The model 20 uses the the new DeSa subtractive double grating monochromator for selecting and scanning the wavelengths. This tiny 7-sided monochromator uses two huge 40 x 45 mm gratings for outstanding light throughput, even down to the lowest wavelengths. These holographically blazed gratings can be for ultraviolet, UV/Vis, visible, Vis-NIR, or NIR. All associated light sources and detectors will be selected by Olis to be compatible with this blazed grating range. The spectral resolution is 0.5-5 nm, based on the slit width used; slits are interchangeable fixed slits of 0.5, 0.6, 1.24, and 2 mm wide, with other sizes available by special request. Like the Olis DSM 17, it can be enhanced to support scanning (or fixed wavelength) excitation and fixed wavelength emission; it is slightly superior to the model 17 in its excitation intensity performance.