CLARA Interferometer Vibration Study
Giulio Stancari and Alexander Shemyakin
February 2, 2023
Introduction
Do mechanical vibrations explain the dip in the coincidence rate during delay scans of the CLARA Mach-Zehnder interferometer?
Are there any differences between the location at ESB and the setup in the IOTA tunnel?
Apparatus
Set delay between interferometer arms near the center of interference curve, where sensitivity to vibrations is maximum.
Set coincidence rate to maximum (equal SPAD rates).
Measurements at ESB, 2023-01-20
MZI interferometer at ESB.
Laser diode (Thorlabs LPS-635-FC, 637 nm) current set to 22 mA (below threshold of 47 mA). Filters installed.
E-log entry: https://www-bd.fnal.gov/Elog/?orEntryId=232032.
Measurements in IOTA, 2023-02-02
Interferometer installed on IOTA M4R dipole magnet.
Laser diode at 4.50 V (163 kOhm), about … \(\mu\)A. No filters.
E-log entry: https://www-bd.fnal.gov/Elog/?orEntryId=232829.
Data acquisition
Event timer configuration (Picoquant HydraHarp 400):
Removed IOTA channels (revolution marker, M2L PMT, M3L PMT, injection trigger)
Ch2 = SPAD1
Ch3 = SPAD2
Trigger = -400 mV, delays = 0 ps
T2 mode (all events recorded with absolute time stamp)
Collected time-tagged photocount events from SPAD1 and SPAD2 in data sets of 10 s each.
Data on the iota-fast.bd network drive.
Data Sets
| start_time | diode_current_mA | acquisition_time_s | HH_filename | location | time_bin_s |
|---|---|---|---|---|---|
| 2023-01-20 14:19:39 | 22.000 | 10 | 2023-01-20_1419_ID_22_mA_10s_vibration_study | ESB | 1e-03 |
| 2023-01-20 14:19:39 | 22.000 | 10 | 2023-01-20_1419_ID_22_mA_10s_vibration_study | ESB | 1e-05 |
| 2023-02-02 10:33:59 | 0.003 | 10 | 2023-02-02_1034_vibration_study_Vd_450V_10s | M4R | 1e-03 |
| 2023-02-02 10:33:59 | 0.003 | 10 | 2023-02-02_1034_vibration_study_Vd_450V_10s | M4R | 1e-05 |
Event Rates vs. Time
The time series is subdivided into time bins. For each time bin the event rates are calculated.
Summary of data sets and average event rates:
| start_time | location | HH_filename | time_bin_s | n_records | rate_SPAD1_Hz | rate_SPAD2_Hz |
|---|---|---|---|---|---|---|
| 2023-01-20 14:19:39 | ESB | 2023-01-20_1419_ID_22_mA_10s_vibration_study | 1e-03 | 10558987 | 5.0518(22)e5 | 5.2092(23)e5 |
| 2023-01-20 14:19:39 | ESB | 2023-01-20_1419_ID_22_mA_10s_vibration_study | 1e-05 | 10558987 | 5.0518(22)e5 | 5.2092(23)e5 |
| 2023-02-02 10:33:59 | M4R | 2023-02-02_1034_vibration_study_Vd_450V_10s | 1e-03 | 9234594 | 4.8584(22)e5 | 4.0781(20)e5 |
| 2023-02-02 10:33:59 | M4R | 2023-02-02_1034_vibration_study_Vd_450V_10s | 1e-05 | 9234594 | 4.8584(22)e5 | 4.0781(20)e5 |
Event rates show large oscillations. SPAD1 and SPAD2 rates are anti-correlated, confirming the hypothesis of changes in relative arm length. Vibrations in IOTA seem more regular.
Fourier Analysis
Spectral analysis is done on the rate difference (most sensitive). Not much activity above 1 kHz (verified up to 50 kHz). Most of the activity concentrated between 100 and 200 Hz. The 120-Hz line is less dominant in the tunnel.
Open Questions and Next Steps
Calibration of the vibrations in nm?
Sources of vibrations?
What fraction of the coincidence rate dip is explained by vibrations?