Practicing Success
A laser beam can be focused on an area equal to the square of its wavelength. A He-Ne laser radiates energy at the rate of 1nW and its wavelength is 632.8 nm. The intensity of focussed beam will be: |
1.5 x 1013W/m2 2.5 x 109W/m2 3.5 x 1017W/m2 None of these |
2.5 x 109W/m2 |
$\text{Area through which the energy of beam passes is }A = (6.328\times 10^{-7})^2 = 4\times 10^{-13}m^2$ $I = \frac{P}{A} = \frac{10^{-3}}{4\times 10^{-13}} = 2.5\times 10^9 W/m^2$ |