1. Electrical modulation of a laser power supply to produce discreet pulses of energy at a given pulse length and pulse period (pulse repetition rate).
  2. Mechanical interruption of the laser beam by a rotating chopper, which alternately blocks or passes the laser beam.
  3. Acousto-optical modulation of the beam within the laser resonator, caused by a device generically called a Q-switch. See Q-Switch.