Figure 1
From: Light-induced rotations of chiral birefringent microparticles in optical tweezers
Sketch of the experimental set-up and chiral particle images.
(a) A laser beam is expanded by a two lens telescope (L1 and L2) to overfill the back aperture of the high numerical aperture objective. Light polarization is controlled by a quarter waveplate. Light scattered from the trapped particle interferes with unscattered laser light in the back focal plane of the condenser of the microscope. The interference pattern is projected by a collection lens onto a four-quadrant photodiode (QPD). The analog outputs from each quadrants are combined to generate signals proportional to the spatial displacements x, y, z of the trapped particle. (b,c) Optical polarization microscopy images of a chiral microparticle taken in transmission (b) and reflection (c) mode through crossed polarizers.
