Femtosecond lasers are actually common nowadays. We use a Ti-sapph at my lab. Unless I'm crazy, Prat's answer is actually unrelated to your question. It's an a

Femtosecond lasers are actually common nowadays. We use a Ti-sapph at my lab. Unless I'm crazy, Prat's answer is actually unrelated to your question. It's an article about pulse shaping, which is used to, well, change the shape of an ultra-short pulse. Not generate it. What you want to look for is mode-locking. Essentially it's based on interference. You have a lot of standing waves in a laser cavity and lock them so that they all have the same phase. Then they'll interfere destructively except at a regular interval where they add up to make a powerful but very short pulse. Imagine water in a pool, if you generate waves just right you can get it to splash suddenly and powerfully in certain spots, even though your wave machine itself can't generate such strong splashes. http://en.wikipedia.org/wiki/Mode-locking http://en.wikipedia.org/wiki/Mode-locking Disclaimer: I use these lasers sometimes, but I'm in signal processing, not physics.