Time-preserving grating monochromators for ultrafast extreme-ultraviolet pulses.

We analyze the time response of single-grating monochromators for application to extreme-ultraviolet ultrashort pulses. It is shown that time-preserving monochromators can be realized in a single-grating configuration if the number of illuminated grooves is the minimum for a given resolution and the grating time response is close to the Fourier limit for such a resolution. Two different grating configurations are compared: the classical diffraction mount (CDM) and the off-plane mount (OPM). We shown that the CDM is preferred for single-grating monochromators with relatively long time responses, i.e., 100-200 fs, while the OPM is suitable for ultrashort time responses in the 10-50 fs range to realize femtosecond time-preserving monochromators.