Variational principle for scattering of light by dielectric particles.

S2 I Fig. 1. Cross-sectional view of dye cell showing aluminum rings AL1 and AL2, substrates S1 and S2, the sealing O-rings, and the Swagelok connectors. the entire cell could be repositioned, and another portion of the mirror could be used. In this way a single mirror could continue to be used following several damaging events. The cell, shown in Fig. 1, consists of two 5.08-cm diam, 0.95-cm thick BK7 substrates, SI and S2, mounted in aluminum rings, ALl and AL2. Substrate SI is coated on its inner surface to reflect 50% at 1064 nm. It is mounted in ring ALl, which has two O-ring grooves, one near its surface and the other along the side. (Although the side O-ring is redundant , it serves as a second seal to prevent dye solution leakage.) The inner reflective surface of S1 is flush with the flat surface of ALl, while the surface O-ring protrudes about 40 ,um above this surface. The second substrate S2 is mounted so that its inner surface protrudes 25,um above the surface of AL2, and it is sealed with a side O-ring. Special care must be taken when machining the aluminum rings so that the rings fit snugly and the substrate surfaces have the proper relationship to the ring surfaces. Each individual substrate must be measured precisely before the machining is begun, as substrate dimensions are not generally held to close tolerances by the manufacturers. All O-rings are 5.08-cm diam and 3.2-mm thick Viton, a material which is tolerant of the dichloroethane dye solvent. The substrate S2 was a 30-ft. wedge, and both surfaces of S2 were antireflection coated at 1064 nm. Before mounting, opposite edges of the inner surface of S2 were beveled off at 450 using a carborundum cutting wheel, while the substrate was held in a simple wooden jig. The optical coatings were protected during the grinding with masking tape. The bevels are each about 1.9 cm long on opposite sides of the surface. When S2 is mounted in AL2 the beveled edges leave a small portion of the inner wall of AL2 exposed, and small holes (56 drill) were drilled at 25° to the normal into these two surfaces. The holes extend until they meet 0.32-cm holes drilled into the back surface of AL2. At the back surface these larger holes are further drilled out and tapped to accept 'li6-in. X %6-in. (1.5-mm …