## Step 10: Real World Applications

According to the Teachspin website http://www.teachspin.com/instruments/faraday/index.shtml, Faraday rotation has a practical application in optical isolators.

"An optical isolator is a device that allows light to go through in one direction but severely attenuates reflected light propagating in the opposite direction. Modern ultra-high field permanent magnets and special paramagnetic glasses have made these devices quite small, but not cheap (about \$2K)."

Optical isolators are applied to optical fiber systems and audio signal switching.  They "have important applications in telecommunications preventing reflected signals on fiber optic cables from producing unwanted signals. Isolators are important when lasers are used because reflected light can cause havoc with the operation of the laser itself."

Also, Faraday rotation is used to detect magnetic fields in interstellar space.

To do this, astronomers/physicists have to estimate the electron density of the space that they are examining, and sum up the cumulative effects of all magnetic fields (parallel to the propagation of the light) between the source and where the measurements of polarization are carried out, on Earth.

In interstellar space, the angle of rotation is proportional to the number of electrons that the light hits times the strength of the magnetic field (parallel to the propagation of the light) multiplied by (integrated over) the distance that the light travels in the field, divided by the wavelength of light squared.  By comparing and analyzing the relative degrees of polarization at various different wavelengths, astronomers can map out magnetic fields far out in the universe!  (At least what they were when the light passed through them, which could have been a very long time ago.)
I ran across this article by C. L. Stong in &quot;The Amateur Scientist&quot; section of a 1970 issue of Scientific American when I was in high school. <a href="http://www.science-project.com/_members/science-projects/1970/11/1970-11-fs.html">http://www.science-project.com/_members/science-projects/1970/11/1970-11-fs.html </a><br> <br>
Wow, very cool! It's funny, though, that the obvious solution now is to simply modulate the voltage on a IR laser diode that is hooked up to a fiber optic.
<p>It is interesting to note that when transmitting in the HF Ham Bands the long distance signal actually rotates with no real need to pay attention to antenna polarization.</p>
i've learned more about light from you in one night than an entire unit in physics class from my techer... mad props man... my mind is blown, yet another reason faraday is the most badass of all scientists... also he got babes and wasn't afraid of people... have you read his candle lectures? they're some of the best lectures i've ever read... i don't remember the exact title, but they're christmas lectures at oxford i think. really really cool. good job, you and homebrewguru &quot;<a href="https://www.instructables.com/member/TheHomebrewGuru/" rel="nofollow">https://www.instructables.com/member/TheHomebrewGuru/</a>&quot; write the most informative instructables i've ever read... nice job.&nbsp;
Neon sign transformers only put out 20,30 or i some cases 60ma. This is not as dangerous as you describe.<br>MOTs do put out a lot of current and are not short circuit protected (which NSTs are). They are dangerous.
The lethal amount of current is usually around 50 mA
It only takes about 5 to 10 mA through your heart to kill you. Its best to always be as safe as possible!
You can perform these types of experiments in silico and get an intuition for what is happening by using the wonderful eletromagnetics animation software available for windows, linux, and osx at: <a href="http://www.enzim.hu/~szia/emanim/emanim.htm" rel="nofollow">http://www.enzim.hu/~szia/emanim/emanim.htm</a>
OMG! very good instrutable.
0.) Put on your laser safety goggles, AMIRITE? =)<br><br>(Very cool instructable by the way)
One problem with laser safety goggles unlike most safety gear is that properly matched goggles will make said laser beam/dot damn near impossible to see unless you are projecting onto something that will fluoresce.
Laser safety goggles are only necessary for lasers with optical power outputs over 5 mW or lasers that have invisible beams (UV and IR).
hey if this bends light that means you could nmake something invisble
Although this entire project is amazing, perhaps the MOST ingenious part is the &ldquo;&hellip;Physics for an English class!&rdquo; twist!
agreed!
