We are reporting on the concept, design, construction, and critical operating parameters of a new photon-counting detector package. It was developed based on silicon SPADs manufactured using K14 technology. Four detection chips with an active area diameter of 25 microns are used. The active quenching electronics enable the detection chips' operation in a bias range of 0.5 to 2.5 Volts above their breakdown voltages in a continuous counting mode. The entire design and construction are prepared for long-term operation in space conditions. Our operation experience of K14 detection chips and all the electronics in numerous space missions was taken into account when designing the device. It can be operated in an extensive temperature range of −55 to +50°C without any active temperature stabilization. The built-in SPAD biase power supply voltage is following the SPAD breakdown voltage temperature dependence. This way, the detection chips are biased fixed bias above their breakdown voltage over the entire temperature range. The critical detector parameters depend on a selected bias above a breakdown voltage. For selected configuration, every single detector's parameters are as follows: photon detection probability at 800 nm is 30%, the maximum count rate is 2 MHz, the timing resolution is better than 80 ps FWHM, detection delay temperature drift is within the range of ±0.3 ps/K. The dark count rate is typically < 50 kHz at +25°C. It may be reduced one order of magnitude, lowering the operating temperature to 0°C. The entire detector package power consumption is well below 1 Watt; its mass will be below 100 grams.
The new photon counting detector package has been developed for applications of the orbiting space debris optical tracking. The advanced construction of the detector control electronics enables to operate the detection chip in continuous and gated photon counting operational modes. Using the proposed construction the detector is capable to monitor the strength of a solar radiation diffused reflected by the space debris. Combining the continuous and gated detection modes enables to measure the photon flux rates over more than three orders of magnitudes ranging from one kHz to several MHz. In addition, the gated mode is optimized for laser ranging of orbiting space debris. The two operation modes of the detector may be switched electronically. The detector is based on a commercial SAP500 avalanche photodiode detection chip with active area diameter of 500 μm, which enables its simple integration into the large input aperture astronomical telescopes. The detection chip is operated at a fixed temperature of −8 °C. In a gated mode the photon detection efficiency exceeds 60% at 532 nm. Its timing resolution is typically better than 100 ps rms. In a continuous mode its dark count rate is well below 10 kHz. This detector package was developed as our contribution to the ESA activity “Space Situational Awareness program P2-SST-VII Expert Coordination Centre; Phase II”.