激光光斑形状和尺寸对扫描显示中散斑对比度的影响

计算了圆形、矩形激光光斑对于激光扫描显示系统中散斑对比度的影响.对于圆形光斑,当光斑尺寸大于散射表面相关长度时,得到的散斑对比度随着光斑尺寸变小而下降;当光斑尺寸接近表面相关长度大小时,由于光斑中包含的散射颗粒变少,得到的是非高斯散斑,散斑的对比度反而会变大;随着激光斑进一步变小,由于镜面反射效果散斑的对比度会很快下降.对圆形光斑部分结果给出了实验验证.为了保证光斑中有足够的散射颗粒,只在一个方向压窄光斑,分别计算了平行于扫描方向和垂直于扫描方向压窄光斑得到的散斑对比度.平行于扫描方向压窄光斑,散斑的时间相关性会下降,平均效果变明显,散斑的对比度变小;垂直于扫描方向压窄,散斑对比度变化不大.

Effect of structure and size of laser spot on speckle contrast in laser scanning display

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.