... | ... | @@ -12,7 +12,7 @@ Reflective polariscopes allow for the visualization of the photoelastic fringes |
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* An *analyzer*, which is a circular polarizer located between the photoelastic specimen and the camera.
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* A camera.
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Similar to the [transmissive polariscope](https://git-xen.lmgc.univ-montp2.fr/PhotoElasticity/Main/wikis/transmission-photoelasticity), both the *polarizer* and the *analyzer* should be circular polarizers. In assembling the circular polarizers, it is important for the principle axis of the quarter-wave plate to make a $`45^{\circ}`$ angle with the direction of polarization of the linear polarizer. Note that for a darkfield polariscope, the analyzer must match the chirality of the polarizer on the incident light path (see section 2. for mathematical proof), and can even be the same optical element. For a brightfield polariscope, the two polarizers are complementary.
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Similar to the [transmissive polariscope](/transmission-photoelasticity), both the *polarizer* and the *analyzer* should be circular polarizers. In assembling the circular polarizers, it is important for the principle axis of the quarter-wave plate to make a $`45^{\circ}`$ angle with the direction of polarization of the linear polarizer. Note that for a darkfield polariscope, the analyzer must match the chirality of the polarizer on the incident light path (see section 2. for mathematical proof), and can even be the same optical element. For a brightfield polariscope, the two polarizers are complementary.
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![reflective_circular_4](uploads/9b9996db2ba507c78fd8e16f65a6144c/reflective_circular_4.png)
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... | ... | @@ -27,7 +27,7 @@ There are two typical ways to implement the mirror in real granular physics expe |
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### 1.2. How to make the photoelastic particles reflective?
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A typical way to create the reflective surface for photoelastic particles is to coat one side of the particles with mirror effect paint. An empirical choice that works well is the [*Rust-Oleum Mirror Effect spray*](https://www.amazon.com/Rust-Oleum-267727-Specialty-Mirror-6-Ounce/dp/B00FMRXJW2/ref=sr_1_1?ie=UTF8&qid=1544796251&sr=8-1&keywords=rust-oleum+mirror+effect) (figure below). To ensure uniform coating, it is typical to first paint a sheet of photoelastic material and then cut particles from it. The lower right figure below shows a picture of the painted photoelastic sheet after [cutting of the particles](https://git-xen.lmgc.univ-montp2.fr/PhotoElasticity/Main/wikis/cutting-sample). The figure below also shows different angles of particles after this coating process.
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A typical way to create the reflective surface for photoelastic particles is to coat one side of the particles with mirror effect paint. An empirical choice that works well is the [*Rust-Oleum Mirror Effect spray*](https://www.amazon.com/Rust-Oleum-267727-Specialty-Mirror-6-Ounce/dp/B00FMRXJW2/ref=sr_1_1?ie=UTF8&qid=1544796251&sr=8-1&keywords=rust-oleum+mirror+effect) (figure below). To ensure uniform coating, it is typical to first paint a sheet of photoelastic material and then cut particles from it. The lower right figure below shows a picture of the painted photoelastic sheet after [cutting of the particles](/cutting-sample). The figure below also shows different angles of particles after this coating process.
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![particles](uploads/ba1713b99aba580dd47cdeb73c15cc8d/particles.png)
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... | ... | @@ -40,7 +40,7 @@ It is very important to note that in reflective polariscope, the circular polari |
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### 1.4. Ensure a uniform distribution of light intensity
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In experiments using photoelastic particles, it is important to keep the light intensity distribution uniform among the system. Because both [empirical pressure measurement](https://git-xen.lmgc.univ-montp2.fr/PhotoElasticity/Main/wikis/gradient-analysis) and the [nonlinear fitting force measurement](https://git-xen.lmgc.univ-montp2.fr/PhotoElasticity/Main/wikis/inverse-analysis) depend sensitively on the background light intensity. The reflective polariscope has a higher chance to suffer from the light heterogeneity, comparing to the transmissive polariscope. First, the reflection light intensity is more sensitive to the relative position between light source, particle and camera (left figure below). Second, if the effective mirror is implemented using coated particles, small tilting of particles may induce big change of background light intensity for that particle (right figure below).
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In experiments using photoelastic particles, it is important to keep the light intensity distribution uniform among the system. Because both [empirical pressure measurement](/gradient-analysis) and the [nonlinear fitting force measurement](/inverse-analysis) depend sensitively on the background light intensity. The reflective polariscope has a higher chance to suffer from the light heterogeneity, comparing to the transmissive polariscope. First, the reflection light intensity is more sensitive to the relative position between light source, particle and camera (left figure below). Second, if the effective mirror is implemented using coated particles, small tilting of particles may induce big change of background light intensity for that particle (right figure below).
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![reflective_light2](uploads/fd6f969c1e6d4944a63863c6870eed51/reflective_light2.png)
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... | ... | @@ -165,4 +165,4 @@ Web of Conference 140, 03049 (2017).](#https://www.epj-conferences.org/articles/ |
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[5] [J.W. Phillips (Ed.), TAM 326—experimental stress analysis, University of Illinois, Champaign, Ill (2000), pp. 1-62](#http://www.ifsc.usp.br/~lavfis/images/BDApostilas/ApEfFotoelastico/photoelasticity.pdf)
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[<go back to home](https://git-xen.lmgc.univ-montp2.fr/PhotoElasticity/Main/wikis/home) |
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[<go back to home](/home) |
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