Grating compressor optimization aiming maximum focal intensity of femtosecond laser pulses

It is shown that the optimal geometry of a Treacy compressor is the full-aperture compressor, in which the beam size at the first diffraction grating is equal to its length. Despite the energy losses and greater size of the focal spot, such compressor provides considerably higher (by 1.5–2 times) focal intensity than an energy lossless compressor. Decreasing the density of grooves from 1200–1400/mm to about 1000/mm also increases the focal intensity by tens of percent. The constructed theory is generalized to the full-aperture two-grating compressor, which is the best design due to the angle of incidence on the first grating smaller than the Littrow angle. Two gratings with a length of 138 cm allow obtaining an intensity of 4.09×10²⁴ W/cm² and 5.01×10²⁴ W/cm² in the focus of F/2 parabola for the projects XCELS and SEL-100PW, reaching the 139 PW and 174 PW power.