A microbolometer FPA with was used for imaging. The corresponding infrared camera (VarioCAM hr head, InfraTec GmbH, Dresden, Germany) was equipped with a standard objective (). A lens system with 12.5 mm focal length was placed in front of the camera, resulting in a nominal magnification of 4:1. The resulting projected pixel pitch in the sample plane was determined to be . The maximum field of view amounted to . The maximum frame rate of the camera is 50 Hz. A single frame was recorded without laser illumination in order to allow for background correction. The laser illumination was switched on thereafter and typically 573 frames were recorded during the duration of one sweep-scan. As this sampling frequency corresponds to 8 frames per of tuning, it is solely the laser linewidth of that governs the spectral resolution of the setup. However, in the experiments described here, the infrared images were averaged over 20 frames (which corresponds to a spectral interval width of ) in order to allow for a better comparison with the FT-IR spectroscopy. For FT-IR experiments, a spectral resolution of and an interval width of were chosen. In passing, we would like to note that a spectral resolution of will frequently suffice for resolving the typical linewidth occurring in the case of biomedical samples.