In vivo dynamic light scattering characterization of a human lens: cataract index.

PURPOSE: To characterize the cataractous state of the living lens by a single parameter, derived from in vivo dynamic light scattering measurements. METHODS: Dynamic light scattering, in conjunction, with a fiber optic transmitter/receiver, was used for measuring the intensity autocorrelation of the light scattered in the backward direction from the living human lens. The fiber optic transreceiver provided a rapid means for active positioning and collection of the back scattered light from any point inside the lens. Intensity autocorrelation, spanning seven decades of delay time, was acquired, in vivo, from the lenses of volunteers ranging in age from 10 to 85. The number weighted size distribution, recovered from the autocorrelation data, was found to be a consistent means of characterizing the aging living lens. RESULTS: The cataract index, representing the average of the number weighted size distribution, varied from five, for clinically clear lenses, to 10,000 for cataractous lenses. Repeated measurements, over a period of two years, on the lens of the same subject established the efficacy of the measurement. In the precataractous stage a single point measurement in the nuclear region of the lens was sufficient to characterize the state of the whole lens. CONCLUSION: The cataract index is a quantitative measure of the cataractous state of any small volume element (50 x 250 microm) inside the human lens. This index is useful for characterizing lenses at any stage of development, that is, from infancy through visual impairment.

Multi-capillary optical waveguides for DNA sequencing.

Cylindrical capillaries can be used as optical elements in a waveguide, where refraction will confine an appropriately focused light beam to pass through the interiors of successive capillaries in a flat parallel array. Such a capillary waveguide allows efficient illumination of samples in multiple capillaries with relatively little laser power. Analytical expressions derived under paraxial and thin-lens approximations provide guidance in selecting the capillary sizes and the refractive indices that will produce the waveguiding effect, but accurate predictions require exact ray tracing. Small reflective losses as the light passes through the capillary surfaces cause cumulative intensity decreases, but the resulting lack of uniformity can be compensated to a considerable extent by illuminating the capillary array from both sides. A 12-capillary waveguide illuminated from both sides in air has a difference of less than 10% from the strongest to the weakest illumination. By increasing the refractive index of both the external medium and the contents of the capillaries, a 96-capillary waveguide for DNA sequencing could be produced that would also provide nearly uniform illumination. A 12-capillary, bi-directionally illuminated waveguide system for DNA sequencing has been constructed. The two focused laser beams are delivered by integrated fiber optic transmitters (IFOTs), and fluorescence is collected by a set of optical fibers whose spacing exactly matches that of the capillaries in the waveguide. The system is easy to align and provides sensitive detection of fluorescence with minimal cross-talk between channels.

Design and characterization of coherent integrated fiber-optic imaging probes.

An integrated fiber-optic probe comprising a short length of multimode fiber that is fusion spliced to a monomode optical fiber has been fabricated for imaging and nonimaging applications. The fiber probe, typically 250 µm in diameter, can deliver a focused Gaussian spot approximately 25 µm in diameter at a distance of approximately 500 µm from the tip. Two off-the-shelf graded-index multimode fibers have been used in the fabrication of imaging and nonimaging probes. These integrated probes have considerably improved the spatial resolution of backscatter lensless fiber probes being utilized in the dynamic light-scattering characterization of colloidal suspension.

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 probe for dynamic light scattering.

An integrated fiber optic probe, comprising a monomode optical fiber fusion spliced to a short length of a graded-index multimode fiber, is fabricated for use as a coherent receiver in dynamic light scattering. The multimode fiber is cleaved to provide a gradient-index fiber lens with a focal length of 125 µm and an ƒ-number close to unity. An integrated fiber receiver is used to measure the intensity-intensity autocorrelation data from a 0.05% by weight concentration of an aqueous suspension of polystyrene latex spheres. Analysis of 100 independent data sets indicates that the particle size can be recovered with an accuracy of ±1%.

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.

Laser measurement of the motility of bull spermatozoa in an egg-yolk diluent.

An objective method of assessing bull sperm motility by specifying the mean swimming speed and number of motile spermatozoa in a sample is described. Laser light was conducted into diluted semen samples using a fibre-optic Doppler anemometer (FODA). The signal correlation of the back-scattered laser light was modelled using least squares computer curve fitting of the resulting data. Agreement was found between the mean swimming speeds obtained and those measured using time lapse photography.