Optics (physics.optics)

Abstract: Plasmonic optical nanoantennas offer compelling solutions for enhancing light-matter interactions at the nanoscale. However, until now, their focus has been mainly limited to the visible and near-infrared regions, overlooking the immense potential of the ultraviolet (UV) range, where molecules exhibit their strongest absorption. Here, we present the realization of UV resonant nanogap antennas constructed from paired rhodium nanocubes. Rhodium emerges as a robust alternative to aluminum, offering enhanced stability in wet environments and ensuring reliable performance in the UV range. Our results showcase the nanoantenna ability to enhance the UV autofluorescence of label-free streptavidin and hemoglobin proteins. We achieve significant enhancements of the autofluorescence brightness per protein by up to 120-fold, and reach zeptoliter detection volumes enabling UV autofluorescence correlation spectroscopy (UV-FCS) at high concentrations of several tens of micromolar. We investigate the modulation of fluorescence photokinetic rates and report excellent agreement between experimental results and numerical simulations. This work expands the applicability of plasmonic nanoantennas into the deep UV range, unlocking the investigation of label-free proteins at physiological concentrations.

Abstract: Resonant enhancement both in passive and active resonators is a well-known technique for boosting the efficiency of nonlinear frequency conversion at high repetition rates. However, this route has remained poorly explored for the generation of few-cycle broadband THz transients due to the inadequacy of typically employed nonlinear crystals. Here, we demonstrate that thin lithium niobate crystals are a promising platform to circumvent current difficulties. Using a 50-um thin lithium niobate plate intracavity of a compact high-power mode-locked thin-disk laser, we generate broadband THz pulses with a spectrum extending up to 3 THz at 44.8 MHz repetition rate, driven by 264 W of intracavity average power. This approach opens the door to efficient high-power single-cycle THz generation at high repetition rates, scalable to kilowatt-level driving power with low cost and complexity.

Abstract: In recent years, there has been notable advancement in programmable metasurfaces, primarily attributed to their cost-effectiveness and capacity to manipulate electromagnetic (EM) waves. Nevertheless, a significant limitation of numerous available metasurfaces is their capability to influence wavefronts only in reflection mode or transmission mode, thus catering to only half of the spatial coverage. To the best of our knowledge and for the first time, a novel graphene-assisted reprogrammable metasurface that offers the unprecedented capability to independently and concurrently manipulate EM waves within both half-spaces has been introduced in the THz frequency band.

Abstract: The joint design of the optical system and the downstream algorithm is a challenging and promising task. Due to the demand for balancing the global optimal of imaging systems and the computational cost of physical simulation, existing methods cannot achieve efficient joint design of complex systems such as smartphones and drones. In this work, starting from the perspective of the optical design, we characterize the optics with separated aberrations. Additionally, to bridge the hardware and software without gradients, an image simulation system is presented to reproduce the genuine imaging procedure of lenses with large field-of-views. As for aberration correction, we propose a network to perceive and correct the spatially varying aberrations and validate its superiority over state-of-the-art methods. Comprehensive experiments reveal that the preference for correcting separated aberrations in joint design is as follows: longitudinal chromatic aberration, lateral chromatic aberration, spherical aberration, field curvature, and coma, with astigmatism coming last. Drawing from the preference, a 10% reduction in the total track length of the consumer-level mobile phone lens module is accomplished. Moreover, this procedure spares more space for manufacturing deviations, realizing extreme-quality enhancement of computational photography. The optimization paradigm provides innovative insight into the practical joint design of sophisticated optical systems and post-processing algorithms.

Abstract: In this article, a spaser (surface plasmon amplification by stimulated emission of radiation) system consisting of a metal nanoparticle surrounded by a large number of quantum dots (QDs) is studied. Usually, the effect of electron-phonon interaction is neglected in the spaser related literature. But some gain media, attributed by the large Raman scattering cross-section, exhibit stronger electron-phonon interaction. No such study has been performed for a QD-based spaser. Hence, it warrants investigation of the same in spaser system. In the present work, we investigate the effects of electron-phonon interaction on a three-level QD-based spaser. We consider two types of interaction potentials, linear and quadratic, and analyze their effects individually. First, we focus on the linear electron-phonon interaction that perturbs the electrons present in the excited state. This yields a periodic steady-state number of localized surface plasmon (LSP). The accompanying analytic solution reveals that the population inversion of the gain medium depends on the linear potential strength (Frohlich constant) but does not affect the threshold of spaser considerably for the given numerical parameters. In addition to the LSP, phonons may be generated during this process, the temporal dynamics of which are also detailed. Initially, the number of phonons exhibit decaying periodic oscillations, whose amplitude depends on the strength of the electron-phonon interaction. Under continuous pumping, at later times, the number of phonons reaches a steady-state value, which may find application in realization of continuous phonon nanolasers. Further, the effect of the quadratic potential is studied phenomenologically by increasing the excited-state decay rate. This results in a large number of LSP and an intense spaser spectrum.