Case Study

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PG&O designed and delivered specialized optical mirrors to Texas A&M University and the University of Texas at Austin for use in building the first-of-its-kind VIRUS (Visible Integral-field Replicable Unit Spectrograph) instrument, a key part of the Hobby-Eberly Telescope Dark Energy Experiment, or HETDEX. The $36M international research project will study the force that causes the expansion of the universe to speed up, rather than slow down. This unknown force, dubbed by scientists as "dark energy," is analogous to throwing a ball into the air and realizing it is speeding up as it flies into the sky, rather than slowing down and returning. Since dark energy makes up over 70 percent of the universe, understanding this mysterious force is considered one of the top challenges in physics today, according to HETDEX researchers.

The innovative VIRUS system is comprised of 150 small, individual replicas of a single spectrograph. The optical mirrors provided by PG&O for the VIRUS collimator fold mirror were specified for operational wavelength range of 345 nm - 700 nm and are optimized from 350 nm - 590 nm with average reflectivity of greater than 99 percent, and greater than 95 percent between 345 nm - 700 nm. The absolute reflectivity is greater than 98 percent between 350 nm - 590 nm and greater than 92 percent at 345 nm - 700 nm. Angle of incidence is at 12.5±5 degrees. This coating also has to perform in extreme environmental conditions (-25 degrees C to 66 degrees C) and to meet Mil-C-48497 abrasion/adhesion durability standards. The other optical specifications include a surface figure of ?/8 at 632 nm RMS surface quality at 40-20 scratch-dig, and surface roughness of 2 nm RMS.