Self-focusing is a phenomenon where a beam of light, such as a laser, can adjust its own shape and intensity as it travels through a medium. This occurs when the light interacts with the material, causing changes in the refractive index that can lead to the beam becoming more concentrated or focused over distance. This effect is often observed in nonlinear optics, where the properties of the medium change in response to the intensity of the light. Applications of self-focusing can be found in areas like fiber optics and laser technology, enhancing the efficiency and performance of optical systems.