Zhou Yun-Song

Effects of interplay between metal subwavelength slits on extraordinary optical transmission

In this paper we study the extraordinary optical transmission of one-dimensional multi-slits in an ideal metal film. The transmissivity is calculated as a function of various structural parameters. The transmissivity oscillates, with the period being just the light wavelength, as a function of the spacing between slits. As the number of slits increases, the transmissivity varies in one of three ways. It can increase, attenuate, or remain basically unchanged, depending on the spacing between slits. Each way is in an oscillatory manner. The slit interaction responsible for the oscillating transmission strength that depends on slit spacing is the subject of more detailed investigation. The interaction most intuitively manifests as a current distribution in the metal surface between slits. We find that this current is attenuated in an oscillating fashion from the slit corners to the center of the region between two adjacent slits, and we present a mathematical expression for its waveform.

Investigation of ultra-thin ferromagnetic films with a simple cubic lattice

Using Greens function method, we investigate ferromagnetic films with a simple cubic lattice containing up to ten monolayers. The Hamiltonian includes the Heisenberg exchange term, surface anisotropy (SA) and dipole interaction (DI). We calculate the magnetization as a function of temperature and film thickness and we analyse the behaviour of spin canting. The result is in agreement with experiments. We calculate phase diagrams of SA versus DI to show the conditions under which spontaneous magnetization can occur. As a special case, we discuss the Heisenberg model without SA and DI.

Numerical Confirmation of Multi-Reflections of Light Inside a Subwavelength Metal Slit Structure

The propagation behavior of light passing through a subwavelength metal slit structure is usually modeled by a Fabry-Perot (FP) resonant cavity based on the feature of transmission spectra. However, this mechanism belongs to a conjecture and it should be proven. We present a direct evidence from the numerical simulations of the amplitude distribution of the magnetic field by employing the time-domain simulation method. The light propagation behavior clearly shows a multi-reflection process inside a subwavelength slit as soon as it enters the slit. An analytical formula for calculating the field distribution involving the multi-reflection process is presented, and the theoretical calculations agree with the numerically simulated results. Our results provide explicit evidence that the FP model is reasonable to the description of the propagation process of light inside a subwavelength slit structure.

Ultra-narrow bandwidth optical filters consisting of one-dimensional photonic crystals with anomalous dispersion materials

We present a new type of optical filter with an ultra-narrow bandwidth and a wide field-of-view (FOV). This kind of optical filter consists of one-dimensional photonic crystal (PC) incorporating an anomalous-dispersion-material (ADM) with, for instance, an anomalous dispersion of 6P(3/2) <- 6S(1/2) hyperfine structure transition of a caesium atom. The transmission spectra of optical filters are calculated by using the transfer-matrix method. The simulation results show that the designed optical filter has a bandwidth narrower than 0.33GHz and a wide FOV of +/- 30 degrees as well. The response of transmission spectrum to an external magnetic field is also investigated.

Magnetization of Coupled Ultrathin Ferromagnetic Films

The magnetization of coupled ferromagnetic films is calculated by Greens function method. The coupling can either be ferromagnetic or antiferromagnetic. For the latter case, a concept of pseudo-spin is suggested to make calculation possible. A pseudo-spin is actually an anti-spin with its properties being analogue to other known anti-particles such as a hole. The decreasing of Curie point as the coupling strength decays is computed. It is noted that with the same strength, antiferromagnetic coupling has higher Curie point than ferromagnetic coupling.

Correspondence between oscillations and emitted photon closed-orbits in spontaneous emission rate of an atom near a dielectric slab

We study the oscillations in the spontaneous emission rate of an atom near a dielectric slab. The emission rate is calculated as a function of system size using quantum electrodynamics. It exhibits multi-periodic oscillations. Four frequencies of the oscillations are extracted by Fourier transforms. They agree with actions of photon closed-orbits going away and returning to the atom. These oscillations are explained as manifestations of quantum interference effects between the emitted photon wave near the atom and the returning photon waves travelling along various closed-orbits.

Characteristics of Spontaneous Emission of Polarized Atoms in Metal–Dielectric Multiple Layer Structures

The spontaneous emission (SE) progress of polarized atoms in a stratified structure of air–dielectric(D0)–metal(M)–dielectric(D1)–air can be controlled effectively by changing the thickness of the D1 layer and rotating the polarized direction of atoms. It is found that the normalized SE rate of atoms located inside the D0 layer crucially depends on the atomic position and the thickness of the D1 layer. When the atom is located near the D0–M interface, the normalized atomic SE rate as a function of the atomic position is abruptly onset for the thin D1 layer. However, with the increasing thickness of the D1 layer, the corresponding curve profile exhibits plateau and stays nearly unchanged. The substantial change of the SE rate stems from the excitation of the surface plasmon polaritons in metal-dielectric interface, and the feature crucially depends on the thickness of D1 layer. If atoms are positioned near the D0–air interface, the substantial variation of the normalized SE rate appears when rotating the polarized direction of atoms. These findings manifest that the atomic SE processes can be flexibly controlled by altering the thickness of the dielectric layer D1 or rotating the orientation of the polarization of atoms.

Interface Effects on the Magneto-Optical Kerr Effect and Optical Properties in Co/Ni Multilayer

The influence of interfaces on the magneto-optical Kerr effect in the Co/Ni multilayer has been investigated. It was found that the magnetic-optical Kerr rotation varies with the numbers of interfaces (x) in the Co/Ni multilayer, which indicated that the interface states play an important role in the Kerr effect. Moreover, ellipticity and optical constants n and k are also found to vary with x. Some possible mechanisms have been discussed.