IMAGINE a pulse of light which lasts foronly a few hundred billionths of a billionth of a second (10-18 seconds, or anattosecond). This is about the time thatlight travelling at 300 million metres persecond takes to move across an atom!
If the calculations of some theoristsare correct, it would be possible to generate such a short-lived pulse. Currently the fastest pulse has a duration of abouta ferntosecond, which is 1,000 timeslonger than the attosecond pulse.Shortening of the pulse time is a difficulttask. The pulse has to be composed ofmany different frequencies, all of whichneed to be coherent or in phase. Thepulse has to be strong enough to be ofuse and the consecutive pulses have tobe separated by about a millionth of asecond (Science, Vol 269).
The theoretical ideas of PaulCorkurn and his colleagues at theNational Research Council at Ottawa,Canada, have the potential of meetingthese challenges. These researchers planto use a pulse from a titanium sapphirelaser to ionize a gas of xenon or argon.The laser light will generate an oscillazing electric field which will force'theelectrons in the ionized gas to move atextremely high energies. These electronswill collide with their parents to generate a high energy photon.
Limiting the number of gas atomsused and making use of special metallicfilters, Corkurn plans to generate a pulseof ultraviolet'light lasting only about400 attdseconds. These short-lived pulses could prove to be a wonderful tool tostudy natural phenomenon which occurat such short time scales. For instance, alaser firing attosecond pulses could beused as ,a high speed flash to "see" themotion.%)f electrons, the formation ofchemical bonds or even the formationof molecules.
The researchers feel that though nogroup has all the equipment required togenerate an attosecond pulse and mea-sure it, it is only a matter of a couple ofyears before it becomes a reality and weare able to actually see the electrons inmotion around the nucleus.