A successful combination of TAS+NSE=TASSE has been built on the Polarised Neutron Triple-Axis Spectrometer PONTA of the ISSP, University of Tokyo, at the JRR-3M reactor, based on optimized field shape (OFS) precession coils. With a pair of simple and short OFS coils, energy resolutions (FWHM) of 0.2μeV have been obtained on the thermal three-axis spectrometer PONTA. With respect to classical TAS, the relative resolution (ΔE/E) was improved from ∼ 10−1to 10−5at a cost representing less than 10 percent of the polarized TAS itself. No intensity loss as compared to the normal polarized mode has been observed. Critical slowing down of (DCO3)2dimmers in KDCO3, with extremely large relaxation times 0.15μeV/K, has been observed near the T=353K order-disorder phase transition. Furthermore, an incomplete slowing down of the quasielastic scattering due to the dynamical Huang scattering at the phase transition has been observed for the first time, which can be related to the softening of the shear elastic constant c66observed in the ultrasonic measurements.