# What is the difference between ultrafast laser and normal laser?

I was reading an article of latest innovation and i came across this 'ultrafast laser' term. What is the difference between it and the laser we normally refer?

Laser in the "normal" sense is continuous wave. Meaning that it is always on and shining light. An ultrafast laser is a special class of pulsed laser systems, where the laser light is pulsed on for a short period of time, typically in a cyclical fashion. The idea being that when you build up the population inversion for the laser, you can extract all of the energy in a shorter time period, which allows for laser pulses at much higher intensity than you could otherwise get from a continuous wave laser. This is useful for a variety of applications, including probing the dynamics of things that have very short time scales. Ultrafast lasers could be useful for probing the dynamics of the nucleus for instance, which occurs on very short timescales ($\sim 10^{-18}\ \text{s}$ if I remember right).