Abstract: The present invention is directed to isotopically enriched optical materials and methods of producing the same. The optical materials provide high isotopic purity silica, calcium, zinc, gallium and germanium materials with increased resistance to optical damage which can be used alone or in combination with other means of preventing damage to decrease lens degradation caused by energy-induced compaction during use.

Abstract: The novel weight-balancing device of the present invention is adapted for use in the improved backpack of the present invention. The device comprises a set of two elongated tubes, disposed in telescoping relation to each other with a spring-loaded push button carried by the inner tube adjustably releasably locking the tubes together so that they can have various desired combined lengths. One of the tubes has a slip resistant backpack shoulder strap connector attached at its front end and the other of the tubes has a backpack rear frame connector pivotally secured to its rear end.The improved backpack utilizes a pair of the described novel devices, connected to opposite sides of the backpack rear frame and projecting forwardly to engage the two backpack shoulder straps. Thus, the two devices are disposed on opposite sides of the backpacker.