Faraday Rotation (EPIC!)

Literally bending (twisting) light.

Step 1: Introduction: Circular Magnetic Birefringence

This project recreates Faraday's 1845 experiment that revealed the fundamental nature of light: electromagnetic waves.


History:

• In 1845, Michael Faraday used a powerful electromagnet to rotate the polarization of a beam of light, unifying electromagnetic force with light in one of the most elegant and seminal experiments ever. 

• Two decades later, James Maxwell confirmed this with his classical electromagnetic equations which showed that light is actually an electromagnetic wave. It wasn't until the 1960s, however, that Faraday rotation was modeled quantum-mechanically.

• Today, this effect is called the Faraday effect or Faraday rotation.  See the last step in this instructable for real-life applications.


About this project:

• A Faraday rotator is a device that rotates the plane of polarization of linearly polarized electromagnetic waves (such as visible light) passing through matter (a "dielectric" - an insulator) by applying a magnetic field parallel to the direction of propagation of the light.  (This is a very informative link: http://www.teachspin.com/instruments/faraday/index.shtml )

• I am currently experimenting with the fully functional device that I have built.  I made this device to demonstrate Faraday rotation and I am still working on learning the physics behind it in greater depth.  This is my senior project for my "WISE" English class.  Nice, eh?  I get to do Physics for an English class!

• It will cost a bare minimum of $150-200.  Take a look at the materials section (Step 3).

• It requires a rather advanced understanding of some topics in physics. The basics are up to you to learn (see bottom of this page to see what they are), but I do my best to explain Faraday Rotation with classical physics in the last steps of this instructable.


For more background Information:

• Watch 20:20 to 21:15 of this video: http://fora.tv/2008/05/01/George_Johnson-The_Ten_Most_Beautiful_Experiments

• This book has a detailed description of the original experiment:  The Ten Most Beautiful Experiments (by George Johnson ) (read chapter 6, "Something Deeply Hidden")  You can get some of it here: http://books.google.com/books?id=3w83rbjVWZgC&pg=PA75&dq=the+10+most+beautiful+experiments+by+george+johnson+faraday&source=gbs_toc_r&cad=4#v=onepage&q&f=false

• This website has a ton of useful physics that will really help you understand how Faraday rotation works: http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html  

• Ask the Van is a great reliable resource for answering your physics questions.  It is a Q+A that is run by people who really know what they are talking about: http://van.physics.illinois.edu/qa/newquestion.php  This is where I first went to make sure that this project would actually be possible to do.  You can see my original questions here: http://van.physics.illinois.edu/qa/listing.php?id=17167

• Being familiar with the following terms would be quite useful if you want to understand Faraday rotation:  electromagnetic waves, linear polarization, circular polarization, index of refraction, birefringence, lasers, wavelength, dispersion, Verdet constant, and magnetism.

Comments

[3creeks]

I ran across this article by C. L. Stong in "The Amateur Scientist" section of a 1970 issue of Scientific American when I was in high school. http://www.science-project.com/_members/science-projects/1970/11/1970-11-fs.html

[dyly]

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.

[XTL]

Neon sign transformers only put out 20,30 or i some cases 60ma. This is not as dangerous as you describe.
MOTs do put out a lot of current and are not short circuit protected (which NSTs are). They are dangerous.

[crazy-blender]

The lethal amount of current is usually around 50 mA

[dyly]

It only takes about 5 to 10 mA through your heart to kill you. Its best to always be as safe as possible!

[Superkuh]

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: http://www.enzim.hu/~szia/emanim/emanim.htm

[_Billa_]

OMG! very good instrutable.

[WebDext]

0.) Put on your laser safety goggles, AMIRITE? =)

(Very cool instructable by the way)

[skrubol]

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.

[dyly]

Laser safety goggles are only necessary for lasers with optical power outputs over 5 mW or lasers that have invisible beams (UV and IR).

[tinker234]

hey if this bends light that means you could nmake something invisble

[Dr. dB]

Although this entire project is amazing, perhaps the MOST ingenious part is the “…Physics for an English class!” twist!

[dyly]

agreed!

[Kristy4n]

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 ..

[dyly]

No, this I'ble has nothing to do with time travel.  And as far as I know, time travel will NEVER be possible for macroscopic objects.

[sitearm]

This has to be the most thoroughly documented, complex "how to" 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...

I love the combination of high-science components and pegboard and pine. I love the detail in the instructions such as "remember to drill pilot holes for..." - those are things learned by hands on experience. Did you do all the work yourself; did you have a partner / team / mentor?

Most interestingly, what new "aha" moments / learnings / realizations have you had so far from this project? When will you be joining the CERN facility? :)

Cheers for a fantastic physics Instructable!

[dyly]

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 "WISE" (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.

[sitearm]

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.

Thanks for your reply and best of luck!

[Todd Harrison]

Best instructable documentation I have ever read! You need to write textbooks in this format. Great JOB!

[dyly]

Thanks!

[dyly]

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.

[matstermind]

would this work with a standard (5-20mW) red or green laser?

[dyly]

yes -- as I mentioned, I did use 5mW laser pointers

[techno guy]

Do you have to be a pro member to be able to put those word box things on pictures?

[dyly]

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.

[Data643]

Agreed. I can only use it on Firefox

[falcotheimpaler]

never got it to work on anything but firefox.

[caarntedd]

Very good instructable, my hat no longer fits comfortably due to brain expansion.

[kelseymh]

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.

[dyly]

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.

[kelseymh]

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 not a good DIY option at all (and isn't even a very good classroom option, in the current litigious climate).

[ilpug]

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.