Thermography cameras penetrate the far-infrared

A commercial infrared thermography camera has been used to build the first video-rate, actively illuminated far-infrared imaging system. The far-infrared region of the electromagnetic spectrum lies between the infrared (approximately 1-30 um wavelength) and microwave (approximately 1 mm-1 m wavelength). This region has been left relatively unexplored due to a lack of good laser sources and sensitive imaging detectors.

The development of a device called the “quantum cascade laser” by researchers at Bell Labs in the 1990’s has now led to the development of bright (mW-level), compact, coherent sources in the far-infrared.[1,2] At the same time, sensitive infrared thermography cameras have been developed for commercial applications such as building inspection and breast cancer imaging. With the combination of sensitive thermography, and high quality illumination, the far-infrared portion of the electromagnetic spectrum has been made available for applications as wide-ranging as imaging of squamous cell carcinoma (cancer of the cheek tissue) and homeland security applications.[3]

Dr. Barry Behnken and Prof. Gamani Karunasiri from the Naval Postgraduate School in Monterrey, CA have used a commercial thermography imaging system such as those used for building inspection to engineer an imaging system that measures not in the traditional infrared wavelengths but in the far-infrared region of the electromagnetic spectrum. The aim of these researchers was to develop a compact imaging system able to detect new threats for homeland security and defense applications. The far-infrared sources used were quantum cascade lasers grown by the group of Prof. Jerome Faist at the University of Neuchatel, Switzerland. The camera used is a commercial bolometer array, however the usual lenses used were removed due to poor transparency in the far-infrared and replaced with lenses made from Tsurupica, a far-infrared transparent polymer.[4]

Because the thermography system, based on a microbolometer array, detects heat and not light, it can sense the far-infrared even though the photon energy is approximately 100 times smaller than an infrared photon. This far-infrared thermography system has been able to identify a knife obscured in an envelope and has shown large promise in imaging of difficult-to-detect security features in currency. [5]

For example, the infrared thermography camera can detect the watermark of Queen Elizabeth and some security threads in a Great Britain Pound note, known to have some of the most advanced anti-counterfeit measures of all currencies. Video images of these were presented at the SPIE Europe Security & Defense Conference in 2008 [6] and are available at the website provided in reference [5].

by Danielle Chamberlin

About the Author:
Danielle worked with collaborators to perform first experiment, and sat on the dissertation committee of the student who performed work.

For more information please visit us online : Thermal Imaging Cameras by ICI

References:

[1] Faist, J., ed. “Mesoscopic Physics Group.” University of Neuchatel. http://www.unine.ch/phys/meso/welcome.html (24 June 2009).
[2] Unknown author, “Quantum Cascade Lasers.” Wikipedia. http://en.wikipedia.org/wiki/Quantum_cascade_laser (24 June 2009).
[3] Unknown author, “THz waves penetrate the world of imaging.” Optics.org. http://optics.org/cws/article/articles/9937 (24 June 2009).
[4] Unknown author, “Microtech THz Spectrometers.” Microtech Instruments, http://www.mtinstruments.com/thzlenses/index.htm (24 June 2009).
[5] B. Behnken, “Barry Behnken’s Research Site.” Googlepages, http://bbehnken.googlepages.com/index.htm (24 June 2009). [6] Behnken, B. N. and Karunasiri, G. "Real-Time Terahertz Imaging of Nonmetallic Objects for Security Screening & Anti-Counterfeiting Applications," Proceedings of SPIE Europe Security & Defence Conference, Cardiff, Wales, United Kingdom, Sept 2008, pp. SPIE 7117-4.