Hatfield near-infrared polarimeter

The design of the Hatfield Polytechnic Observatory's near-infrared (IJHKLM) polarimeter is described and its performance iliustrated by some representative observations on bright standard stars. Preliminary measurements show an instrumental polarization (in units of l0- f) of 5 1 3 (K), 6 15 (H), 8 14(J) and 3 14(I), comparable with the instrumental polarization of the telescope used. The problems which were encountered in achieving this level of instrumental polarization without sacrificing either overall system transmission or modulation efficiency are discussed.