Half-plane diffraction in a case of oblique incidence

Abstract

The classical problem of half-plane diffraction is examined in a particular case of oblique incidence. A scalar solution to the problem is proposed using boundary diffraction wave theory and some limitations of the solution are discussed.     

Intrinsic optical bistability in doped polymer

One of the most interesting and applicable effects of nonlinear optics is optical bistability. This phenomenon is exhibited by certain resonant optical structures where it is possible to have two stable steady transmission states for the device, depending on the history of the input. Such a bistable device may be useful for optical computing elements as a result of its memory characteristics. Optical bistability behaviour is usually observed by inserting a nonlinear matter inside a Fabry–Perot interferometer. But in this study, it was shown that this can be achieved without the application of any optical resonator. Two laser beams were used to interact with the photorefractive media (doped PMMA polymer) which resulted in the bistability of the intensity of transmitted wave. Feedback was provided by a periodic grating created in the photorefractive polymer PMMA.     

Intrinsic optical bistability in layered crystals

The parametric excitation of the low-frequency overtone in GaSe crystal by a biharmonic optical field is shown to lead to bistability of both the crystal refractive index and the optical field generated in the four-wave-mixing process. The effect appears to be much stronger in layered crystals than in crystals of higher symmetry.     

Optical bistability in vertical-cavity semiconductor optical amplifiers

We present an overview of the properties and applications of optical bistability in vertical-cavity semiconductor optical amplifiers (VCSOAs). The basic physics and analytical models of this optical nonlinearity are discussed. Experimental results obtained from a VCSOA operated in the 850 nm wavelength region are presented. Counterclockwise hysteresis loops are obtained over a range of initial phase detuning and bias currents. One hysteresis loop is observed experimentally with an input power as low as 2 muW when the device is biased at 98% of its lasing threshold. Numerical simulations based on the Fabry-Perot resonator model and rate equations we developed show good agreement with our experimental observations. In addition, a low input intensity high contrast (10:1) optical and gate and 2R regeneration are demonstrated. We believe that bistable VCSOAs can significantly advance the prospect of a dense two-dimensional array of low-switching-intensity all-optical logic and memory elements.     

Phase optical bistability in structures with surface plasmons

A theoretical analysis is made of the phenomenon of phase optical bistability in structures with surface plasmons. It is shown that in an optical waveguide with a nonlinear layer, not only amplitude but also phase bistability may occur when p-polarized radiation is reflected from the nonlinear waveguide. Pis’ma Zh. Tekh. Fiz. 24, 60–65 (August 26, 1998)     

Protection effectiveness of an oblique plate against a long rod

Protection effectiveness of an oblique metallic plate against a long rod projectile has been evaluated through a three-dimensional dynamic finite element computer program. The parameters considered in the simulations are the impact velocity, oblique plate thickness, gap distance between oblique plate and witness block, and obliquity. It was found that protection performance of an oblique plate was maximized in case that the ratio of line-of-sight (LOS) plate thickness to projectile diameter is around 2.0. This result may be used as a guide for the design of obliquely spaced armour structures against long rod projectiles.     

Optical properties of a slightly absorbing film for oblique incidence

Approximate equations are derived for calculating the transmittance and reflectance of a slightly absorbing film when radiation is incident at an arbitrary angle. These formulas are compared with those derived from wave optics. Examination of the real and the imaginary parts of the complex phase change and the complex angle of refraction shows the simple equations to be consistent with the wave-optics formulation under the assumption that the imaginary part of the refractive index of the film is much smaller than its real counterpart.     

Scattering by a dense finite layer of infinite cylinders at oblique incidence

This paper presents the scattering solution for a finite dense layer of cylinders irradiated by an arbitrarily polarized plane wave at a general incident direction. The theoretical formulation utilizes the effective field approach and quasi-crystalline approximation to derive the governing equations for the propagation constant and amplitudes of the effective waves. The finite layer thickness gives rise to effective waves propagating in both the forward and backward directions inside the dense medium. Formulas are developed for the far-field coherent and incoherent scattered intensities, as well as the extinction and scattering cross sections of the dense layer. The forward peak of the incoherent scattered intensity is shown to be shifted to the propagating direction of the effective waves. The influence of incident direction, layer thickness, and solid volume fraction on the scattering properties is illustrated by means of a numerical example.     

The scattering of oblique flexural waves of a cracked conducting plate in a uniform magnetic field

Summary Following a classical plate bending theory for magneto-elastic interactions under quasistatic electromagnetic field, we consider the scattering of time harmonic flexural waves by a through crack in a conducting plate under a uniform magnetic field normal to the crack surface. It is assumed that the plate has the finite electric conductivity, and the electric and magnetic permeabilities of the free space. An incident wave giving rise to moments symmetric about the crack plane is applied in an arbitrary direction. Fourier transform method is used to solve the mixed boundary value problem which reduces to a pair of dual integral equations. These dual integral equations are further reduced to a Fredholm integral equation of the second kind. The dynamic moment intensity factor versus frequency for several values of incident angle is computed and the influence of the magnetic field on the normalized values is displayed graphically.     

