Time-resolved spectroscopy

physics on extremely short timescales, approximately 10⁻¹⁸ seconds

thumb|403x403px|An illustration of electron excitation, showing excitation by photon (left) and by particle collision (right). This is the simplest case of photoexcitation, sinca a single photon excites a single quantum particle. Photoexcitation is a phenomenon in physics where an excited state of a quantum system (an atom or a molecule) is created by photon absorption. The excited state originates from the interaction between a photon and the quantum system when the energy of the photon is too low to cause photoionization. A very simple example of this process is electron excitation.

technique for studying free-radical reactions in gases; an intense flash of light dissociates molecules in the sample creating free radicals, which can be detected spectroscopically