Figure 1
From: Characterization of gap-plasmon based metasurfaces using scanning differential heterodyne microscopy
Optical scheme of a scanning differential heterodyne microscope: (1) beam splitter; (2) microobjective 40×/0.65; (3) substrate with an object; (4) positive lens; (5) pinhole in the Fourier plane; (6) photodetector. Probing beams at different frequencies come from acousto-optic modulator (AOM) driven by two-frequency signal.
