The optical laser was invented in 1960 and is responsible for several Nobel prizes. Last year's Nobel prize in physics included an award to Art Ashkin for the invention of the optical tweezer, a laser beam that traps a nanoparticle at its focus.  In this talk I will present our theoretical prediction, and its experimental verification in  the group of N. Vamivakas, for using an optical tweezer to realize a phonon laser, that is, a laser for sound waves generated by the center-of-mass oscillation of the trapped nanoparticle. Our work provides a source of coherence for exploring quantum mechanics at mesoscopic mass scales.