A laser beam can be focussed on an area equal to the square of its wavelength `A` `He-Ne` laser radiates energy at the rate of focussed beam will be

Options

A. `1.5xx10^(13)W//m^(2)`
B. `2.5xx10^(9)W//m^(2)`
C. `3.5xx10^(17)W//m^(2)`
D. None of these

Answer

b

Explanation

Area though which the energy of beam passes `=(6.328xx10^(-7))=4xx10^(-13)m^(2)`
`:. I =(P)/(A)=(10^(-3))/(4xx10^(-13))=2.5xx10^(9)W//m^(2)`