Abstract: A narrow-band interference filter is placed in the path of reflected opti energy for rejecting undesirable signals to thereby improve the signal-to-noise ratio. The interference filter functions as a bandpass filter having a center frequency centered around the frequency of the transmitted optical beam. The filter includes four identical quarter annulus sections, each composed of a mosaic of interference filter elements cemented to a glass substrate. Each substrate is itself positioned within a skeletal spider structure to provide the desired shape and rigidity.