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What Is an Ultrashort Pulse Laser?

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  • Written By: Ray Hawk
  • Edited By: E. E. Hubbard
  • Last Modified Date: 05 November 2016
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The ultrashort pulse laser is a generic name for any type of laser that produces pulses or bursts of coherent light in extremely short periods of time, usually measured in picoseconds or femtoseconds. A picosecond is one-trillionth of second and a femtosecond is 1,000 times shorter than a picosecond or one-quadrillionth of a second. These switching rates for the ultrashort pulse laser allows it to overcome some degradation effects that normal non-pulse lasers encounter. This gives them applications in military technology, data communications, and in medical science such as for the killing of viruses in the body through external laser treatment, without harming normal living tissue.

The time range that the pulse duration spans in current ultrashort pulse laser technology as of 2011 is from a few picoseconds for every laser pulse down to 5 femtoseconds. The technology is being driven towards creating an ultrashort pulse laser in the attosecond range, however, which would have pulses that occurred 1,000 times more quickly than a femtosecond laser, or once every quintillionth of a second. Attosecond lasers would allow researchers to track the movement of electrons around atomic nuclei in real time, which would aid in both physics and chemistry research and development.

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Whereas early lasers were based on generating beams of coherent light using ruby crystals, femtosecond lasers use titanium-doped aluminum oxide, a type of blue-green sapphire first produced in 1986 for this purpose. Typical pulse energy from such a 20 femtosecond laser is about 3 nanojoules per pulse, or three-billionths of a joule. Since this is an extremely small amount of energy, the beam is amplified using an external source of radiation. Solid-state materials have proven to be the best amplifiers, with ytterbium glass being the most effective and amplifying the pulse up to 100 joules per square centimeter. Early attempts using dyes or neodymium:yttrium aluminum garnet crystals increased pulse energy from 1 millijoule to 0.5 joules per square centimeter.

There are many potential applications for the use of the ultrashort pulse laser. They would take fiber optic communications by light signal transmission to a new level, allowing for much more data to be carried on a pulse beam than fiber optics is currently capable of as of 2011, giving the term broadband a whole new meaning. They could be used as well for ablating materials away from a surface and changing it from a solid to a gas without adding any heat in the process, which would improve upon various industrial cutting and shaping processes for metals and composites. The technology also offers the advantage of serving as an extremely precise form of scalpel in medicine for removing cancerous tumors or repairing the optical cornea in people with failing eyesight.

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