Monolayers with closely packed molecules of amphiphilic EuTTA deposited on plasmonic metal demonstrate bright luminescence in contrast with diluted systems and theoretical predictions of full quenching. In order to better understand the role of intermolecular interactions and surface plasmons, we study the spontaneous emission in EuTTA ultra-thin films in dielectric and plasmonic environment. The emission kinetics in systems with closely packed emitters strongly differs from that in diluted emitters. The kinetics and spectra are very sensitive to the environment. Using multilayered structures, we were able to enhance the magnetic to electric dipole transition branching ratio by more than order of magnitude.
Quantum ghost imaging can be an important tool in making optical measurements. One of the most useful aspects of ghost imaging is the unique ability to correlate two sets of independently collected information. We aim to use the principles of ghost imaging to build out a 3-dimensional microscope which utilizes detection from two imaging detectors that simultaneously capture entangled light. Further advancements and application of this relatively new imaging method depends on understanding the limits of the optical system. What quality should we expect? Can we image out-of-focus objects? How long do we need to expose? For ghost imaging, these answers are not so obvious. This is because entangled light sources are atypical: the light profile, frequency distribution, and intensity, for instance, all depend on an assortment of parameters associated with how the entangled light was generated. While we cannot practically explore the extent of this configuration space, we present here an exploration of a very accessible range. We show in which ways a commonly used bulk non-linear crystal can alter the imaging capabilities. In this study, we utilize a pair of state-of-the-art, single-photon avalanche diode (SPAD) array detectors. Thus, we also use this study as an opportunity to demonstrate the capabilities of these detectors in their use for ghost imaging applications.
Fluorescence microscopy has become integral to biological studies for the technique’s ability to elucidate structures of biomolecules for in-situ studies with high selectivity and specificity. Imaging of intrinsic indicators, such as fluorescent amino acids in proteins, provides important information, but can be challenging to accomplish. Current microscopy techniques that measure native fluorescence without the use of exogenous labels involve either direct UV excitation which is commonly non-localized and can be detrimental to the system, or multiphoton absorption which must be conducted at high intensities, therefore posing high risks of photodamage. As such, we seek to investigate an efficient way to gently excite native fluorescence in biological systems in a way that overcomes these limitations. Quantum entangled photon pairs generated via spontaneous parametric downconversion (SPDC), may be an alternative to conducting two-photon absorption (TPA) to excite fluorescence in amino acids without the high fluences currently used. These photon pairs are highly correlated in time. Thus, the arrival of one photon is simultaneously followed by the arrival of its sister photon. As a result, a molecule interacting with the photon pair should simultaneously absorb both photons, leading to a linear two-photon absorption rate, and the linearity of the two-photon process should dramatically reduce the light intensity necessary for TPA. Therefore, quantum entangled photon pairs offer the possibility of performing low intensity UV excitation using photons in the visible wavelength range. With this work, we generated and characterized entangled photons generated via SPDC, and investigated whether fluorescent amino acids can be excited, and the subsequent fluorescence induced with entangled two-photon absorption. Results show that much higher entangled two-photon rates than what are currently available are needed to measure significant signals with entangled two-photon excitation.
Electrochromic polymers incorporated into plasmonic systems provide a possibility to control plasmonic properties with the applied voltage. Using gold-polyaniline (PANI) bilayers, we study the effect of coloration switching on surface plasmon polaritons propagating at the PANI-gold interface. The width of the resonance, magnitude of the plasmon wave-vector and dielectric permittivity of PANI are estimated as the function of the applied voltage.
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