The beam emerging from a ruby laser passes through a...

The beam emerging from a ruby laser passes through a circular aperture $5.0 \mathrm{~mm}$ in diameter. (a) If the spread of the beam is limited only by diffraction, what is the angular spread of the beam? (b) If the beam is aimed at the Moon, how large a spot would be illuminated on the Moon's surface?

Key Concepts

Diffraction

Diffraction is a fundamental wave phenomenon where light bends and spreads when it encounters an obstacle or aperture. This effect limits the performance of optical systems by preventing perfectly collimated beams and setting a fundamental bound on resolution and focus.

Fraunhofer Diffraction

Fraunhofer diffraction deals with the far-field pattern of light that has passed through an aperture or around an object. It simplifies the analysis of light spread by assuming that the light source and the observation screen are at effectively infinite distances, which is particularly useful for analyzing laser beam divergence over long ranges.

Diffraction Limit and Angular Spread

The diffraction limit defines the lowest possible angular spread of a beam due to its wave nature, typically estimated by the relation ? ? ?/D, where ? is the wavelength and D is the aperture diameter. This limit is crucial in understanding how narrow a beam can be made before diffraction effects cause inevitable spreading.

Laser Beam Propagation

Laser beam propagation studies how lasers emit a coherent, collimated beam and how that beam spreads over distance. Diffraction, being the primary source of beam divergence, is integral in predicting both the beam's angular spread and the resulting spot size when the beam travels vast distances, such as aiming a laser at the Moon.

Transcript

Please give Ace some feedback