Segmental Ronchigram Autocorrelation Function
Matrix (SRAM) for Aberration Correction
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Sawada et al. [1] had used segmental Ronchigram autocorrelation function matrix (SRAM) method to measure the aberration coefficients before and after aberration corrections. Figure 2743a shows the central parts of the Ronchigram patterns in a focal series. The Ronchigrams from the amorphous film were divided into 7 × 7 segments in order to calculate the aberration coefficients (up to fifth-order) and to perform autocorrelation functions. The absolute values of each aberration coefficient were calibrated by referring to the difference between the defocus values of the two Ronchigrams [2]. Furthermore, the residual aberration can also be obtained by comparing the experimental and calculated simulations of Ronchigrams.

focal series of Ronchigrams and Autocorrelation functions

Figure 2743a. The focal series of Ronchigrams: (a) Under-focus of 128 nm and (b) Over-focus of 128 nm. (c) and (d) Grided images of (a) and (b), respectively. (e) and (f) Autocorrelation functions from (a) and (b), respectively. Adapted from [1]

 

 

 

[1] Sawada H, Sannomiya T, Hosokawa F, Nakamichi T, Kaneyama T, Tomita T, Kondo Y, Tanaka T, Oshima Y, Tanishiro Y, and Takayanagi K (2008) Measurement method of aberration from Ronchigram by autocorrelation function. Ultramicroscopy 108: 1467–1475.
[2] J. A. Lin, J.M. Cowley, Ultramicroscopy 19 (1986) 31.

 
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