CHOPPER FOR MODULATING INFRARED RADIATION BEING ADAPTED TO THE USE UNDER VARYING TEMPERATURES

摘要

A chopper (10) for an imaging system includes a frame (12, 14) and a sheet (16) that have different coefficients of thermal expansion. The frame has a space between a lower frame part (12) and a upper frame part (14), and has at least one opening (106-109) that allows radiation to pass through the opening. The sheet (16) has structure which influences radiation passing through the sheet, and the sheet is movably disposed within the space in the frame, in a manner so that the sheet can expand and contract relative to the frame in a direction approximately parallel to the sheet. The frame prevents any significant movement of the sheet in a direction transverse to the sheet.