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 C , Φ 1mm, extended blue sensitivity. PMT BURLE Blue LED 470 nm. Pulsed at 2 Hz, same rate as the laser. The supply voltage charges a capacitor which discharges through theLED. Devices

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 Shield The 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 mV.

PMT Linearity 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. 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 the blue 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 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.