Pulsed wideband IR thermal source

A pulsed mid-IR thermal source based on electrical heating of a thin metal alloy foil up to red heat (~900°C) and cooled by its own radiation has been studied. The device, with emitting area diameters ranging from 25 mm to 1.7 mm, is based on a suspended bispiral metal foil geometry which offers substantial thermal isolation from the supporting structure. The infrared emission is two sided, but the reverse side radiation may be reflected through the plane of the bispiral heater to enhance the total forward emission. Practical devices are described in respect of their mechanical, electrical and infrared emitting properties. An encapsulated form of the smallest device incorporates an infrared transmitting window and infrared beam directivity and intensity-enhancing focusing reflector, and has a typical modulation depth of 85% at 10 Hz. Thermal target and gas detector applications of these sources are discussed