## Optics B/C

Skink
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State: IL

### Re: Optics B/C

Great, that's the same take I got. See, my State more than encourages hands-on work at the State level, so my Optics team should probably drag out the lenses just in case.

kenniky
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Location: ABRHS --> UMichigan

### Re: Optics B/C

Something I'm confused on -

http://hyperphysics.phy-astr.gsu.edu/hb ... ar.html#c3

It says that reflectance for waves parallel to the plane of incidence is $\frac{tan^2(\alpha - \beta)}{tan^2(\alpha + \beta)}$

if $\alpha$ and $\beta$ add to 90, (which is the Brewster angle condition), shouldn't it be zero? but obviously it isn't

is it wrong?

On wikipedia it states that the actual equations are somewhat different...
https://en.wikipedia.org/wiki/Fresnel_equations
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jkang
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### Re: Optics B/C

I actually just went over this in my EM class. Due to the way Maxwell's equations and boundary conditions at the interface work out, there'll be two different polarizations of light with separate equations - one where the magnetic component of the wave is parallel to the interface, and one where the electric component is parallel.
For the first polarization, the Fresnel relations can be derived as $R=(\frac{\beta-\alpha}{\beta+\alpha})^2, T=\frac{4\alpha\beta}{(\beta+\alpha)^2}$, where $\alpha = \frac{cos(\theta_{t})}{cos(\theta_{i})}$ and $\beta = \frac{n2}{n1}$ (note that the notation I'm using is different than hyperphysics').
For the second polarization, the Fresnel relations can be derived as $R=(\frac{1-\alpha\beta}{1+\alpha\beta})^2, T=\frac{4\alpha\beta}{(1+\alpha\beta)^2}$.
If you plot these out, you can find that for the polarization where the magnetic component is parallel to the interface, there is no reflection at the Brewster angle ($\theta_{B}=tan^{-1}(\frac{n2}{n1})$). For the polarization where the electric component is parallel, there is no such thing.
Looking at hyperphysics, it seems the first polarization is $r_{\bot}$ (s-polarized), and the second is $r_{||}$ (p-polarized). From there, you can try messing around with trig identities and algebra and see if you can derive hyperphysics' equation. If not, I'd go with what I (and seemingly Wikipedia) provided.
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kenniky
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### Re: Optics B/C

Oh, I figured out what was going on. $\alpha$ and $\beta$ add to 90 degrees, so the bottom of the $r_\parallel$ goes to infinity which causes the whole thing to go to zero, but that doesn't happen for $r_\perp$

Also, @jkang, I think the first polarization would be $r_\parallel$ and the second would be $r_\perp$
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jkang
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### Re: Optics B/C

Also, @jkang, I think the first polarization would be $r_\parallel$ and the second would be $r_\perp$
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ChingCL
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Posts: 4
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### Re: Optics B/C

I have made a Laser Shoot Setup for my Science Olympiad students to practice positioning mirrors for a laser beam to hit a target. The setup was built using the instructions on the SO website except the following: The laser was mounted on a 3D printed fixture (white part on the LSS picture) with three adjustable screws to align the laser beam to the center of the back wall. Batteries can be changed without disturbing the laser alignment. The laser is protected from accidental bump.

kenniky
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State: MA
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### Re: Optics B/C

I have made a Laser Shoot Setup for my Science Olympiad students to practice positioning mirrors for a laser beam to hit a target. The setup was built using the instructions on the SO website except the following: The laser was mounted on a 3D printed fixture (white part on the LSS picture) with three adjustable screws to align the laser beam to the center of the back wall. Batteries can be changed without disturbing the laser alignment. The laser is protected from accidental bump.

How much are you willing to sell it for

Haha just kidding, looks amazing though! I'd love to have a similar one for practice, or even just to see it used in competition
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ChingCL
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Posts: 4
Joined: April 10th, 2017, 9:43 pm

### Re: Optics B/C

I have made a Laser Shoot Setup for my Science Olympiad students to practice positioning mirrors for a laser beam to hit a target. The setup was built using the instructions on the SO website except the following: The laser was mounted on a 3D printed fixture (white part on the LSS picture) with three adjustable screws to align the laser beam to the center of the back wall. Batteries can be changed without disturbing the laser alignment. The laser is protected from accidental bump.

How much are you willing to sell it for

Haha just kidding, looks amazing though! I'd love to have a similar one for practice, or even just to see it used in competition
Kenny, Thanks for sharing videos and files! If you plan to build an LSS, I offer one 3D printed Laser Mount device sent to you free of charge. Additional files are uploaded.

kenniky
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Posts: 283
Joined: January 21st, 2016, 6:16 pm
State: MA
Location: ABRHS --> UMichigan

### Re: Optics B/C

I have made a Laser Shoot Setup for my Science Olympiad students to practice positioning mirrors for a laser beam to hit a target. The setup was built using the instructions on the SO website except the following: The laser was mounted on a 3D printed fixture (white part on the LSS picture) with three adjustable screws to align the laser beam to the center of the back wall. Batteries can be changed without disturbing the laser alignment. The laser is protected from accidental bump.

How much are you willing to sell it for

Haha just kidding, looks amazing though! I'd love to have a similar one for practice, or even just to see it used in competition
Kenny, Thanks for sharing videos and files! If you plan to build an LSS, I offer one 3D printed Laser Mount device sent to you free of charge. Additional files are uploaded.
Oh, wow, that's great, thank you! I can 3D print it myself, don't worry about it (:
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### Re: Optics B/C

Actually, if you're willing to give out the schematics, I think a lot of us around here could do with an "idiot-proof" design (having messed up my LS in practice quite a few times myself).
Lower Merion 2017
Subtitled: Revenge of the Non-Harriton

Placement Record:

Code: Islip | Conestoga | Tiger | Regionals | States
Out of: 61 | 42 | 36 | 37 | 36

Chemistry Lab: 9 | - | - | 4 | 4
Astronomy: 14 | - | 5 | 10 | 3
Material Science: 12 | 19 | 9 | 5 | 9
Optics: 14 | 7 | 3 | 4 | 2