  The instrumental layout and technical realisation of the neutron resonant
spin echo (NRSE) spectrometer RESEDA at the Heinz Maier-Leibnitz Zentrum (MLZ)
in Garching, Germany, is presented. RESEDA is based on a longitudinal field
configuration, boosting both dynamic range and maximum resolution of the
spectrometer compared to the conventional transverse layout. The resonant
neutron spin echo technique enables the realisation of two complementary
implementations: A longitudinal NRSE (LNRSE) option comparable to the classical
neutron spin echo (NSE) method for highest energy resolution and large momentum
transfers as well as a Modulation of Intensity with Zero Effort (MIEZE) option
for depolarising samples or sample environments such as high magnetic fields,
and strong incoherent scattering samples. With their outstanding dynamic range,
exceeding nominally seven orders of magnitude, both options cover new fields
for ultra-high resolution neutron spectroscopy in hard and soft condensed
matter systems. In this paper the concept of RESEDA as well as the technical
realisation along with reference measurements are reported.
