While some of you may yawn when I talk optics, it is what I do for a living, and actually, it is big business here. Tucson is sometimes referred to as "Optics Valley" with all of the associated industry. One of the main reasons is the University of Arizona's College of Optical Sciences, formerly known at the Optical Sciences Center (OSC). Located on the SE corner of Cherry and University, it is shown in an IR shot here. Developed in the mid-1960s, if there is an experimental application of optics, research is likely going on here. From thin film applications, optical computing, materials research, it all goes on here. And like the Mirror Lab and the National Optical Astronomy Association (NOAO) another block to the north, it is home to an precision optical shop capable of making large optics.
Of the 3 optical shops within a few blocks of each other, Steward Observatory Mirror Lab has specialized in the 6.5 and 8.4 meter diameter mirrors for large telescopes. NOAO's shop, active in the late '50s and '60s for development of telescope mirrors and instrumentation for Kitt Peak National Observatory (here near Tucson) and Cerro Tololo (down in Chile), is mostly inactive now. The OSC shop is very diverse and usually finds work that no one else will bid on - deemed too difficult or impossible to build by other optics shops. I actually got my start in optics at the OSC shop back in the '80s doing precision metrology and surface generating. The multiple shops are not in competition - in actuality they cooperate and borrow equipment and supplies back and forth quite frequently.
At the moment, the highlight of the OSC optics shop is the 4.2 meter diameter mirror for the Discovery Channel Telescope. The project is a partnership between Lowell Observatory, a private observatory located in Flagstaff, Arizona and yes, the company that brings the Discovery Channel to your cable TV system. The new Observatory will be located in Happy Jack, Arizona, an excellent site near 7,800 feet elevation 45 miles SE of Flagstaff. There are a number of interesting features of the mirror, probably the biggest challenge in fabrication is that it is only 10cm (4") thick. Because the large mirror is so thin, it is flexible, so it is extremely difficult to make into a precision surface. The solution OSC uses is 100+ passive supports to overcome the flexibility. In a recent visit, these pictures show Norm working on a zone near the center of the mirror. The thin mirror and numerous supports are seen.
The latest news I've heard is that the mirror is nearing completion in the next few weeks. The image at left shows a posted map of the surface errors as of the end of June. Opticians use interferometers to measure the surface profile of mirrors. Like a carpenter uses a ruler to measure a structure, an interferometer uses wavelengths of light as a ruler to measure mirror errors. Using these devices, errors of millionths of a millimeter can be reliably obtained. One of the neat aspects of the north end of the OSC shop is that the machine is built under a test tower, so after a polishing run, the mirror is washed and dried and can be measured without moving the mirror or support system.
Ok, enough about optics and telescopes - I promise our next post will NOT be about glass, astronomy or telescopes!