A pulsed master oscillator power amplifier system is constructed using a double-cladding polarized Yb- doped fiber and an all-fiber Q-switched narrow-linewidth pulsed laser used as seed laser. This system has a high repetition rate and provides a nanosecond pulsed laser with a narrow linewidth and linear polarization. Moreover, it generates amplified radiation with up to 14 W of average power, narrow linewidth （full-width at half-maximum is smaller than 0.12 am）, linear polarization at 1080-am wavelength, repetition rate of 51 kHz, and pulse duration of approximately 50 ns. Based on this pulsed amplified radiation, 3.5 W of green laser, with an optical-to-optical efficiency of 27.3%, is obtained via single-pass frequency doubling using a noncritical phase matching KTP crystal.
A new method to obtain linear polarization operation by Brewster＇s angle-polished fiber end is demonstrated. By using the special polarization operation technique together with introducing a narrow-linewidth fiber grating into the laser cavity, a cladding-pumped linear polarization and single-transverse-mode （M2 〈 1.1） Yb-doped fiber laser with narrow linewidth whose full-width at half-maximm （FWHM） is less than 0.2 nm, is obtained in a simple configuration. The output power is up to 10 W which is continuous- wave output at 1085 nm, and the slope efficiency is 63% with respect to the coupled pump power and 75% with respect to the absorbed pump power, respectively. The measured 21-dB polarization extinction ratio does not degrade with the output power. The simplicity of such an approach is highly beneficial for a number of applications, including the use of a fiber laser for the nonlinear wavelength conversion （especially for the intracavity frequency doubling） and for the coherent and spectral beam combination.
