Figure 5.10 describes the shape of a single pulse out of a Ruby laser, compared to the pumping pulse from the flash lamp.

Figure 5.10: single pulse out of a Ruby laser, compared to the pumping pulse from the flash lamp

The output laser pulse is about 1 millisecond, and it is composed of hundreds or thousands of small pulses.
Each of the small pulses is called a spike, and last about a microsecond.
The spikes appear randomly in time, and differ from each other in its length and peak power.
Usually only the entire pulse is measured, without consideration of each spike.

The average power per pulse is calculated by timing the entire pulse, and measuring its energy.

In figure 5.10 it can be seen that the laser pulse starts after a short time from the pumping pulse. This is the time it takes the active medium to arrive at the threshold value for lasing.