Applied Optical Imaging Techniques with Nonlinear Optical Source Development
Open Access
- Author:
- Ghosh, Atriya
- Graduate Program:
- Electrical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- August 07, 2020
- Committee Members:
- Zhiwen Liu, Dissertation Advisor/Co-Advisor
Iam-Choon Khoo, Committee Member
Xingjie Ni, Committee Member
Saptarshi Das, Committee Member
Saptarshi Das, Outside Member
Kultegin Aydin, Program Head/Chair
Zhiwen Liu, Committee Chair/Co-Chair - Keywords:
- fiber laser
holography
digital holography
optical imaging
nonlinear optics
second harmonic generation
TMD
2D materials
ultrafast lasers
Spectroscopy
autocorrelation
autocorrelator - Abstract:
- As N. R. Narayana Murthy once said, ‘Engineering and Technology is all about the power to make life better for people, to reduce cost and to improve productivity’. One such technology that completely embodies this philosophy is the area of Optical Imaging. In the past decade, Optical imaging technology has progressed in leaps and bounds, forever fueled by mankind’s desire to see things far smaller, farther, and faster than could be perceived with the naked eye. In this thesis, the power of experimental linear and non-linear optical imaging techniques is combined with digital computational reconstruction to quantitative imaging and characterization. For linear imaging, a digital holographic microscope is demonstrated, capable of single-shot, sub-nanometer topography measurement and subsequently demonstrated a digital holographic method that can quantitatively image two-dimensional materials, such as transitional metal dichalcogenide (TMD) MoS2 and WS2. We can holographically image a monolayer sample of ~0.6nm thickness, quantify its complex refractive index, as well as predict the number of layers contained within a thick flake, all with one single capture. A Bland-Altman analysis was performed to compare our experimental results with the standard Atomic Force Microscopy (AFM) measurements, yielding a limit of agreement < ±5 nm for samples with thickness ranging from 15-60 nm. Furthermore, we perform simulations to study how the thickness of the SiO2 layer of the substrate housing the 2D material, as well as the laser wavelength influence the amplitude and phase response of a two-dimensional material. For non-linear imaging, a femtosecond, high-powered, broadly wavelength tunable optical excitation source capable of stable turn-key operation is demonstrated. The laser source is a combination of an Yb-doped fiber laser based on all normal dispersion mechanism and a high power double clad Ytterbium fiber based optical amplifier. We harness the phenomenon of soliton self frequency shift and pulse division to make this source broadly tunable.