Surface plasmon-assisted optical bistability in the quantum dot-metal nanoparticle hybrid system

We theoretically investigated optical bistability (OB) of a coupled excition–plasmon hybrid system in a unidirectional ring cavity. It is found that the threshold and the region of OB can be tuned by adjusting the center–center distance between the quantum dot and metal nanoparticle (MNP), the Rabi frequency of the control field and the radius of the MNP. Due to the significantly enhanced optical nonlinearity by the surface plasmon effect, the threshold of OB can be decreased greatly when the probe field is parallel to the major axis of the hybrid system. The enhanced OB may have promising applications in optical switching and optical storage.     

Modification of the electrical and optical properties of hydrated vanadium pentoxide as a result of proton electromigration

Variation of the optical and electrical properties of films of hydrated vanadium pentoxide under the action of an applied electric field was studied. The samples exhibited an “internal” electrochromic effect caused by a redistribution of hydrogen ions in the film, rather than by their penetration from outside (electrolyte). The process of cathodic polarization at a current of I～10^?5 A for t～10 min is accompanied by a local increase in the hydrogen concentration (confirmed by direct measurements of the ionic conductivity), leading to a change in the optical properties. This is manifested by an increase in the transmission coefficient in the longwave spectral region and by a shift of the absorption edge (at hν=2.3 eV) toward greater wavelengths. According to the IR spectroscopy data, this is also accompanied by some increase in the water content in colored regions of the V₂O₅·nH₂O film.     

Broadband high-reflection multilayer coatings at oblique angles of incidence

The angular properties of various wideband high reflectors are investigated. The theory is developed for the design of high reflectors based on contiguous quarter-wave stacks for use at one oblique angle or for a range of angles of incidence. Numerical results are presented for several high reflectors designed to have a high reflectance in the 0.4-0.8-mum spectral region for use at 50 degrees and with angles of incidence ranging between 0 degrees and 50 degrees . A random error perturbation analysis shows that such layer systems can be produced experimentally.     

Water penetration fronts in thin films deposited at oblique incidence

Water penetration spots in thin films deposited at oblique incidence are shown to be nearly elliptical in shape. Water spreads laterally at greatest speed in the direction normal to the plane of incidence of the evaporant molecules. The ratio of the maximum and minimum speeds increases with the angle of incidence of the vapour and, for magnesium fluoride, is about 1.5 for an angle of 60°. The primary cause of the anisotropic water penetration effect is believed to be self-shadowing which occurs during the deposition of thin films, leading to a columnar microstructure with intermediate voids which act as sinks for penetrating liquids.     

The optical bistability of polarisation in B5NH4 crystal caused by the optical Kerr effect

We present experimental results concerning the polarisation optical bistability in the B₅NH₄ crystal together with an attempt of its theoretical explanation based on third-order optical nonlinearity and Fresnel's boundary conditions. In our experiments a strong laser beam is transmitted through a crystal plate of B₅NH₄. The polarisation state of the transmitted light depends in a bistable way on the intensity of the incident light.     

Tunable beam focusing based on optical bistability with a composite Kretschmann configuration involving a Kerr medium

A beam focuser with a composite Kretschmann configuration involving a Kerr medium is investigated theoretically. The structure employs a silver film with four slits filled with the Kerr medium. Optical bistability and beam focusing are demonstrated, and changes to the incident intensity result in optical bistability characteristics in the reflection, focused intensity, spot size, and depth of focus. The proposed structure has the potential to be applied for optical switching and nano-illumination.     

4x4 ray matrix for a curved chirped grating at oblique incidence

The general 4x4 ray matrix of a grating is presented. This matrix suits the cases of transmission and reflection by a chirped grating with curved lines lying on a curved interface. The matrix presented applies to the general oblique incidence of the optical axis and therefore to nonorthogonal cases and to conical diffraction.     

Controllable optical bistability and Fano line shape in a hybrid optomechanical system assisted by kerr medium: possibility of all optical switching

We theoretically analyse the optical and optomechanical nonlinearity present in a hybrid system consisting of a quantum dot(QD) coupled to an optomechanical cavity in the presence of a nonlinear Kerr medium, and show that this hybrid system can be used as an all optical switch. A high degree of control and tunability via the QD-cavity coupling strength, the Kerr and the optomechanical nonlinearity over the bistable behaviour shown by the mean intracavity optical field and the power transmission of the weak probe field can be achieved.The results obtained in this investigation has the potential to be used for designing efficient all-optical switch and high sensitive sensors for use in Telecom systems.     

Modification of the structure of Bessel beams under oblique incidence

The stability of a Bessel beam generated via an annular slit on the focal plane of a convergent lens as a function of the angle of incidence of a plane wave into the slit was measured. Although the paraxial approximation, along with an infinite lens assumption, predicts that the only change in the Bessel beam should be a displacement, experimental results showed that other slight changes were present. It was shown numerically that the way to take into account those changes is to abandon the quadratic phase approximation for the lens. Good agreement was then found between the experimental data and the numerical simulation.