There are several calibration lines whose injection amplitudes are set to give a signal-to-noise ratio of 100 for a 10-second integration time. Thus in typical strain noise spectra, made with a frequency resolution of order 0.1 Hz, these calibration lines show up about 100x above the noise floor. I have been concerned whether there is any non-linear noise conversion with the calibration lines at these amplitudes. Certainly we see upconversion around the test mass bounce and roll modes when they are at a high amplitude. Any egregious upconversion would have been flagged before, but it wasn't clear whether smaller effects had been ruled out before.

To test this, a few days ago the calibration folks made a controlled test where the calibration lines were turned off and then on, while everything else in the interferometer remained (nominally) the same. These times are:

• 		Sep-11-2015 1:45:25 UTC, calibration lines turned off, no excitations, fully locked at NOMINAL_LOWNOISE

• 		Sep-11-2015 1:59:06 UTC, calibration lines turned back on

• 		Sep-11-2015 2:50:03 UTC, unlocked

I made 0.05 Hz-resolution spectra of H1:CAL-DELTAL_EXTERNAL_DQ during these times; see the attached plots. I see no signs of any upconversion around the calibration lines in the 35-38 Hz band, nor the one near 332 Hz. I also looked around the first harmonics of the 35-38 Hz lines; there is no sign of twice the frequency of any of these lines showing up. So the calibration line amplitudes look ok from this standpoint. (Comment: I thought all 3 lines in the 35-38 Hz band were to have a high amplitude -- SNR ~ 100 -- but the 37.3 Hz line is smaller by a large factor.)

First figure: zoom around the 331.9 Hz line

Second figure: zoom around the 35-38 Hz band (upper) and twice that frequency (lower)

Note: the FFTs were performed with a Hanning window; the strong calibration lines in these spectra display the spectral leakage associated with the windowing/finite time series