Observation of continuous-wave on-resonance "self-focusing".

We report what to our knowledge are the first observations of an increase in the on-axis intensity of an intense cw on-resonance beam resulting from nonlinear absorption and diffraction during its propagation through a highly absorbing medium (sodium vapor). This "self-focusing" is not a self-lensing; instead it is modeled well by placing an aperture part way through the cell: The stripping by the aperture approximates the effect of the nonlinear absorption, and then Fresnel diffraction results in on-axis minima and maxima.

Neurological mapping using an electron microscope/microprocessor data acquisition system.

Quantitative electron microscopy is used widely in many neurobiological laboratories but can be greatly enhanced by the computer storage, display and analysis of features or boundaries observed under the microscope. An interactive system is described, in which a microprocessor and microcomputer combination controls the data acquisition and display; more detailed analysis can be carried out on a mainframe computer. The performance of this system is examined and it is shown to be a cheap and effective solution, capable of expansion in many directions.