What happens to the beam diameter in the far zone when focusing?

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Sharpen your skills for the Davies Publishing SPI Test with targeted flashcards and multiple-choice questions, complete with hints and clarifications. Prepare thoroughly for success!

Multiple Choice

What happens to the beam diameter in the far zone when focusing?

Explanation:
When a beam is focused, you create a tight spot (a waist) at the focus, but diffraction causes the beam to spread as it propagates beyond that point. In the far zone the wavefronts diverge, so the cross-sectional diameter grows with distance from the focus. For a Gaussian beam, the radius w(z) increases with z, and in the far field this growth is roughly linear, meaning the diameter gets larger as you move farther away. So the beam diameter increases in the far zone after focusing.

When a beam is focused, you create a tight spot (a waist) at the focus, but diffraction causes the beam to spread as it propagates beyond that point. In the far zone the wavefronts diverge, so the cross-sectional diameter grows with distance from the focus. For a Gaussian beam, the radius w(z) increases with z, and in the far field this growth is roughly linear, meaning the diameter gets larger as you move farther away. So the beam diameter increases in the far zone after focusing.

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