Mid- and far-infrared digital holography with quantum cascade lasers

Extension of hologram recording to the infrared (IR) spectrum has attracted a considerable interest since the early stage of holography, due to the intrinsic relaxation of the mechanical stability requirements and to the IR transparency of many materials opaque to the visible radiation [1]. In addition, IR hologram recording benefits from a large field of view and is well suited for measuring optical path variations, since the use of a long wavelength reduces the need for phase-unwrapping algorithms. In the last decade, in the wake of the establishment of digital holography (DH) in the visible range, the development of pyrocameras and focal plane array microbolometers, combined with powerful and highly coherent CO2 lasers, has finally boosted IR holography: thanks to sensors including 100,000s of pixels as small as few tens of ?m and operating at room temperature, CO2 laser based DH has proved its potential for practical applications [2].