Upconversion nanoparticles (UCNPs) are luminescent nanoparticles that can absorb two or more photons and emit a single photon of a higher energy. In contrast to two photon absorption which involve virtual intermediate states, UCNPs have real metastable excited states that allow for multiphoton absorption. UCNPs are good candidates for bioimaging due to various advantages such as deep tissue penetration, excellent biostability, low cytotoxicity, and no autofluorescence.
My research is focused on the design and implementation of various measurements of cross-sections for entangled two-photon absorption, a process in which entangled photon pairs are used to excite two-photon transitions. Entangled two-photon absorption has shown promise for biological imaging at low excitation intensity, however the magnitude of the “quantum advantage” of the process needs further study.
My scientific interests cover an intersecting area of nonlinear optics, ultrafast laser spectroscopy, physical chemistry and quantum optics where a combination of diverse experimental methods can be employed together to obtain new insights about complex physical and biological systems.
Ralph’s interests are in experimental studies of dynamics in complex molecular systems. Over the years, he has worked on a wide range of areas where ultrafast spectroscopy is useful such as femtosecond dynamics of liquids, energy transfer in photosynthetic systems, protein-ligand interactions in antibodies, chromophore dynamics of fluorescent proteins. As part of his research, he has developed a number of optical and microfluidic technologies to advance experimental capabilities in liquid-phase chemical dynamics using time-resolved optical or laser-based x-ray techniques.
Since the isolation of the first naturally fluorescing protein from jelly fish in the 1960s, fluorescent proteins (FPs) have become integral to a wide range of biological/medical applications, allowing visualization of biomolecules and processes in living cells and tissues to a much greater degree than was previously possible. Extensive molecular engineering of naturally occurring FPs has led to several families of recombinant proteins tailored to specific biophysical and imaging purposes.
Our group is actively engaged at the interface of quantum optics with physical chemistry. In this research, we manipulate the properties of light at the single photon or few photon level. By employing “quantum engineered” light for spectroscopy, we aim to harness the remarkable quantum mechanical properties such as entanglement, superposition, and coherence in order to increase the sensitivity and information content of spectroscopy.
Physics Frontiers Centers (PFCs)
The Physics Frontiers Centers (PFC) program supports university-based centers and institutes where the collective efforts of a larger group of individuals can enable transformational advances in the most promising research areas. The program is designed to foster major breakthroughs at the intellectual frontiers of physics by providing needed resources such as combinations of talents, skills, disciplines, and/or specialized infrastructure, not usually available to individual investigators or small groups, in an environment in which the collective efforts of the larger group can be shown to be seminal to promoting significant progress in the science and the education of students. PFCs also include creative, substantive activities aimed at enhancing education, broadening participation of traditionally underrepresented groups, and outreach to the scientific community and general public. Read more about this program at the NSF website.