¶ Violin Mode Harmonic
The LIGO test masses are 40 kilogram mirrors suspended from thin glass fibers. These fibers have resonances, called violin modes because they are like the resonances on a violin string when playing music. Because LIGO is so sensitive, thermal excitations of the violin modes of the fibers move the LIGO test masses at the violin mode frequencies. The LIGO violin modes are centered around 500Hz and harmonics, i.e. 1000, 1500, 2000 Hz, etc. Violin mode harmonic glitches look like short glitches at around 500 Hz and sometimes also at the harmonics at the same time.
Note: the exact frequencies that the violin modes can take have a spread because the glass fibers have some spread in properties and experience slightly different loads. The range in measured violin mode frequencies are:
L1 first order: 508-515 Hz, second order: 991-1025 Hz
H1 first order: 500-509 Hz, second order 991-1010 Hz, third order 1456-1485 Hz
¶ Examples
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Audio of Violin Mode Harmonic (with associated spectrogram) Make sure to wear good headphones!
