By David Órdenes D.
ALVA, Lund University
See instructions on how to
make you own twisted beams below!
All Screwed Up, Scientific American.
November 3, 2003.
"Optical Vortices" Might Extract Abundant
Information From Matter, AIP; Physics News Update, Number 721.
Twisting the light away, New Scientist, Issue 2451. June 12, 2004.
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Light With Orbital Angular Momentum. http://www.aip.org/png/2005/229.htm
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Phys. Rev. Lett. 96, 163905 (28 April 2006)
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The Astrophysical Journal 597, 10 November 2003
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Astronomy and Astrophysics, Volume 488, Issue 3, pp.1159-1165 (2008)
(Preprint version: http://arxiv.org/abs/0706.2675)
Photon angular momentum: selection rules and multipolar transition moments. Roger Grinter
Journal of Physics B: Atomic, Molecular and Optical Physics
Volume 41, Number 9, 14 May 2008
An image of an exoplanet separated by two diffraction beamwidths from a star. E. Serabyn, D. Mawet & R. Burruss
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Constructing your own fork mask
The image used for the demonstration was taken from the web page "Light Beams in High-Order Modes", of the Colgate University, Physics and Astronomy Department. (Link: http://departments.colgate.edu/physics/research/optics/oamgp/gp.htm). There you can also learn more about the physics behind. :)
Since the image is in jpeg format, in order to obtain a high-quality print copy, it's better to vectorize it. This can be accomplished using tools like Potrace and Autotrace (see links below.)
The result is a cleaner, scalable image in black and white:
A pdf version can be downloaded here.
This image must be printed in a normal sheet of paper at a smaller scale. A reduced copy of this print is taken in a photocopier, using an overhead slide as final target. This procedure shoud be followed procuring that the final version is about 6 mm on a side. For better results it's better to print the same image several times in the same sheet, with some variation in size, so you can test with different results in the overhead copy. You might want to try first using the smallest versions that retain enough detail.
The reason for using a photocopier is that they usually can yield a much more detailed copy on reduction than a typical laser or inkjet printer.
Use a laser pointer (safety reccomendations in the links below) to illuminate the mask right in the middle, perpendicularly to its plane. (Be careful with reflections, so be sure the mask is being kept stable and is not going to tumble down or turn around, potentially reflecting a fraction of the beam to someone's eyes). You might need to check for a clear pattern with the "dougnuts" several meters away; it will all depend on the characteristics and quality of both your beam and the printed mask. You can apply some clever method to hold and finely change the position of the mask... And that's it!
The result should look more or less like the image on top of the page, or even better. Enjoy!
Laser Safety Recommendations
Image Vectorization Software (free tools)