1.

A laser beam has a wavelength of `7 xx 10^(-7) m` and aperure `10^(-2)m`. The beam is sent to moon at a distance of `4 xx 10^(5) km` from earth. Find the angular spread and areal spread of the beam on reaching the moon.

Answer» Here, `lambda = 7 xx 10^(-7) m, a = 10^(-2)m`
`D = 4 xx 10^(5) km = 4 xx 10^(8)m`
For diffraction at a circular aperture,
angular spread `= theta = (1.22 lamda)/(d) = (1.22 xx 7 xx 10^(-7))/(10^(-2))`
`= 8.54 xx 10^(-5) radian`
Areal spread `= (D theta)^(2)`
`= (4 xx 10^(8) xx 8.54 xx 10^(-5))^(2) = 1.197 xx 10^(9)m^(2)`


Discussion

No Comment Found

Related InterviewSolutions