In laser front projection display, the observer in the far field of the ima
ge pixels on the screen will observe serious speckle noise. For the first t
ime we show a way to eliminate speckles in the far field by modulating a la
ser beam with traveling ultrasonic waves in a liquid cell. The resulting ru
nning interference fringes in a pixel on the screen will produce a boiling
speckle pattern, which will be time-averaged in the eye of the observer. By
superposition of ultrasonic waves of different frequencies, the speckle co
ntrast can be reduced even further. We optimized the modulation frequencies
, as well as the scattering properties of different screen materials. The i
ntensity modulation depth of the speckle pattern could be reduced to a few
percent without noticeable influence on the beam quality. (C) 2000 Society
of Photo-Optical Instrumentation Engineers. [S0091-3286(00)03306-7].