If I have polarized laser beam. How I can perform de-polarization of it. Or that is already not possible? Thank you in advance!
Hi Vladimir,
There are several methods to do so, all rely on birefringent media:
http://en.wikipedia.org/wiki/Depolarizer_%28optics%29
I hope it helps,
Assaf
Hello Vladimir!
First of all, all laser light is polarized, since you use Brewster windows to act as both mirror and light output, thus polarizing it (you can read more here: http://en.wikipedia.org/wiki/Brewster%27s_angle) . However, the degree of polarization varies from laser to laser, with the Nd-YAG laser being highly polarized.
As for you question, yes, it is possible, apparently, although I'm not inside this theme. Nevertheless, after a quick search, I came across an 1975 article by A. A. Scribot (http://dx.doi.org/10.1016/0030-4018(75)90163-7) on this theme, describing 'the depolarization of a coherent laser beam in the far field of a thick diffusing medium made from stacks of ground glass.' Nevertheless, Havely's comment above is also quite important to understand the basis of this work.
Best,
Alcides
http://dx.doi.org/10.1016/0030-4018(75)90163-7
Dear Vladimir,
Often under the depolarization of light understand the procedure of artificial lowering of the degree of polarization of the light needed for the functioning of a particular experiment or optical devices. In those cases where the loss of brightness beam acceptable for this purpose, light scattering in the turbid medium or a matte surface. Complete the task (or, more precisely, true) depolarization of the light without reducing the brightness of the light beam seem almost insurmountable. Therefore at the solution of specific objectives of polarizing optics procedure of true depolarization of light is replaced with pseudo-polarization procedure.
Wherein each monochromatic light beam component at each time point and each spatial point (more precisely within any coherence area) retains the initial degree of polarization, but because of the spatial, temporal or spectral modulation of the polarization state of the beam as a whole becomes for practical purposes, be indistinguishable from unpolarized.
Temporal modulation of the polarization state of light can be carried out, for example, by rotating at different speeds is placed in the beam of linear phase plates. For spatial (across the beam) polarization modulation can be used wedge phase plates. When working with beams wide spectral composition can serve as effective pseudo- depolarizers the stronglychromatic phase plates made of transparent crystals with a large birefringence (so-called depolarizers Lio ) . Their use leads to a spectral modulation of the polarization state of light.
Best regards, Leonid
The polarized light may be convert into circular un-polarized light by using 1/4 wave plate or an optical element which use the internal total light reflection, like Fresnel rhomb.
In laser microscope imagers, partial depolarisation is often required to improve image quality by speckle reduction. Usually, a clear piece of thin polyethylene plastic (from a plastic bag, or a similar source) is made to vibrate across the beam. This makes some practical approximation of the case of using random scatterers/turbid media for partial depolarisation of the transmitted beam. A very thin flat piece of spectralon (a polymer similar to teflon) used as transmission element can also be useful.
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