  We propose to use table-top-size ultra-stable optical cavities from the
state-of-the-art optical atomic clocks as bar gravitational wave detectors for
the frequencies higher than 2 kHz. We show that 2-20 kHz range of gravitational
waves' spectrum can be accessed with instruments below 2 meters in size. The
proposed cavities' materials and properties are being within the present-day
technology grasp. The ultra-stable optical cavities allow detecting not only
predicted gravitational wave signals from such sources as binary neutron star
mergers and post-mergers, subsolar-mass primordial black-hole mergers, and
collapsing stellar cores, but can reach new physics beyond standard model
looking for ultralight bosons such as QCD axions and axion-like particles
formed through black hole superradiance.
