What is a femtosecond and why is that important?
August 29, 2009 @ 06:28 PM — by Jon Dishler
Light is the fastest thing we know of, it travels 186,000 miles in just one second. And the distance to the sun is reached in under 10 minutes at light speed. A femtosecond is a unit of time, a tiny piece of a second. It is 10 to the -15 power seconds or 1/100000000000000 of a second. How small you might wonder is that, well in a femtosecond that same beam of light that can travel around the earth 25 or so times in a second, travels just a third of a micron in a femtosecond. This means that in 1000 femtoseconds, light travels 300 microns or about 1/3 of a millimeter -- those tiny little gradations on the ruler you can barely see! This is less than the thickness of a credit card in 1000 femtoseconds, and we have a laser that has pulses so short, that they are only a few hundred femtoseconds. This means that the laser is shooting out pulses of light, or photons, in packets that span just a tiny fraction of a millimeter, light photon bullets and these tiny light bullets are what makes femtosecond LASIK possible. The "bullet" is only a micron in size and has very low energy, but when focused at the proper spot will create a very tiny break in the tissue of the cornea. When combined with hundreds of thousands of similar spots, it allows surgeons to cut a precise plane in tissue in a way that is more exact than the precision of any other kind of cutting of tissue that exists. All this techno-talk means that a femtosecond laser can do what no laser has ever been able to do before. It is light years beyond cutting with a scalpel. It is the right tool for the job.
Dishler Laser Institute



