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?

The wavelength (wl) of the light has to fit within the pulse.  Light does not travel in partial wavelengths.  Using the speed of light (c) and the maximum frequency (fr).

wl = c * fr

c = 3 *10^8 m/s

fr = 10^-18

wl = 3*10^8 m/s * 10^-18s = 3*10^-10 m = 0.3 nm

A wavelength of 0.3 nm is in the X-ray region of the light spectrum and not visible.

fr = 10^-15 would give wl = 300 nm which is still slightly outside the visible light range of 380 to 740 nm.  It would be at best "ultra-violet".

Edited on October 6, 2006, 12:27 pm

Posted by Leming on 2006-10-06 12:24:59