HOW LIGO WORKS


LIGO must measure the movements of its mirrors, separated by two and a
half miles, with phenomenal precision. To achieve its goal, LlGO must
detect movements as small as one thousandth the diameter of a proton,
which is the nucleus of a hydrogen atom. Achieving this degree of
sensitivity requires a remarkable combination of technological
innovations in vacuum technology, precision lasers, and advanced
optical and mechanical systems.
LIGO's interferometers are the world's largest precision optical
instruments. They are housed in one of the world's largest vacuum
systems, with a volume of nearly 300,000 cubic feet. The beam tubes
and associated chambers must be evacuated to a pressure of only one-
trillionth of an atmosphere, so that the laser beams can travel in a
clear path with a minimum of scattering due to stray gases. To do
this, LIGO scientists and engineers have worked with industry to
produce steel with a very low dissolved hydrogen content.

The LIGO laser light comes from high-power, solid-state lasers that
must be so well regulated that, over one hundredth of a second, the
frequency will vary by less than a few millionths of a cycle. This
severe requirement makes the LIGO detectors among the most precise
test beds available for laser stabilization and has attracted
significant laser development activity worldwide.

The suspended mirrors must be so well shielded from vibration that the
random motion of the atoms within the mirrors and suspension fibers
can be detected. The high-precision, vibration-isolation systems
needed to achieve this are very closely related to equipment used for
the masking and etching of circuitry on silicon in semiconductor
manufacturing.

More than 30 different control systems are required to hold all the
lasers and mirrors in proper alignment and position, to within a tiny
fraction of a wavelength over the four-kilometer lengths of both arms
of the interferometers. These control systems must be monitored
continuously and able to function without human intervention.
Sophisticated simulation software and state-of-the-art electronics
design are used to perform these tasks.

I preformed the precision optical alignment on this project at the
Hanford site.This was a very difficult assignment ,considering the
tolerances,clean room environment and working with new technologies.

Millwright Ron

www.unionmillwright.com