Holocamera for 3-D micrography of the alert human eye.

A holocamera that safely records holograms of the full depth of the alert human eye with a spatial resolution of ~20 microm is described. A single-mode argon-ion laser generating 2 W at 5145 A serves as the illuminating source. Holographic exposure times of 0.3 msec are achieved by means of a fail-safe electromechanical shutter system. Integrated retinal irradiance levels are well under the American National Standards Institute safety standards. Reconstructed real images are projected directly onto the vidicon faceplate of a closedcircuit TV system, enabling convenient scanning in the x-y-z dimensions of the reconstructed eyeball. Serially reconstructed holograms of cataractous rabbit eyes and normal human eyes are presented.

Backscattering of a picosecond pulse from densely distributed scatterers.

A theoretical and experimental study of the backscattering characteristics of a picosecond pulse scattered from a dense diffusing medium is presented. The theory uses a diffusion solution to the time-dependent equation of radiative transfer and the formulation of a picosecond range-gating technique. The experimental system consists of a high-power laser range-gating system, based on a picosecond Kerr-effect shutter. The results of experiments carried out on aqueous solutions of latex microspheres agree well with the theoretical calculations, not only in the pulse shape but in the relative magnitudes of the pulse height for different particle sizes and concentrations.

Picosecond light scattering measurements of cataract microstructure.

A picosecond range-gated light scattering technique is used to measure the microstructure of cataracts in the living eye, with a resolution of the order of the wavelength of light. The cataract is illuminated with ultrashort pulses of light derived from a mode-locked Nd:glass laser. The pulses backscattered by the opacity are collected at several angles simultaneously by an array of fiber-optic light guides whose outputs are sequentially sampled by a multichannel picosecond Kerr shutter. This shutter transmits only that light which is scattered from the desired depth in the eye, while blocking from the detector any light scattered by foreground or background tissue and reducing multiple scattering effects. The size distribution of scatterers in the cataract is deduced from the angular distribution of scattering intensities by application of Mie theory. The results of experiments with suspensions of latex microspheres and with rabbit cataracts in vivo are presented. Cataract microstructure down to 0.5 microm has been measured in a rabbit eye and verified with electron microscopy.

Fluid mechanical light guide.

It is shown that a beam of light can be deflected continuously through large angles along a curved path using the gas flow from a convergent-divergent nozzle sector whose throat lies on the arc of a circle. The amount of deflection depends on the included angle of the nozzle sector and on the density gradients created by the expanding gas flow. For a 360 degrees included angle the beam can in principle be bent into a closed path with a radius of the order of a few tens of centimeters: Nozzle sectors with included angles of 30 degrees and 180 degrees are studied both theoretically and experimentally. It is demonstrated that a well-defined region exists in the flow wherein light rays are trapped in near-circular paths whose radii are close to the radius of the nozzle throat. The trapping region in effect constitutes a curved light guide. Very low light losses are predicted and measured, even for large deflections. Using nitrogen at a stagnation pressure of 110 atm as the working fluid, a laser beam is deflected as much as 180 degrees with a transmission approaching 100%.