A High-Resolution Combined Scanning Laser- and Widefield Polarizing Microscope for Imaging at Temperatures from 4 K to 300 K

Polarized light microscopy, as a contrast-enhancing technique for optically anisotropic materials, is a method well suited for the investigation of a wide variety of effects in solid-state physics, as for example birefringence in crystals or the magneto-optical Kerr effect (MOKE). We present a microscopy setup that combines a widefield microscope and a confocal scanning laser microscope with polarization-sensitive detectors. By using a high numerical aperture objective, a spatial resolution of about 240 nm at a wavelength of 405 nm is achieved. The sample is mounted on a $^4$He continuous flow cryostat providing a temperature range between 4 K and 300 K, and electromagnets are used to apply magnetic fields of up to 800 mT with variable in-plane orientation and 20 mT with out-of-plane orientation. Typical applications of the polarizing microscope are the imaging of the in-plane and out-of-plane magnetization via the longitudinal and polar MOKE, imaging of magnetic flux structures in superconductors covered with a magneto-optical indicator film via Faraday effect or imaging of structural features, such as twin-walls in tetragonal SrTiO$_3$. The scanning laser microscope furthermore offers the possibility to gain local information on electric transport properties of a sample by detecting the beam-induced voltage change across a current-biased sample. This combination of magnetic, structural and electric imaging capabilities makes the microscope a viable tool for research in the fields of oxide electronics, spintronics, magnetism and superconductivity.Comment: 14 pages, 11 figures. The following article has been accepted by Review of Scientific Instruments. After it is published, it will be found at http://aip.scitation.org/journal/rs

Laser-based fibre-optic sensor for measurement of surface properties

This project deals with the design and development of an optoelectronic sensor system and its possible use in online applications. There are two different configurations of this sensor a sensor for surface roughness and another for defect detection. In each configuration the mechanical and optical design are almost identical - optical fibres convey light to and from a surface Light source driving circuits and photodetection circuits were developed for each sensor Data acquisition and analysis algorithms were developed for each sensor. The defect sensor detects through holes and blind holes in sample plates of the following materials brass, copper, stainless steel, and polycarbonate Edge detection is achieved through the development of a photoelectric sensor system that senses the proximity of a surface within a certain displacement range using a multimode laser diode light source emitting at 1300 nm. This sensor uses a voltage cut-off system to avoid the effects of light source intensity variation, vibration, surface roughness and other causes of variable reflectivity in online measurement of engineering surfaces. The through holes had 2 mm diameter and the blind holes had 3 mm diameter and a depth of 0 6 mm. A spatial resolution of approximately 100 (Jim was achieved - the diameter of the collecting fibre’s core. Surface roughness is estimated between 0 025 \im and 0 8 \im, average surface roughness, through a light scattering technique Specular reflectivity was measured at incident angles of 45° and 60°. The causes of error, noise and drift are investigated for this system and recommendations are made to account for these problems. A carrier frequency system using an electronically modulated LED light source was implemented to improve the noise rejection of the system Digital signal processing system was implemented to digitally filter the acquired signal

An optical fiber measurement system design on tool radial vibration

The effects of tool radial vibration bring not only poor surface quality, inferior dimensional accuracy, but also disproportionate tool wear or tool breakage and excessive noise. Therefore, online measurement and monitoring of tool vibration are necessary. In order to monitor the tool vibration, an optical fiber measurement system was design in this pater. Firstly, the structure and basic principle of the optical fiber sensor was given; secondly, the light intensity to voltage converter circuit was introduced; then, an experiment platform was built for verify the feasibility of the optical measuring system, and the result shows that the radial vibration of a smooth 10 mm diameter shaft can be measured quickly

Fiber optic control system integration

A total fiber optic, integrated propulsion/flight control system concept for advanced fighter aircraft is presented. Fiber optic technology pertaining to this system is identified and evaluated for application readiness. A fiber optic sensor vendor survey was completed, and the results are reported. The advantages of centralized/direct architecture are reviewed, and the concept of the protocol branch is explained. Preliminary protocol branch selections are made based on the F-18/F404 application. Concepts for new optical tools are described. Development plans for the optical technology and the described system are included

Review: optical fiber sensors for civil engineering applications

Optical fiber sensor (OFS) technologies have developed rapidly over the last few decades, and various types of OFS have found practical applications in the field of civil engineering. In this paper, which is resulting from the work of the RILEM technical committee “Optical fiber sensors for civil engineering applications”, different kinds of sensing techniques, including change of light intensity, interferometry, fiber Bragg grating, adsorption measurement and distributed sensing, are briefly reviewed to introduce the basic sensing principles. Then, the applications of OFS in highway structures, building structures, geotechnical structures, pipelines as well as cables monitoring are described, with focus on sensor design, installation technique and sensor performance. It is believed that the State-of-the-Art review is helpful to engineers considering the use of OFS in their projects, and can facilitate the wider application of OFS technologies in construction industry

Dynamic fiber-optic shape sensing using fiber segment interferometry

Dynamic fiber-optic shape sensing, often also referred to as curvature or bend sensing, is demonstrated using fiber segment interferometry, where chains of fiber segments, separated by broadband Bragg grating reflectors, are interrogated using range-resolved interferometry. In this work, the theory of interferometric curvature sensing using fiber segments is developed in detail, including techniques to infer lateral displacements from the measured differential strain data and methods for directional calibration of the sensor. A proof-of-concept experiment is performed, where four fiber strings, each containing four fiber segments of gauge length 20 cm each, are attached to the opposing sides of a flexible support structure and the resulting differential strain measurements are used to determine the lateral displacements of a 0.8 m cantilever test object in two dimensions. Dynamic tip displacement measurements at 40nm . HZ-0.5 noise levels over a 21 kHz bandwidth demonstrate the suitability of this approach for highly sensitive and cost-effective fiber-optic lateral displacement or vibration measurements

Reflectance-based low-cost disposable optical fiber surface plasmon resonance probe with enhanced biochemical sensitivity

A reflectance-based surface plasmon resonance (SPR) fiber sensor with enhanced sensitivity for biochemical sensing is reported after comparing its result with the transmittance-based SPR optical fiber sensors. The fabricated SPR sensor contains a gold-coated multimode fiber with the implementation of a standard source-sensor-spectrometer interrogation system. As the refractive index of the liquid under test is increased, a redshift of the SPR is observed. The coupling of the source to the fiber sensor is optimized by investigating the effect of an intentional misalignment in transmission-based setup. When a fiber tip coated with the silver mirror and the bifurcated fiber bundle is used, an alignment-free disposable sensor probe is achieved. A comprehensive characterization of the proposed reflectance-based SPR probe is discussed. The maximum sensitivity of 3212.19  nm/refractive index unit (RIU) is obtained

Fiber Optical Sensing of Bearing Performance and Pump Conditions

Lectur