Multispectral thermal camera using copper plasmonics

Spectral imaging allows data acquisition at any particular frequency range in the electromagnetic (EM) spectrum to extract additional information. The light energy emitted from the sources or reflected by the objects is selectively sensed in specific bands of the EM spectrum to produce images. Multispectral imaging in long-wave infrared (thermal wavelengths) is an emerging research area due to its ability to identify objects precisely from the emission spectrum for chemical detection, gas sensing, night vision, and surveillance applications.1 The multispectral imaging in the long-wave infrared is limited by the conventional filter technologies and limited materials responding in the thermal wavelengths. Wavelength filters based on surface plasmon resonance can overcome such limitations and can produce filters using a single nanoscale thick metal film with wide wavelength tunability. This paper presents a wavelength filter technology operating in six bands of the thermal region (7 – 14 μm). With copper (Cu) as the metal layer and germanium (Ge) as the cap layer, the transmission efficiency of lithographically patterned multilayer plasmonic filters on gallium arsenide (GaAs) substrate has improved up to 60% in thermal wavelengths. Thus, a thermal multispectral filter system is realized to acquire narrow transmission bands in the thermal region using surface infrared plasmonics of Cu in a dielectric-metal-dielectric (DMD) mosaic of GaAs-Cu-Ge. The filters are then integrated on thermal image sensors mounted on an in-house processing electronic platform to develop a six-band multispectral thermal sensor system. The working of the snapshot thermal multispectral sensor system is demonstrated by capturing the images at six different bands. The developed multispectral system can be adopted for non-destructive thermal imaging or can be used directly as a microspectrometer for various thermal spectroscopy applications