Engineering
LIGO presents unique engineering challenges: complex mechanical systems and control strategies, high power lasers, state of the art optics and metrology, low noise electronics, ultra-high-vacuum technology. The MIT-LIGO engineering team is pursuing Research & Development in all of these areas.Active Mode Matching
Mode matching means adapting an optical beam's waist size and position to meet some requirement. In advanced LIGO,
the mode matching at the output of the interferometer is critical to getting the most sensitivity improvement out of
squeezed state injection.
Active Wavefront Control
Optical loss currently present in the Advanced LIGO detectors has been limiting the amount of squeezing we can
achieve. The majority of squeezing loss is due to the mode-mismatch in various optical paths, for example, path from
squeezer to filter cavity. The active wavefront control technology is developed to enhance the mode-matching and
further reduce the quantum noise.
Heavy Suspensions
One of the major mechanical noise sources in LIGO originates from unwanted cross-couplings in their suspensions. This double pendulum prototype serves as a proof-of-concept experiment to reduce longitudinal-to-pitch cross couplings by changing its physical geometry. The setup is much simpler than the full LIGO quadruple suspension. Therefore, this setup allows us to better understand the consequences of various geometrical changes before implementing them in the full LIGO suspensions.
Violin Mode Dampers
Mirrors of Advanced LIGO interferometers are ~88 pound cylinders made of fused silica. These test masses as they are
called in LIGO are suspended using thin fibers as a 4 stage pendulum. Resonances of these fibers manifest as ultra
high-Q modes in LIGO noise spectrum.
When rung up during an earthquake, engineers at LIGO has to wait for those modes to damp down which could take up
hours of crucial detector observation time. With this project at LIGO MIT we are aiming to reduce the Q's of violin
modes by attaching oscillators to the penultimate suspension stage. That in turn would reduce the decay time of
violin modes.
Acoustic Mode Dampers
Due to the large amount of stored optical power in the LIGO interferometers and the high mechanical quality factors of the LIGO mirrors, we observe non-linear optomechanical couplings that can lead to instabilities. These instabilities prevent the interferometers from functioning at high power, therefore limiting their duty cycles and sensitivities. To reduce these instabilities, the LIGO MIT team has designed and tested an electro-mechanical device, called ’Acoustic Mode Damper’ (AMD), to damp the mechanical modes associated with instabilities.