  This work theoretically investigates high-order harmonic generation in rare
gas atoms driven by two temporally delayed ultrashort laser pulses. Apart from
their temporal delay, the two pulses are identical. Using a single-atom model
of the laser-matter interaction it is shown that the photon energy of the
generated harmonics is controllable within the range of one eV -- a bandwidth
comparable to the photon energy of the fundamental field -- by varying the time
delay between the generating laser pulses. It is also demonstrated that
high-order harmonics generated by double pulses have advantageous
characteristics, which mimick certain properties of an extreme ultraviolet
(XUV) monochromator. With the proposed method, a simpler setup at a much lower
cost and comparatively higher spectral yield can be implemented in contrast to
other approaches.
