Method for detecting subtle spatial structures by fluctuation microscopy

Subtle spatial structures are often reflected on higher-order correlations. Fluctuation microscopy is a good method for detecting such spatial structu res in disordered materials, because the method detects the contribution of the fourth-order density distribution function. We propose an improvement for fluctuation microscopy that increases its sensitivity to subtle spatial structures by enhancing the contributions of both the third- and the fourt h-order density cumulant functions to the observable. We demonstrate numeri cally that the proposed method provides better detection of subtle structur al changes than the original approach with improved stability against exper imental noise. Although we illustrate the method in terms of transmission e lectron microscopy, it is not confined to this microscopy. [S0163-1829(99)0 7925-4].