  We present the concept of a novel time-focusing technique for neutron
spectrometers, which allows to disentangle time-focusing from beam divergence.
The core of this approach is a double rotating-crystal monochromator that can
be used to extract a larger wavelength band from a white beam, thus providing a
higher flux at the sample compared to standard time-of-flight instruments, yet
preserving energy resolution and beam collimation. The performances of a
spectrometer based on this approach are quantitatively discussed in terms of
possible incident wavelengths, flux at the sample and $(Q,E)$-resolution.
Analytical estimates suggest flux gains of about one order of magnitude at
comparable resolutions in comparison to conventional time-of-flight
spectrometers. Moreover, the double monochromator configuration natively shifts
the sample away from the source line-of-sight, thus significantly improving the
signal-to-noise ratio. The latter, in combination with a system that does not
increase the beam divergence, brings the further advantage of a cleaner access
to the low-$Q$ region, which is recognized to be of fundamental interest for
magnetism and for disordered materials, from glasses to biological systems.
