Strobing
the illumination laser allows a better look at a Coulomb crystal. Here
the laser is pulsed on briefly every 1/60th of a second, effectively
"freezing" the 60-Hz micromotion of the particles. Because the
particles have like charges and repel one another, they self-assemble
into a lattice-like pattern. The pattern only approximately resembles a
hexagonal lattice for a number of reasons: 1) the trap is
three-dimensional and the trapping forces push the particles toward the
trap center; 2) the photograph projects the 3D pattern onto a 2D image,
and 3) the particles do not all have identical charges or masses.
Residual micromotion blurs the particle images somewhat.
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