Working Towards Finding an Upper Limit for Crackle in LIGO’s Maraging Steel Blade Springs

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Abstract:: Crackle is a type of nonlinear, high frequency noise generated as individual molecules in a material shift when the entire system is driven at low frequencies. Such unwanted noise may occur in components of LIGO’s gravitational wave observatories. Components of specific importance in studying this phenomenon are the steel blade springs that hold the observatories’ highly sensitive mirrors in place. These blade springs were the primary focus of this investigation of crackle. For the project, an optical apparatus was created to determine the upper limit for the intensity of crackle that could occur in such springs. Several improvements were made to the apparatus for the purpose of amplifying the crackle, while decreasing the effects of other background noise sources, and a detailed data simulation was created for use in testing the analysis process. Using a demodulation technique to analyze preliminary data, I found that in the worst case scenario, crackle could cause displacement noise of up to 1.84 × 10−14 m/sqrt(Hz) against a background displacement noise of 4.00 × 10−13 m/sqrt(Hz). Longer data collection runs will be needed in order to make more conclusive statements. Ultimately, this study will help LIGO to ascertain whether provisions will be necessary to mitigate the effects of such nonlinear noise in its observatories.

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LIGO Document T1300839-v1