A polyimidemetal composite sheet is composed of a metal film and a polyimide film polyimide which is prepared by reaction of asymmetric biphenyltetracarboxylic acid dianhydride and 1,3-bisbenzene. These tractable approximations are employed in lieu of exact inferences that are normally NP-hard to solve. The water vapor then can be condensed to form purified water. The modular system includes a reclining chair and a four-legged stacker chair with arm rests and plugs so that the chairs can be reconfigured as desired by the user. Other novel aspects of the system include a system for compensating for variations in the pulse energy of a Q-switched laser output, methods for autofocussing of the wafer imaging system, and novel methods for removal of repetitive features of the image by means of Fourier plane filtering, to enable easier detection of wafer defects.