When focusing, what happens to the near-field beam diameter?

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Multiple Choice

When focusing, what happens to the near-field beam diameter?

Explanation:
Focusing makes the waves converge toward a focal point, which tightens the beam laterally. As the rays bend inward, the cross-sectional size of the beam shrinks, so the near-field diameter becomes smaller as you move toward the focus. This tightening is what increases energy concentration and improves lateral resolution at the focal region. After the focus, the beam starts to diverge again, but in the near-field portion the diameter has decreased compared with an unfocused beam.

Focusing makes the waves converge toward a focal point, which tightens the beam laterally. As the rays bend inward, the cross-sectional size of the beam shrinks, so the near-field diameter becomes smaller as you move toward the focus. This tightening is what increases energy concentration and improves lateral resolution at the focal region. After the focus, the beam starts to diverge again, but in the near-field portion the diameter has decreased compared with an unfocused beam.

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