Robert L. Rosenberg

Interior‐surface acoustic waveguiding in capillaries

Capillary tubing, used as a waveguide for surface acoustic waves confined to the interior surface, is shown to be a guiding structure that has a number of properties useful for long‐delay‐line applications. Very clean rf pulse transmission has been achieved, with spurious bulk modes stripped away by absorption at the outer surface. Low dispersion is available with bore diameters of a few Rayleigh wavelengths. In a fused silica structure flame‐drawn to a half‐meter length, the propagation loss was experimentally found to be limited by material bulk attenuation constants.

TUNNEL‐DIODE PHOTORESPONSE

The photoresponse of tunnel diodes has been found to be fast enough under suitable conditions to follow subnanosecond light pulses from a mode‐locked He–Ne laser. The nonlinearity of the diode electrical characteristic has yielded threshold detection of optical pulses having a peak power of a few milliwatts. Tunnel diodes of varied materials and construction show a similar photoresponse so long as optical frequency exceeds the (indirect) band gap.