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Transcript
APD Gain Measurement System APD Gain Measure Goal: measure the APD (Hamamatsu S8664-1010) intrinsic gain as a function of the bias voltage and of the temperature. Tecnique: the APD is lighted with a stable, continuous, light source (blue LED) and the current flowing trough it is measures as a function of the bias voltage. The same measure is repeated turning off the LED. Experimental result: Gain is given by: For V “small” the APD avalanche mechanism is off, and G=1: Ion and Ioff @ G=1 are measured performing a linear fit to these points and taking the intercept of the result. APD Gain Measure I realized the following circuit to measure the gain of a single APD: note that the voltmeter is redundant, since knowing the current trough the APD and the value of the resistances one can easily calculate the “real” voltage drop across the APD. Experimental results (@ room T) for the 9 APDs in the FT-Proto. The system works fine, but it takes the operator ~ 40 minutes to take a single measurement (at a single temperature!). Not useable to measure ~ 400 APDs APD Gain Measure We need an automatic system (“ACCOS-style”) to measure the gain of multiple APDs at the same time, possibly at different temperatures, in a short time (~10 APDs/day). Idea: use a “current de-multiplexer”, so I can measure more APDs contemporary, one at time. After some R&D I decided to use commercial relays: other (simpler) solutions were not applicable because I need to measure very low currents (~ 10 nA). APDs holder (note the LED in the middle and the pipes to work at controlled temperature using an external chiller) PicoAmmeter: Keithley 6517A HV Generator: Lambda Gen600 Current de-multiplexer (black-box are relays). Each APD is connected to a relay using a coax cable. APD Gain Measure The software to control the whole system is written in LabView. LIGHT CURRENT I did a first measure with 2 APDs (@ room temperature) to check the behavior of the system: it works! GAIN DARK CURRENT