The dark count rate (DCR) is defined as pulses per second in dark condition, that is, the count rate that is measured in the absence of photons. The false detection events are mostly of thermal origin and can therefore be strongly suppressed by using a cooled type of detector. The dark-count rate (DCR) is a key parameter of single-photon detectors.
And I want to know, how to understand the dark count approximate $10^3$ cps, and the count rate is not more than 1M/s? But in someplace, I see the dark count rate can be 0-40 GHz. I don't understand the unit of them.