Interferometric Detection of Gravitational Waves :
5 Needed Breakthroughs -- Rana Adhikari
[Rana Adhikari is a young, charismatic and dependable leader in the field of gravitational wave interferometry. His knowledge and experience with the operation of LIGO detectors with its variety of noise sources, feedback loops and subsystems are held in high respect by his fellow researchers. (Note: LIGO Laboratory operates 3 L-shaped long-baseline interferometers at two locations: Livingston, Louisiana has one of 4 Km arm length and Hanford, WA has one of 4Km and another of 2 Km armlength within the same vacuum enclosure) .
Rana started working on laser interferometers in LIGO around the turn of the century as a graduate student at MIT. He spent some time living with the Livingston interferometer and helped to reduce the noise in all 3 of the LIGO interferometers. In 2005, he received the first LIGO thesis prize. On that occasion, his thesis-supervisor Rai Weiss said,"He taught us how to make the interferometers sing and did this with wit and good humor coupled to precision and clear thinking".
Now, as an Assistant Professor of Physics at Caltech, he works on designing, prototyping and debugging the next generations of interferometric observatories. Here is a list of 5 breakthroughs Rana would like to see in gravitational wave interferometry.
-- 2Physics.com Team]
1) Development of the 'wonder' material (e.g. ultra hard Fullerite): capable of being grown to a 1 ton mass and a 1 meter diameter. Would be incredibly high purity (no mechanical loss), high thermal conductivity (no thermal lens) and very low thermal expansion. In one stroke this would make interferometric detectors immune to quantum radiation pressure noise, lower thermal noise (especially because of larger beam size), and reduce noise due to stray forces.
2) Neural networks for tuning the all digital control systems: in the future the machines will run simulations exploring the possible parameter space of mirror positions, laser power, feedback topologies, etc. They will also then tune themselves for maximum sensitivity and iteratively design their own signal analysis algorithms with only qualitative input from scientists.
3) More Laser Power: the upcoming generation of interferometers in 2011 will be able to sense a part in 1011 of a wavelength. This sensitivity will scale with the square root of the laser power. Quiet lasers with ~10 kW power levels would enable interferometry good enough to hear coalescing binaries anywhere in the universe.
4) Long baseline interferometers: 50 km scale interferometers would reduce the contribution of the low frequency (displacement) noise by a factor of 10 in a very clean way. One can find such sites using Google Earth.
5) Squeezed light injection through the interferometer's dark port to reduce the 'shot noise', phase sensing limit. With 1 ton masses (reducing the effects of photon pressure fluctuations) and very long arms, the gravitational wave sensitivity would be 30 to 300x better than the current generation and only limited by light scattering off of the 10-8 torr of residual molecular hydrogen in the interferometer's beam tubes. Doing better than the LIGO vacuum system would be a real challenge.