  Multi-gigahertz mechanical vibrations stemming from interactions between
light fields and matter, also known as acoustic phonons, have long been a
subject of study. In recent years, specially designed functional devices have
been developed to enhance the light-matter interaction strength, since the
excitation of acoustic phonons by a continuous wave laser alone is
insufficient. However, with such structure-dependent enhancements, the strength
of the interaction cannot be aptly and instantly controlled. We propose a new
technique to control the effective interaction strength, which is not via the
material structure in the spatial domain, as with the above-mentioned specially
designed functional devices, but through the structure of light in the time
domain. Here we show the effective excitation and coherent control of acoustic
phonons in a single-mode fiber using an optical frequency comb by tailoring the
optical pulse train. We believe this work represents an important step towards
"comb-matter interactions."
