Way back in the late 1990′s – back when the zone membership was becoming frustrated by the loons on the MSNBC space board- I was a graduate student working on an ultrafast laser… it was ‘ultrafast’ because the light pulses from the laser had a duration of ~100 femto-seconds, or 100 millionths of a billionth of a second. A pulse that short has a physical length measured in 10′s of microns.

Why were we interested in such tiny bursts of light? Well, there are quite a few reasons, but the one that concerned me is that femto-second pulses offered a way to achieve extremely high intensities. Our laser had an AVERAGE output power of 1 Watt (1 Joule per second), firing 1000 of the pulses a second- so each pulse carried 1 milli-Joule of energy. 1 milli-Joule of energy packed into just a 100 femto-second duration gives you a PEAK power of 10 billion Watts. When focused down tightly this can yield a Peak INTENSITY at the focus approaching 10-million-billion Watts per square centimeter. At these intensities interesting physics happens as the electric field of the laser rips the electrons from atoms.

When concentrated onto matter it doesn’t melt, or boil it… it strips electrons away, leaving behind a collection of highly positively charged ions that explode away from each-other due to Coulomb repulsion- often termed a Coulomb explosion which has been used to create fusion on a tabletop (ok, a BIG optical table-top).

At the time it was cutting edge technology, now it is something pretty standard.

Back then it was known these lasers offered unique capabilities for material processing… it can remove or modify material so quickly, without heating the material around it… allowing you to do extremely precise micromachining:

The unique processes that can occur with these short pulses allow you to do things that were not previously possible- such as weld glass directly to metal:
https://www.osapublishing.org/ao/abstract.cfm?uri=ao-54-30-8957

When focused INSIDE a piece of glass, it can modify the index of refraction, allowing you to write optical waveguides, and photonic devices directly inside a piece of glass.

And they can also be used for micron-scale 3D printing:

20 years on and we are still learning the possible applications…
All this with pulses that last a trillionth of the blink of an eye…

The ‘cutting edge’ in short pulse lasers has moved on- now atto-second laser pulses are in the lab, (attosecond is one billionth of a billionth of a second) … and zepto-second pulses are being discussed… (1 thousandth of an attosecond)