Problem 31.76 In laser eye surgery, the laser emits a 1.12-ns pulse focused on a

Question

Problem 31.76 In laser eye surgery, the laser emits a 1.12-ns pulse focused on a spot that is 36.3 um in diameter. Part A If the energy contained in the pulse is 2.84 mJ, what is the power per square meter (the irradiance) associated with this beam? 2.7-10 W/m2 Submit Previous Answers Request Answer X Incorrect; Try Again; 5 attempts remaining Part B Suppose a molecule with a diameter of 0.686 nm is irradiated by the laser beam. How much energy does the molecule receive in one pulse from the laser? (This much energy is likely to dissociate the molecule.) Emol MeV Submit Request Answer

Explanation / Answer

a) P / A = E / (pi r2 * t)

= (2.84 * 10-3) / (pi * (18.15 * 10-6)2 * 1.12 * 10-9)

= 2.45 * 1015 W/m2

b) E = E1 * (d / D)2

= 2.84 * 10-3 * (0.686 * 10-9 / 36.3 * 10-6)2

= 1.01 * 10-12 J

= (1.01 * 10-12) / (1.6 * 10-13) = 6.3 MeV

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