Improving nanoscale terahertz field localization by means of sharply tapered resonant nanoantennas

AbstractTerahertz resonant nanoantennas have recently become a key tool to investigate otherwise inaccessible interactions of such long-wavelength radiation with nano-matter. Because of their high-aspect-ratio rod-shaped geometry, resonant nanoantennas suffer from severe loss, which ultimately limits their field localization performance. Here we show, via a quasi-analytical model, numerical simulations, and experimental evidence, that a proper tapering of such nanostructures relaxes their overall loss, leading to an augmented local field enhancement and a significantly reduced resonator mode volume. Our findings, which can also be extended to more complex geometries and higher frequencies, have profound implications for enhanced sensing and spectroscopy of nano-objects, as well as for designing more effective platforms for nanoscale long-wavelength cavity quantum electrodynamics

Post-operative acute urinary retention after greenlight laser. Analysis of risk factors from a multicentric database

Purpose: Greenlight laser is a mini-invasive technique used to treat Benign Prostatic Obstruction (BPO). Some of the advantages of GreenLight photoselective vaporization (PVP) are shorter catheterization time and hospital stay compared to TURP. Post-operative acute urinary retention (pAUR) leads to patients' discomfort, prolonged hospital stay and increased health care costs. We analyzed risk factors for urinary retention after GreenLight laser PVP. Materials and methods: In a multicenter experience, we retrospectively analyzed the onset of early and late post-operative acute urinary retention in patients undergoing standard or anatomical PVP. The pre-, intra- and post-operative characteristics were compared betweene patients who started to void and the patients who developed post-operative urinary retention. Results: The study included 434 patients suitable for the study. Post-operative acute urinary retention occurred in 39 (9%). Patients with a lower prostate volume (P < .001), an adenoma volume lower than 40 mL (P < .001), and lower lasing time (P = .013) had a higher probability to develop pAUR at the univariate analysis. The multivariate logistic regression confirmed that lower lasing time (95% CI: 0.86-0.99, OR = 0.93, P = .046) and adenoma volume (95% CI: 0.89-0.98, OR = 0.94, P = .006) are correlated to pAUR. Furthermore IPSS ≥ 19 (95% CI: 1.19- 10.75, OR = 2.27, P = .023) and treatment with 5-ARI (95% CI: 1.05-15.03, OR = 3.98, P = .042) are risk factors for pAUR. Conclusion: In our series, post-operative acute urinary retention was related to low adenoma volume and lasing time, pre-operative IPSS ≥ 19 and 5-ARI intake. These data should be considered in deciding the best timing for urethral catheters removal

Subwavelength coherent control and coupling of light in plasmonic nanoresonators on dielectric waveguides

We report results on the possibility of subwavelength coherent control of light in coupled plasmonic nanoresonators on dielectric waveguides. Our calculations show that subwavelength regions of the plasmonic structure, spatially separated by a few nanometers, can be individually addressed by controlling the relative phase of the injected fields. We also show the complementary possibility to efficiently inject a guided mode into a planar dielectric waveguide by collecting the radiation emitted by wire-like and/or point-like sources, placed into the resonators. For example, this configuration provides a useful and powerful tool to control the emission of the localized sources such as stripes of fluorescent molecules or quantum dots placed in the gaps between the plasmonic structures. Possible applications of the considered study include plasmonic logic gates, integrated sensors for single-molecule fluorescence, and ready-to-use devices based on plasmonic single-photon sources. © 2013 Optical Society of America

Molding of Plasmonic Resonances in Metallic Nanostructures: Dependence of the Non-Linear Electric Permittivity on System Size and Temperature

In this paper, we review the principal theoretical models through which the dielectric function of metals can be described. Starting from the Drude assumptions for intraband transitions, we show how this model can be improved by including interband absorption and temperature effect in the damping coefficients. Electronic scattering processes are described and included in the dielectric function, showing their role in determining plasmon lifetime at resonance. Relationships among permittivity, electric conductivity and refractive index are examined. Finally, a temperature dependent permittivity model is presented and is employed to predict temperature and non-linear field intensity dependence on commonly used plasmonic geometries, such as nanospheres

Molding of Plasmonic Resonances in Metallic Nanostructures: Dependence of the Non-Linear Electric Permittivity on System Size and Temperature

In this paper, we review the principal theoretical models through which the dielectric function of metals can be described. Starting from the Drude assumptions for intraband transitions, we show how this model can be improved by including interband absorption and temperature effect in the damping coefficients. Electronic scattering processes are described and included in the dielectric function, showing their role in determining plasmon lifetime at resonance. Relationships among permittivity, electric conductivity and refractive index are examined. Finally, a temperature dependent permittivity model is presented and is employed to predict temperature and non-linear field intensity dependence on commonly used plasmonic geometries, such as nanospheres

Femtosecond laser-inscribed non-volatile integrated optical switch in fused silica based on microfluidics-controlled total internal reflection

We demonstrate a non-volatile optical power switch, fabricated by femtosecond laser inscription in a fused silica substrate, with switching operation based on microfluidics-controlled total internal reflection. The switch consists of crossed waveguides and a rectangular, high aspect ratio microfluidic channel, located at the waveguide crossing. The switching between total internal reflection and transmission at the channel wall is determined by the refractive index of the medium inside the channel. Femtosecond laser inscription allows for co-integration of low-loss optical waveguides and channels with smooth sidewalls and thus the fabrication of low insertion loss switches that are broadband and show low polarization dependent losses. The measured total internal reflection loss of the fabricated switch is about 1.5dB at the wavelength 1550 nm. The loss due to transmission through the channel filled with refractive index matching liquid is about 0.5 dB. Detailed finite difference time domain and beam propagation method simulations of the switch's performance indicate that the losses can be further reduced by optimizing its geometry, together with further adjusting the inscription parameters