The distance from earth surface to moon surface is 3.8x105 km. Calculate areal spread and angular spread for a laser of wavelength 632.8 nm and aperture 0.5 mm when it reaches moon.
Answers
Given:
The distance from the earth surface to the moon surface is 3.8 x 10⁵ km.
To find:
Calculate areal spread and angular spread for a laser of wavelength 632.8 nm and aperture 0.5 mm when it reaches the moon.
Solution:
The wavelength of the laser, λ = 632.8 nm = 6.328 × 10⁻⁷ m
The aperture diameter, d = 0.5 mm = 5 × 10 ⁻⁴ m
The distance from the earth's surface to the moon's surface, D = 3.8 × 10⁵ km = 3.8 × 10⁵ × 10³ m = 3.8 × 10⁸ m
Due to diffraction, the laser beam will spread out after coming out of the aperture. Therefore, the following are the formulas we will use to further solve the problem:
Finding the angular spread:
The angular spread of the laser beam is,
= θ
=
=
Finding the areal spread:
The areal spread of the laser beam is,
= (Dθ)²
=
=
=
=
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