Abstract: Improved/efficient fiber laser systems are provided for medical/cosmetic applications, comprising at least one pump source, optically coupled with at least one fiber laser. The fiber laser comprises an irregularly-shaped single-, double- or multiple-clad fiber of unconventional structure and geometry, and means for partially/completely reflecting the pump radiation, such as Bragg gratings. The fiber laser system further comprises at least one fiber optic delivery device optically coupled with the pump source, with the irregularly-shaped single-, double- or multiple-clad fiber laser, or with both, to convey laser radiation to a treatment site. The fiber optic delivery device comprises one or more waveguides, preferably optical fibers. The irregularly-shaped fiber laser and waveguides of the fiber optic delivery device have the same or different tip configurations to perform the treatment according to therapeutic needs.