Time Scales: What is a femtosecond?

Let's start with understanding the time scale in which we are working.

We need to use time units that may be unfamiliar to you. Let's get an appreciation of these very unusual time scales.

millisecond 1x10^-3 second
microsecond 1x10^-6 second
nanosecond 1x10^-9second
picosecond 1x10^-12 second
femtosecond 1x10^-15 second

In other words, a femtosecond is a million times shorter than a nanosecond. Yes, that's very fast. It's "ultrafast". A femtosecond is more than a million times shorter than the several nanosecond duration pulses used in "traditional" industrial lasers micromachining systems. A million times shorter!

In the mathematician's lexicon, a femtosecond is 1x10^-15 seconds.
In words, it's a quadrillionth of a second.

Still confused about these incredible time scales? Here is another way to look at it. How "short" is a femtosecond?
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Moving downward on the scale of time, ultrafast science passes quickly beyond human experience. One second is a familiar and manageable piece of time. It's not hard to create a second's worth of light by turning a flashlight on, then quickly off. What's harder is to comprehend that in that second the light has gone 186,000 miles -- three quarters of the way to the moon.

From one second, let's move on to other time scales:

One thirtieth of a second is the time it takes human eyes to react to light. Project each frame of a home movie for one thirtieth of a second, and viewers, unable to distinguish separate frames, see continuous motion. Light, during the time one frame is projected, travels 6,200 miles. If you climb aboard a light beam in Chicago, you'll be in Tokyo in the blink of an eye.

One microsecond -- a millionth of a second -- is the duration of the light from a camera's electronic flash. Light that short freezes motion, making a pitched ball or a bullet appear stationary.

One nanosecond -- a billionth of a second -- is the speed at which transistors in today's computers turn on and off to represent the ones and zeros of binary logic and arithmetic. It is a time-duration so short that light, which can speed seven times around Earth in the second between our heartbeats, travels only one foot.

One picosecond -- a trillionth of a second -- is a spot of time from the domain of molecules. Light, traveling for one picosecond, would barely make it across the period at the end of this sentence. Only with a laser that generates picosecond light pulses can scientists freeze the short-duration motion of molecules and produce images of what goes on at the molecular level. Used in this way, the picosecond laser is comparable to a strobe, which can freeze the motion of a sprinter's stride in time-lapse photography.

One femtosecond -- a quadrillionth, or million billionth, of a second -- is a thousand times shorter than the picosecond snippets of time in which molecules react. Light, in one femtosecond, goes only far enough to traverse about 1,000 silicon atoms.

-- Excerpted from proto magazine, AT&T