成人大片

Researchers have developed a new type of deformable mirror that could increase the sensitivity of ground-based gravitational wave detectors such as the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO).

Advanced LIGO measures faint ripples in space time called gravitational waves, which are caused by distant events such as collisions between black holes or neutron stars.

鈥淚n addition to improving today鈥檚 gravitational wave detectors, these new mirrors will also be useful for increasing sensitivity in next generation detectors and allow detection of new sources of gravitational waves,鈥� said research team leader Huy Tuong Cao from the 成人大片 node of the .

Deformable mirrors, which are used to shape and control laser light, have a surface made of tiny mirrors that can each be moved, or actuated, to change the overall shape of the mirror. As detailed in The Optical Society鈥檚 (OSA) journal聽, Cao and colleagues have, for the first time, made a deformable mirror based on the bimetallic effect in which a temperature change is used to achieve mechanical displacement.

鈥淚n addition to improving today鈥檚 gravitational wave detectors, these new mirrors will also be useful for increasing sensitivity in next generation detectors and allow detection of new sources of gravitational waves.鈥�Dr Huy Tuong Cao

鈥淥ur new mirror provides a large actuation range with great precision,鈥� said Cao. 鈥淭he simplicity of the design means it can turn commercially available optics into a deformable mirror without any complicated or expensive equipment. This makes it useful for any system where precise control of beam shape is crucial.鈥�

The new technology was conceived by Cao and Aidan Brooks of LIGO as part of a visitor program between the 成人大片 and , funded by the Australian Research Council and National Science Foundation.

Building a better mirror

Ground-based gravitational wave detectors use laser light traveling back and forth down an interferometer鈥檚 two arms to monitor the distance between mirrors at each arm鈥檚 end. Gravitational waves cause a slight but detectable variation in the distance between the mirrors.聽

Detecting this tiny change requires extremely precise laser beam steering and shaping, which is accomplished with a deformable mirror.聽

鈥淲e are reaching a point where the precision needed to improve the sensitivity of gravitational wave detectors is beyond what can be accomplished with the fabrication techniques used to make deformable mirrors,鈥� said Cao.

Most deformable mirrors use thin mirrors to induce large amount of actuation, but these thin mirrors can produce undesirable scattering because they are hard to polish. The researchers designed a new type of deformable mirror using the bimetallic effect by attaching a piece of metal to a glass mirror. When the two are heated together the metal expands more than the glass, causing the mirror to bend.

The new design not only creates a large amount of precise actuation but is also compact and requires minimum modifications to existing systems. Both the fused silica mirrors and aluminum plates used to create the deformable mirror are commercially available. To attach the two layers, the researchers carefully selected a bonding adhesive that would maximize actuation.

鈥淚mportantly, the new design has fewer optical surfaces for the laser beam to travel through, said Cao. 鈥淭his reduces light loss caused by scattering or absorption of coatings.鈥�

Precision characterisation

Creating a highly precise mirror requires precision characterisation techniques. The researchers developed and built a highly sensitive Hartmann wave front sensor to measure how the mirror鈥檚 deformations changed the shape of laser light.

鈥淭his sensor was crucial to our experiment and is also used in gravitational detectors to measure minute changes in the core optics of the interferometer,鈥� said Cao. 鈥淲e used it to characterise the performance of our mirrors and found that the mirrors were highly stable and have a very linear response to changes in temperature.鈥�

The tests also showed that the adhesive is the main limiting factor for the mirrors鈥� actuation range. The researchers are currently working to overcome the limitation caused by the adhesive and will perform more tests to verify compatibility before incorporating the mirrors into Advanced LIGO.