Specific mechanisms and associated measurement techniques

These are pump-probe techniques in which a particular metastable level is excited, usually with a laser tuned to the excitation wavelength in question, and the absorption (or excitation of higher-energy emitting levels) is probed with a broadband lamp associated with a monochromator, or with a tunable laser. Depending on the wavelength range, the radiative lifetimes of the excited levels and the cross-sections of the optical transitions involved, a set-up using pulsed or continuous-wave light sources is chosen.

• Pulsed light sources

  The first set-up (figure