Question

A 10 mW laser beam (λ₀ = 0.6 μm) is launched on a lens of focal length 10 cm . The diameter of the laser beam is 4 mm . The area of the focused spot is approximately given by:

(a) 2.25 x 10^-10 cm²

(b) 2.25 x 10^-6 cm²

(c) 2.25 x 10^-8 cm²

(d) 2.25 x 10^-9 cm²

Answer 1

Correct option (d) 2.25 x 10^-9 cm²

Explanation:

If D is diameter of the laser beam, then D sinθ = λ If θ is very small, then sinθ = dθ