A new laser system that measures gravitational waves directly will be integrated into a gravitational-wave detector in the US at LIGO’s site in Hanford, Wash. The first direct measurements of these minuscule ripples in space-time are expected to take place in 2014 at Hanford and at LIGO’s Livingston, La., site. LIGO, an acronym for Laser Interferometer Gravitational-Wave Observatory, is operated by the California Institute of Technology in Pasadena and MIT of Cambridge, Mass. LIGO consists of several interferometers, each with an arm length of 4 km. The observatories are located in Hanford, Wash. (seen here), and Livingston, La. (Images: LIGO) The third and latest high-power laser installment, for the “Advanced LIGO” phase, was developed by Laser Zentrum Hannover eV (LZH) in collaboration with the Albert Einstein Institute Hannover (AEI) and the company neoLase, also of Hannover. Two identical systems were installed for LIGO last year. A 350-kg laser head and several hundred kilograms of wiring, electronics and optics are expected to reach the US soon. This high-power laser system has an output power of 200 W at 1064 nm and is five times more efficient than the laser produced during LIGO’s previous phase, “Enhanced LIGO.” The current laser system couples a high-power laser oscillator to its predecessor’s pure amplifier system. The inner workings of a 200-W laser oscillator for LIGO. The measurements are carried out in large Michelson interferometers. Each interferometer is situated in a vacuum in one of the observatory’s 4-km-long arms, which are perpendicular to one another. When gravitational waves pass through the observatory, the relative lengths of the interferometer arms change. One arm is lengthened and the other shortened, causing a phase shift in the laser lightwaves. This interference alters the intensity of the light measured at the interferometer exit. The whole setup can measure a relative difference of 10 to 22 in the arm lengths. Scientists at LZH, AEI and neoLase have been working on prototypes for the past 10 years. “One of the greatest challenges for the scientists and engineers was to take the system used in one of the first lab prototypes, which demonstrated the basic specifications, and to develop it into a system with constant output and frequency, that runs reliably day in, day out for several years,” said Dr. Peter Wessels, who is the head of the group working on the LIGO laser. The scientists have already begun to develop lasers for the third-generation gravitational-wave detector. For more information, visit: www.lzh.de