European Laser Timing (ELT) Experiment on ACES
Description of the demonstration experiment at Wettzell
Part 1, K14 SPAD detector package
Prague, April 14, 2009
Ivan Prochazka
Czech Technical University in Prague, Brehova 7, 115 19 Prague 1, Czech Republic
prochazk@fjfi.cvut.cz
DOCUMENT CONTENT
1.
2.
3.
4.
5.
6.
Objectives and tasks list
K14 SPAD detector package description and main characteristics
K14 SPAD detector package results & performance demonstration
K14 SPAD detektor integration into the WLRS station in Wettzell
Hardware specifically developed for the ELT experiment
Summary and Conclusion
1. OBJECTIVES, TASKS and other as specified by „Statement of Work“
Set-up of a breadboard demonstration making use of the K14 SPAD detector from the
University of Prague and the MWL FS System Timing Module modified to time tag the
time of arrival of laser pulses in the local time scale. The breadboard shall be integrated in a
test set-up which shall make use of the Fundamentalstation Wettzell satellite laser ranging
(SLR) station to simulate the ground to ACES and return laser path. Key system
performances (e.g. stability and accuracy of the time transfer link, absolute calibration of
propagation delays, ranging capabilities...) .. Design of a demonstration model laser
detector representative in performance to the intended flight model design. It does not
include the laser corner reflector or the accommodation of the detector diode inside the
reflector structure.
On-site test support at Fundamentalstation Wettzell during preparation and conducting
performance test of the SPAD detector
On-site test support at Fundamentalstation Wettzell during preparation and conducting test
of the complete EL T chain (SPAD detector + EL T event timer board)
K14 SPAD detector and detector power supply; delivered to and commissioned at Wettzell
test site Technical description of the detector model, including stand-alone test results.
Any hardware specifically developed for this test.
2. K14 Detector Package
Figure 1 K14 SPAD detector package (right) with the matched
power supply and power cable.
The standard version of the K14 SPAD detector package developed for satellite laser ranging
was provided together with the matched power supply, see Figure 1 as delivered for
experiments in Wettzell.
The main detector package parameters are as follows:
General
self consistent all solid state photon counter
Principle of operation
Single Photon Avalanche Photodiode (SPAD)
pulse biased above the break voltage
Version / application
Satellite Laser Ranging
Detection diode
K14 SPAD on Silicon, active area 200 um diameter, TE cooled
Avalanche quenching
active by electronic circuit, HCT
External gating
insulation
> 109 (optical)
logic
FLIP-FLOP built in
levels TTL low < 1V, high > 2.5 V, 50 Ohms
connector
BNC
gate pulse
> 8 ns wide
gate is opened by the pulse leading edge and closed by the first
output pulse.
Output signal
NIM like, AC coupled
Dark count (effective)
Is measured as an inverse value to the mean time interval
between the opening of the gate and the first output signal.
measured
< 25kHz, gate 10 Hz
Collecting optics
doublet, AR for 532 nm, accepts collimated beam 12 mm
Power supply
dedicated, AC 210-250V , 30VA, DC connect.WK ser., 12 pins
Detection chip quantum efficiency in relative units, for SPAD configuration for SLR,
the QE at 532 nm is typically reaching 40 %.
Dimensions in millimetres, the overall length and the “8mm” part may vary due to focus
adjustment
3. Stand alone test results
The typical example of the SPAD detector package in SLR, the effect of precision increase by
data averaging. The data were obtained by re-scaling the Graz SLR data down to 10 Hz
repetition rate. These results illustrate the K14 SPAD detector package resolution and timing
stability, as well.
The demonstration of the K14 SPAD detector package timing resolution ( < 30 ps rms) when
detecting single photon signals.
The dependence of the detection delay versus background proton flux intensity. Note the
detection delay stability +/- 2 ps of the entire chain and the dependence +/- 4 ps over an entire
dynamical range reaching 100 million photons / second background flux.
