Figure 5 : Intensity distribution at different positions of the sensing setup.

From: Mid-infrared surface transmitting and detecting quantum cascade device for gas-sensing

Figure 5

The standard farfield without lenses and/or external optical elements (a) exhibits the concentric ring shaped intensity fringes of a ring-QCL without farfield modifications. The intensity ring at ±4° is due to cryostat window reflections. A magnified bolocamera image of the emitting ring-QCL surface taken with a f = 50.8 mm lens. The two shadowed parts on the ring shaped intensity distribution are due to the bond wires which contact the detector element. The central intensity spot is due to the reflections on the ZnSe lens.