This PhD project aims at investigating how biphoton fields can enhance nonlinear imaging.
It has been predicted that the temporal correlations between twin photons generated by parametric down-conversion can significantly increase the two-photon absorption cross-section . In the presence of a resonant nonlinearity, such as two- photon absorption in a fluorophore or a semiconductor, biphoton states are absorbed with a cross-section orders of magnitude higher than classical radiation at the same wavelength. This concept is currently being tested experimentally and is one of the most exciting topics in quantum imaging also due to the possibility it entails of improving bioimaging.
This PhD project expands on such concept exploring the impact of biphotons on the real, rather than the imaginary part of optical nonlinearities.
The down-converted field is composed only of photon pairs (biphotons) that are strongly correlated in space and time. For this reason, under proper conditions, they effectively behave as a single particle for the light-matter interaction [2,3]. As a consequence, they can be absorbed with a cross-section approaching that of one-photon processes yet being in a transparent spectral region of the material. The PI is currently engaged with colleagues further to develop this aspect of quantum imaging.
The very same concept is expected to hold also for other two-photon processes, such as those underpinning parametric interactions in χ(3) media, e.g., self and cross-phase modulation, parametric amplification, and Raman scattering.
The objective of this project is to investigate the biphoton-induced enhancement of the Kerr nonlinearities for nonlinear imaging applications.
Phase front correction by (nonlinear) phase conjugation typically requires counterpropagating beams and long interaction lengths, which translate in bulky setups and narrowband operation. We have reported high phase-conjugation conversion efficiencies using a single-pump scheme in graphene , transparent conductive oxides  and, more recently in strongly coupled plasmonic systems at the epsilon-near-zero condition . This last system shall be investigated to understand how biphotons excite plasmonic resonances and to quantify the enhancement induced by the use of nonclassical radiation in the efficiency of phase conjugation. The first application we plan to investigate is phase-front correction based on phase conjugation.
Similar plasmonic systems can be employed for enhanced spectroscopy, e.g., mediated by the Raman nonlinearity or for all- optical switching, e.g. using the strong nonlinearities in transparent semiconductors . We shall further investigate the enhancement biphotons can provide to spectroscopy and ultrafast switching.
The cases discussed above are only examples, and a broader phenomenology and applications are expected to be uncovered by the study of biphoton enhanced nonlinearities.
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How to Apply: Please refer to the following website for details on how to apply:
Funding is available to cover tuition fees for UK applicants for 3.5 years, as well as paying a stipend at the Research Council rate (estimated £15,245 for Session 2020-21).
How good is research at University of Glasgow in Chemistry?
(joint submission with University of Strathclyde)
FTE Category A staff submitted: 30.80
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