Thermo-optical far infrared system

DETAILED DESCRIPTION The invention consists of five major components.
These are: a far infrared objective lens (or mirror system); an infrared modulator, or chopper, whose "off" state approximates the mean background temperature; a thin film thermal-to-optical transducer in an evacuated cell; a visible or near infrared read beam light source; an ac-coupled visible imaging system; and an output image display, or an electronic processor for guidance or tracking applications.
The objective forms a thermal image on the transducing film.
Because of the modulator, this image includes a time varying signal which is locally proportional to the difference in temperature of the corresponding scene element compared to the apparent "off" state temperature of the modulator.
The transducing film is uniformly illuminated by the read beam.
Since the transducing film includes a layer whose complex index of refraction varies with temperature, its local transmission (or reflection) is proportional to the thermal image.
In this way, an optical image is produced, at the read beam wavelength, corresponding to the thermal image, including the time varying portion induced by the modulator chopper.
This optical image is amplified by the ac-coupled visible (or near infrared) imaging system.
Since it is ac-coupled, only the time varying portion of the signal is amplified.
Therefore, the static background level is suppressed yielding a high contrast signal which can be fed directly to a visible display or a missile guidance system.