Wavefront shaping as a fundamental block for photonic interaction
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Authors
Tran, Quy Tuan Viet
Issue Date
2025-12
Type
Electronic thesis
Thesis
Thesis
Language
en_US
Keywords
Physics
Alternative Title
Abstract
A spatial light modulator is a powerful optical tool that enables modulation of the amplitude and phase profile of incident light with high complexity, accuracy, and speed. As a consequence, this wavefront shaping tool has been incorporated into many studies of various optical disciplines: nonlinear optics, quantum optics, biomedical microscopy, material science, etc. In this work, we present several studies that utilize the spatial light modulator's ability to manipulate light fields. Firstly, we perform phase retrieval through scattering media such that the output signal can be shaped at will. This study has strong application prospects for fiber telecommunication, fiber endoscopy, and biomedical imaging. Furthermore, building off of this work, we present a new method to generate line focus for biomedical microscopic purposes. Next, we utilize the spatial light modulator's ability to perform complex modulation to generate light carrying orbital angular momentum. These structured lights are then used for interactions with nonlinear crystals and ferroelectric materials to study new phenomena. As mentioned prior, a spatial light modulator possesses the ability to impart phase profiles onto incoming light fields with a response time of ~50 ms. This high speed allows us to probe the scattering medium with a large amount of input phase profiles, such that the linear transformation that links input and output signals can be calculated. One such scattering medium is multimode fiber, which has strong application potential in telecommunication and medical endoscopy. The measured linear transformation is called a transmission matrix. We propose a method to completely recover the transmission matrix of a multimode fiber without a reference beam. Our method leverages the correlation coefficient between neighbouring positions in the output speckle to perform phase correction. The result from our work indicates high accuracy and practicality. Expanding on the concept of using correlation coefficients for phase correction, we apply this principle to speckle fields at different propagational planes. As a result, we are able to precisely control interferences between positions along the axial direction, which allows for the generation of a line focus using wavefront shaping. This result has a strong implication for wide-field imaging behind biological tissues. We perform a demonstration of volumetric imaging behind a scattering medium using the generated line focus. Finally, we look at the nonlinear behaviour of Laguerre-Gaussian beams. These are light that carries orbital angular momentum due to their helical phase profiles. Previous studies have indicated the conservation of angular momentum in nonlinear processes. Here, we investigate the dynamics of this conservation of momentum through a combination of astigmatic transformation and second harmonic generation. Through an astigmatic transformation, which can be achieved via a tilted spherical lens or a pair of cylindrical lenses, a Laguerre-Gaussian beam is turned into a general Hermite-Laguerre-Gaussian beam. Second harmonic generation is a nonlinear process in which two photons of the same frequency are combined to create a new photon with twice the frequency, half the wavelength, and double the energy. We provide a detailed study into the combination of these two processes, which yields novel beam profiles with a strong dependency on the tilted angle of the spherical lens, the topological charge, and the radial mode of the input beam.
Description
December2025
School of Science
School of Science
Full Citation
Publisher
Rensselaer Polytechnic Institute, Troy, NY