In laser eye surgery, the laser emits a 1 20-ns pulse focused on a spot that is

Question

In laser eye surgery, the laser emits a 1 20-ns pulse focused on a spot that is 30.0 mu m in diameter. If the energy contained in the pulse is 2.80 mJ, what is the power per square meter (the irradiance) associated with this beam? Express your answer to three significant figures. I = 3.30 times 10^15 W/m^2 Suppose a molecule with a diameter of 0 450 nm is irradiated by the laser beam. How much energy does the molecule receive in one pulse from the laser? (The energy obtained in this part is more than enough to dissociate a molecule.) Express your answer to three significant figures.

Explanation / Answer

We know that the energy receive by any area will be given by
Energy = Intenstiy*area
Energy = 3.3*1015*(Pi*R2) = 3.3*1015*(Pi*(0.5*0.45*10-9)2) = 5.248*10-4 J/s
total energy in one pulse
Energy = 5.248*10-4 *(1.2*10-9) = 6.298*10-13 J
But we want energy into MeV
So 1eV = 1.6*10-19 J
Energy = 6.298*10-13 /(1.6*10-19) = 3.936*106 eV = 3.936 MeV

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