Entanglement-Enhanced Bioimaging and Sensing

Citation

He, Manni (2024) Entanglement-Enhanced Bioimaging and Sensing. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/3zg0-4135. https://resolver.caltech.edu/CaltechTHESIS:02262024-021912071

Abstract

Studies of entangled light-matter interactions have been gaining momentum because of their potential applications in bioimaging and sensing. Entangled photons are predicted to linearize nonlinear optical processes and offer orders of magnitude of enhancement to the interaction cross sections. To investigate the validity of entanglement-enhanced bioimaging techniques, a continuous wave (CW)-powered, on-chip, broadband entangled light source based on periodically poled lithium tantalate (ppLT) was designed and characterized. This light source achieved femtosecond entangled correlation times comparable to classical ultrafast lasers with an unprecedented power of ~100 nW in near-infrared (NIR), which is a crucial first step toward fully integrated, thin-film lithium niobate (TFLN)-based, visible to NIR entangled photon sources. This light source was then used for subsequent spectroscopy/microscopy experiments to systematically investigate the feasibility of entanglement-enabled microscopy techniques such as entangled two-photon absorption (ETPA) microscopy and entangled fluorescence lifetime measurements. A novel method was developed to measure fluorescence from ETPA using a spectrotemporally resolved Michelson interferometer which is good at eliminating false signals due to one-photon absorption and scattering. Careful experimental attempts at detecting virtual-state mediated ETPA from rhodamine 6G (R6G) and resonance-enhanced ETPA from indocyanine green (ICG) were made, and the ETPA signals were found to be below the instrument detection limits and often masked by one-photon effects such as scattering and linear absorption. Instead, experimental upper bounds were placed on the ETPA cross sections of the studied molecules, with an emphasis on continued improvement of the light source and instrument detection limits. On-chip entangled fluorescence lifetime imaging microscopy (entangled-FLIM) has also been identified as a new future development focus. The feasibility of the technique was demonstrated via a proof-of-principle experiment which measured the fluorescence lifetime of ICG in various solvents. Using entangled photons produced from a CW laser, the lifetime measurement scheme achieved a temporal resolution of 50 ps and a minimum measurable lifetime of 365 ps, which can be used to distinguish most biologically relevant fluorophores in the corresponding wavelength range. This experiment is a critical first step toward scalable, high-throughput, wavelength-multiplexed, and on-chip FLIM or lifetime measurements which could be used in label-free health monitoring technologies.

Thesis Files