Each photon breaks up a number of Cooper pairs which depends on its wavelength, thus the detector can also serve as a spectrometer, with spectral resolution limited by the shot noise fluctuations in the released charge.
Each photon breaks up a number of Cooper pairs. This number of Cooper pairs depends on its wavelength. The detector can also serve as a spectrometer. This is with spectral resolution. This spectral resolution is limited by the shot noise fluctuations in the released charge.