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Thursday, September 06, 2012

Shortest-ever laser pulses produced.

The quest for the shortest pulse has been ongoing since the laser's invention 

Researchers in the US have produced the shortest-ever laser pulses: just 67 billionths of a billionth of a second.

The feat surpasses the prior record of 80 attoseconds, set in 2008.

Like a camera with an ever-shorter flash, these 67-attosecond pulses will allow researchers to examine the very fastest natural processes.

The team behind the pulses,   reporting in Optics Express,  have also developed a novel detector to capture them - like a camera with a shutter speed to match.

The quest for the shortest laser pulse has been underway since the laser's first demonstration in 1960; the very first laser created pulses of about a thousandth of a second.

In recent years the field of "femtosecond" lasers - producing pulses lasting just millionths of a billionths of a second - have become widespread research tools.

These have allowed researchers to examine fast processes such as the making and breaking of chemical bonds, the study of which earned Ahmed Zewail   the 1990 Nobel prize in chemistry. .

But even at those short time scales, some of the secrets of the microscopic world remain hidden, and it is only by moving to attosecond science that researchers can examine, for example, the very motion of subatomic particles within atoms or the mysterious world of quantum mechanics.

So Zenghu Chang, a professor at the University of Central Florida (UCF) in the US, has now smashed the record   reported in Science in 2008  by refining a technique in which short pulses beget even shorter ones when they are shot into a focussed jet of inert gas.

The resulting pulses, still more than a femtosecond, include a wide range of colours in a region of the spectrum known as extreme UV, with wavelengths far shorter than those we can see: about 10-20 billionths of a metre.

"Attosecond science" will permit us to watch electrons move in their orbitals in real time 

But to get down to the world-record pulse length status, the team passed the pulses through a thin piece of zinc foil, which acts to slow some parts of the pulse relative to others - the result is that all of the colours within the pulses were squeezed into a shorter period of time.

As has become customary in this field of "ultrafast optics", the team has come up with an animal-based acronym to describe the approach: Dog, for double optical grating. (Other established acronymic approaches include Frog, Spider, and Grenouille - French for frog).

"Dr Chang's success in making ever-shorter light pulses helps open a new door to a previously hidden world, where we can watch electrons move in atoms and molecules, and follow chemical reactions as they take place," said physicist Michael Johnson, dean of UCF's College of Sciences.

"It is astounding to imagine that we may now be able to watch quantum mechanics in process."



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