Cross-frequency correlation of intensity fluctuations for a deeply modulated phase screen

摘要

We consider the intensity fluctuation patterns produced beyond a deeply modulated phase changing screen when two plane waves, each with a different frequency, are incident on the same screen. The spatial frequency spectrum corresponding to the cross-correlation between these two different intensity fluctuation patterns is derived. This spectrum has two distinct regions, one of low spatial frequencies which is independent of the incident wave frequencies, and another at high spatial frequencies which is wave frequency dependent. As the difference between the incident wave frequencies increases the upper cut-off spatial frequency of the spectrum decreases. The corresponding cross-scintillation index is also considered and it is shown that this is independent of the incident wave frequencies close to the phase screen and including the focal region where there is a peak in the index. In the far field the scintillation index approaches unity as the distance from the screen increases in the monochromatic case. However, for different incident wave frequencies the far-field scintillation index falls off both with distance from screen and with increasing wave frequency difference.