Abstract: The invention is a method of producing oriented, essentially perfect colloidal crystals by subjecting a suspension of colloidal spheres, which is contained betwen two narrowly spaced substantially parallel surfaces, to oscillating motion. This motion must have a frequency greater than the Brownian motion of the spheres and an amplitude approximately equal to the thickness of the surface's separation. This method is suitable for monosized spheres of radii between about 0.1 and 1 micron. The suspension of colloidal spheres must have a volume fraction greater than 0.49. This method produces colloidal crystals with a uniform face centered cubic structure, which are suitable for use as notch optical filters, high strength ceramics, or thin film dielectric materials.

Abstract: A multichannel digital signal correlator or structurator receives pulses e.g. from a photo multiplier (1) and passes them through a standardizer into channels 1 to M. Each channel has a counter (5.sub.m, m=1 to M) and shift register (6.sub.m) together with a multiplier (7.sub.m) and accumulator (8.sub.m). Clock pulses are applied to each counter (9) and shift register (6.sub.m) from a clock (4) through frequency dividers (9.sub.m) each set to different values giving increasing sample times (T.sub.s) in successive channels. Each multiplier (7.sub.m) has one input to the first stage of its associated shift register (6.sub.m) and another input connected to the fourth stage of the shift register (6.sub.m). Thus the multipliers receive two inputs one delayed (by .tau.) with respect to the other input. Accumulators (10, 11) count the number of photomultiplier pulses and clock pulses respectively during an experimental run. The correlator thus correlates two signals with increasing sample times (T.sub.