Diffraction Column
Ryan Zhu
Award: Top 100
School: fayetteville-manlius high
Teacher: joshua buchman
Category: Contrived
Photo #19579
Diffraction Column
In this photo, a flashlight beam reflects off the surface of a CD, producing a striking halo and
column of blue light on a nearby wall. This occurs due to the thousands of microscopic grooves
on the CD's surface. The grooves are set in a spiral shape, effectively creating a diffraction
grating, causing constructive and destructive interference when light bounces off of the CD's
reflective aluminum. As a result, when the white light from my flashlight hit the grooves, each
wavelength is diffracted at different angles depending on its wavelength, creating the spectrum
of colors displayed. Since my CD was angled upwards, the resulting light rays get stretched
upwards and outward as they travel towards the wall, creating what looks like a vertical column.
Although the diffraction grating creates a full rainbow spectrum, the colors are so close together
that our eyes blend them together into a brilliant blue.
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