Recently physicists have managed to build "attosecond lasers", lasers which emit pulses 10^-18 seconds long, interrupted by much longer periods of darkness (at least 10^-14 seconds). Before them, lasers emitting femtosecond (10^-15 seconds) pulses have been around. Assuming they produce visible light, what colour is it?

A pulse that goes on and then off is a square wave.  A Fourier transform of this is an infinite sum of sine waves.  The largest component of this is a sine wave whose period is double the length of the pulse.

So I think the key wavelength would be 600 nm (red light), along with harmonics of decreasing intensity and shorter wavelengths.

Posted by Larry on 2006-10-06 18:04:03