So on this science listserve, I said that Hamamatsu makes cheap thermopiles, like these,
Reading the fine print these all come with 3-5 um AR coating or even narrower BP at 4.5 um. They plot the response of the tp out to 20 um and I wonder if they sell a version with no IR AR. Or if you can decap one.. (or is that a death warrant?)
George H.