  Optical spectrometers, instruments that work with monochromatic light, are
commonly rated by the spectral bandwidth, which defines the ability to resolve
closely spaced spectral components. The ability to detect faint objects among
these components, spectral contrast, is another desired aspect. Here we
demonstrate that a combined effect of angular dispersion (AD) and anomalous
transmission (AT) of x rays in Bragg reflection from asymmetrically cut
crystals can shape spectral distributions of x rays to profiles with record
high contrast and small bandwidths.
  The AD&AT x-ray optics is implemented as a five-reflection three-crystal
arrangement featuring a combination of the above mentioned attributes, so much
desirable for x-ray monochromators and analyzers: a spectral contrast of ~ 500,
a bandwidth of ~ 0.46 meV and a remarkably large angular acceptance of ~ 107
urad. The new optics can become a foundation for the next generation inelastic
x-ray scattering spectrometers for studies of atomic dynamics.
