Shigeo KUBOTA^*

Yokohama Branch, Oxide Corporation, 4-10-4 Tsunashimahigashi, Kouhoku-ku, Yokohama 223-0052, Japan

(Received May 9, 2012; Accepted August 22, 2012)

Spatial coherence of the scanning laser beam was observed on the Young's experimental set up using 50-μm-wide, 200-μm-separation double slits, which measured the less than unity fringe visibility in the Fraunhofer diffraction pattern of the double slits illuminated by the scanning laser beam at horizontal scan frequency 21 kHz, while approximately unity in case of the illumination by the laser beam at rest. This fact allow us to use the Zernike's approximation when applying the van Cittert Zernike theorem to the scanning laser system such as the laser pico-projectors in order to estimate its speckle contrast in the projected image on the screen diffuser. The predicted and measured speckle contrasts showed excellent agreement on the screen illuminated by the laser projector.

Key words: spatial coherence, Young's experiment, double slits, laser, van Cittert Zernike theorem, laser display, diffuser, speckle

^*E-mail address: kubota@opt-oxide.com