Noise reduction using mean shift algorithm for estimating 3D shape

Abstract

The technique to estimate the three-dimensional (3D) geometry of an object from a sequence of images obtained at different focus settings is called shape from focus (SFF). In SFF, the measure of focus — sharpness — is the crucial part for final 3D shape estimation. However, it is difficult to compute accurate and precise focus value because of the noise presence during the image acquisition by imaging system. Various noise filters can be employed to tackle this problem, but they also remove the sharpness information in addition to the noise. In this paper, we propose a method based on mean shift algorithm to remove noise introduced by the imaging process while minimising loss of edges. We test the algorithm in the presence of Gaussian noise and impulse noise. Experimental results show that the proposed algorithm based on the mean shift algorithm provides better results than the traditional focus measures in the presence of the above mentioned two types of noise.     

Aberration Tolerances Based on the Line Spread Function

Abstract

Approximate formulae are obtained for the influence of aberration on the image of an incoherent line, by a method corresponding to that used by Maréchal for the image of a point. The best forms of correction in the presence of higher-order aberrations, and the best focal planes, may be easily determined using tables of coefficients that are provided. For the case of asymmetric aberrations, the image shift to the diffraction focus is also simply found. This, and the tolerance formulae, also apply to the gradient of intensity in the image of an edge.     

Relative phase shift in laguerre-gaussian beams propagating through an apertured paraxial ABCD system

Abstract

Based on the generalized Huygens-Fresnel diffraction integral, closed-form expressions for the relative phase shift of Laguerre-Gaussian beams propagating through an apertured paraxial optical ABCD system are derived. The dependence of the relative phase shift on the beam and system parameters, and the condition for eliminating phase shift are analysed and illustrated with numerical examples.     

Direct Static Strain Measurement Utilizing Signal Fading and Spectrum Analysis in a Fibre Optic Interferometric Sensor

Abstract

An accurate linear method of static phase shift measurement in a fibre optic interferometric strain sensor, based on the concurrent utilization of signal fading, photovoltage spectrum analysis and the arctangent function, is presented. The static phase shift is superimposed on a controlled dynamic phase modulation derived from an optical phase modulator in one arm of the interferometer. Good agreement is demonstrated between the phase shift obtained through experiment and that from the theoretical expression. This detection scheme has wide applications to static and dynamic phase shift measurements in fibre optic interferometric sensors, and to optical interferometry in general.     

Confinement of Electrons to the Centre of a Laser Focus Via the Ponderomotive Potential

Abstract

The use of the ponderomotive potential to focus electrons into the centre of a laser focus, as discussed by Phillips and Sanderson in 1966, is examined for modern laser conditions. For a laser focus with a minimum along the beam axis, an electron is confined to the centre of the focus. Electron trajectories are obtained by solving the classical equations of motion in the presence of the ponderomotive potential. A method of creating a focus with a minimum at the centre is also discussed.     

Radiative frequency shift and linewidth of an atom dipole in the vicinity of a dielectric microsphere

Abstract

The frequency shift and linewidth variation of an oscillator placed next to a dielectric microsphere are found within the framework of the classical approach. Both the frequency shift and the linewidth are shown to be substantially dependent on the location of the atom and the size of the microsphere and are capable of reaching very high values near the surface of the microsphere under resonance conditions. Near microsphere resonance, a blue frequency shift is predicted, leading to repulsive forces between the atom and the dielectric microsphere.     

Observation of Lateral Displacement of an Optical Beam Enhanced by Surface Plasmon Excitation

Abstract

The lateral shift of a light beam suffering total reflection can be enhanced by the excitation of a surface plasmon wave. A shift of ?19 μm was obtained in one total reflection at the surface plasmon resonance. A characteristic double-peak structure was observed in the reflected field as predicted by theory.     

On a Structural Distortion Effect in the NMR Spectra of Alkali Fullerides

Abstract

An investigation is reported on a possible effect in the NMR-spectrum of the fee-alkali fullerides, caused by the off-centre displacements of the alkali cations. The effect consists in a slight, asymmetrical distortion of the NMR-lines of the tetrahedrally-coordinated alkali cations, in the direction of lower shift values. A typical example is K₃C₆₀.     

Phase Recovery in Interferometers by Optothermal Diode Laser Modulation

Abstract

A technique is described for the frequency modulation of a diode laser based on the optothermal effect. It is shown that it is possible to generate the frequency modulation with a minimum of power modulation. A frequency shift of approximately 1 GHz per mW of optothermal pump power was achieved in practice. The power modulation was about 7% of that observed when injection current modulation was used to generate a similar frequency shift. The optothermal frequency modulation technique was applied in a phase recovery scheme for a fibre interferometer based on pseudo-heterodyne signal processing.     

