Quantum Optical Applications in Spectroscopy: Investigations of Entangled Two-Photon Absorption and Entangled Two-Photon Excited Fluorescence in Organic Dendritic Systems.

Abstract

Entangled states of light have been utilized successfully in a wide variety of experiments and applications. This dissertation will discuss the application of entangled states of light toward spectroscopy wherein entangled pairs of photons generated via the process of spontaneous parametric down-conversion (SPDC) are utilized to excite entangled two-photon absorption (ETPA) in organic molecules. An enhancement of the brightness of the SPDC entangled photon source under focused pumping conditions is discussed for the purpose of maximizing the entangled-pair flux available in these experiments. The entangled-pair flux utilized in ETPA experiments, however, still constitutes approximately 10 orders of magnitude fewer photons than any classical counterpart requires. Further, the effects of various conditions under which entangled photons are generated via the process of SPDC, specifically the phase-matching conditions and their resulting impact on the interaction of said photons with matter is presented. It is shown that spatial indistinguishability of entangled photons generated via SPDC is a necessary requirement for ETPA in organic nonlinear optical materials. Investigations of the ETPA response of a wide range of organic dendritic materials with differing geometry, donor-acceptor strength, and charge-transfer character are also presented, where it was observed that materials whose classical TPA cross-section is attributed to a dipole transition, without involvement of an intermediate state, were nearly transparent to entangled photons. In addition, the premiere demonstration of fluorescence from an organic dendrimer subsequent to two-photon excitation by entangled pairs of photons is presented. A novel, high geometric efficiency, spherically-enclosed optical collection system for collection of fluorescence photons is introduced, which is utilized to circumvent any drawbacks related to the weak quantum yield of the organic materials, and it is observed that the dependence of the rate of fluorescence collected from the material on the entangled excitation flux follows that of the ETPA response of the material. This is the first ever demonstration of the ETPEF phenomenon in any kind of material, and these novel results have widespread impact in applications ranging from spectroscopy to chemical and biological sensing, where the demonstration of the ETPEF phenomenon enables advancement in fields such as quantum imaging and microscopy.