Fluorescence readout is uniquely powerful for biological assays and imaging because it combines the detection of specific biotargets with high spatial and temporal resolution. Recently, several strategies for the modulation in time of fluorescence emission have been proven useful to separate the target signal from constant background contributions. Here, we investigate the emission modulation of organic fluorophores located in the nanometric vicinity of plasmonically heated gold nanorods and apply it to a novel, all-optical homogeneous biosensing scheme. The combination of plasmonic heating and temperature sensitive molecular fluorescence enables the robust quantification of surface reactions.
The inclusion of self-steepening in the linear stability analysis of modulation instability (MI) leads to a power cutoff above which the MI gain vanishes. Under these conditions, MI in mid-IR waveguides is shown to give rise to the usual double-sideband spectrum, but with Raman-shaped sidelobes. This results from the energy transfer of a CW laser simultaneously to both Stokes and anti-Stokes bands in pseudo-parametric fashion. As such, the anti-Stokes gain matches completely the Stokes profile over the entire gain bandwidth. This remarkable behavior, not expected from an unexcited medium, is shown not to follow from a conventional four-wave mixing interaction between the pump and the Stokes band. We believe this observation to be of relevance in the area of Raman-based sensors which, in several instances, rely on monitoring small power variations of the anti-Stokes spectral component.
Pulse propagation in nonlinear waveguides is most frequently modeled by resorting to the generalized nonlinear Schrödinger equation (GNLSE). In recent times, exciting new materials with peculiar nonlinear properties, such as negative nonlinear coefficients and a zero-nonlinearity wavelength, have been demonstrated. Unfortunately, the GNLSE may lead to unphysical results in these cases since, in general, it does not preserve the number of photons and, in the presence of a negative nonlinearity, predicts a blue shift due to Raman scattering. In this paper, we put forth a modified GNLSE that can be used to model the propagation in media with an arbitrary, even negative, nonlinear coefficient. This novel photon-conserving GNLSE (pcGNLSE) ensures preservation of the photon number and can be solved by the same tried and trusted numerical algorithms used for the standard GNLSE. Finally, we compare results for soliton dynamics in fibers with different nonlinear coefficients obtained with the pcGNLSE and the GNLSE.
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