Depolarization introduced by a high NA microscope objective.

<p>3(a) The microscope objective is illuminated by a linearly polarized plane wave and focuses the beam onto the sample. This mode of illumination is used in confocal microscopy. (b) The linearly polarized beam is focused into the back-focal plane of the objective (widefield illumination). The sample is illuminated by a collimated plane wave. The “pupil” polarization states in the image planes are depicted using vertically polarized incident beams. Widefield illumination (b) leads to lower loss of polarization in the illumination field than focused beam illumination (a) as confirmed by optical ray tracing simulations.