Browse Prior Art Database

Differential Scanning Device

IP.com Disclosure Number: IPCOM000075821D
Original Publication Date: 1971-Nov-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Morgan, TN: AUTHOR [+2]

Abstract

A double LED (light-emitting diode) structure is used for measuring differential optical properties. Each diode emits light on alternate cycles of an AC drive voltage. Phase sensitive detection of optical differences in the target is obtained with great precision, because of the differentiation process inherent in the use of this diode.

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Differential Scanning Device

A double LED (light-emitting diode) structure is used for measuring differential optical properties. Each diode emits light on alternate cycles of an AC drive voltage. Phase sensitive detection of optical differences in the target is obtained with great precision, because of the differentiation process inherent in the use of this diode.

In U. S. 3,440,497 and in an article entitled "Interaction of Two Avalanching Layers in GaAs", by K. Weiser, appearing in Solid State Electronics 10, 109 (1967), a double LED structure is proposed and a method for making it is presented. The beams originating from this AC activated device are incident on a target and a single detector is used to monitor the transmitted or reflected beams from the target. If the two regions of the target which are struck by the beams have the same optical properties, a circuit connected to the detector and tuned to the AC frequency will not produce a signal. However, if the two regions have different properties, a signal will result. By focussing the image of the LED device on the target the resolution can be reduced to approximately one micron.

The advantage of the double LED structure over a single light source is that the differentiation capability is increased.

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