Detectors
Light must be converted from photons into volts to be measured
We must select the correct detector system according to how many photons we have available
In general, we use photodiodes for forward scatter and absorption and PMTs for fluorescence and side scatter
Silicon photodiodes
A silicon photodiode produces current when photons impinge upon it (example are solar cells)
Does not require an external power source to operate
Peak sensitivity is about 900 nm
At 900 nm the responsivity is about 0.5 amperes/watt, at 500 nm it is 0.28 A/W
Are usually operated in the photovoltaic mode (no external voltage) (alternative is photoconductive mode with a bias voltage)
Have no gain so must have external amps
quantum efficiency ()% = 100 x (electrons out/(photons in)
