Recently, the biological sensors based on surface plasmon resonance (SPR) have been highly investigated due to their versatile application in the field of medicine and pharmacy. In this study, we introduce a Kretschmann based sensor including a BK7 prism, gold, Pb5Ge3O11 (PGO) and graphene layers. The special optical properties of the ferroelectric PGO layer plays a key role on improving the sensor performance. Initially the sensing sample is considered to be water where the sensor is sensitive to the refractive index changes of the sensing medium, Δn=0.005 (RIU), connected to outer layer. The structure sensitivity and the figure of merit (FOM) obtained as 228.22 (Deg/RIU) and 22.36 (1/RIU) at the wavelength of 632.8nm, respectively, which are higher than conventional structures properties. The main goal of the introduced sensor is to detect hypothyroidism caused by deficiency of thyroid hormones that is directly related to lack of hemoglobin level in the human body. According to the relationship between hemoglobin concentration and refractive index of blood, the sensor can be used to diagnostic tool. Also, by replacing blood profile of healthy people and patients into sensor structure some characteristics such as FWHM and reflectivity is obtained. Eventually, any impairment in refractive index of blood due to disease is recognizable with this group of sensors. For example, the achieved FWHM and reflectivity are 10.4308 (Deg) and 0.4739 (a.u) for healthy people and 10.3862 (Deg) and 0.4482 (a.u) for patients, respectively.
In this work, we theoretically investigate optical bistability and optical response of a hybrid system consisting of semiconductor quantum dot (SQD) coupled with a vanadium dioxide nanoparticle (VO2NP) in the infrared (IR) regime. The VO2 material exists in semiconductor and metallic phases below and above the critical temperature, respectively where the particle optical properties dramatically change during this phase transition. In our calculations a filling fraction factor controls the VO2NP phase transition when the hybrid system interacts with a laser field. We demonstrate that the switch-up threshold for optical bistability is strongly controlled by filling fraction without changing the structure of the hybrid system. Also, it is shown that, the threshold of optical bistability increases when the VO2NP phases changes from semiconductor to metallic phase. The presented results have the potential to be applied in designing optical switching and optical storage.
We numerically investigate the electromagnetically induced transparency (EIT) of a hybrid system consisting of a three-level quantum dot (QD) in the vicinity of vanadium dioxide nanoparticle (VO2NP). VO2NP has semiconductor and metallic phases where the transition between the two phases occurs around a critical temperature. When the QD-VO2NP hybrid system interacts with continuous wave laser fields in an infrared regime, it supports a coherent coupling of exciton–polariton and exciton–plasmon polariton in semiconductor and metal phases of VO2NP, respectively. In our calculations a filling fraction factor controls the VO2NP phase transition. A probe and control laser field configuration is studied for the hybrid system to measure the absorption of QD through the filling fraction factor manipulations. We show that for the VO2NP semiconductor phase and proper geometrical configuration, the absorption spectrum profile of the QD represents an EIT with two peaks and a clear minimum. These two peaks merge to one through the VO2NP phase transition to metal. We also show that the absorption spectrum profile is modified by different orientations of the laser fields with the axis of the QD-VO2NP hybrid system. The innovation in comparison to other research in the field is that robust variation in the absorption profile through EIT is due to the phase transition in VO2NP without any structural change in the QD-VO2NP hybrid system. Our results can be employed to design nanothermal sensors, optical nanoswitches, and energy transfer devices.
Gold and silver plasmonic nanoparticles (NPs) are widely used as a contrast agent for photoacoustic (PA) imaging, taking advantage of the strong optical absorption cross-section of these particles due to their localized surface-plasmon resonance. Inspired by recent developments in ultra-high frequency wide-bandwidth transducers, we propose utilizing off-resonance ultrashort laser sources with a pulse width in the femtosecond (fs) and picosecond (ps) range to increase the efficiency of PA imaging. Also, from the fact that the laser pulse duration is shorter than the heat diffusion time of the materials, we expect practically no collateral damage of the laser irradiated biological tissues. Our preliminary studies show that irradiating the NPs with an ultrashort-pulsed laser has the potential to achieve substantially higher efficiency at generating the PA signal. Enhanced by the presence of NPs, the laser field causes a highly localized plasma nucleation around the vicinity of the NPs. Plasma relaxes through electron-ion interaction and releases a pressure wave in the surrounding medium. However, in this process, it is crucial to precisely control the heat energy absorption in the NPs to avoid their fragmentation. In this talk we present a model to simulate an optimized plasma–mediated PA signal dynamics generated from off-resonance ultrashort laser excitation (λ =800 nm, τ = 70 fs – 2 ps) of a variety of plasmonic NPs with sizes ranging from 50 nm to 100 nm.
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