A 0.1 watt LASER beam with an aperture of 5.0 mm emits a light of wavelength 6943 Å. Calculate the areal spread and intensity of the image when the beam is focused with lens having a focal length of 100 mm.
Answers
Answer:
Given A laser light beam of power 20 m W is focused on a target by a lens of focal length 0.05 m. If the aperture of the laser be 1 mm and the wavelength of its light 7000 Å calculate the angular spread of the laser, the area of the target hit by it, and the intensity of the impact on the target.
Given P = 20 mW = 20 x 10^-3 W
Focal length f = 0.05 m, d = 1 mm = 1 x 10^-3 m, λ = 7000 A = 7000 x 10^-10 m, theta = 7 x 10^-4 radians
Linear speed of the laser s = f x theta
= 0.05 x 7 x 10^-4
= 0.35 x 10^-4 m
Now area of target hit by laser = s^2
= (0.35 x 10^-4)^2
= 0.1225 x 10^-8
= 1.225 x 10^-9 sq m
So intensity of impact on the target = power of the laser beam / area hit by the laser beam.
= 20 x 10^-3 / 1.225 x 10^-9 W / m^2
= 16.326 x 10^6 W/m^2
= 1.632 x 10^7 W / m^2
Explanation: