Eleonora, Eleonora, Irene, Yuhang, Federico

Day one: first measurements on "in-air" bench and on some (supposed) critical optical devices/mounts.

We used an accelerometer Wilcoxon 731 (low frequency, low noise) for bench measurements, and a PCB 352C68 (low weight - see photos) for optical mounts.

Bench characterization (accelerometer placed in horizontal and vertical over the bench; later over a top cover).

In fig.1 we see a main horizontal bench mode at 13.5Hz

In fig.2 we see some vertical mode of the bench (broad, not well defined) around 45Hz

In fig.3 we see a comparison (vertical only) between floor and bench acceleration: they are quite similar except the 45Hz region that is a bit amplified on bench as expected because of the resonance. We also notice a line at 26.75 that goes on/off, maybe is some devices into the building.

In fig.4 Bench lines at 24.75Hz and 49.5Hz are due to the vacuum Scroll pump always running near the bench.

In fig.5 we tapped ont the top panel (bench cover) and we excited a fundamental mode (drum?) at 4.5 Hz with harmonics.

Optical mounts characterization (accelerometer clamped on devices using some dedicated harware - if you need it in Italy, ask for a "fattapposta" - see photos)

In fig.6 "Infrared Phase shifter" (Coherent Control) placed horizontal, tapping on the bench we excited a resonant mode of this mount at 468Hz

In fig.7 the same but with the accelerometer placed in vertical, broad structures excited (one around 1212Hz and one around 1748Hz)

In fig.8 accelerometer horizontal on a similar mount but without the piezo: we excited a structure at 576Hz (very near to the 604Hz coming from the many turbo vacuum pumps)

In fig.9 "Green Phase shifter" (Coherent Control) placed horizontal, tapping on the bench we excited resonant modes at 500Hz, 1144Hz, 1584Hz

In fig.10 we placed the accelerometer horizontal (well, in line with the PD box) on the "homodyne" and we excited modes at 132Hz, (maybe) 281Hz, 393Hz, 508Hz

Preliminary conclusions:

It seems some optical devices are sensitive to vibrations, and moreover some eigenfrequencies are present also in quiet seismic spectra.

The bench has its own "natural" frequencies 813.5Hz horizontal, 45Hz vertical).

Mounts have their own frequencies above 100Hz (see the numbers quoted above).

Some external noise sources (Scroll Pump, Turbo Pump, etc) come to the bench via direct coupling and/or air coupling; worth to suspend it with air legs and close it with the 1cm thick panel covers.