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MIP equivalent
hjansen
31-08-2015 14:57
Hi all, did someone already make an absolute calibration of the laser output power of a certain setting of DAC and frequency? It would be interesting to know what the number of MIP equivalent of the produced charge is - for red and infra-red laser. Cheers, Hendrik
gregor
01-09-2015 11:25
Hi, The DAC setting varies from laser to laser and it is difficult to make a general statement. This is particularly true for different iris settings and use of filters, where such calibration is almost impossible without so called beam-monitoring system. As a rule of thumb the signal integral-charge collected in the sensor of around ~2000 mV ns (on 50 Ohm input - i.e. 300 mV signal of 6-7 ns duration) corresponds to roughly ~1M e-h pairs or ~30 MIPs in 300 um thick non-irradiated silicon detector. The development of so called plasma effect/space charge screening can become an issue for red laser where the penetration depth is small and corresponding density of non-equilibrium carriers very high. It is difficult to see it with IR where carriers are generated with lower density. In order to make an absolute charge measurement one needs to know the intensity of light when it leaves the optical system (so called in-beam monitoring system which utilizes semi-reflective mirror and photodiode). Usually this is done in such a way that the signal from alpha source is compared to the signal from the laser pulse and the signal from the laser to the output from the in-beam-monitoring photo diode. Regards, Gregor
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