Well.. wasn't light bending supposed to be an 'aid' in time travel ? I thought that bending light in a circular way , could create something that resembles a worm-hole. I know that this experiment only rotates light , but it's a start right ? Just asking ..
No, this I'ble has nothing to do with time travel. &nbsp;And as far as I know, time travel will NEVER be possible for macroscopic objects.
This has to be the most thoroughly documented, complex &quot;how to&quot; that I've ever read - kudos! Reading the Safety cautions alone made my blood race - whether from fear or desire to play with magnets, I'm still not sure... <br> <br>I love the combination of high-science components and pegboard and pine. I love the detail in the instructions such as &quot;remember to drill pilot holes for...&quot; - those are things learned by hands on experience. Did you do all the work yourself; did you have a partner / team / mentor? <br> <br>Most interestingly, what new &quot;aha&quot; moments / learnings / realizations have you had so far from this project? When will you be joining the CERN facility? :) <br> <br>Cheers for a fantastic physics Instructable!
I did all of the work on my own but I talked to professors and grad students to get help or advice for some parts of the project. I have a &quot;WISE&quot; (Wise Individualized Senior Experience) project mentor who assists me in finding contacts and working out problems. My two biggest realizations that came from doing this project are that I love to work with my hands to create things, and that I am really intrigued by physics. Although I still plan to major in chemistry, I now think I'll take at least a few extra physics classes next year.
Most excellent. I was a Physics major myself, many moons ago. I think you know this but Chemistry was revolutionized by Physics (electron interactions and so forth) so having a hand in both makes you extremely marketable... well positioned... whatever you want to call it. The only possible addtion would be a tad of Biology but you probably know that too. <br> <br>Thanks for your reply and best of luck!
Best instructable documentation I have ever read! You need to write textbooks in this format. Great JOB!
Thanks!
I hope everyone realizes that this is not supposed to be an easy instructable. It took me quite a lot of effort, time, and money. It is mainly educational.
would this work with a standard (5-20mW) red or green laser?
yes -- as I mentioned, I did use 5mW laser pointers
Do you have to be a pro member to be able to put those word box things on pictures? <br>
No. I had a lot of trouble tagging photos because it only works when you use certain browsers and/or certain computers -- I'm not really sure which. I just got my pro membership for getting this I'ble featured. The script for tagging the photos is just a little buggy, I think.
Agreed. I can only use it on Firefox
never got it to work on anything but firefox.
Very good instructable, my hat no longer fits comfortably due to brain expansion.
Awesome -- actual real physics on Instructables! It's a pity that the effect pretty much requires an expensive purchase-only component (the terbium-doped rod). Since the basic requirement is a transparent paramagnetic material, I wonder whether there might not be organic alternatives (like liquid crystals) that would be a bit more DIY friendly.
Based on all my research, there is only one alternative paramagnetic rotator material; however, it costs much more, is very dangerous, and restricts you to creating a Faraday rotation that is orders of magnitude smaller. This option would be to purchase a liquid cell from TeachSpin for \$142 (or somehow make your own), and then fill it with a volatile, toxic carcinogen such as CS2, Xylene, or CCl4 (which dissolve most plastics, by the way). Although Faraday rotation occurs in harmless liquids such as water, the resulting Faraday rotation is not nearly as big as to be observable by the DIY-er. Thus, I concluded that buying the glass rod was my best option.
Thank you for that information! Quantum optics is not my field (I'm a particle physicist), so I very much appreciate the level of research you did to put this together. You're absolutely right that a xylene or carbon-tet liquid cell is <i>not</i> a good DIY option at all (and isn't even a very good classroom option, in the current litigious climate).
After i read this, my IQ had increased. i am struggling through high school physics now, and i hope to one day understand this, because it sounds awesome. Very well done. I understand that this Instructable is highly technical, and therefore must be explained. If you added a couple more pictures, some people might understand the technicalities more. thank you for this instructable.