  Ultrafast light sources have become an indispensable tool to access and
understand transient phenomenon in material science. However, a simple and
easy-to-implement method for harmonic selection, with high transmission
efficiency and pulse duration conservation, is still a challenge. Here we
showcase and compare two approaches for selecting the desired harmonic from a
high harmonic generation source while achieving the above goals. The first
approach is the combination of extreme ultraviolet spherical mirrors with
transmission filters and the second approach uses a normal-incidence spherical
grating. Both solutions target time- and angle-resolved photoemission
spectroscopy with photon energies in the 10-20 eV range but are relevant for
other experimental techniques as well. The two approaches for harmonic
selection are characterized in terms of focusing quality, efficiency, and
temporal broadening. It is demonstrated that a focusing grating is able to
provide much higher transmission as compared to the mirror+filter approach (3.3
times higher for 10.8 eV and 12.9 times higher for 18.1 eV), with only a slight
temporal broadening (6.8% increase) and a somewhat larger spot size (~30%
increase). Overall, our study establishes an experimental perspective on the
trade-off between a single grating normal incidence monochromator design and
the use of filters. As such, it provides a basis for selecting the most
appropriate approach in various fields where an easy-to-implement harmonic
selection from high harmonic generation is needed.
