Abstract: An infrared detector and envelope arrangement for the detector have a novel mount (21,22,23,24) for a Joule-Thomson or other cooling element (10). The mount is a single unit (21,22,23,24) which includes an inner part (23) on which the cooling element (10) is mounted e.g. via an adaptor (30). The cooling element (10) is secured in a dewar (1,2) of the envelope arrangement by attaching an outer part (21,22) of the mount (21,22,23,24) to a dewar mount (13) e.g. by bolts (22). These inner and outer parts (23 and 21,22) which may have overlapping flanges (43,37 and 21, see FIGS. 2 to 6) are elastically coupled together by a resilient part (24) of the mount (21,22,23,24). The resilient coupling reduces movement and strain of the inner dewar wall (1) caused by movement of the cooling element both during assembly and use of the detector.