1. Fast Detectors and Electronics for Nanosecond Time Resolved Experiments
O. Leupold, H.C. Wille, I. Sergueev, M. Herlitschke, P. Alexeev, C. Strohm, W. Roseker
FS-PE, Deutsches Elektronen-Synchrotron (DESY), Hamburg, Germany
Avalanche Photo Diode Detectors
General features of APDs
16 element APD detector
Standard APD Excelitas 5x5mm2
100 µm thick
Single element
> ns time resolution > fast recovery time, < 2 ns
> single photon counting > high count rates up to 108s-1 > high efficiency at energies < ~10 keV > semi-transparent´at energies > ~10 keV
Typical pulse from APD / fast amplifier
Efficiency of standard APD assemblies
600 µm ↔ 4 inclined APDs stacked
400 µm ↔ 4 APDs stacked
100 µm ↔ 1 APD
Single APD
Hamamatsu S5443
3mm diameter
30 µm thick
Efficiency of ~15% at energy of ~73 keV due to extreme shallow angle of incidence on the 16 APDs
Beam
Data Acquisition Systems and Applications
Nuclear Resonance Scattering on 193Ir at 72.9 keV
Standard setup:
Veto around t=0 needed, width usually >20 ns, max. 1 acquisition per pulse
Time-to-Digital-Converter(TDC) [2]
No veto needed
Time resolution 100ps, in up to 5 channels
Pulse repetition rate <5 GHz
(might be limited by detector)
Multiple events per sweep
Bunch purity measurements also
possible on specific main bunches
Digitizer (ongoing project) [3]
No veto needed, direct digitalization
Event-based acquisition and pulse-height
On-board data processing
Fig.: Nuclear inelastic scattering from a 57FePt sample with 6.4 keV (Fe K-α) and 14.4 keV (inelastic scattering) levels
TAC
CFD
MCA PC
VETO
Signal
ADC
This nuclear resonance - nuclear life time ≈ 8ns - was observed recently at the PETRA III beamline P01
Nuclear Forward Scattering (NFS) experiments were possible due to the fast APDs of the 16 element APD detector, which enables one to start time resolved measurements already about 3ns after the strong exciting SR pulse
For more details see [1]
Fig.: NFS on IrO2 at about 15 K exhibits pure quadrupole interaction: splitting ΔEQ ≈ 670 neV
A small external field of 0.5T does not change the NFS pattern significantly
Application in XPCS – distinction of one and two photon correlations
Application in NRS – multihit events
4 photons photons photons photon per bunch
It was shown [4] that photon correlation spectroscopy on a bunch to bunch basis yields different results for 1-photon events and 2-photon events
With the TDC 1- and 2-photon events can be distinguished by the puls width at fixed threshold
time
Exciting SR pulses
FeBO3 single crystal in pure nuclear scattering geometry
Experiment at ESRF / ID18 in 4 bunch mode
threshold
1- photon event
2- photon event
1 photon per bunch
2 photons per bunch
3 photons per bunch
4 photons per bunch
Pulse Width Distribution
1- photon events
2- photon events
3 and more photon events
Events
Fig.: NFS on Ir metal at two different temperatures exhibits no hyperfine interaction
The time modulation at 13K and the decay faster than the natural lifetime at 300K are due to multiple scattering, which is more pronounced at low T
References: [1] P. Alexeev, 2017 User meeting, Poster 306
[2] FAST ComTec GmbH,
[3] Involved institutes and funding: DESY, ESRF, TU Kaiserslautern, BMBF, XFEL
[4] Hruszkewycz, S. O., Sutton, M., Fuoss, P. H., Adams, B., Rosenkranz, S., Ludwig, K. F. J., Roseker, W., Fritz, D. M., Cammarata, M., Zhu, D., et al. (2012). Phys. Rev. Lett DOI: /PhysRevLett