  The rapid development of infrared spectroscopy, observational astronomy, and
scanning near-field microscopy has been enabled by the emergence of sensitive
mid- and far-infrared photodetectors. Owing to their exceptional
signal-to-noise ratio and fast photoresponse, superconducting hot-electron
bolometers (HEBs) have become a critical component in these applications. While
superconducting HEBs are traditionally made from sputtered superconducting thin
films like Nb or NbN, the potential of layered van der Waals (vdW)
superconductors is untapped at THz frequencies. Here, we report the fabrication
of superconducting HEBs out of few-layer NbSe$_2$ microwires. By improving the
interface between NbSe$_2$ and metal leads connected to a broadband antenna, we
overcome the impedance mismatch between this vdW superconductor and the radio
frequency (RF) readout circuitry that allowed us to achieve large responsivity
THz detection over the range from 0.13 to 2.5 THz with minimum noise equivalent
power of 7~pW$\sqrt{Hz}$. Using the heterodyne sub-THz mixing technique, we
reveal that NbSe$_2$ superconducting HEBs are relatively fast and feature a
characteristic response time in the nanosecond range limited by the slow heat
escape to the bath through a SiO$_2$ layer, on which they are assembled, in
agreement with energy relaxation model. Our work expands the family of
materials for superconducting HEBs technology, reveals NbSe$_2$ as a promising
platform, and offers a reliable protocol for the in-lab production of custom
bolometers using the vdW assembly technique.
