Figure 1

Optical setup. A dark field imaging system (a), incorporates a rotated polarizer, which is positioned between the condensing lens and the sample. Polarizer rotation induces signal flickering, allowing signal amplification by the lock-in technique. A bright field imaging system (b), incorporates a λ/4 plate, creating a circularly-polarized light. Here, the rotating polarizer is located between the tube lens and the camera.