In analogy to the amplification of light in a laser, vibrations of a semiconductor crystal, so called phonons, were enhanced by interaction with an electron current. Excitation of a metal-semiconductor nanostructure by intense terahertz (THz) pulses results in a ten-fold amplification of longitudinal optical (LO) phonons at a frequency of 9 THz. Coupling such lattice motions to propagating sound waves holds potential for ultrasound imaging with a sub-nanometer spatial resolution.
