  The problem of optimizing the parameters of a laser pulse compressor
consisting of four identical diffraction gratings is solved analytically. The
goal of optimization is to obtain maximum pulse power, completely excluding
both beam clipping on gratings and the appearance of spurious diffraction
orders. The analysis is carried out in a general form for an out-of-plane
compressor. Two particular plane cases attractive from a practical point of
view are analyzed in more detail: a standard Treacy compressor (TC) and a
compressor with an angle of incidence equal to the Littrow angle (LC). It is
shown that in both cases the LC is superior to the TC. Specifically, for 160-cm
diffraction gratings, optimal LC design enables 109 PW for XCELS and 115 PW for
SEL-100 PW, while optimal TC design enables 86 PW for both projects.
