PULSED WIDE-BAND IR THERMAL SOURCE

A pulsed mid-IR thermal source based on electrical heating of a thin m etal alloy foil up to red heat (similar to 900 degrees C) and cooled b y its own radiation has been studied. The device, with emitting area d iameters ranging from 25mm to 1.7mm, is based on a suspended bispiral metal foil geometry which offers substantial thermal isolation from th e supporting structure. The infrared emission is two sided, but the re verse side radiation may be reflected through the plane of the bispira l heater to enhance the total forward emission. Practical devices are described in respect of their mechanical, electrical and infrared emit ting properties. An encapsulated form of the smallest device incorpora tes an infrared transmitting window and infrared beam directivity and intensity-enhancing focusing reflector, and has a typical modulation d epth of 85% at 10Hz. Thermal target and gas detector applications of t hese sources are discussed.