Infrared fiber-optic endoscope

NASA Tech Briefs, Oct 2002

Thermography could be performed in confined spaces and harsh environments.

Langley Research Center, Hampton, Virginia

A proposed infrared transmitting fiber-optic endoscope, which would partly resemble a visible-light fiber-optic endoscope, instrument could be used to perform thermal imaging in harsh environments and/or confined spaces in a variety of situations in aerospace, industrial, automotive, and medical settings.

Like a typical visible-light fiber-optic endoscope, the proposed instrument would include a coherent fiber-optic infrared bundle with an objective lens attached to its distal end. The lens would focus energy from the scene under observation onto the input face of the fiber-optic bundle. Of course, unlike in a visible-light fiber-optic endoscope, both the lens and the optical fibers would be made of materials that transmit a substantial proportion of the infrared energy in a wavelength range useful for observing at the temperature range of interest.

Another infrared-transmissive lens at the proximal end of the coherent fiber-optic bundle would focus the infrared image of the scene from the output face of bundle onto a planar array of infrared photodetectors. The outputs of the photodetectors would be processed by electronic circuitry to generate a temperature map of the scene and/or a visible analog of the infrared image of the scene. In the processing, the photodetector outputs would be converted to temperatures at corresponding locations in the scene on the basis of a photodetector calibration and radiative properties that may be known or assumed in accordance with physical conditions in the scene.

The main advantage of this instrument is that the relatively compact, rugged viewing optic could be inserted in the confined and/or inhospitable environment containing the scene to be observed, while the rest of the instrument could be accessible and located in a hospitable environment. The instrument would be tailored for the temperature range of interest through the choice of lens and fiberoptic materials as mentioned above plus the choice of photodetectors suitable for the wavelength range corresponding to the temperature range. For example, one could choose a PtSi-based detector array for shorter wavelengths corresponding to higher temperatures or an HgCdTe-based array for longer wavelengths corresponding to lower temperatures.

This work was done by Stephen E. Borg and Christopher E. Glass of Langley Research Center. For further information, access the Technical Support Package (TSP)free on-line at www.nasatech.com/tsp under the Physical Sciences category.

LAR-16149