Continuous-wave operation:
There are some applications in which the use of the laser depends upon the beam which has an output power that is constant over time. This type of lases is known as continuous wave (CW). There are many specialized lasers that are constructed in order to work in continuous wave mode to satisfy such an application. Many of these lasers are actually lasers in multiple longitudinal modes at the same time, and the beats of those oscillations between slightly different optical frequencies are, in fact, shorter time scales than the round-trip time (the reciprocal of the frequency) there but the dimensions produce variation difference between modes), typically a few nanoseconds or less. In the glass optical lenses industry, optical windows are fabricated with the help of industrial lasers optics.
In the majority of cases, there are some lases which are still referred to as continuous waves as their output power is constant when they are approximated over large time periods, with the very high-frequency variations having almost negligible or no effect on the intended application.
Pulse operation:
The pulse operation of lasers happens in those lasers which are not classified as continuous wave; therefore, the optical power appears to be in interval or pulses in some duration at some repetition rate.
This includes a wide range of technologies addressing many different motivations. Some lasers are pulsed simply because they cannot be operated in continuous mode. There are some other cases, in which the application needs the production of those pulses which will have large energy as possible. Although the energy of the pulse is equal to the average power divided by the repetition mode, this goal can be fulfilled by decreasing the rate of pulses so that more energy can be built up in between pulses. For example, in laser ablation, a small amount of material on the surface of the workpiece can be evaporated if it is heated over a very short period of time while supplying energy to slowly absorb the heat in the bulk is performed will allow the piece is not achieving a high enough temperature at a particular point.
There are some other applications that depend upon the peak pulse power (instead of the energy in the pulse), especially in order to get the nonlinear optical effects. For given pulse energy, pulses of the shortest possible duration need to be created using techniques such as Q-switching.
