What is the typical frequency response of PbS/PbSe detectors?
The detector has a 1/f noise characteristic, so the lower frequencies have higher noise and consequently a lower D* value. The signal level stays relatively constant as the chopping frequency is increased, up to the detector response limit. Therefore, if the system is not band limiting the noise measurement (wide band amplification) the Signal/Noise (D*) will be constant below the response limit. If the noise reading is band limited around the chopping frequency, D* will increase up to the point that the detector response starts to roll off because of its time constant. For PbSe detectors, 1 kHz is chosen as a standard chopping frequency because it is away from the 1/f noise but lower than the time constant response limit. You can find a graph of the typical frequency response of the detectors in section 8 of our technical notes.
Source (with permission to reproduce): http://optodiode.com/resources.html