Precision Glass & Optics delivers custom mirrors for HETDEX spectrograph to study dark energy
Santa Ana, CA--Precision Glass & Optics (PG&O) is helping to create a VIRUS. The Visible Integral-field Replicable Unit Spectrograph, or VIRUS, will be an essential component in the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX), which will help in understanding "dark energy."
PG&O delivered specialized optical mirrors to Texas A&M University and the University of Texas at Austin, which will be assembling, aligning, and testing VIRUS. The innovative VIRUS system is composed of 150 small individual replicas of a single spectrograph. The optical mirrors provided by PG&O for the VIRUS collimator fold mirror have an operational wavelength range of 345 to 700 nm and are optimized from 350 to 590 nm with average reflectivity of greater than 99%, and greater than 95% between 345 and 700 nm. The absolute reflectivity is greater than 98% between 350 and 590 nm and greater than 92% at 345 to 700 nm. Its angle of incidence is 12.5±5°.
Coating with 20 year operational lifetime
The coating must perform in extreme environmental conditions (-25°C to 66°C) and to meet Mil-C-48497 abrasion/adhesion durability standards. Its other optical specifications include a surface figure of lambda/8 at 632 nm root-mean-square (RMS) surface quality at 40-20 scratch-dig, and a surface roughness of 2 nm RMS. To meet the requirements for VIRUS, the reflective coatings on borosilicate glass have an operational lifetime of 20 years.
Dark energy is hypothesized to be the major component of the mass-energy of the universe, as well as the reason that the universe's rate of expansion is accelerating. Little is known about dark energy, other than it supposedly makes up more than 70% of the universe's mass-energy. The $36 million international HETDEX project will aim to more-accurately determine how fast the universe expanded at different periods in its history.
Spectra obtained by VIRUS of distant astronomical galaxies will reveal their chemical composition, their temperature, and the speed at which the universe is stretching between the detected galaxies and Earth. VIRUS will capture spectra from 33,000 points on the sky simultaneously, using fiber optics to transfer the light from the Hobby-Eberly Telescope focal plane to the huge replicated array of spectrographs. This will permit HETDEX astronomers to produce a 3D of a large volume of space, which will help reveal the role that dark energy has played during different eras. It will search for any evidence that the strength of dark energy changes over time and also will provide the most precise measurement of the geometry of the universe, which is related to the physics of the universe at the moment of Big Bang.
Interesting telescope design, by the way
The Hobby-Eberly Telescope is located on Mt. Fowlkes in West Texas. Unlike most large telescopes, its segmented primary mirror is spherical and stationary; the secondary optical system, which corrects for spherical aberration, is what moves to allow tracking of objects. The primary is 11.1 x 9.8 m in size, with a 9.2 m diameter being usable at any one time.
To learn more about VIRUS and the Hobby-Eberly Telescope Dark Energy Experiment, see http://hetdex.org.
John Wallace | Senior Technical Editor (1998-2022)
John Wallace was with Laser Focus World for nearly 25 years, retiring in late June 2022. He obtained a bachelor's degree in mechanical engineering and physics at Rutgers University and a master's in optical engineering at the University of Rochester. Before becoming an editor, John worked as an engineer at RCA, Exxon, Eastman Kodak, and GCA Corporation.