  We demonstrate an inverse designed achromatic, flat, polarization-insensitive
diffractive optic element, i.e., multilevel diffractive lens (MDL), operating
across a broadband range of UV light (250 nm - 400 nm) via numerical
simulations. The simulated average on-axis focusing efficiency of the MDL is
optimized to be as high as ~86%. We also investigate the off-axis focusing
characteristics at different incident angles of the incoming UV radiation such
that the MDL has a full field of view of 30 degrees. The simulated average
off-axis focusing efficiency is ~67%, which is the highest reported till date
for any chromatic or achromatic UV metalens or diffractive lens to the best of
our knowledge. The designed MDL is composed of silicon nitride. The work
reported herein will be useful for the miniaturization and integration of
lightweight and compact UV optical systems.
