Status and performance of the Asgard/NOTT cold nulling camera

Abstract

Long-baseline nulling interferometry suppresses the on-axis light of a star, enabling high-contrast observations of faint circumstellar emission and exoplanets at high angular resolution. The Nulling Observations of dusT and PlaneTs (NOTT) instrument is the L'-band nulling interferometer of the Asgard instrument suite and will be the first nuller installed at the Very Large Telescope Interferometer (VLTI). Its main scientific goals are to characterise hot/warm exozodiacal dust and young Jupiter-like exoplanets at close (<10 AU) orbital separations, where indirect detection methods are most sensitive. NOTT uses a four-telescope integrated-optics photonic beam combiner operating over 3.5-4.0 micrometres. The photonic chip produces photometric, bright, and nulled outputs that are polarization-split, spectrally dispersed, and imaged onto a 5-micrometre-cutoff HAWAII-2RG detector by the NOTT cold nulling camera. The cold optical assembly includes the photonic-chip interface, injection optics, collimator, Wollaston prism, dispersive element, imager, and cryogenic detector stage. The mechanical implementation is designed for operation near 90 K using aluminium support structures, spring-loaded optical mounts, and cryogenic-compatible mechanisms to preserve alignment during cooldown. We present the current status and performance of the NOTT cold nulling camera and cryostat assembly. The system is undergoing assembly, integration, and verification to validate thermal stability, detector operation, vacuum performance, and opto-mechanical repeatability. Initial cryogenic tests have demonstrated operation near 100 K for the cold optics and 30 K for the detector, cryogenic validation of the filter wheel, and a vacuum pressure of 8 x 10^-8 mbar. These activities represent a key step toward deploying NOTT as the first nulling interferometer at the VLTI.