Re: strange pictures of lenses between crossed polarisers

yosi wrote:
It is known that stresses patterns inside transparent materials between crossed polarisers show up when illuminated with white light. It was found that many lenses when inserted between crossed polarisers show a black cross as shown in the following picture. This is not a stress pattern, since it does not rotate with the lens. Is anybody aware of an explanation? Most articles dealing with crossed polarisers deal with unisotropic crystals, whereas the pattern appears for many glass lenses.

The picture was taken with an ordinary digital camera and the lens was lying flat on glass plate ( not held in a holder )

The light source may have to be quite bright to see the effect.

You don't give many details about the lens, but microscope lenses (high numerical aperture) often exhibit a "Maltese cross" pattern at the back pupil plane:

http://www.olympusmicro.com/primer/techniques/polarized/firstorderplate.html

Has the best image I could find online..

My understanding is that this effect is produced by diffrences in the Fresnel transmission coefficients between S- and P- polarized light for a surface, and azimuthally around the lens, the amount of linearly polarized light has an angularly varying decomposition of S- and P- components.


--
Andrew Resnick, Ph.D.
Department of Physiology and Biophysics
Case Western Reserve University
.