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