Larmore L, El-Sum H M, Metherell A F
Appl Opt. 1969 Aug 1;8(8):1533-6. doi: 10.1364/AO.8.001533.
Optical signals require square-law detectors and hence direct phase measurement is not feasible without the use of a coherent reference beam. On the other hand, acoustic beams can be directly converted to useful electrical signals with linear transducers. Consequently, an external reference beam can be provided electronically rather than acoustically to form an acoustical hologram. A scheme is described where a second external electronic reference beam, phase-locked with the signal beam, is used in combination with the first electronic reference to record only the phase of the signal in an acoustical hologram. All fringes in such a hologram have the same visibility, and the resulting hologram reconstructs the original two-dimensional object. Improved reconstructions were obtained when appropriate spatial filtering eliminated the interference from the conjugate image in a narrow field, coaxial (Gabor) type hologram. The optical analogue of acoustical phase-only holography, is to record an optical hologram on a photographic film having linear characteristics, and variable gamma depending on the signal intensity.
光信号需要平方律探测器，因此在不使用相干参考光束的情况下直接进行相位测量是不可行的。另一方面，声束可以通过线性换能器直接转换为有用的电信号。因此，可以通过电子方式而非声学方式提供外部参考光束来形成声全息图。描述了一种方案，其中与信号束锁相的第二外部电子参考光束与第一电子参考光束结合使用，以仅在声全息图中记录信号的相位。这种全息图中的所有条纹都具有相同的可见度，并且所得全息图可以重建原始的二维物体。当适当的空间滤波消除了窄场同轴（伽柏）型全息图中共轭图像的干扰时，可以获得改进的重建效果。声纯相位全息术的光学模拟是在具有线性特性且伽马值随信号强度变化的照相胶片上记录光学全息图。
