Harbans S. Dhadwal

A fiber‐optic probe for particle sizing in concentrated suspensions

A fiber‐optic probe employing two monomode optical fibers, one for transmitting a Gaussian laser beam to the scattering volume and the second, positioned at some backscatter angle, for receiving the scattered light is described. Performance and suitability of the system for a process control environment is assessed by studying a suspension of polystyrene latex particles over a wide range of sizes and concentrations. The results show that the probe is ideal for a process control environment in industrial and laboratory applications. Particle size is recovered, without any additional corrections for multiple light scattering, in concentrations containing up to 10% solids of 39‐nm polystyrene latex spheres.

A fiber‐optic light‐scattering spectrometer

A new fiber‐optic light‐scattering spectrometer, which uses fiber‐optic detector probes each comprising of an optical fiber and a graded index microlens is described. The fiber‐optic detectors form an integral part of the scattering cell, which no longer requires transparent windows for the exit (or entrance) light beam. This feature eliminates the need for a goniometer which is one of the most bulky and expensive components of a conventional light‐scattering spectrometer. Thus, the spectrometer, unlike all of its predecessors, has no moving parts. Our fiber‐optic light‐scattering spectrometer can utilize a reaction vessel of whichever shape or composition as the scattering cell for light‐scattering measurements because the fiber‐optic detector probes are directly immersed in the scattering medium. Furthermore, with the miniaturization using the optical fiber/microlens combination, the light‐scattering spectrometer can be held in the palm of one hand and the signals processed by standard optical fiber remote sensing techniques.

Regularized iterative and non-iterative procedures for object restoration from experimental data

A regularized algorithm for the recovery of band-limited signals from noisy data is described. The regularization is characterized by a single parameter. Iterative and non-iterative implementations of the algorithm are shown to have useful properties, the former offering the advantage of flexibility and the latter a potential for rapid data processing. Comparative results, using experimental data obtained in laser anemometry studies with a photon correlator, are presented both with and without regularization.

Regularized iterative and noniterative procedures for object restoration in the presence of noise: an error analysis

An analysis is carried out, using the prolate spheroidal wave functions, of certain regularized iterative and noniterative methods previously proposed for the achievement of object restoration (or, equivalently, spectral extrapolation) from noisy image data. The ill-posedness inherent in the problem is treated by means of a regularization parameter, and the analysis shows explicitly how the deleterious effects of the noise are then contained. The error in the object estimate is also assessed, and it is shown that the optimal choice for the regularization parameter depends on the signal-to-noise ratio. Numerical examples are used to demonstrate the performance of both unregularized and regularized procedures and also to show how, in the unregularized case, artefacts can be generated from pure noise. Finally, the relative error in the estimate is calculated as a function of the degree of superresolution demanded for reconstruction problems characterized by low space–bandwidth products.

Coherent fiber optic sensor for early detection of cataractogenesis in a human eye lens

A lensless backscatter fiber optic probe is used to measure the size distribution of protein molecules inside an excised, but intact, human eye lens. The fiber optic probe, about 5 mm in diameter, can be positioned arbitrarily close to the anterior surface of the eye; it is a transreceiver, which delivers a Gaussian laser beam into a small region inside the lens and provides a coherent detection of the laser light scattered by the protein molecules in the backward direction. Protein sizes determined from the fast and slow diffusion coefficients show good correlation with the age of the lens and cataractogenesis.

Prism laser light‐scattering spectrometer

A prism light‐scattering spectrometer capable of measuring both the angular distribution of scattered intensity and Rayleigh linewidth is described. The spectrometer employs a unique prism light‐scattering cell capable of making small‐angle self‐beating dynamic light‐scattering measurements down to a scattering angle of 2° and is able to achieve an optical coherence factor β∼0.9 routinely, with the theoretical limit for β being 1. The prism light‐scattering cell also permits refractive index measurements in the 1.33–1.60 range to a precision of 8×10−7 using a single‐axis lateral position sensor. It is a flow cell with potential as a detector for other analytical techniques once the cell volume can be minimized. The apparatus can be controlled by a computer for measurements, as well as acquisition, display, computation, and storage of data.

High pressure fiber optic light scattering spectrometer

A high-pressure fiber-optic light-scattering spectrometer has been constructed for in situ observation of molecular dissolution/association as well as the polymerization process in supercritical fluids. Single (or multiple) fiber-optic probes, each comprised of a single optical fiber (or multiple optical fibers) and a graded index microlens, are used to transmit the incident laser beam and to receive the scattered light as well as the transmitted light from the high pressure cell. The direct immersion in the scattering medium of the fiber-optic probes makes the spectrometer more compact and more flexible with an easier alignment process. With the miniaturization and flexibility, our high-pressure light-scattering cell can be transported and adapted in combination with other physical techniques, such as synchrotron small angle x-ray scattering which requires a different set of windows (e.g., made of diamond) suitable for x-ray transmissions. This spectrometer has been successfully used for the in situ stud...

Fiber optic detector probes for laser light scattering

An experimental investigation of the role of fiber optic detector probes in laser light scattering is presented. A quantitative comparison between different detector configurations is accomplished by measuring the time taken for one million photocounts to be accumulated in the extrapolated zeroth delay channel of the net unnormalized intensity time correlation function. A considerable reduction in the accumulation time is achieved by relaxing a rather stringent requirement for the spatial coherence of the optical field.

Microemulsion characterization by the use of a noninvasive backscatter fiber optic probe

This paper demonstrates the utility of a noninvasive backscatter fiber optic probe for dynamic light-scattering characterization of a microemulsion comprising sodium dodecyl sulfate/1-butanol/ brine/heptane. The fiber probe, comprising two optical fibers precisely positioned in a stainless steel body, is a miniaturized and efficient self-beating dynamic light-scattering system. Accuracy of particle size estimation is better than ±2%.

Integrated fiber optic light probe: Measurement of static deflections in rotating turbomachinery

This paper describes the design, fabrication, and testing of an integrated fiber optic light probe system for monitoring blade tip deflections, vibrational modes, and changes in blade tip clearances in the compressor stage of rotating turbomachinery. The system comprises a set of integrated fiber optic light probes which are positioned to detect the passing blade tip at the leading and the trailing edges. In this configuration measurements of both blade vibrations and steady‐state blade deflection can be obtained from the timing information provided by each light probe, which comprises an integrated fiber optic transmitting channel and a number of high numerical aperture receiving fibers, all mounted in the same cylindrical housing. A spatial resolution of 50 μm is possible with the integrated fiber optic technology, while keeping the outer diameter below 2.5 mm. Additionally, one fiber sensor provides a capability of monitoring changes in the blade tip clearance of the order of 10 μm. Measurements from a...