Arthur Ashkin, at Bell Laboratories, develops in 1986 a technique that exploits the radiation pressure of light — the fact that photons, although massless, carry momentum and can exert physical force upon striking an object — to trap and manipulate individual microscopic objects with no physical contact. Ashkin discovers that a carefully focused laser beam can attract and hold motionless at its focal point a tiny particle, ranging from viruses to individual cells or even living bacteria, forming what he calls "optical tweezers" — an instrument able to hold, move, stretch, and manipulate with extraordinary precision objects too small and delicate for any conventional mechanical tool, without damaging them in the process. The technique allows biologists to directly measure the mechanical forces exerted by individual molecular motors — such as the ATP synthase characterized by Walker — or to stretch individual DNA molecules to study their mechanical properties, opening an entirely new avenue of research in single-molecule biophysics. Optical tweezers become a standard tool in cell biology and biophysics laboratories worldwide, also used in atomic physics to trap and manipulate individual atoms in quantum physics experiments.