Increasing spot size helps keep scattered photons in the:

Increasing the spot size in laser applications is an important technique to manage the interaction of the laser beam with the target and its surroundings. When the spot size is larger, it helps to diffuse the energy more broadly over a greater area, which reduces the intensity and potential for scattering. This increased size diminishes the likelihood that scattered photons will deviate too far from the original laser path.

By expanding the spot size, the overall energy density on the target surface is reduced, which can lead to less scattering of photons in various directions. This containment of scattered photons aids in maintaining them closer to the beam path, ensuring that more of the energy remains directed towards the intended area of treatment or application. This principle is particularly crucial in medical or cosmetic laser therapies, where precision and control are necessary to minimize damage to surrounding tissues.

In contrast, smaller spot sizes can lead to higher energy density, potentially resulting in greater scattering, which may detract from the effectiveness of the laser treatment and increase unwanted collateral damage. Therefore, the option relating to maintaining scattered photons in the beam path accurately captures the advantages of using an increased spot size in laser practice.