A LASIK vision correction system uses a laser that emits 10 ns long pulses of li

Question

A LASIK vision correction system uses a laser that emits 10 ns long pulses of light, each with 4.5 mJ of energy. The laser is focused to a 0.85 mm -diameter circle. What is the intensity of the laser light at the focus point? Express your answer using three significant figures. What is the peak electric field strength of the laser light at the focus point? Express your answer using three significant figures. What is the peak magnetic field strength of the laser light at the focus point? Express your answer using three significant figures.

Explanation / Answer

P = energy/t

P = 0.0045/(1 x 10^-8) = 450000 W

I(ave) = P/A = 450000 / (3.14*(0.425 x 10^-3)^2) = 7.934 x 10^11 W/m^2 ..........(b)

I(peak) = 2I(ave) = 1.587 x 10^12 W/m^2

free-space impedance Z0 = sqrt(µ0/e0) = 376.73031 ohms

Electric field E = sqrt(I(peak)*Z0) = 2.445 x 10^7 N/C ...........(c)

B = E/c

B = (2.445 x 10^7) / (3 x 10^8)

B = 0.0815 T ..........(c)

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