Diffuser mounted on tuning fork efficiently reduces laser speckle

Shigeo Kubota of the University of Tokyo (Tokyo, Japan) and Joseph Goodman of Stanford University (Palo Alto, CA) have determined that to reduce laser speckle, a moving diffuser on a tuning fork does a better job than the more conventional rotating diffuser with less motion. The result is important for laser-projection displays, which are on their way to becoming commercial products. The researchers both calculated and experimentally verified that a diffuser vibrating in an approximately sinusoidal fashion over a displacement on the order of an autocorrelation length can reduce the speckle contrast to 0.034, or 3%, with very little motion needed.

 

In the experiment, a small frosted-glass diffuser was fastened to a window with desiccated air between them (dry air keeps the diffuser properties from changing); the assembly was mounted to a tuning fork and made to oscillate at 100 Hz with an amplitude of only 60 μm. Other improvements, such as polarization "diversity" (or depolarization of the incoming light by the diffuser) and an oscillatory motion with smaller nonsinusoidal overtones, will further reduce the speckle contrast. Contact Shigeo Kubota at kubota@iis.u-tokyo.ac.jp.

 


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