  Levitated nanodiamonds containing nitrogen vacancy centres in high vacuum are
a potential test bed for numerous phenomena in fundamental physics. However,
experiments so far have been limited to low vacuum due to heating arising from
optical absorption of the trapping laser. We show that milling pure diamond
creates nanodiamonds that do not heat up as the optical intensity is raised
above 700 GW/m$^2$ below 5 mbar of pressure. This advance now means that the
level of attainable vacuum for nanodiamonds in optical dipole traps is no
longer temperature limited.
