  Mechanical oscillators based on levitated particles are promising candidates
for sensitive detectors and platforms for testing fundamental physics. The
targeted quality factors for such oscillators correspond to extremely low
damping rates of the center-of-mass motion, which can only be obtained if the
particles are trapped in ultrahigh vacuum (UHV). In order to reach such low
pressures, a noncontaminating method of loading particles in a UHV environment
is necessary. However, loading particle traps at pressures below the viscous
flow regime is challenging due to the conservative nature of trapping forces
and reduced gas damping. We demonstrate a technique that allows us to overcome
these limitations and load particles into a Paul trap at pressures as low as
4x10^-7 mbar. The method is based on laser-induced acoustic desorption of
nanoparticles from a metallic foil and temporal control of the Paul trap
potential. We show that the method is highly efficient: More than half of the
trapping attempts are successful. Moreover, since trapping attempts can be as
short as a few milliseconds, the technique provides high throughput of loaded
particles. Finally, the efficiency of the method does not depend on pressure,
indicating that the method should be extensible to UHV.
