Effect of structure and size of laser spot on speckle contrast in laser scanning display
激光光斑形状和尺寸对扫描显示中散斑对比度的影响

Speckle contrast in laser scanning display system with circular and rectangular laser spot on screen was calculated. For scanning with circular laser spot, the speckle contrast reduces with the decrease of the diameter of laser spot when the diameter of the laser spot is lager than the correlation length of the screen. When the laser spot is about the same size of the correlation length of the screen, the speckle contrast becomes higher owing to the non-Gaussian speckle effect. If we continue to reduce the size of laser spot, because of the specular reflection the speckle contrast decreases quickly. To ensure enough scattering elements in laser spot, the laser spot is just narrowed in one direction. If the laser spot is narrowed in the scanning direction, the speckle contrast is reduced due to the reducing temporal correlation of speckle, while if the laser spot is narrowed in the other direction, speckle contrast changes slightly. For the circular laser spot, some experimental results are given.