Linearity Tests The laser induced high noise pulses on the APD rendering it useless. We tried...
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Transcript of Linearity Tests The laser induced high noise pulses on the APD rendering it useless. We tried...
Linearity Tests
The laser induced high noise pulses on the APD rendering it useless.
We tried several methods to shield and filter the noise.
With a stabilized version of filtering used the APD.
Comparing pulses from PMT and APD for different voltages, different filters, we noticed inconsistent results.
Corrected the results for non linearities in order to get consistent results.
Linearity Tests
•APD Hamamatsu C5331-11, Φ 1mm, extended blue sensitivity.
•PMT BURLE 8575.
•Blue LED 470 nm.
•Pulsed at 2 Hz, same rate as the laser.
•The supply voltage charges a capacitor which discharges through theLED.
Devices
APD output
y = 38,941x - 504,01
0
50
100
150
200
250
300
350
400
10 15 20 25
LED Suppply V
AP
D m
V
APD
Γραμμική (APD)
Calculation of N phot from APD
0
1000
2000
3000
4000
5000
10 15 20 25
LED suplly
Nu
mb
er
of
Ph
oto
ns
Calculation of N phot fromAPD
Nonlinear above
300 mV
Limited by noise below 50 mV
We can extend the linearity if we correct for the broadening of the pulse
APD plots
The APD module is linear but has a limited dynamic range.
We can possible extend the lower range if we can reduce the noise from the laser.
APD Range
Laser ShieldThe laser is enclosed in cage of copper sheet 0.5
mm thick. All gaps are covered with copper tape with conductive adhesive.
The APD module is closed in a cast aluminum box, gaps covered with copper tape.
Power is delivered through RG58 cable, with filter inside the box.
Signal cable passes through a ferrite core, to reduce induced currents on feedback.
The lowest we can get are spikes of 10-15 mV.
PMT LinearityTube Output
y = 528,85x - 6666,6
y = 331,52x - 4322,4
y = 133,67x - 1757,9
0
500
1000
1500
2000
2500
10 11 12 13 14 15 16 17 18 19 20 21 22
LED Supply V
Pu
lse
mV PMT 1200
PMT 1300
PMT 1100
Calculation for N phot from tube
0,00E+00
2,00E+04
4,00E+04
6,00E+04
8,00E+04
1,00E+05
1,20E+05
1,40E+05
1,60E+05
10 12 14 16 18 20 22
Led supply
# o
f P
ho
ton
s
1200 v
1300 V
1100 V
Linearity for big pulses.
Looks better if we use number of Photons (charge). We have used the measured width.
Notice change of slope below 500 mV.
PMT Range• Tubes have a wide dynamic range but there not linear in all this range. We have to chose operating range.
• What we see in the first plot is “overlinearity” , because we use big pulses. The gain with high light input is bigger than with low. This is before the region of “sagging”.
• Correction for width has to be applied.
Repeat previous test.
•A fiber is attached to each PMT and APD.
•Recording the output pulse high from PMT and APD. Calculate Charge and then number of Ph-el.
•Compare Center and Bottom positions.
First option: Laser + fibers
Common Source: A low power UV laser (by courtesy of IU)
Diffuser : A 10*10*10 cm3 plastic scintillator excited by the laser
Box with holes for theblue light output
Scintillator
Distribution: bunch of 15 plastic fibers, 4m long, 100μm diameter
Input,diameter ~0.1mm
outputs x15
Fiber Bundle, PMT
APD box
Light yield from the scintillator block
1460
1550
5110
450
N ph-el PMT
N ph-el APD
Ratio C/B =3.3
Ratio C/B=3.2
Summary
•APD has a good linearity within its range.
•PMT has to be corrected for width. Use charge rather than voltage for pulse high.
•The light pulse coming out of the lower hole is wider by 2-3 ns compared to the one from the center. Contribution of internally reflected light.
Last improvement.We were able to reduce the pick-up noise on the
APD using a double shield on the output cable. The noise level was reduced down to 2 mV !