Panel a: schematic overview of the adapted CODULAB optical train as seen from above. Shown is the filter wheel (FW), polarizer (P), modulator (M), diaphragm (D), analyzer (A), quarter wave plate (Q), and photomultiplier (PM). Panel b: the sample is located on a conical-tip holder mounted on an x–y–z rotating table. Panel c: illuminated cylindrical sample located on the conical holder. The illuminated area covers a circular region with a diameter of 0.3 cm.