Question

With the help of appropriate energy level diagram, explain the working of a He-Ne laser. A He-Ne laser emits a beam of diameter 2103m and wavelength 630 nm. It is directed towards an aeroplane flying at a height of 11 km. Calculate the diameter of the light patch produced on the surface of the aeroplan

Answer 1

$D=H\sin\theta=1.22H\cdot \frac \lambda d=4 .23~m .$