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