Effect of Film Thickness on the Far- and Near-Field Optical Response of Nanoparticle-on-Film Systems

<p>We study the near-field and far-field optical response of nanoparticle-on-film systems using single-nanoparticle spectroscopy and numerical simulations. We find that the optical spectra contain three dominant modes - a transverse dipole and quadrupole mode, and a dominant vertical antenna mode. We vary the thickness of the metal film from 10 – 45 nm, and find that the vertical antenna mode wavelength is nearly independent of the film thickness. In contrast, we find that the associated near-field enhancement in the gap between the particle and the film strongly depends on the film thickness. This trend is also observed in the far-field where the vertical antenna mode strongly increases in amplitude for increasing film-thicknesses up to the skin depth of gold. These findings are in good agreement with a numerical model and pave the way to study field-mediated processes such as fluorescence, SERS, and localized chemistry at the same resonance wavelength but at varying degrees of field enhancement.</p>

Effect of Film Thickness on the Far- and Near-Field Optical Response of Nanoparticle-on-Film Systems

<p>We study the near-field and far-field optical response of nanoparticle-on-film systems using single-nanoparticle spectroscopy and numerical simulations. We find that the optical spectra contain three dominant modes - a transverse dipole and quadrupole mode, and a dominant vertical antenna mode. We vary the thickness of the metal film from 10 – 45 nm, and find that the vertical antenna mode wavelength is nearly independent of the film thickness. In contrast, we find that the associated near-field enhancement in the gap between the particle and the film strongly depends on the film thickness. This trend is also observed in the far-field where the vertical antenna mode strongly increases in amplitude for increasing film-thicknesses up to the skin depth of gold. These findings are in good agreement with a numerical model and pave the way to study field-mediated processes such as fluorescence, SERS, and localized chemistry at the same resonance wavelength but at varying degrees of field enhancement.</p>

USRP 2901 Based FM Transceiver with Large File Capabilities in Virtual and Remote Laboratory

The radio signal processing capability can be provided by Universal software radio peripheral (USRP) hardware. The received signal frequency can be controlled and transmitting the signal through wireless is possible by installing NI USRP utility configuration. The programmable USRP was running VI snippet program in block diagram panel with radio companion integrated through USB cable on windows 7 64 bit OS. With the parameters such as IQ rate, transmitter gain, carrier frequency along with device name which is given as ni2901_1 the students can able to tune the radio signal. In addition to this the students can able to record the FM signal and extract the IQ data and plot the spectrum of signal and analyze it using graph palette. The standard FM equation contains the modulation index, carrier frequency, message signal amplitude, frequency deviation and frequency sensitivity can also analyzed using LabVIEW. By using Carson’s rule the bandwidth of wideband FM signal can be calculated. In this project RF0 module is used USRP device is connected with dual band vertical antenna with 2.4 and 5GHz frequency as Tx1 and the receiver is connected to Tri band vertical antenna with 144, 400 and 1200 MHz. while transmitting red color will blink in the device for transmitting and green color indicates the received signal. The purpose of doing this experiment was to gain experience in signal processing and receive hands on experience with the USRP. This VI snippet program will support all file formats. Up sample we used in front panel should be -1 always and if large size files is transmitted the value should be increased. The iPhone received the signal with high quality using ear pods the students can able to listen all the information which is transmitted through USRP. Here the transmitted frequency we used in the front panel is 94.7 MHz. The transmitted signal through USRP is successfully tested in the campus of Institute of Aeronautical Engineering, Hyderabad, India.

Application of Genetic Algorithm to Estimation of Function Parameters in Lightning Currents Approximations

Genetic algorithm (GA) is applied for the estimation of two-peaked analytically extended function (2P-AEF) parameters in this paper. 2P-AEF is used for approximation of measured and typical lightning discharge currents. Lightning discharge channel is often modeled as thin-wire vertical antenna at perfectly conducting ground. Engineering lightning stroke models assume that the current along that channel is related to the channel-base current which may be measured at the instrumented tall towers and in triggered lightning experiments. Mathematical modeling of lightning currents is important in verification of lightning strokes models based on simultaneously measured electromagnetic fields at various distances, so as in lightning protection studies, computation of lightning induced effects and simulation of overvoltages in power systems. Typical lightning discharge currents of the first positive, first negative, and subsequent negative strokes are defined by IEC 62305 Standard based on comprehensive measurements. Parameters of 2P-AEF’s approximation of the typical negative first stroke current are determined by GA and compared to approximations obtained by other functions. Measured currents at Monte San Salvatore in Switzerland, at Morro de Cachimbo Station in Brazil, and in rocket-triggered lightning experiments at Camp Blanding in Florida are approximated by 2P-AEFs, and good agreement with experimentally measured waveshapes is obtained.