Abstract: A radiation detector 10 has a base 12 and a window 16 that define a vacuum chamber 20. Within the vacuum chamber 20 is a temperature controlled filter 32 and a focal plane array (FPA) 22 defining a gap h therebetween. The filter 32 is heat sunk to a readout integrated circuit (ROIC) 24 and thermoelectric elements 28 to inhibit heat transfer from non-scene sources 38, 40 to the FPA 22. The temperature controlled filter 32 may also incorporate a bandpass filter to reflect all sources of radiation not within the desired wavelength region of interest. The temperature controlled filter 32 is maintained at substantially the same temperature as the FPA 22.