Context — The Large Interferometer for Exoplanets (LIFE) is a proposed space mission to characterise the atmosphere of terrestrial exoplanets, which is planned to operate in the mid-infrared wavelength region from 6μm to 16μm. A key requirement needed to study the feasibility of this mission is to demonstrate broadband nulling at cryogenic temperatures (15K), at flux levels comparable to the astronomical sources that LIFE will detect. The Nulling Interferometer Cryogenic Experiment (NICE) is a technology demonstrator built to fulfil this purpose.

Aim — The objective of NICE is to demonstrate a broadband null with a null depth of 10⁻⁵ and stability of 10⁻⁸ while maintaining a high system throughput, and consequently a high level of sensitivity, sufficient to detect an Earth twin at 10pc. We describe the optical requirements, the current progress of NICE in the warm phase, and future plans.

Methods — NICE is a Single-Bracewell nuller with closed loop optical path-length control, currently operating at ambient conditions. We use a 3.85μm laser with 150nm bandwidth to demonstrate achromatic nulling capability, and a narrowband (< 0.5nm bandwidth) 4.5μm laser to demonstrate stability.

Results — We achieve an achromatic null depth of 4.39 · 10⁻⁴ with a stability of σ = 5.02 · 10⁻⁴ over a duration of 60s without closed loop control, and a stabilised narrow-band null of 2.05 · 10⁻⁴ with σ = 9.36 · 10⁻⁵ over a duration of 120s.

Conclusions — NICE has both demonstrated achromatic operation and closed loop control to stabilise the null. However, the mean null depth and the null stability achieved do not yet meet the requirements, by a factor of 20 and 104 respectively. This will be improved in future iterations.

The multislit spectro-polarimeter (MSSP) is a grating-based littrow spectrograph with five slits at the entrance aperture. The polarimeter consists of a nematic liquid crystal variable retarder as the modulator and a Savart plate as an analyzer. It is one of the facility instruments on the Multiapplication Solar Telescope at the Udaipur Solar Observatory, developed to measure the magnetic fields of the Sun in the photosphere and chromosphere. MSSP currently operates only at 630.2 nm (FeI), but will be upgraded to cover CaII at 854.2 nm, HeI at 1083.2 nm, and FeI at 1565.3 nm. The spectrograph has a spectral dispersion of 15.8  mÅ  ±  1.2  mÅ at 630.2 nm. The polarimeter has a sensitivity of the order of ^{10  −  2} and the root mean squared noise in the Stokes spectrum (continuum wavelength points of Stokes Q, U, and V) is 0.015I. To obtain an estimate of the instrument induced polarization, an analytical model is developed to determine the polarization introduced by the telescope. A polarimetric calibration (PolCal) unit is used to calibrate the downstream optical path from the telescope exit pupil up to the detector in MSSP. A residual polarization cross talk of 10% is measured in the data after applying PolCal corrections. The polarimetric data obtained from the engineering run (first-light) are inverted using NICOLE, to extract the magnetic field parameters. The field strength derived from MSSP observations is compared with the data obtained from helioseismic and magnetic imager and is found to lie within ±70  G in the umbral region and ±200  G in the penumbral region.

Stokes V, the circular polarization of light, from the solar corona is weak of the order of ^{10  −  4} times the intensity (Stokes I). Measuring weak source polarization, for a faint source such as corona, is difficult and requires long integration time. To obtain long uninterrupted measurements, a space-based polarimeter would be preferable over a ground-based observatory. A full-Stokes polarimeter is designed such that the modulation matrix provides high efficiency in measuring the weak Stokes V signal, while minimizing the cross talk from Stokes Q and Stokes U. The prototype polarimeter consists of a single crystal retarder as the modulator and a Wollaston prism as a dual beam analyzer. The modulation is performed by rotating the retarder continuously. An optimum modulation matrix is derived taking into account the systematics and polarization cross talk due to satellite jitter. We present the results of cross talk simulation and the steps taken to obtain the modulation matrix. A polarimeter designed to observe the solar corona at Fe XIII 1074.6-nm emission line is presented. Jitter and drift from a low earth orbit satellite are taken to simulate and experimentally verify the cross talk and polarimetric efficiency of the polarimeter. A plane parallel crystal retarder produces polarized fringes. F-ratio of the beam incident on the retarder is one of the factors that effects the contrast of the polarized fringes. Results from a simulation performed to compare the polarizance produced by the retarder, when placed in a converging beam and a collimated beam of light, is presented.