Question

A LASIK vision-correction system uses a laser that emits 10-ns-long pulses of light, each with 3.0 mJ of energy. The laser beam is focused to a 0.80-mm-diameter circle on the corneaWhat is the electric field amplitude of the light wave at the cornea?.

Answer 1

 P = energy/t = 0.0025/1E-8 = 250000 W 
I(ave) = P/A = 250000/(pi*0.425E-3^2) = 4.4056732E11 W/m^2 
I(peak) = 2I(ave) = 8.8113463E11 W/m^2 
Electric field E = sqrt(I(peak)*Z0) = 1.8219499E7 V/m, where 
free-space impedance Z0 = sqrt(µ0/e0) = 376.73031 ohms