The Prague indoor calibration facility - optical bench: pulsed laser diode (left) neutral density
filters and focusing optics (center) and SPAD detector package and its power supply (right
front)
4. K14 SPAD detector integration into the WLRS station in Wettzell
Wettzell Laser Ranging Station, where the experiment was installed
The optical receiver box, dicroic beam splitter directing 95% optical signal on the MCP
detector package (to the left) and transmitting 5% of the signal to the K14 SPAD detector
package (top rear)
SPAD detector (left center) package installed in WLRS receiver bench.
The calibration, satellite laser ranging on both WLRS and TimeTech timers were
completed. The examples of the real time data screen shots when ranging to Ajisai and
Starlette satellites are on the following two figures.
Real time data screen shots when ranging to Ajisai satellite, the different slopes are caused
by different calibration types associated with two detectors.
Real time data screen shots when ranging to Starlette satellite
The results will be summarized in the report of the Wettzell staff. In general, the single shot
precision was impaired by unexpected problem associated with the Wettzell SLR station the laser pulse length has been found to be 250 ps instead of 50 ps expected in our previous
calculations. This fact causes higher SPAD single shot jitter – about 100 ps.
To verify the laser pulse length, the calibration experiment was repeated using another
SPAD detector having an extremely low jitter below 18 ps. This low jitter value was
measured in Prague indoor calibration facility using 48 ps long laser pulses.
5. Additional hardware developed for this test in Prague
The test sample of the SPAD detector package optimized for ELT experiment has been
developed and tested, as well in CTU labs. The package consists of the detection chip (left),
detector control electronics, power supply with the controlled temperature drift (right).
The laboratory sample of the ELT detektor package, Ver. 01, detection chip (left), detector
control electronics, power supply with the controlled temperature drift (right).
The timing resolution of the ELT detector Ver. 01 versus chip bias. Obviously for biases
above 31.3 Volts the resulting timing resolution is below 30 ps as required for ELT
experiment.
6. Summary and conclusion
The following tasks were completed so far:
 the SPAD detector package has been delivered to WLRS in Wettzell,
 prior to it, the detector package has bee tested for its timing resolution, detection
delay stability and dependence of the delay on the background flux with picosecond
resolution
 results of the indoor tests: timing resolution better than 20 ps rms, timing stability
typically +/- 2 ps / hour, dependence on the background flux +/- 4 ps for dynamical
range of 1 to 100 M counts / s. Detection efficiency exceeding 20 % at 532 nm,
effective dark count rate lower than 25 kHz for the gate on rate of 10 Hz.
 The package has been integrated into the WLRS set-up, both the calibrations and
satellite laser ranging were performed, the system delays and jitter were evaluated.
(The detailed figures will be provided by Wettzell team separately).
 The internal path calibrations and satellite laser ranging was performed on different
flying targets in both system configurations – using WLRS timer for ELT detector
and using TimeTech timer as well.
 The single shot precision acquired was slightly impaired by unexpected problem
associated with the Wettzell SLR station - the laser pulse length has been found to
be longer (250 ps instead of 50 ps) than expected in our previous calculations. This
fact causes higher SPAD single shot jitter – about 100 ps.
 To verify the WLRS laser pulse length, the calibration experiment was repeated
using another SPAD detector having an extremely low jitter below 18 ps. This low
jitter value was measured in Prague indoor calibration facility using 48 ps long laser
pulses. The independent SAPD measurements verified the WLRS laser pulse length
of about 250 ps.
 April 9 the SPAD package was modified in Prague labs: the compensation capacity
of the processing electronics was increased from 15pF to 57 pF to match the WLRS
needs (the appearance of the output pulse was suppressed on the Gate opening).
 The additional hardware was developed and tested in Prague: the laboratory sample
of ELT photon counting detector package. The package consists of the 100um
diameter K14 SPAD chip, control electronics and temperature compensated power
supply. The detector package performance reaches project specs in sensitivity,
timing resolution and stability, as well. The package is ready for further test and
development.
 The experiment continues at Wettzell to acquire time series long enough for system
performance evaluation in all the configurations.
 The experiment progress was reported to EADS Astrium.
Prague, April 15, 2009
Ivan Prochazka, professor
Czech Technical University in Prague
Brehova 7, 115 19 Prague 1, Czech Republic