Disclosed is a retroreflector-based sensor system for optical characterization of a sample, having a transmitter for irradiating the sample, a retroflector positioned behind the sample, the transmitter, the sample, and the retroreflector being positioned such that radiation reflected back from the retroreflector is again incident on the sample and is reflected back from the latter in the direction towards the transmitter, and a receiver which is positioned in the receiving beam path such that it detects radiation reflected back from the retroreflector, incident again on the sample and reflected back from the latter, in the direction towards the transmitter.