Signature of strong atom-cavity interaction on critical coupling

We study a critically coupled cavity doped with resonant atoms with metamaterial slabs as mirrors. We show how resonant atom-cavity interaction can lead to a splitting of the critical coupling dip. The results are explained in terms of the frequency and lifetime splitting of the coupled system.Comment: 8 pages, 5 figure

Novel biosensor for detecting Hemoglobin and its oxidation state based on nonreciprocity in a coupled waveguide system

We study the reflection of a tightly focused Gaussian beam off a near symmetric resonant tunneling structure comprising two identical coupled waveguides. The coupled waveguides are loaded on each side by a spacer layer and a high index prism. Reflection of a Gaussian beam from such a resonant structure is associated with beam distortion and even beam splitting. We start with the distortion of the beam profile for a symmetric structure as a function of various parameters of the system. The broken spatial symmetry is introduced through the reference channel on one side and the sample channel on the other side as spacer layers. We monitor the dip in the beam profile when the two channels are filled with the sample and the reference liquid. We show that presence and absence of hemoglobin and its oxygenation states can be quantified by looking at the beam profile dip. Our results may find applications in high resolution sensing

Substrate interaction mediated control of phase separation in FIB milled Ag-Cu thin films

Nanofabrication is an integral part of realization of advanced functional devices ranging from optical displays to memory devices. Focused ion beam (FIB) milling is one of the widely used nanofabrication methods. Conventionally, FIB milling has been carried out for patterning single-phase stable thin films. However, the influence of FIB milling on phase separation of metastable alloy films during subsequent treatments has not been reported. Here, we show how FIB milling of Ag-Cu thin films influences the separation process and microstructure formation during post-milling annealing. Phase-separated microstructure of the film consists of fine, randomly distributed Ag-rich and Cu-rich domains, whereas adjacent to milled apertures (cylindrical holes), we observe two distinctly coarser rings. A combination of imaging and analysis techniques reveals Cu-rich islands dispersed in Ag-rich domains in the first ring next to the aperture, while the second ring constitutes mostly of Ag-rich grains. Copper silicide is observed to form in and around apertures through reaction with the Si-substrate. This substrate interaction, in addition to known variables like composition, temperature, and capillarity, appears to be a key element in drastically changing the local microstructure around apertures. This current study introduces new avenues to locally modulate the composition and microstructure through an appropriate choice of the film-substrate system. Such an ability can be exploited further to tune device functionalities with possible applications in plasmonics, catalysis, microelectronics and magnetics

CuInS2 Nanosheet Arrays with a MoS2 Heterojunction as a Photocathode for PEC Water Splitting

Developing cost-effective noble metal-free co-catalysts as alternatives to platinum group metals is an impeccable strategy to enhance photoelectrochemical (PEC) water splitting. In this report, we successfully fabricated CuInS2 nanosheet array-based photocathode modified with CdS and co-catalyst MoS2 in a green approach to improve water splitting under solar irradiation. The visible light absorption of the modified hybrid photocathode (CIS/CdS/MoS2) was significantly enhanced due to introducing CdS and MoS2. Photoluminescence, impedance spectroscopy, and Mott-Schottky analysis depicted improved separation of excited electron-hole pairs, minimized resistance of charge transfer, and increased excited-state charge carrier concentration, resulting in increased photocurrent. Typical results indicated that composite photoelectrodes delivered higher photocurrent (−1.75 mA/cm2 at 0 V vs RHE) and HC-STH conversion efficiency (0.42% at 0.49 V vs RHE) than those of CIS and CIS/CdS photoelectrodes. This improved PEC performance is accredited to the synergetic impact of CdS in charge generation and transfer and MoS2 as a cocatalyst with active surface sites for proton reduction. This study not only reveals the promising nature of CuInS2-based light absorber photocathodes for solar energy utilization but also recommends the use of MoS2 as a cocatalyst for the proton reduction reactions for widespread applications in solar to hydrogen conversion

Coupling Strength Can Control the Polarization Twist of a Plasmonic Antenna

The far-field polarization of the optical response of a plasmonic antenna can be tuned by subtly engineering of its geometry. In this paper, we develop design rules for nano antennas which enable the generation of circular polarized light via the excitation of circular plasmonic modes in the structure. Two initially orthogonal plasmonic modes are coupled in such a way that a rotational current is excited in the structure. Modifying this coupling strength from a weak to a strong regime controls the helicity of the scattered field. Finally, we introduce an original sensing approach that relies on the rotation of the incident polarization and demonstrates a sensitivity of 0.23 deg·nm -1 or 33 deg·RIU-1, related to changes of mechanical dimensions and the refractive index, respectively. © 2013 American Chemical Society

Infrared spectroscopy of live cells from a flowing solution using electrically-biased plasmonic metasurfaces

Spectral cytopathology (SCP) is a promising label-free technique for diagnosing diseases and monitoring therapeutic outcomes using FTIR spectroscopy. In most cases, cells must be immobilized on a substrate prior to spectroscopic interrogation. This creates significant limitations for high throughput phenotypic whole-cell analysis, especially for the non-adherent cells. Here we demonstrate how metasurface-enhanced infrared reflection spectroscopy (MEIRS) can be applied to a continuous flow of live cell solution by applying AC voltage to metallic metasurfaces. By integrating metasurfaces with microfluidic delivery channels and attracting the cells to the metasurface via dielectrophoretic (DEP) force, we collect the infrared spectra of cells in real time within a minute, and correlate the spectra with simultaneously acquired images of the attracted cells. The resulting DEP-MEIRS technique paves the way for rapid SCP of complex cell-containing body fluids with low cell concentrations, and for the development of a wide range of label-free liquid biopsies. This journal is © The Royal Society of Chemistry