... | ... | @@ -3,26 +3,33 @@ Imaging photoelastic samples |
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In the [previous section](https://git-xen.lmgc.univ-montp2.fr/PhotoElasticity/Main/wikis/method-make) we explain the different ways to make a photoelastic sample. In this section we will show you the different ways to image it considering the optic, dynamic and geometric constraints you can have, and considering want you want to measure.
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Using transmission photoelasticity method:
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In the most favourable case you you have optically access to both sides of the sample and can then have light going through from a polarised source to a crossed polarised camera.
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This is a method to image photoelastic material when you have optically access to both sides of the sample. In this case you lit the sample from one side and observe it from the other side. More details about this method are give [here](https://git-xen.lmgc.univ-montp2.fr/PhotoElasticity/Main/wikis/transmission-photoelasticity).
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[here](https://git-xen.lmgc.univ-montp2.fr/PhotoElasticity/Main/wikis/transmission-photoelasticity)
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In the most favourable case you have optically access to both sides of the sample and you can then have light going through it from a polarised source to a crossed polarised camera. In this case you can use [the transmission photoelasticity method](https://git-xen.lmgc.univ-montp2.fr/PhotoElasticity/Main/wikis/transmission-photoelasticity). This section presents the method and answers basic questions like:
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* Should I use a circular or a linear polarizer?
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* Should I add a quater-wave plate?
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* How to orient the whole thing and check that I did it properly?
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This is the most simple case so even if you do not use this method, we strongly suggest you to clearly understand it before going further.
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![Capture_du_2019-01-09_13-11-21](uploads/f86accad9f20032a02090f1637a79207/Capture_du_2019-01-09_13-11-21.png)
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Using reflection photoelasticity method:
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----------------------------------------
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[here](https://git-xen.lmgc.univ-montp2.fr/PhotoElasticity/Main/wikis/reflection-photoelasticity)
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When the sample is optically accessible from one side only because au the loading mechanism for example, the [transmission method](https://git-xen.lmgc.univ-montp2.fr/PhotoElasticity/Main/wikis/transmission-photoelasticity) cannot be used anymore. In this case the sample must be both lit and image from the same side. This means the other side, whether it is the back of the particle or the or anything on the non accessible side, must be reflective. So the light is reflected on the back of the sample and go trough it two times. More details about this method are given [here](https://git-xen.lmgc.univ-montp2.fr/PhotoElasticity/Main/wikis/reflection-photoelasticity).
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Using different wavelengths:
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----------------------------
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[here](https://git-xen.lmgc.univ-montp2.fr/PhotoElasticity/Main/wikis/wavelength-imaging)
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To make photoelastic measurements only monochromatic light is enough even if polychromatic light can permit to get more beautiful picture. This mean that the sample can be light and imaged with polarized light of a given wavelength. So other wavelengths can be used for other purpose like detecting the sample geometry, position and orientation. In the figure below extracted from [this article](https://aip.scitation.org/doi/abs/10.1063/1.4983049), for example red light is used to localized the particles while green one is used to measure the photoelastic response. More detail about how to use different wavelengths when imaging photoelastic samples are given [here](https://git-xen.lmgc.univ-montp2.fr/PhotoElasticity/Main/wikis/wavelength-imaging)
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![Capture_du_2019-01-09_13-05-39.rotated](uploads/b0439f1ea9f2fad899f679d5b2a50d0f/Capture_du_2019-01-09_13-05-39.rotated.png)
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Picture extracted from [this article](https://aip.scitation.org/doi/abs/10.1063/1.4983049). Red light is used to localized the particles while green one is used to measure the photoelastic response.
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... | ... | @@ -42,20 +49,9 @@ Using terahertz photoelasticity method: |
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Using polarizers properly:
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--------------------------
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Should I use a circular or a linear polarizer? Should I add a quater-wave plate? How to orient the whole thing and check that I did it properly? [This section](https://git-xen.lmgc.univ-montp2.fr/PhotoElasticity/Main/wikis/tuning-polariser) gives details about all these points.
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Reflection photoelasticy:
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------------------------
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This is a method to image photoelastic material when you have optically access to just one side of the sample. In this case you lit the sample from the side you also observe it, the light is reflected on the back of the sample and go trough it two times.More details about this method are give [here](https://git-xen.lmgc.univ-montp2.fr/PhotoElasticity/Main/wikis/reflection-photoelasticity).
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[<go back to home](https://git-xen.lmgc.univ-montp2.fr/PhotoElasticity/Main/wikis/home)
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