CW vs. Pulsed laser (compress the energy by time dimension)
Laser sources can be categorized into either CW (Continuous Wave) or Pulsed by its beam output mode. We can use the following simple diagram to explain how a pulsed beam output is formed.
Assume we set a 90% reflective mirror at one end of the lamp-pumped laser cavity, and a highly reflective mirror at the other end. When the arc lamp irradiates the Nd:YAG rod with light, the rod emits light at a wavelength of 1064nm from either end which heads towards the mirrors. These photons of light bounce back and forth between the two mirrors, pulling additional photons along with them each time they pass through the Nd:YAG rod. Because the one mirror is only 90% reflective, a percentage of the photons can also pass through this mirror, which is the usable laser energy for marking.
If we place a switching element between the Nd:YAG rod and one of the two mirrors (this is generally an Acusto-Optic Modulator, or ‘Q-Switch’) and then ‘close’ the switch to prevent photons from reflecting off of the mirror, there will be a build up of energy within the laser rod. When the switch is ‘opened’ and the photons are allowed to flow through again, this energy will be stripped off the rod with the initial surge of photons, creating a high-energy pulse.
Now, looking at the following chart, we can see the effect of pulsing the laser beam.
The energy-over-time (continuous power) is identical between the two modes; however, when the laser is pulsed, we build up a very large spike of power which is followed by a correspondingly lower power section.