Detector Frequency Response --
To determine system frequency

At a given chopping frequency (f), detector responsivity (R_f) is related to its responsivity at 0 Hz (R₀) as follows:

R_f=    R₀
   (1+4π ²f ²τ²)^1/2

where τ is the detector time constant.

PbS and PbSe detectors exhibit typical 1/f noise, and accordingly, at a given chopping frequency, detectivity, D*(f) can be expressed as:

D*(f)=   K f  ^{½                   where K= √Ad}

         (1+4π²f ²τ²)^1/2                  Vnoise
Typical frequency response of PbS/PbSe detectors is shown to the Right:

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