Ion beams are accelerated to high voltages (speeds
ms-1) in laser photofragment experiments in order to utilise kinematic compression. This reduces the Doppler broadening of spectral lines, giving high resolution spectra (<0.01 cm-1 resolution) when used in conjunction with low linewidth laser radiation. The high speed of the molecular ion beam (which travels in the same direction as the laser radiation) causes a Doppler shift.