The light intensity distribution in the focal region of a high-numerical
aperture optical system (NA=0.85). The focused beam propagates in
the vertical direction (see arrows). In the lower horizontal plane
the intensity distribution is shown in the nominal focal plane. The
two other horizontal cross-sections correspond to defocused image
planes. The state of polarization of the beam initially was linear.
The arrows represent the power flow in the focal region (Poynting
vector). The cone illustrates the ray picture of image formation
Special thanks to Arthur van de Nes for writing the
software that generates the above picture.