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Message ID: 1140     Entry time: Fri Nov 5 00:59:57 2010
Author: Frank 
Type: Misc 
Category: Pulser 
Subject: no results so far 

did some test runs the last couple of days to see at which power level something happens to the device performance.
Current devices are the old, already very noisy 3mm GTRAN diodes.
Devices are mounted in OMC heatsink using prototype of OMC invac preamp (100R fixed resistance) and the higher bias voltage of 12V (originally 5V).
DC current on PD before pulsing is adjusted to 30mA, pulse comes on top of that. No additional current limit for bias voltage. Spot size ~1mm.

I measure the following device parameters before each new cycle

  • dark current noise spectrum (1Hz to 100kHz)
  • I/V-curve to 20V reverse bias
  • Impedance, then fitting series resistance and capacitance
  • implemented (but not recorded so far): shunt impedance, calculated from slope of I/V-curve from 10mV to -10mV bias (that's how it is measured)

time for each cycle: about 28min.

 

I started with the following parameters about a week ago

  • peak power: 1W
  • pulse duration: 1ms
  • number of pulses/cycle: 1000
  • time between pulses (for diode cooling off): 1s
  • number of cycles: 50

As nothing changed i increased the peak power step by step until i reached the following parameters today:

  • peak power: 20W
  • pulse duration: 2ms
  • (rest the same)

so far no visible changes in measured parameters. Also didn't visually damage a device so far. So if i don't see anything tomorrow i will try to physically damage one diode to see where the damage threshold is.
I probably don't see changes in noise performance as the excess noise of these 3mm diodes is about three orders of magnitude higher as the good EG&G ones. Unfortunately we sent all diodes to the sites.

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