For reference purposes, the diameter of a typical human hair is about 100 microns. The heating rate is rapid and causes molecules in the focal spot of the laser to evaporate and leave the surface. This rising gas plume of evaporated molecules is intercepted by a second pulsed laser beam whose wavelength is in the ultraviolet. Those molecules in the gas plume that absorb these more energetic photons go on to ionize. In the ionization process, an electron is knocked off the neutral molecule and flies away, leaving the molecule as a positively charged molecular ion.
Different molecules produce ions with different weights or masses.
The ions are produced between two metal screens held at different voltages. The resulting electric field between the two screens exerts a force on each ion of the same amount because the charge on each ion is the same. Recall that according to Newton 's second law of motion, force equals mass times acceleration. Consequently, ions with differing masses receive differing accelerations from being born in the electric field. As a result, lighter ions hit an ion collector in a shorter time than heavier ions.