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2Physics Quote:
"Can photons in vacuum interact? The answer is not, since the vacuum is a linear medium where electromagnetic excitations and waves simply sum up, crossing themselves with no interaction. There exist a plenty of nonlinear media where the propagation features depend on the concentration of the waves or particles themselves. For example travelling photons in a nonlinear optical medium modify their structures during the propagation, attracting or repelling each other depending on the focusing or defocusing properties of the medium, and giving rise to self-sustained preserving profiles such as space and time solitons or rapidly rising fronts such as shock waves." -- Lorenzo Dominici, Mikhail Petrov, Michal Matuszewski, Dario Ballarini, Milena De Giorgi, David Colas, Emiliano Cancellieri, Blanca Silva Fernández, Alberto Bramati, Giuseppe Gigli, Alexei Kavokin, Fabrice Laussy, Daniele Sanvitto. (Read Full Article: "The Real-Space Collapse of a Two Dimensional Polariton Gas" )

Sunday, March 18, 2007

Interferometric Detection of Gravitational Waves :
5 Needed Breakthroughs -- David Reitze

[In our ongoing feature '5-Breakthroughs' , today's guest is Prof. David Reitze of University of Florida, Gainesville.

Prof. Reitze is the newly elected Spokesperson of the LIGO Science Collaboration (LSC), a self-governing collaboration seeking to detect gravitational waves, use them to explore the fundamental physics of gravity, and develop gravitational wave observations as a tool of astronomical discovery. It includes scientists from the LIGO Laboratory as well as collaborating institutions from US, Australia, Germany, India, Japan, Russia, UK. The mission of LSC is to insure equal scientific opportunity for individual participants and institutions by organizing research, publications, and all other scientific activities. In fact, the March meeting of LSC on scientific collaborations between LIGO and the French-Italian group Virgo is starting tomorrow in Baton Rouge, Louisianna.

In the field of gravitational wave interferometry, Prof. Reitze's research activities spanned a wide range of topics crucial for successful operation and improvement of the sensitivity of interferometric detectors: Investigation of thermal lensing in passive and active optical elements; development of high power optical components; development of new interferometer topologies for next generation detectors; design, construction and operation of the LIGO interferometers.

Here we present the 5 important breakthroughs that the new Spokesperson of LIGO Science Collaboration (LSC) wishes to see in the worldwide effort for the detection of gravitational waves.-- 2Physics.com Team]

"In order from 'most possible in the near term' to 'most ambitious' are my five most important breakthroughs needed for gravitational wave astrophysics :

1) The direct detection of gravitational waves from astrophysical events such as the inspiral and merger phases of binary neutron star or black hole systems. Observations of these events will reveal significant astrophysical information about neutron stars and black holes, including their masses, spins, and the nature of strong-field gravity in regions of high space-time curvature. As a side wish, I would like to see the development of computational waveform templates for BH-BH collisions as well as supernovae waveforms.

2) Large scale interferometer implementations of quantum optical methods which circumvent the 'standard quantum limit' imposed by the statistics of photons. Such methods include but are not limited to the use of non-classical states of light, ponderomotive squeezing, and line-broadened cavities. Any of these methods would enable GW astrophysicists to improve the sensitivity of interferometers, resulting in an improved rate of detection for gravitational wave events. In order to make these techniques work, however, we would need to develop mirrors which possess lower thermal noise, so I would like to see that too!

3) The development of large scale interferometers underground to push the sensitivity of ground-based instruments below a few Hz. Placing interferometers even 100 m underground dramatically reduces the disturbances due to seismic motion and improves the detection efficiency and event rates for low frequency emitters such as 20-50 solar mass black holes.

4) The development of the Laser Interferometer Space Antenna. LISA will allow astrophysicists to look at even lower frequencies and observe high mass black hole collisions.

5) The observation of the residual gravitational wave radiation from the Big Bang. Unlike the cosmic microwave background, the observation of relic gravitational waves provides a direct snapshot of the universe at the moment of its birth (or about 10-43 sec after). "

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