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LIGO MIT NewsA Summer Vacation
Fifth LIGO Scientific Collaboration Meets At Stanford University
Earlier this year, a "suggestion" was made to a certain freshman graduate student at MIT (namely, me) that he spend some time at the LIGO Hanford Observatory. His mission was apparently to "shakedown" and "characterize" the 2K interferometer's 15-meter Mode Cleaner.
So plans were made and tickets were bought. And as the time to depart for the site drew nigh, he periodically asked himself questions, such as:
-- What exactly does "shakedown" mean? And won't that hurt the equipment?
-- For that matter, what does characterize mean? And how can a set of three mirrors have character?
-- How am I supposed to characterize something which hasn't been installed?
-- What's a Mode Cleaner? (which was since answered eloquently by Fred Raab in the June 1999 issue).
So, with these vital questions largely unanswered, this grad student headed out to the Washington desert...
After two years as an undergraduate at the University of Florida, bothering the Input Optics group, I still hadn't seen a single piece of LIGO. But I had spent countless hours calculating, simulating, and prototyping pieces of the subsystem. So it was with awe when I saw for the first time this humongous thing that I had previously known only through drawings.
At the outset of my stay, I spent a few weeks at work on hooking up and testing a piece of the monstrous data acquisition system, namely the fast channels (>2kHz) of the pre-stabilized laser. The thinking here was that this knowledge would parlay easily into doing the same for the Mode Cleaner (MC). I give many thanks to Rick Savage and Dave Barker for helping me to understand the electronics and software. The size of the 4-pin LEMO connectors were measured to within about 1/4" for cable fitting using the "Ocular Vernier" technique I developed while in kindergarten.
Seeing as the MC still had no character, I decided to get in on its installation and alignment (see Figure 1 above). So for the next few weeks we (Dan Dickerell, Peter Fritschel, Bill Kells, Nergis Mavalvala, Guido Mueller, Haisheng Rong, Dave Tanner and I) climbed around Horizontal Access Modules (HAM) 7 and 8 like ants in their tunnels. The long, long hours put in by these people resulted in the success captured by the pictures of the laser beam shown in last month's newsletter.
Above: (Left) From left to right, Dave Tanner, Dan Dickerell, and Guido Mueller from in front of the west side of HAM7. (Right) Starving grad student demands of Peter Fritschel that he be allowed to get some lunch or he will,"...huff and puff and blow your interferometer down!"
Below: (Left) Shot of the Mode Cleaner's two flat mirrors (MC1 & MC3) in their respective Small Optics Suspensions. The large optic in the Large Optic Suspension on the right is the last Mode Matching Telescope mirror. (Right) Inside HAM8 the Mode Cleaner's curved mirror (MC2) standing proudly in front of the incredibly baffled Recycling Mirror.
One of the most inspiring things I witnessed this summer was the coordinated way in which things progressed (at least, most of the time). It seemed that as soon as we would hit a snag, whoever it was in the LIGO community that had the solution would just "happen" to show up, almost as if it had been planned ahead of time.
Having the opportunity to spend over two months living with the Mode Cleaner (see Figure 6 at right) allowed me to get to work with anyone and everyone who arrived at the site looking to work on the coolest thing in town. And, of course, the permanent site staff is excellent. For fellow green students, I can recommend nothing higher than getting out there as a way of learning about LIGO.
As of last month's newsletter, brief "locks" of the MC were witnessed in air. After pumping down the vacuum system we still saw only a meager 33 percent "visibility," meaning the ratio between the locked and unlocked states of the reflected laser power. This is a loose indication of how much power you're getting into your cavity versus how much your shooting at it. More recently we have seen more healthy amounts, such as 80-90 percent.
To throw out a couple numbers, the MC is designed to have a finesse of approximately 1500, which means that it will hold roughly 10 kW of laser power when its running at full throttle. That's concentrated into a spot of about 1/7 of an inch on the mirrors.
One of the more spectacular windows we have of this cavity isn't a view at all but a sound, provided by a pair of headphones hooked up to the output of the mixer (Figure 7, at left) on the "Demod Board" supplied by the Control and Data System group. This is like listening to the "heartbeat" of the thing, which seemed to have all kinds of noises as of a few weeks ago. After strapping on the headphones, we heard a thumping noise which led us directly to a servo oscillation. We promptly quashed this noise source using the "Holistic Damping" method for tuning the Small Optics Suspensions developed by MIT graduate student Ryan Lawrence this summer. Within about a minute and a half of putting the headphones on, this beautiful 15 meter cavity was aligned, locked and cleaning modes. That's what I call character.
The National Astronomical Observatory of Japan TAMA Group joined the LIGO Scientific Collaboration (LSC). Initially, the group will work on the development of signal recycling for LIGO II.
A near-term development plan for LIGO II was presented and discussed, which promises to improve by over a factor of 10 the strain sensitivity at the noise minimum, as well as to extend the observational bandwidth at both high and low frequencies. The plan is part of the basis for a proposal by the LIGO Laboratory to the National Science Foundation for an upgrade to LIGO to be installed after the LIGO I initial data run.
A draft of the LSC White Paper on Data Analysis was discussed in the data analysis groups. Significant changes were suggested in the draft, which will be reflected in the final draft to be issued in September 1999.
A revised LSC Publications and Presentation Policy was presented and discussed. Small changes to the wording of the policy were suggested and the spirit of the policy was approved. A new draft of the policy was sent to the LSC Council for vote shortly after the meeting.