Developing Pulsed Fiber Lasers

Abstract

Abstract : Laser power is at a premium and a diffraction limited optical beam delivers the maximum intensity on target. Therefore, the better the beam quality, the lower the system cost and complexity is reduced considerably by using high quality beams. Single mode optical fiber lasers and amplifiers produce near diffraction limited beams and therefore will result in near diffraction limited optical beams thus they will provide the highest intensities at the lowest laser powers. In the case of pulsed fiber lasers the factors that limit the output power are the fiber nonlinear effects and surface damage on the exit aperture. The nonlinear optical effects include Stimulated Brillouin Scattering (SBS), Stimulated Raman Scattering (SRS), self-phase modulation (SPM) and four-wave mixing (FWM) depending upon the application. For pulse durations of greater than 1-ns SPM and FWM can be neglected. The lowest threshold nonlinear process for long pulse duration is SBS. SBS can be effectively suppressed. The surface damage on the exit aperture can be eliminated by allowing free expansion in an end cap' before the beam exits into free space.