A ‘baffle’ is a perforated disk or disks spaced inside your ‘shade tube’. The idea is to trap all reflections, leaving only the light coming in on the exact axis of the tube to strike the IR Detector.
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DET <--- IR LIGHT
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^Baff ^Baff ^Baff
Off-axis light, ’noise’, will be caught by the baffles and dissipated through reflection between the baffles. Paint the inside of your tube black … in fact, check into what paints/coatings are ‘black’ to IR wavelenghts. Just because a paint LOOKS black does not mean it won’t reflect IR.
Check into an astronomy or optics group to get the formula for the ideal spacing of the baffles and how big a hole should be in them. Getting this right will improve your system performance.
Sources
- jrm[at]gnv.ifas.ufl.edu