As suggested by its name, peculiar type of radiation(which fall in infrared range) is used in this procedure and their wavelength is in the range of a femtosecond i.e. 10^-15
I always have a weird feeling when I read a number without any unit attached to it... :D The physics professor speaks here. I am just used to be very unhappy when units are not there :p
Well he did define the unit as a femtosecond :p
On the left hand side of the i.e only :p
Ouch :p . Now I have put "s" at the right hand side :) .