A laser used in eye surgery emits a 2.00mJ pulse in 1.00 ns, focused to a spot 4

Question

A laser used in eye surgery emits a 2.00mJ pulse in 1.00 ns, focused to a spot 40.0 µm in diameter on the retina. (a) Find (in SI units) the power per unit areaat the retina. (This quantity is called theirradiance.)
1 W/m2

(b) What energy is delivered per pulse to an area of molecular size(say, a circular area 0.800 nm indiameter)?
2 J (a) Find (in SI units) the power per unit areaat the retina. (This quantity is called theirradiance.)
1 W/m2

(b) What energy is delivered per pulse to an area of molecular size(say, a circular area 0.800 nm indiameter)?
2 J

Explanation / Answer

energy E = 2 m J = 2 * 10 ^ -3 J time t = 1 n s           = 1 *10 ^ -9 s diameter d = 40 m                  = 40 * 10 ^ -6 m (a). The power per unit area at the ratina P = EA /t where A = Area = d ^ 2 / 4               = 1.256 * 10 ^ -9 m ^ 2 So, P = 2.512 * 10 ^ -3 W / m ^ 2 (b). energy is delivered per pulse to an area of molecularsize = P* A ' where A ' = area of the circular area 0.800 nm in diameter                = D ^ 2 / 4            D= diameter = 0.8 nm               = 0.8 * 10 ^ -9 m substitue values we get answer

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