Engineering News

From the article: Speckle happens because laser light is coherent - that is, its waves have their peaks and valleys aligned perfectly in phase, like soldiers marching on parade. When those ranks of light waves hit turbulence in the air, they stumble and interfere with each other, producing ever-shifting speckled patterns.

Actually I worked with lasers for a long time and I don't think that this explanation is correct. The speckle phenomenon occurs at the viewer's retina, and it's due to constructive/destructive interference of the coherent light at the retina. I've observed that the pattern changes when I'm wearing or not wearing my glasses, and it always appears sharp, never fuzzy (not out of focus) as it would be if the speckle occurred anywhere else.

The technique described in the article breaks up this coherence, so the constructive/destructive interference at the retina cannot occur.

I recall as a grade school student looking at a tarnished penny in the sunshine. As you move your head, you see a colored speckle pattern that moves one way if you focus your eyes closer than the penny and the other way if you focus them farther away. The pattern always seems to be sharply in focus. I remember asking my teacher about that and she said that was something that we hadn't covered yet. (She didn't have a clue, I know now and suspected then).

I think its similar to the laser speckle effect. I believe that the sunlight, which is bright and fairly well collimated, reflects from the tiny crystals of copper oxide and causes an interference pattern on the retina.