Techniques for coordinating updates to replicated data are disclosed. The input coupler is arranged to direct a pump beam to the gain medium and to define an optical path between the output coupler and the rear optical element. The tank are dedicated to the assembly, and preferably are closely adjacent thereto. The leading end of each prismatic vortex generators is inclined away from the direction of flow. The calculation of the backlight illumination levels may be done in advance or on remand. Each second extendable member has two outer pickup elements mounted adjacent the end furthest from the body member when the second extendable member is in the second position.