Page "Laser" Paragraph 45

Another method of achieving pulsed laser operation is to pump the laser material with a source that is itself pulsed, either through electronic charging in the case of flash lamps, or another laser which is already pulsed.

Pulsed pumping was historically used with dye lasers where the inverted population lifetime of a dye molecule was so short that a high energy, fast pump was needed.

The way to overcome this problem was to charge up large capacitors which are then switched to discharge through flashlamps, producing an intense flash.

Pulsed pumping is also required for three-level lasers in which the lower energy level rapidly becomes highly populated preventing further lasing until those atoms relax to the ground state.

These lasers, such as the excimer laser and the copper vapor laser, can never be operated in CW mode.