Optical and Electrical Properties of Star-Like Fullerene-Containing Polymers

Abstract

Polystyrene and polyethyleneoxide films both containing fullerene, C₆₀, designated as FPS and FPEO were investigated by the ellipsometry, photoluminescence spectra and electrical dc conductivity methods. The FPS and FPEO films display complex refractive index of 1.7 ? 10.05 and 1.45 ? 10.0 respectively. The photoluminescence maximum attributed to C₆₀ shifted to higher photon energies proportionally to with the increase of the number of the polymer rays attached. The shift can be described by the linear relationship ΔE=004N, where ΔE is the shift in eV and N is the number of polymer rays attached. The magnitude of dc conductivity exhibited by the FPS films varied directl proportionally to molar concentration of C₆₀     

Phase shift calibration in speckle photography—a first step to practical real-time analysis of speckle correlation fringes

Abstract

The paper is focused on the implemention of phase shift calibration in speckle photography with a view to introducing the possibility of realtime analysis of displacement data obtained by the method. Phase reversal is accomplished by varying pressure within an air-filled quartz cell inserted in the pump beam in a conventional two-beam coupling arrangement. It is shown that phase reversal is achieved when a π-shifted speckle pattern overlaps on an unshifted speckle pattern at the observation plane. This phenomenon is exploited for calibration of the phase shift. Experimental results show good agreement with the theory.     

Generalized Bloch-Siegert Shift in a Squeezed Vacuum

Abstract

The time evolution of the atomic dipole moment of a two-level atom damped by an off-resonance squeezed vacuum is studied. Our results are valid for arbitrary detuning between the carrier frequency of the squeezed vacuum and the atomic transition frequency and show that the atomic dipole moment can oscillate with two dominant frequencies. These frequencies are shifted from their central values by an amount which is proportional to the degree of squeezing. We show that this shift of the frequencies is the exact equivalent of the optical Bloch-Siegert shift in the case of the ordinary vacuum damping without the rotating-wave approximation.     

On the linear shift invariance of photon diffusion imaging in highly scattering media

Abstract

We present an analytical perturbation analysis for studying the imaging characteristics of photon diffusion imaging in highly scattering media such as human tissues. Factors affecting the image formation in practical imaging system are taken into account, including the photon source, the optical properties of the sample, and the measurement system. A concise relationship between the internal structure and the detected signal is derived. Based on this, it is proved that photon diffusion imaging possess the property of linear shift invariance. The image formation mechanism in measurements such as functional imaging or tumour early diagnosis is illustrated from the viewpoint of the linear shift invariant system.     

Maréchal Intensity Criteria for Apertures with Polynomial Non-uniform Transmission. Evaluation of the Diffraction Focus and the Strehl Ratio

Abstract

General formulae for the wave aberration weighted variance are obtained for rotationally symmetric systems with a non-uniform transmission pupil expressed by polynomials. They are valid for any combination of residual aberrations and any polynomial transmission function on the pupil. Expressions to obtain the position of the diffraction focus and the Strehl ratio are given. The accuracy in the evaluation of the diffraction focus is studied for optical systems with different residual aberrations.     

Solitary Pulses in an Amplified Nonlinear Dispersive Medium in the Presence of Gain Saturation

Abstract

The steady state solitary solution in a two-level homogeneously broadened amplifier with host nonlinearity and dispersion is perturbatively studied by consideration of gain saturation up to second-order energy terms normalized to the saturation energy of the transition. Carrier frequency shift occurs as a result of the saturation. The chirped solitary pulses derived exist in the anomalous group velocity dispersion region only.     

NMR investigation of the magnetic susceptibility anisotropy in3He-A

We have investigated transverse continuous wave NMR in a geometry where the modes are influenced by susceptibility anisotropy. The helium sample is separated by mylar foils into layers 12 m thick perpendicular to the external dc magnetic field. In this geometryl is constrained to be parallel to the field andd switches from parallel to perpendicular to the field over a small range of field around the dipole unlocking field. The mode frequencies below this critical field yield a value for the susceptibility anisotropy. Above the critical field the expected negative frequency shift is observed, as well as a positive frequency shift due to bulk material and an unexpected signal close to the Larmor frequency.     

Chemical doping of MoS2 multilayer by p-toluene sulfonic acid

Abstract

We report the tailoring of the electrical properties of mechanically exfoliated multilayer (ML) molybdenum disulfide (MoS₂) by chemical doping. Electrical charge transport and Raman spectroscopy measurements revealed that the p-toluene sulfonic acid (PTSA) imposes n-doping in ML MoS₂. The shift of threshold voltage for ML MoS₂ transistor was analyzed as a function of reaction time. The threshold voltage shifted toward more negative gate voltages with increasing reaction time, which indicates an n-type doping effect. The shift of the Raman peak positions was also analyzed as a function of reaction time. PTSA treatment improved the field-effect mobility by a factor of ~4 without degrading the electrical characteristics of MoS₂ devices.     

A High-accuracy Formula for Fast Evaluation of the Effect of Focal Shift

Abstract

A simple formula for computing focal shifts in systems of different Fresnel numbers is proposed based on an analysis of factors that limit the extent of a focused field. This formula gives the focal shift accurately to about 2%, which is currently the best approximation that can be made.     

The focal shift in converging waves

Abstract

The focal shift effect in converging spherical waves diffracted by circular apertures is analysed, based on a geometrical interpretation of the mathematical expressions taken from scalar wave theory. The approach leads to a quasi-exact formula for the axial complex amplitude without the need for calculating any integral. The procedures can naturally be extended to image-forming instruments and an application to a single-lens system is also presented.