Laser Speckle from Laser Pointer and Candle?
Many common and inexpensive laser pointers now use laser diodes with excellent coherence properties so that laser speckle and other interference effects can be quite dramatic. “I noticed an interesting animation effect when a laser pointer was pressed against the bottom of a red candle. While viewing through good reading glasses, the side surface of the candle was literally swimming with sharp grainy dots like a bad motion picture show. I’ve since observed these micro animations when illuminating other translucent objects, i.e., a white candle and white glass.” This is most likely a form of laser speckle due to interference from the coherent light source.
Many common and inexpensive laser pointers now use laser diodes with excellent coherence properties so that laser speckle and other interference effects can be quite dramatic. “I noticed an interesting animation effect when a laser pointer was pressed against the bottom of a red candle. While viewing through good reading glasses, the side surface of the candle was literally swimming with sharp grainy dots like a bad motion picture show. I’ve since observed these micro animations when illuminating other translucent objects, i.e., a white candle and white glass.” This is most likely a form of laser speckle due to interference from the coherent light source. In the case of a translucent object like a candle, the wax as well as unavoidable motion of the pointer, candle, glasses, and observer, results in varying path lengths and refractive effects which produce constructive and destructive interference at the retina of the eye – thus the constantly changing pattern of bright and dark spots.
