Coherent phonons in carbon nanotubes and graphene

► We studied coherent phonons in carbon nanomaterials using ultrafast spectroscopy. ► Coherent phonon signal depends the laser excitation energy and polarization. ► Coherent phonons of specific-chirality nanotubes were excited using pulse shaping. ► Nanotubes can expand or shrink in response to ultrashort laser excitation. ► We examined how the armchair nanoribbon width changes by laser excitation.