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Uncovering the secrets of the cosmos … with a little help from Gerbig.

Ligo ObservatoryCompleted in 1999, the Laser Interferometer Gravitational-Wave Observatory (LIGO) is a facility dedicated to the detection of cosmic gravitational waves and the measurement of these waves for scientific research. It consists of two widely separated installations within the United States – one in Hanford, Washington and the other in Livingston, Louisiana – operated in unison as a single observatory.

Gerbig played a role in supplying cleanrooms for the LIGO facility. As one of their contractors we designed and built over 46 softwall and hardwall cleanrooms as well as two laser enclosures and many other portable clean enclosures.

What are gravitational waves?

Gravitational waves are ripples in the fabric of space and time produced by violent events in the distant universe, such as the collision of two black holes or shockwaves from the cores of supernova explosions. These ripples then travel toward Earth, bringing with them information about their cataclysmic origins, as well as invaluable clues as to the nature of gravity.

Albert Einstein predicted the existence of these gravitational waves in his 1916 general theory of relativity, but only now in the 21st Century has technology advanced to enable their detection and study by science. Joseph Taylor and Russel Hulse were awarded the 1993 Nobel Prize in Physics for their studies in this field.

How does LIGO work?

Ligo Scientist 1LIGO will detect the ripples in space-time by using a laser interferometer, in which the time it takes light to travel between suspended mirrors is measured with high precision using controlled laser light. In an L-shaped structure with 2.5-mile arms, two mirrors hang far apart forming one arm of the interferometer and two more mirrors make a second arm perpendicular to the first. These mirrors are the sensors of gravitational waves.

Laser light enters the arms through a beam splitter located in the corner of the L, dividing the light between the arms. The light bounces between the mirrors repeatedly before it returns to the beam splitter.

When gravitational waves pass through this L-shaped detector, they will decrease the distance between the test masses in one arm while increasing it in the other. These changes are minute: just 10-16 centimeters, or one-hundredth-millionth the diameter of a hydrogen atom over the 2.5-mile length of the arm. These changes are then recorded by a photodetector.

Why are two installations necessary?

At least two detectors located at widely separated sites are essential for the certain detection of gravitational waves. Regional phenomena such as micro-earthquakes, acoustic noise and laser fluctuations can cause disturbances that simulate a gravitational wave event. This may happen locally at one site, but such disturbances are unlikely to happen simultaneously at two widely separated sites.

Pushing the limits of technology.

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 laser beams can travel in a clear path with a minimum of scattering due to stray gases.

Ligo Scientists 2The 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.

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.

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 2.5-mile 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.

LIGO, an observatory for the 21st century.

LIGO should be able to detect and measure gravitational waves created by violent events in the distant universe, initially out to distances of 70 million light years. In the world of physics, LIGO has the possibility to test several of general relativity’s predictions; it will be the most stringent test ever of Einstein’s general relativity theory.

In the area of astronomy, among other things studies might reveal are the gravitational waves produced at that first shudder when space and time came into being, in the Big Bang creation of the universe. And astronomers may have no inkling yet of what else they may discover.

Who knows what new experiences await us when we begin exploring the heavens with LIGO?

For more information on LIGO, visit
www.ligo-la.caltech.edu/LLO/overviewsci.htm

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