A 0.6 Joule - 30 femtosecond pulse of laser light is focused to a spot with a di
ID: 2089550 • Letter: A
Question
A 0.6 Joule - 30 femtosecond pulse of laser light is focused to a spot with a diameter of
20 ?m. (1 femtosecond = 10^?15 seconds). The time dependence of the electric field is
illustrated schematically (and not to scale) below. The central wavelength of the laser
pulse is 800 nm.
#1 Based on pulse energy and duration obtain an estimate for the power (Watts) in the
pulse.
#2 At the focus, what is the intensity (Watts/m^2) of the laser pulse?
#3 What are the strength of the electric (V/m) and magnetic (T) fields in the pulse?
#4 Based on the central wavelength, estimate the time between peaks in the electric
field. Note the figure above is just schematic.
1.5 T T T TE 0.5 LT 0.5 L 1.5 -80 60 -40 20 0 20 40 60 80 time IfslExplanation / Answer
1. Power after 15 seconds will be P =Energy/time(15)=0.6/30e-15=2^13 Watt 2. Area=pi*d^2/4=3.14e-10 m^ --> Intensity = 2^13/3.14e-10=6.36e22 W/m^2 4. time between peaks=20/4=5 fs because there are 4 peaks in interval of 20 fs 3.strength of electric field=2 V/m
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