The Web Newsletter Front Page Livingston Caltech MIT

LIGO Hanford Observatory News

Ladies and Gentlemen, Your New Year's Tables Are Ready!

Ladies and Gentlemen, Your New Year's Tables Are Ready!

- Contributed by Fred Raab

Here at Hanford, our seismic isolation system crew has completed installation of vibration-isolated optical tables that will hold the injection optics for the first LIGO interferometer. This clears the way for installation of the optics right after New Year's Day.

Uses of the Seismic Isolation System

The seismic isolation system ensures that vibrations of the earth and noises in our labs do not affect the LIGO interferometers in our signal band, from 35 Hz to 5 kHz. In other words, if the vibration isolation does its job, the major sources of mirror vibrations in our signal band will either be gravitational waves or a background of sounds generated by the interferometer itself. This background is the sound of atoms at work: the steady rustling of the vibrating atoms in the mirrors, the sound of violins (generated as the suspension fibers recoil from their own vibrating atoms) and the occasional fiberquakes (due to sudden realignments of microscopic crystal boundaries in the suspension fibers). Effectively the goal of the seismic isolation is to build the practical realization of an inertial frame--an idealized concept since the days of Isaac Newton.

Corey Gray with HAM Chamber The 'Men In White' LIGO's seismic isolation was designed by scientists and engineers at LIGO and at HYTEC, Inc. in Los Alamos, New Mexico. Manufactured component-by-component in factories across the US--and tested in labs here at the LIGO Hanford Observatory and at HYTEC--the seismic isolation follows a basic "stack" design that has been used in test interferometers at Caltech and MIT. The basic idea is to stack up strong, stiff, lightweight, structural members interleaved with soft, compliant, shock-absorbing springs--all built to the very exacting standards of ultra-high vacuum hardware. It's also big, as you can judge from the two photos here. In Figure 1 at left, Corey Gray stands outside a HAM chamber with some of the blue and steel-colored structural members showing. And in Figure 2 at right, Rick Savage, Haisheng Rong and again Corey (the "Men In White") can be seen installing an optical table into the same HAM chamber.

While Caltech and Hanford team members assembled the stacks, other groups have also been racing to get ready for the optics installation in January. The University of Florida scientists, teamed with LIGO scientists and engineers, have been hard at work getting the mirrors and mirror-suspension hardware ready for the New Year. Team PSL (Pre-Stabilized Laser) has busily prepared the injection source, a 10W precision, solid-state laser. Team PSL achieved a major milestone by locking their laser onto a reference cavity fringe for 11 days in the midst of the installation frenzy.

When the Dust Clears...

Often unnoticed but worthy of recognition is the large effort that went into getting the vast equipment halls up to optical cleanliness standards. Recent dust counts typically showed less than 500 particles per cubic foot (over 0.3 micron size) during work hours in the cavernous (three-quarter acre and three-stories tall) corner-station hall. Open chambers are surrounded by portable cleanroom enclosures (the pink see-through curtains in Figure 2 above) that supply air with less than 100 particles per cubic foot, and with peaks--during those times when heavy activities outside the cleanrooms drive the dust counts up--to 5000 particles per cubic foot.

This lab is now primed for optics in the New Year.