Sensors and Electron Devices Directorate Research Areas

Low-Quantum-Defect Diode-Pumped Er-Doped Fiber Lasers and Rod Lasers

Advisor: White, Jeffrey Owen (Jeffrey.owen.white@us.army.mil 301.394.0069)
Adelphi, MD

Key words: Solid-state laser, Erbium laser, Fiber laser, Phase conjugation, Brillouin scattering, Beam combining, Eye-safe, Diode pumping

This research focuses on new science and technology that will be useful in the next generation of high power fiber lasers and high power solid-state lasers at wavelengths greater than 1.6 μm. Our approach usually involves low-quantum-defect laser diode pumping.
One specific project involves designing and building a high average power Erbium fiber laser with beam quality close to the diffraction limit. Stimulated Brillouin scattering (SBS) limits the power scaling of conventional fiber amplifiers because it can reflect ~100% of the incident wave when the product of gain, intensity, and effective length reaches the level gIL~30, where I is the intensity within the Brillouin linewidth. Our approach uses a large mode area fiber in a highly multimode configuration. The diffraction-limited quality will be recovered through phase conjugation or beam cleanup, using SBS in a separate fiber.
Another project involves the engineering of solid-state laser rods to increase the power output. Multi-kilowatt rod lasers designed for end-pumping by stacks of diode bars are typically polished on the barrel surface, to waveguide the pump. This inevitably leads to parasitic oscillations at the laser wavelength, known as whispering gallery modes (WGM), due to total internal reflection at the barrel surface. For YAG immersed in cooling water, the index difference is so high that the WGM occupy 50% of the rod volume. Suppressing the WGM can theoretically lead to a doubling of output power. Several methods for suppressing WGM will be explored.

References
White JO, et al: Journal of the Optical Society of America B24: 2454, 2007
White JO, IEEE J. Quantum Electronics 45: 1213, 2009