Laser measurement of absolute charge collection efficiency of a silicon detector

A setup for testing silicon position sensitive detectors using a focused pulsed laser beam has been developed. An optical head monitoring the intensity of both incident laser light and reflected light improves long-term stability and reproducibility of measurements. We show that measurements using red (682 nm) laser light are reliable and robust, providing 4% precision for collected charge determination in our studies. Measurements using infrared light (1055 nm) are highly sensitive to fine details of detector material properties, which cannot be easily measured and/or compensated for.