Ultrafast laser pulses

By “ultrafast” we mean those light pulses that last from about ${10}^{\text{−13}}$ seconds to a few tens of picoseconds. The anticipation of using them to study ultrafast processes in physics and chemistry has stimulated efforts to produce these pulses, and the results have been good; in 1962 the shortest pulse available was ${10}^{\text{−8}}$ sec, but by 1968, ${10}^{\text{−13}}$ ‐sec pulses had been produced at powers up to ${10}^{\text{−12}}$ watts. Progress has been due largely to the perfection of “mode‐locking” methods, through which we arrange the phase relations between the axial modes of the laser. Here we shall discuss the ways ultrafast pulses are produced and measured. Then we can consider their usefulness in, for example, studying stimulated scattering, measuring excited‐state lifetimes and creating high‐temperature plasmas.