On Sunday, 16 August 2020 12:14:59 PDT Diana Tomchick wrote:
> If only glass is placed between the polarizer and analyzer, the crystal will
> not show artificial colors (try it in a 9-well Pyrex depression plate). The
> artificial colors come from the diffraction of visible light from the plastic
> ware, which depending upon the type of plastic and the way the plate is
> manufactured, will have some preferred orientation of the polymer chains.
> Although it could have more to do with the method of manufacture of the plate.
>
> I would love to hear a different explanation from someone that either sells
> or manufactures crystallization plastic ware.
The question was about using a circular polarizer, which has two components,
a linear polarizing component and a quarter wave plate.
A pair of circular polarizers with a crystal between them will have the same
primary effect as a pair of linear polarizers. But the "quarter wave plate" is
by its nature wavelength dependent. So you get selective removal/transmission
of different color components.
Ethan
>
> Diana
>
> ******************************
> Diana R. Tomchick
> Department of Biophysics, Rm. ND10.214A
> University of Texas Southwestern Medical Center
> 5323 Harry Hines Blvd.
> Dallas, TX 75061 USA
> 214-645-6383 (office)
>
> On Aug 16, 2020, at 12:19 PM, Nukri Sanishvili <sannu...@gmail.com> wrote:
>
>
> EXTERNAL MAIL
>
> Hi All,
>
> Adding some more details to what's been said already. Only because I've seen
> too many times the polarizers being used incorrectly.
> First, you need two polarization filters which are typically called polarizer
> and analyzer. First one (the polarizer) lets through only the light waves of
> a certain polarization. Then one needs to rotate the other one (analyzer)
> until there is no more light getting through. At this point the analyzer
> blocks the light that was let through by the polarizer This is what Diane
> referred to as 90 degrees. Please note that the polarizer-analyzer plates
> stay parallel to each other. After that, a crystal is placed between them and
> is rotated. Unless it is a crystal with cubic symmetry, at some angles it
> will light up in beautiful colors and at some angles it will not. This is
> because the crystal changes the polarization of the light passing through and
> "90 degree setup" of the polarizer/analyzer pair is no longer valid for newly
> polarized light.
> Please note that using plastic plates in this context is not quite
> appropriate. The plastic polymer itself changes the polarization as well and
> therefore it breaks the main principle of this method. With plastic
> interference, it will be impossible to reach complete darkening of the field
> of view. I can almost hear a lot of people saying that they've used it with
> plastic plates without a problem. I believe it to be the case but it still
> doesn't make it right.
> Best,
> Nukri
>
> On Sun, Aug 16, 2020 at 9:15 AM Matthias Zeug
> <matthias.z...@gmx.de<mailto:matthias.z...@gmx.de>> wrote:
> Hi all,
>
> The polarizer-microscope in our facility is not working properly, and I have
> to check my plates using a standard stereo-microscope. As a workaround, I
> thought about buying one at Amazon, placing it on top of the plates and
> rotating it to still test for birefringence.
>
> The product is linked below. Does anyone have some experience with this kind
> of "homemade" system? And also (this might be a stupid question), does the
> product even work? As far as I know, the polarizers in the microscopes are
> linear polarizers, whereas the product linked below is a circular polarizer.
> I would also be happy for product recommendations (optimally available at the
> German Amazon).
>
> Cheers
>
> Matthias
>
> https://www.amazon.de/dp/B00XNMXYBY/ref=cm_sw_r_cp_apa_i_5YsoFbFQXTBP9
>
> ___________________
> Buchmann Institute of Molecular Life Sciences
> Goethe University Frankfurt
> ________________________________
> ________________________________
>
> UT Southwestern
>
> Medical Center
>
> The future of medicine, today.
>
--
Ethan A Merritt
Biomolecular Structure Center, K-428 Health Sciences Bldg
MS 357742, University of Washington, Seattle 98195-7742
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