It is specified that a frame containing at least the plurality of slots is repeated. A rotor chamber has a top casing forming an upper portion defining a volume of space between the rotor and the top casing. The rotating shaft is intermittently rotated to locate the aliquotingdispensing mechanisms individually in the positions whereupon tip mounting, aliquoting, dispensing, and tip casting operations are performed continuously. A decorative cap on the assembly is configured so that it holds the washer on the nut, a gap between the cap and washer to enable the washer to freely rotate and move laterally relative to the nut. A periodicity of the periodic structure in which the refractive index changes periodically can be controlled with a simple configuration.