Sharpe J P, Barbier P R, Moddel G, Johnson K M
Appl Opt. 1995 Jul 10;34(20):4013-21. doi: 10.1364/AO.34.004013.
We demonstrate the application of an asynchronous image-subtraction optically addressed spatial light modulator to particle image velocimetry fringe processing. The device comprises an amorphous silicon p-i-n-i-p photosensor and a ferroelelectric liquid-crystal light-modulating layer. The images to be subtracted are encoded on two separate wavelengths. The operation of the device is described, and characterization shows a frame rate of 100 Hz, a resolution of 3 line pairs/mm, and a write-light sensitivity of ≈1 mW/cm(2) at a wavelength of 514 nm. The device is read by the use of light with a 633-nm wavelength whereas the subtraction light is at a wavelength of 670 nm. Using this device to subtract a nonuniform pedestal from the optically computed power spectral density function (the Young's fringe pattern), we find we can improve the signal-to-clutter ratio of peaks in the image-transmittance autocorrelation function of particle image velocimetry transparencies. The device also permits processing of very low-visibility fringe patterns, generated from doubly exposed images, in which one image has half the transmittance of the other. These could not be processed with a nonsubtracting, binary, liquid-crystal optically addressed spatial light modulator.
我们展示了一种异步图像减法光学寻址空间光调制器在粒子图像测速条纹处理中的应用。该器件包括一个非晶硅p-i-n-i-p光电传感器和一个铁电液晶光调制层。要相减的图像被编码在两个不同的波长上。描述了该器件的操作，其特性表明帧率为100Hz，分辨率为3线对/毫米，在514nm波长处的写入光灵敏度约为1mW/cm²。该器件使用633nm波长的光进行读取，而减法光的波长为670nm。使用该器件从光学计算的功率谱密度函数（杨氏条纹图案）中减去不均匀的背景，我们发现可以提高粒子图像测速透明片图像透射率自相关函数中峰值的信杂比。该器件还允许处理由双曝光图像产生的极低可见度条纹图案，其中一幅图像的透射率是另一幅的一半。使用非减法的二进制液晶光学寻址空间光调制器无法处理这些图案。
