Lorentz Nanoplasmonics for Nonlinear Generation.

While past works have suggested that the Lorentz magnetic contribution to second harmonic generation from metal nanostructures is negligible as compared to other terms, here we demonstrate a dominant Lorentz contribution from T-shaped apertures in a gold film. The apertures are designed to have overlapping magnetic and electric near-field intensities at the plasmonic resonance. This gives 65% greater nonlinear generation from the Lorentz term than the sum of the other two terms. We demonstrate this effect experimentally by milling of nanoapertures of different size and orientation in a metal film and measuring their second harmonic generation. Good agreement is seen between the experiments and comprehensive calculations. In the development of highly efficient nonlinear metasurfaces, careful optimization of the Lorentz contribution should be considered in addition to all other contributions. Following the approach of this work, the Lorentz contribution may also be optimized for THz generation.

Characterization of Individual Magnetic Nanoparticles in Solution by Double Nanohole Optical Tweezers.

We study individual superparamagnetic Fe3O4 (magnetite) nanoparticles in solution using a double nanohole optical tweezer with magnetic force setup. By analysis of the trapping optical transmission signal (step size, autocorrelation, the root-mean-square signal, and the distribution with applied magnetic field), we are able to measure the refractive index, magnetic susceptibility, remanence and size of each trapped nanoparticle. The size distribution is found to agree well with scanning electron microscopy measurements, and the permeability, magnetic susceptibility and remanence values are all in agreement with published results. Our approach demonstrates the versatility of the optical tweezer with magnetic field setup to characterize nanoparticles in fluidic mixtures with potential for isolation of desired particles and pick-and-place functionality.

Systematic review and meta-analysis of extended high-frequency audiometry in tinnitus patients.

BACKGROUND: This study aimed to systematically evaluate the detection effect of extended high-frequency audiometry (EHFA) in tinnitus patients and provide a theoretical basis for the clinical diagnosis of tinnitus. METHODS: We conducted a computer-based search for randomized controlled trial (RCT) literature on extended audiometry in tinnitus patients using the PubMed, Web of Science, China National Knowledge Infrastructure (CNKI), and Elsevier Science Direct databases. The search dates ranged from the database establishment date to February 2020. Risk of bias in the included literature was evaluated using the RCT bias risk assessment standard provided in the Handbook for Systematic Reviews for Interventions (version 5.0.2, 2008, Chapter 9). Finally, Review Manager 5.3 software was used to conduct a meta-analysis of the included literature. RESULTS: The retrieved literature was systematically screened. A total of 10 RCTs were included in the meta-analysis, which involved a total of 1,389 tinnitus patients. The results of the meta-analysis showed that at the frequencies of 14 kHz and 16 kHz, there was visible difference in detection rate of hearing threshold (DR-HT) between the 2 groups [odds ratio (OR) =0.21, 95 confidential interval (CI): 0.14-0.32, Z=7.29, P<0.00001] and (OR =0.14, 95% CI: 0.07-0.27, Z=5.96, P<0.00001) respectively. When the frequency was 18 kHz, there was a significant statistical difference in DR-HT between the 2 groups (OR =0.13, 95% CI: 0.07-0.24, Z=6.50, P<0.00001), and at 20 kHz, the statistically significant difference in DR-HT between the 2 groups was high (OR =0.17, 95% CI: 0.12-0.23, Z=10.38, P<0.00001). DISCUSSION: EHFA had a critical effect on tinnitus patients. The meta-analysis provided evidence for early hearing loss in tinnitus patients. EHFA played a crucial role in the clinical diagnosis of tinnitus patients.

Nanorod Surface Plasmon Enhancement of Laser-Induced Ultrafast Demagnetization.

Ultrafast laser-induced magnetization dynamics in ferromagnetic thin films were measured using a femtosecond Ti:sapphire laser in a pump-probe magneto-optic Kerr effect setup. The effect of plasmon resonance on the transient magnetization was investigated by drop-coating the ferromagnetic films with dimensionally-tuned gold nanorods supporting longitudinal surface plasmon resonance near the central wavelength of the pump laser. With ~4% nanorod areal coverage, we observe a >50% increase in demagnetization signal in nanorod-coated samples at pump fluences on the order of 0.1 mJ/cm(2) due to surface plasmon-mediated localized electric-field enhancement, an effect which becomes more significant at higher laser fluences. We were able to qualitatively reproduce the experimental observations using finite-difference time-domain simulations and mean-field theory. This dramatic enhancement of ultrafast laser-induced demagnetization points to possible applications of nanorod-coated thin films in heat-assisted magnetic recording.