  We have developed low-dispersion (1480 l/mm), resonance-free, diffraction
gratings made of dielectric materials resistant to femtosecond laser damage
$(SiO_{2}/HfO_{2})$. A 14 cm diameter sample was fabricated resulting in a mean
diffraction efficiency of 99.1% at {\lambda} = 810 nm with 0.4% uniformity
using equipment which can fabricate gratings up to 1m diagonal. The
implementation of these gratings in the compression of 30 fs pulses in an
out-of-plane geometry can result in compressor efficiencies of ~95%. The
measured laser absorption is 500x lower than current ultrafast petawatt-class
compressor gratings which will enable a substantial increase in average power
handling capabilities of these laser systems.
