Analysis of coherent optical transition radiation interference patterns produced by SASE-induced microbunches

We present an analysis of data published recently on coherent optical transition radiation interferometry (COTRI) angular distributions made on the Argonne experiment on microbunching. These COTRI distributions exhibited some intriguing characteristics: highly enhanced lobe patterns in the ±θ_y direction, instead of circularly symmetric fringes; and asymmetries in intensities in +θ_y vs. -θ_y in some cases. We have done calculations that produce patterns consistent with those observed. The role of the microbunch´s elliptical transverse beam profile in accounting for the θ_x-θ_y asymmetry is illustrated. Similarly, a beam profile with a ±y asymmetry gives a lobe asymmetry in +θ_y vs. -θ _y. The interplay of the interference fringe pattern and the microbunch´s transverse form factor accounts for the angular positions of the lobes. The fringe visibility was calculated by convolving the beam divergence distribution with the COTRI pattern. Thus, we have shown that COTRI angular patterns can be used to characterize the effective transverse size, microbunch length, divergence, and the bunching fraction