  Ultra-high frequency acoustic resonances ($\backsim$2 GHz) trapped within the
glass core ($\backsim$1 $\mu$m diameter) of a photonic crystal fiber are
selectively excited through electrostriction using laser pulses of duration 100
ps and energy 500 pJ. Using precisely timed sequences of such driving pulses,
we achieve coherent control of the acoustic resonances by constructive or
destructive interference, demonstrating both enhancement and suppression of the
vibrations. A sequence of 27 resonantly-timed pulses provides a 100-fold
increase in the amplitude of the vibrational mode. The results are explained
and interpreted using a semi-analytical theory, and supported by precise
numerical simulations of the complex light-matter interaction.
