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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?

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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).

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    $\begingroup$ Ultrafast lasers use mode locking to generate pulses of a picosecond or less; when chirped pulse amplification (CPA) is used it is also possible to obtain high power: a train of pulses one millisecond apart, each with a milijoule of energy corresponds to 1 watt average power; but if each pulse is 100 femtoseconds long, when focused you can convert steel directly to plasma, a form of laser cutting with no heating. Thus the physical response to ultrafast pulses is quite different than that of longer pulses, or CW lasers. $\endgroup$ – Peter Diehr Mar 10 '16 at 14:46
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    $\begingroup$ The attosecond pulses are generated by femtosecond lasers, typically 10 fs pulses; the excitation generates electrons which in turn generate the x-ray pulses; this is very leading-edge science. $\endgroup$ – Peter Diehr Mar 10 '16 at 14:50
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    $\begingroup$ I wouldn't consider a CW laser more "normal" than pulsed. Typically the first lasers made in any new technology (including Maiman's first laser ever, the first diode lasers, etc) are pulsed. CW lasers are only possible once the technology improves enough that CW operation doesn't overheat the laser. Of course these lasers have pulse widths that are only short on thermal time scales, and there's a different technical challenge in reducing the pulse width down to picoseconds or femtoseconds. $\endgroup$ – The Photon Mar 10 '16 at 18:42
  • $\begingroup$ @ThePhoton I agree. I had to infer what the OP meant by "normal", which I took to mean a laser pointer type laser, which is CW, which is something that one is more likely to come across in everyday life. I take it based on the acceptance of this answer that this is, in fact, what the OP meant. But your point is well taken. $\endgroup$ – tmwilson26 Mar 10 '16 at 18:46

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