A UNIQUE LASER DETECTOR UTILIZING THE PHOTODIELECTRIC EFFECT IN COOLED SEMICONDUCTORS.
Abstract
A change in the real part of the dielectric constant of semiconductors is observable at 4.2K. The dielectric perturbation can be optically induced and subsequently used to vary the resonant frequency of a high Q, superconducting re-entrant cavity. The frequency changes are predictable from a classical treatment of the complex dielectric constant in the presence of optical and thermal carriers. A transmission line equivalent circuit is used to accurately predict the behavior of a photodielectric detector. The important parameters which affect the performance of the detector are the free carrier relaxation time, recombination lifetime, the unloaded cavity resonant frequency, sample thickness, and the capacitive loading effects. These are referred to as the sensitivity parameters. The ultimate frequency response (i.e. the rate at which the frequency can be varied) is shown to be limited by the free carrier lifetime in the semiconductor sample. The photodielectric receiver is used in the design of an optical communications system which was used to detect video rate, amplitude modulation of a 9000A infrared light source. Three such systems are described but practical considerations of the state-of-the-art limit attention to the one utilizing the phase change of a frequency modulated re-entrant cavity. A cryogenic environment was used to suppress thermally generated free carriers and to allow operation of the cavity in the superconducting mode. A 60 ohm-cm, p-type germanium sample was used to detect a video modulated (bandwidth of 1.5 MHz) 9000A light source. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 1967
- Accession Number
- AD0659738
Entities
People
- Jackie L. Stone
- William H. Hartwig
Organizations
- University of Texas at Austin