  A region 140 square degrees toward the Galactic Centre was searched for
monochromatic optical light, both pulses shorter than 1 sec and continuous
emission. A novel instrument was constructed that acquires optical spectra of
every point within 6 square degrees every second, able to distinguish lasers
from astrophysical sources. The system consists of a modified Schmidt
telescope, a wedge prism over the 0.28-meter aperture, and a fast CMOS camera
with 9500 x 6300 pixels. During 2021, a total of 34800 exposures were obtained
and analyzed for monochromatic sources, both sub-second pulses and continuous
in time. No monochromatic light was found. A benchmark laser with a 10-meter
aperture and located 100 light years away would be detected if it had a power
more than ~60 megawatt during 1 sec, and from 1000 light years away, 6000 MW is
required. This non-detection of optical lasers adds to previous optical SETI
non-detections from more than 5000 nearby stars of all masses, from the Solar
gravitational lens focal points of Alpha Centauri, and from all-sky searches
for broadband optical pulses. These non-detections, along with those of
broadband pulses, constitute a growing SETI desert in the optical domain.
