GT Crystal Systems gets gravity-wave detector order

27 Sep 2011

Optics firm to deliver a large optical sapphire blank to the Large-Scale Cryogenic Gravitational Wave Telescope in Japan early next year.

GT Crystal Systems is set to deliver a large, high-precision sapphire blank to Japan’s Large-Scale Cryogenic Gravitational Wave Telescope (LCGT) early next year, providing a key component within a giant optical system being set up by engineers to detect gravitational waves.

The LCGT will be the latest optical system to attempt to detect the mysterious waves, usually described as “ripples” in space-time predicted by Einstein’s general theory of relativity and caused by giant cosmic events such as the Big Bang, or collisions between black holes.

To detect the waves, a series of giant interferometers have been built. Any gravitational waves passing through these interferometers would slightly change the distance between two masses placed at each end of one of the interferometer arms. Thanks to their giant size, this change should be detectable with a laser fired around the interferometer.

Because of the incredibly high sensitivity needed to detect any such change, the interferometer mirrors must be based on very high-purity materials, and have extremely low heat absorption at the laser wavelength of 1064 nm – since any build-up of heat would cause thermal lensing and enough of an error to ruin the experiment. The sapphire provided by GT Crystal Systems has an absorption of only 40 ppm/cm at the key 1064 nm wavelength, says the company.

“Only the purest and most perfect sapphire can be used for this demanding application,” said Cheryl Diuguid, VP and general manager of the sapphire equipment and materials group at GT Advanced Technologies – the parent company of GT Crystal Systems. The firm is one of the world’s largest providers of polysilicon production technology to the solar industry, and it also sells growth furnaces, as well as sapphire materials for both industrial and LED manufacturing applications.

The large optical blank for the LCGT will measure ten inches in diameter and six inches in thickness, and will form the basis of the interferometer mirror. It will reflect a 300 W laser with a beam radius of 3 cm along a cavity 3 km long, built deep inside the Kamioka mine in Japan, the site chosen for the LCGT because of its extreme stability and quietness. Other photonic components used in the system will include large-scale lithium niobate electro-optic modulators.

GT Crystal Systems’ more regular sapphire applications include high-end optical components for surveillance and defense, as well as titanium-doped sapphire for ultrafast lasers, while the company has already provided a large, low-absorption sapphire optic for the existing Laser Interferometer Gravitational Wave Observatory (LIGO) in the US, the first phase of which was built in the 1990s and switched on in 2003.

Video: Sapphire production at GT's new manufacturing facility:

Video: Detecting gravity waves: