What happens to laser energy as it exits a fiber?

When laser energy exits a fiber, it no longer remains divergent because the fiber optic design is intended to confine and direct the laser light through total internal reflection along the length of the fiber. As the light exits the fiber, this confinement is lost, and the energy can spread out in different directions, which is what is appreciated in a non-divergent output.

This quality of losing divergence upon exiting is crucial for many applications, such as in medical and therapeutic settings where localized treatment is required. Light exiting the fiber tends to spread out, making the treatment area larger and potentially more effective depending on the desired outcome.

The classifications of monochromatic and coherent properties refer to the nature of the laser light itself, which remains consistent regardless of its situation within or outside the fiber. Thus, while the energy may have these properties, they are not directly related to the behavior of the light as it leaves the fiber. The key point here is the change in divergence, emphasizing how the laser behaves differently when transitioning from the fiber medium to the free space environment.