DESHIMA 2.0

Abstract

Context. The Deep Spectroscopic HIgh-redshift MApper (DESHIMA) is a broadband integrated superconducting spectrometer for millimeter (mm) and submillimeter (submm) wave astronomy based on kinetic inductance detectors (KIDs). The first generation, DESHIMA 1.0, was successfully tested in 2017. This paper describes the upgrade to DESHIMA 2.0 and presents its characterization in laboratory settings. Aims. We enhanced the performance by increasing the band coverage and efficiency while developing a fast sky-position chopper for the efficient removal of atmospheric fluctuations. Methods. The instrument features NbTiN superconducting microstrip (MS) filters with a low-loss a-SiC:H dielectric and an ultra-wideband leaky-wave antenna. A laboratory setup was designed, incorporating the cryostat housing cryogenic optics and integrated superconducting spectrometer chip comprising 339 KIDs connected to MS filters tuned for (sub)mm wave frequencies. Room-temperature mirrors on a hexapod stage allowed us to precisely position and align the optical elements. The sky-position chopper was positioned on a motor-controlled stage for a fine-tuned control over its position and alignment. The multiplexing capability of KIDs enabled us to simultaneously measure multiple performance metrics across the entire frequency range. Results. DESHIMA 2.0 achieved significant improvements in the performance compared to its predecessor: the measured instantaneous frequency coverage was 200–400 GHz with a mean filter Q_filter of 340 ± 50, the instrument efficiency reached ~8%, indicating a four times wider band coverage and a four times higher sensitivity. The yield rate for the MS filters exceeded 98%. The data loss caused by the sky-position chopper was limited to <20% without beam truncation. The estimated aperture efficiency from measured beam patterns agreed well with the designed value of approximately 70%. The telescope far-field beam patterns calculated from the measured patterns also agree well with the design specifications. We also demonstrated that a new method of absolute frequency calibration is valid using the data from the beam pattern measurement.