Soon, Very Soon Now
Charles Kennemore of JDSU in Santa Rosa, a Senior Engineer from the Optical Coating Labs part of JDSU, now Viavi, invited us on a tour of the operation with his team of engineers who will coat the 40-inch mirror. Members of his team have visited Steve Follett’s garage shop to see the mirror and got our “tour” of the mirror grinding, testing and interferometer setup.
Steve, Mark, Larry and I came to the JDSU offices in Santa Rosa on a sunny Friday afternoon to show us what preparations his team had made and what we could expect from them in the coating process. One comparison of the two tours is that there was MUCH more walking involved with the OCLI tour. Charles and his engineering team hosted us for lunch and showed us a video of a precision domed window coating process. We saw all of the handling equipment and all of the processes that would be used to take our mirror from crate to cleaning to coating to testing and back to the crate.
Charles made it clear from the start that our mirror was as important to them as the multi-million dollar projects that they work on every day. Our first stop on the tour was the receiving shop where the mounting ring was prepped and final adjustments were being made for accepting the mirror.
The mounting fixture is a steel ring more than a meter across with many attachment points. When the mirror is uncrated, this ring will be slipped over the mirror’s circumference, supports will be secured under the mirror, the ring will be lifted to support the mirror, and then supports will be secured on top of the mirror’s edge, with rubber cushions between the steel supports and the mirror, top and bottom.
The ring has interface attachment points for the electric moving cart to grab and two large knobs outside the ring that will let the robot flip the mirror. That is necessary because the mirror will be face up for cleaning and face down for coating.
Even though OCLI at JDSU is a much smaller company than it was 20 years ago, the laboratories, offices and shops are labyrinthine and feel huge to those of us used to working our home shops. On the way to the main event of the tour, the chamber where the mirror will be coated, we saw smaller machine-controlled coating chambers, coating chambers that use lithography to precisely coat miniature optics integrated on a chip and mirror grinding shops that looked very familiar – a pitch pot is still a pitch pot even in a sophisticated enterprise like OCLI. And they use the same 9 micron polishing material that we do – they just buy it in 20 pound boxes!
The 40-inch mirror will be coated in this 120-inch chamber and manually controlled throughout the process by one of the engineers we met. We will be invited to watch the whole process which will likely take a full day to get through the cleaning, coating and testing.
In this image of the coating machine you can see the rotation mounts at the top. The mirror in its ring will be suspended, face down, and will be slowly rotated during the coating run. Five planetary rotating mounts around the central one will hold “witness” glass that will be coated along with the mirror that can be used to evaluate the goodness of the coating without disturbing the mirror itself.
The bottom of the chamber contains the pots of aluminum and other substances that are heated to melting point and vaporize within the evacuated chamber. Outside this chamber were the huge pumps used to pump the atmosphere out of the chamber once it is locked down, and oil diffusion pumps which pump the last molecules our of the chamber in preparation for the coating. The whole process is controlled by an operator and monitored in a number of ways, including a sensor which weighs the mirror and is sensitive enough to see the increased mass as the coating is deposited on the mirror surface in a very thin layer. The chamber room itself is surrounded by rooms dedicated to preparation of the mirror before and post-coating processing.
Finally, as we made our way out of the heart of the shops, we got to see the optical testing lab where a 24-inch zygo interferometer was kept under wraps for testing large optics, especially flats (it has a 24-inch flat incorporated into its optics!) along with optical benches that would be very familiar to any amateur telescope maker for setting up and doing Foucault test of a mirror. Charles was especially keen to show us one more testing lab with electron microscopes and a large atomic force microscope where we ran into a very tall Phillip Hebenstreit, who turned out to be his father, Willy! Here, Charles and Willy are able to troubleshoot problems in coatings by actually imaging them at nanometer scales to find the causes of unwanted bumps and wiggles in a coating (was the mirror clean? was there a disturbance during the coating process?). Demonstration images of the process of investigating mysteries in a process at this scale were fascinating to hear about and to see.
Back in the conference room where we started, Charles explained why we had been delayed for so long and then asked us how soon he could have the mirror. We all looked at each other and, pretty much as one, said we could get it there in its crate in the next couple of hours, if he liked! He said he was going to try and insert our project into the chamber schedule in between a couple of delayed projects and that he would let us know in the next week when to bring it in. We said we could manage that with no problem.