Optical aspects of Near-Infrared Imager Spectrometer and Polarimeter instrument (NISP)

As a Near- IR instrument to PRL's upcoming 2.5 m telescope, NISP is designed indigeniously at PRL to serve as a multifaceted instrument. Optical, Mechanical and Electronics subsystems are being designed and developed in-house at PRL. It will consist of imaging, spectroscopy & imaging-polarimetry mode in the wavelength bands Y, J, H, Ks i.e. 0.8 - 2.5 µm. The detector is an 2K x 2K H2RG (MCT) array detector from Teledyne, which will give a large FOV of 10⁰ x 10⁰ in the imaging mode. Spectroscopic modes with resolving power of R ∼ 3000, will be achieved using grisms. Spectroscopy will be available in single order & a cross- dispersed mode shall be planned for simultaneous spectra. The instrument enables multi-wavelength imaging- polarimetry using Wedged-Double Wollaston (WeDoWo) prisms to get single shot Stokes parameters (I, Q, U) for linear polarisation simultaneously, thus increasing the efficiency of polarisation measurements and reducing observation time.