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SR Measurement in 1mm Spot

Philipp Gottesleben

27. Sept. 2015

Single photon counters are engaged in many scientific applications for high energy physics or biological, chemistry experiments, but can be found also in medical applications. There are many good reasons to exchange the traditional PMTs (Photo Multiplier Tubes) by digital silicon photomultipliers using a conventional CMOS process technology.
The spectral response of silicon photomultipliers has to be measured with a programmable monochromatic light source.

Please check the video below...


A calibrated reference diode monitors the irradiance to the DUT (Device Under Test).


To reduce temperature dependence, drift, dark signal and noise, aSpect uses a 2 channel lock-in amplifier system (idOP) which enables to sense currents down to 100fA:


The area of the calibration diode of idOP is much more than the pixel size (1-4 mm). aSpect developed the optical path to change the spot size without changing the irradiance:

  1. large area for calibration

  2. spot size < 1 mm for single pixel illumination

Following depicts a uniform spot with diameter=0.9 mm:

Spatial uniformity is ca. 2%

Take a Closer Look

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