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HOME > PAST ISSUE > July-August 1999 > Article Detail

MARGINALIA

Pulse, Pump & Probe

Roald Hoffmann

Power

Whatever the pump pulse does, it does it for a very short time. It better do its controlled violence with substantial power, or there will be nothing for the probe pulse to probe. The output of a modern femtosecond-pulsed laser used in one of the experiments described below is 75 millijoules (mJ) in 20 fs. Were it to operate continuously for one second, this laser would require 3.75 ? 1012 joules of energy. The same energy would keep all of Milan, Italy—residential and industrial—lit up for more than one hour. No amount of funding, no power station will provide power at that rate—for that matter, were the laser output continuous the sample (maybe the lab) would be consumed in a mighty flash in no time (well, in some microseconds)!




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