An integrating optical collector with a diffusely reflective interior surface and with at least one wavelength selective absorptive filter located therein in a position that nearly bisects the interior of the collector. The filters are highly transmissive in a first wavelength band corresponding to an emission band of a storage phosphor, but highly absorptive in a second wavelength band corresponding to a stimulation band of the phosphor. The filter's wavelength selective properties and nearly bisecting position in the collector minimizes re-illumination of a phosphor at the stimulation wavelength, while permitting efficient radiation collection and detection at the emission wavelengths. A cylindrical collector with two parallel lengthwise slits permitting passage of the scan beam to the phosphor surface is preferred. Two filter plates on opposite sides of the slit may be used, which can either be parallel to each other and to the slits or oriented at an angle with respect to each other.