GWsensitivity
2015 saw the first detection of gravitational waves from merging black hole binary systems. The waves are detected by monitoring tiny variations in the relative arm lengths in huge interferometers. There are many sources of noise which can mask these miniscule signatures.
Shot Noise - due to the limited number of photons present in the instrument.
Radiation Pressure Noise - the stochastic nature of photon impacts on the instrument mirrors causes them to vibrate.
Seismic Noise - external disturbances, primarily at low frequencies, which are damped out using multiple pendulums and active noise cancellation technology.
Suspension Noise - the wires on which the mirrors are suspended will vibrate.
Coating Noise - thermal noise and jiggling of atoms/molecules in the mirror coatings.
Gravity Noise - the small motions of the Earth close to the detector will cause small disturbances in the local gravitational field at low frequencies.
All these contributions must be added to determine the overall minimum gravitational wave "strain amplitude" that can be detected. In this simulation, the various parameters of the interferometer can be varied to work out which sources of noise are most important (the curve which is highest) at which frequencies and to look at some of the trade-offs and compromises that must be made.
The parameters are:
Input Power - the input NdYAG laser power incident upon the beam splitter (aLIGO 125W).
Power Recycling - the gain in power introduced by the power recycling mirror (aLIGO 32).
Finesse - the phase gain introduced by the Fabry-Perot resonators that form each interferometer arm. Roughly speaking, the number of times the light bounces up and down in each arm (aLIGO 286).
Arm Length - the length of each interferometer arm (aLIGO 3.995 km).
Test Mass - the mass of the mirrors at each end of the arms (aLIGO 40 kg).
Temperature - affects the thermal noise contributions (aLIGO ?).
No. Pendulums - the number of pendulums in the test mass "stacks" (aLIGO 4).
Pendulum f - the natural frequency of each pendulum (aLIGO ~1 Hz).
Bounce f - the bounce resonance frequency of the final pendulum (aLIGO 9 Hz).
Interesting investgations:
Does increasing the laser power improve the instrument sensitivity at all frequencies?
Would increasing the finesse of the Fabry-Perot arms be sensible?
A cryogenic interferometer would be an expensive upgrade - what would be the benefits and how cold would it need to be?
Would adding another pendulum to the stack be a useful improvement?
Increasing the test mass looks like it has no penalty? Is there anything missing from the simulation do you think? What else would have to increase and what could be the consequences of that?