When the radiation power is described as a function of time (as in figure 7.1),the total energy in a specific time interval can be calculated by the area under the graph (specific integral).

The radiation out of a laser can be emitted as a continuous beam (as in He-Ne laser), or as pulsed radiation.

A pulse of radiation from a laser can be long (parts of a second), or very short (pulses as short as 10^-14 [s] are available).

Laser pulses can appear as single pulse or repetitive pulses, and the rate of pulses can be as high as thousands of millions per second.