Q-switched laser

Q-switched laser is the technique of active or passive Q switching is applied, so that it emits energetic pulses. Typical applications of such lasers are material processing (lasr cutting, drilling, laser marking), pumping nonlinear frequency conversion devices, range finding, and remote sensing. Red more about Q-switching laser at wisegeek here. One of the important parts is acoustic optical modulator (AOM). The acoustic optical modulator control  the power, frequency or spatial direction of a Q-switch laser.

Types of Q-switched Lasers :
The most common type is the actively Q-switched solid-state bulk laser. 
For wavelengths in the 1-μm spectral region, the most common pulsed lasers are based on a neodymium-doped laser crystal such as Nd:YAG, Nd:YVO4, or Nd:YLF.
Q-switched lasers with longer emission wavelengths are often based on erbium-doped gain media.
A passively Q-switched laser contains a saturable absorber (passive Q switch) instead of the modulator.

Details here. 

Nd:YAG laser

Effect of 1064-nm Q-Switched Nd:YAG Laser on Tattoos Studied