Ultrashort-Pulse Lasers: Big Payoffs in a Flash; September 2000; Scientific American Magazine; by John-Mark Hopkins, Wilson Sibbett, side bar by Graham P. Collins; 8 Page(s)
How long did it take you to read this sentence? Just recognizing the first letter took only milliseconds. Around 0.05 millisecond, or 50 microseconds, passes each time chemicals diffuse across a synapse, carrying a signal from one neuron to another in your brain. Are you holding the magazine at a comfortable reading distance? It takes light one or two nanoseconds to travel from the page to your eye and about 20 picoseconds to pass through the lens in your eye. And yet these brief natural events are epically long compared with the shortest man-made events, which proceed 1,000-fold more swiftly: pulses of laser light that last for only a few femtoseconds (quadrillionths of a second).
It is hard to comprehend the brevity of a femtosecond (10-15 second). One femtosecond is to one second as one second is to 32 million years. Put another way, more than 10 times as many femtoseconds elapse every second than hours have passed since the big bang! Some of the most fundamental processes in the universe-for example, electrons moving between atoms and molecular bonds breaking or forming-occur on timescales of hundreds of femtoseconds or less. Scientists have used femtosecond pulses to record and study such fast events in detail, much as Harold E. Edgerton of the Massachusetts Institute of Technology used microsecond flashes of light to produce unforgettable photographs of splashing droplets and flying bullets. The pioneering work of Ahmed H. Zewail of the California Institute of Technology enabled chemists to see how reactions proceed on timescales of a few hundred femtoseconds, earning him the Nobel Prize in Chemistry [see ¿The Nobel Prizes for 1999," Scientific American, January]. Researchers have also effectively "freeze-framed" the dynamics of electrons within semiconductor materials to enable them to design better optoelectronic devices to achieve the ever faster signal processing demanded by the computer and telecommunications industries.