Showing papers by "Umar Mohideen published in 2011"

Reduction of the Casimir Force from Indium Tin Oxide Film by UV Treatment

Abstract: A significant decrease in the magnitude of the Casimir force (from 21% to 35%) was observed after an indium tin oxide sample interacting with an Au sphere was subjected to the UV treatment. Measurements were performed by using an atomic force microscope in high vacuum. The experimental results are compared with theory and a hypothetical explanation for the observed phenomenon is proposed.

Impact of surface imperfections on the Casimir force for lenses of centimeter-size curvature radii

Abstract: The impact of imperfections, which are always present on surfaces of lenses with centimeter-size curvature radii, on the Casimir force in the lens-plate geometry is investigated. It is shown that the commonly used formulation of the proximity force approximation is inapplicable for spherical lenses with surface imperfections, such as bubbles and pits. More general expressions for the Casimir force are derived that take surface imperfections into account. Using these expressions, we show that surface imperfections can both increase and decrease the magnitude of the Casimir force up to a few tens percent when compared with the case of a perfectly spherical lens. We demonstrate that the Casimir force between a perfectly spherical lens and a plate described by the Drude model can be made approximately equal to the force between a sphere with some surface imperfection and a plate described by the plasma model, and vice versa. In the case of a metallic sphere and a semiconductor plate, approximately the same Casimir forces are obtained for four different descriptions of charge carriers in the semiconductor if appropriate surface imperfections on the lens surface are present. The conclusion is made that there is a fundamental problem in the interpretation of measurementmore » data for the Casimir force using spherical lenses of centimeter-size radii.« less

Fluctuation-induced forces between inclusions in a fluid membrane under tension.

Abstract: We develop an exact method to calculate thermal Casimir forces between inclusions of arbitrary shapes and separation, embedded in a fluid membrane whose fluctuations are governed by the combined action of surface tension, bending modulus, and Gaussian rigidity Each object's shape and mechanical properties enter only through a characteristic matrix, a static analog of the scattering matrix We calculate the Casimir interaction between two elastic disks embedded in a membrane In particular, we find that at short separations the interaction is strong and independent of surface tension

Control of the casimir force using semiconductor test bodies

Abstract: We describe experimental and related theoretical work on the measurement of the Casimir force using semiconductor test bodies This field of research started in 2005 and several important and interesting results have already been obtained Specifically, the Casimir force or its gradient was measured in the configuration of an Au-coated sphere and different semiconductor surfaces It was found that the force magnitude depends significantly on the replacement of the metal with a semiconductor and on the concentration of charge carriers in the semiconductor material Special attention is paid to the experiment on the optical modulation of the Casimir force In this experiment the difference in Casimir force between an Au-coated sphere and a Si plate in the presence and in the absence of laser light was measured Possible applications of this experiment are discussed, specifically, for the realization of the pulsating Casimir force in three-layer systems Theoretical problems arising from the comparison of the experimental data for the difference in Casimir force with the Lifshitz theory are analyzed We consider the possibility to control the magnitude of the Casimir force in phase transitions of semiconductor materials Experiments on measuring the Casimir force gradient between an Au-coated sphere and a Si plate covered with rectangular corrugations of different characters are also described Here, we discuss the interplay between the material properties and nontrivial geometry and the applicability of the proximity force approximation The review contains comparison between different experiments and analysis of their advantages and disadvantages

Critical steps in data analysis for precision casimir force measurements with semiconducting films

Abstract: Some experimental procedures and corresponding results of the precision measurement of the Casimir force between low doped Indium Tin Oxide (ITO) film and gold sphere are described Measurements were performed using an Atomic Force Microscope in high vacuum It is shown that the magnitude of the Casimir force decreases after prolonged UV treatment of the ITO film Some critical data analysis steps such as the correction for the mechanical drift of the sphere-plate system and photodiodes are discussed

Capacitance measurements and electrostatic calibrations in experiments measuring the casimir force

Abstract: We discuss the possibility of determining the properties and quality of spherical surfaces used in precise experiments with the help of capacitance measurements. The results of this kind measurements for the lens-plane and sphere-plane, Au coated surfaces are compared with theoretical predictions from various models of perfect and broken sphericity. It is shown that capacitance measurements are incapable of discriminating between models of perfect and modified centimeter-size spherical surfaces in an experiment demonstrating the anomalous scaling law for the electric force. Claims to the contrary in the recent literature are explained by the use of improper comparison. The data from capacitance measurements in an experiment measuring the Casimir force by means of a micromechanical torsional oscillator employing micrometer-size spheres are shown to be in excellent agreement with theoretical predictions using the model of a perfect spherical surface.

Capacitance measurements and electrostatic calibrations in experiments measuring the casimir force

Abstract: We discuss the possibility of determining the properties and quality of spherical surfaces used in precise experiments with the help of capacitance measurements. The results of this kind measurements for the lens-plane and sphere-plane, Au coated surfaces are compared with theoretical predictions from various models of perfect and broken sphericity. It is shown that capacitance measurements are incapable of discriminating between models of perfect and modified centimeter-size spherical surfaces in an experiment demonstrating the anomalous scaling law for the electric force. Claims to the contrary in the recent literature are explained by the use of improper comparison. The data from capacitance measurements in an experiment measuring the Casimir force by means of a micromechanical torsional oscillator employing micrometer-size spheres are shown to be in excellent agreement with theoretical predictions using the model of a perfect spherical surface.

Control of the Casimir Force Using Semiconductor Test Bodies

Abstract: We describe experimental and related theoretical work on the measurement of the Casimir force using semiconductor test bodies. This field of research started in 2005 and several important and interesting results have already been obtained. Specifically, the Casimir force or its gradient were measured in the configuration of an Au-coated sphere and different semiconductor surfaces. It was found that the force magnitude depends significantly on the replacement of the metal with a semiconductor and on the concentration of charge carriers in the semiconductor material. Special attention is paid to the experiment on the optical modulation of the Casimir force. In this experiment the difference Casimir force between an Au-coated sphere and Si plate in the presence and in the absence of laser light was measured. Possible applications of this experiment are discussed, specifically, for the realization of the pulsating Casimir force in three-layer systems. Theoretical problems arising from the comparison of the experimental data for the difference Casimir force with the Lifshitz theory are analyzed. We consider the possibility to control the magnitude of the Casimir force in phase transitions of semiconductor materials. Experiments on measuring the Casimir force gradient between an Au-coated sphere and Si plate covered with rectangular corrugations of different character are also described. Here, we discuss the interplay between the material properties and nontrivial geometry and the applicability of the proximity force approximation. The review contains comparison between different experiments and analysis of their advantages and disadvantages.

Critical Steps in Data Analysis for Precision Casimir Force Measurements with Semiconducting Films

Abstract: Some experimental procedures and corresponding results of the precision measurement of the Casimir force between low doped Indium Tin Oxide (ITO) film and gold sphere are described. Measurements were performed using an Atomic Force Microscope in high vacuum. It is shown that the magnitude of the Casimir force decreases after prolonged UV treatment of the ITO film. Some critical data analysis steps such as the correction for the mechanical drift of the sphere-plate system and photodiodes are discussed.

IR photodetector based on an optically cooled micromirror as a light pressure sensor

Abstract: We consider mid-infrared (5 - 25 μm), optically cooled detectors based on a microcantilever sensor of the radiation pressure. The significant enhancement of sensitivity is due the combination of low effective temperature (10 K), non-absorption detection and a high quality optical microcavity. Spectrometry applications are analyzed. It is shown that an optically cooled radiation pressure sensor potentially has an order of magnitude better sensitivity than the best conventional uncooled detectors.