High-luminosity multipass cell for infrared imaging spectroscopy

An original imaging multipass cell for infrared spectroscopy has been designed and built. The cell design is aimed at overcoming intrinsic sensitivity limitations associated with the low specific spectral radiance power of blackbody sources. Owing to the implemented low f number, the detector collects a large amount of the energy emitted over a wide angle by a blackbody source. In addition, the adopted optical configuration allows maintenance of the same spatial distribution of the radiance pattern at the cell entrance and exit (imaging capability) within an aperture area of several square millimeters. This feature allows the use of uncollimated blackbody-type emitter arrays and infrared sensor arrays coupled with linear, spectrally variable filters, and performance of spectroscopic measurements of infrared absorption for low concentrated gases detection. In the present design the cell has an f number of about 2, and the optical path is ten times larger than the cell length.