. 501.
https://louis.uah.edu/uah-dissertations/501