Theory of field attenuation in photon detection, with an application to resonance fluorescence

Detection of photons from electromagnetic radiation can be considered as the appearance of random events on the time axis. When an attenuator is placed in front of the detector, which attenuates the intensity by a factor of α, the statistical properties of the detected photons are altered. We show that simple relations exist between the statistical functions of the photons detected from the attenuated field and the same functions for the photons that would be detected from the unattenuated field. We also derive several recurrence relations for the statistical functions involving their dependence on the parameter α. For photon detection from resonance fluorescence, the parameter α appears naturally as the probability that an emitted photon is detected. In this case, there is no attenuator, but the parameter α appears in the same way. We show that the probability for the emission (α=1) of n photons in a given time interval can easily be computed, and with the general theory we can then obtain the result for the detection of n photons (α<1).