Research On Single Frequency Ytterbium Doped Fiber Laser Oscillator And Narrow Linewidth Nanosecond Fiber Amplifier Laser

With the increasing competition in the international laser market,and gradually,fiber laser has been replace other lasers in many applied areas. There are several direction of application for fiber laser, of which, the single-frequency narrow line-width fiber laser have been wildly using in many application due to ultra-narrow line-width and the excellent coherence, such as detection of weak signal in ultra-precision, laser radar, optic fiber sensor. However,it is also a great challenge for the marketization and engineering of single-frequency narrow line-width fiber laser. In order to enhance the engineering of fiber laser and break the foreign technological monopoly, it is significant to analyze the basic physical problem and key technology of the single-frequency narrow line-width fiber laser. In addition, it also important to grasp the magnified technique of high-power laser and enhance the output power and performance of double-clad fiber laser. Our study focus on the realization of all-fiber fiber laser with narrow line-width, high power, high stability and low noise. We will do a simple introduction for the following sentences.Firstly, the definition and the main application fields of single frequency fiber laser are introduced. Besides, we explain the significance and the background of our research. In addition, preliminary works of study are shown. The investigate basing on research actuality is also exhibited.Secondly, fabrication of seed source of single frequency fiber laser. Comparable analysis of the technology which can realize single frequency operation have been done, ring cavity and ultra-short cavity were both employed to do a comparison in our research. For the ring cavity, feedback configuration was obtained through the interference of feedback light and intrinsic light. Primary mode was selected by the utilization for line-width fiber Bragg grating, and the second mode selection can be realized by using the spaced grating structure which generating by interference. We achieve the single frequency laser at 1064 nm and with an output power of 13.54 m W, but it has a inferior stability. For the linear cavity, single frequency laser was attained through decreasing the length of laser cavity. A pair of Bragg grating(with narrow line-width) and ytterbium doped phosphate fiber(with only 1 cm length) were used to constitute a resonant cavity. We get the single frequency laser at 1064 nm with an output power of 7.5 m W and a superior stability.Thirdly, the theoretical module of 1 ?m fiber laser was analyzed deeply. Basing on the energy level structure of ytterbium ion and the output characteristics, the process of laser generation by pumping motivating was discussed. The realization of pulse laser output was investigated, and the mechanism of outside cavity acousto-optic modulation be in this study have been introduced. In addition, we also analyzed the nonlinear factors in the process of narrow line-width fiber laser amplifier, while the nonlinear factors mainly behave as stimulated Brillouin scattering(SBS) and stimulated Raman scattering(SRS). It provided powerful theoretical basis and greater space for advancement the technique on limit nonlinear factors of fiber laser.Fourthly, we introduced the modulation technique of fiber laser and the narrow line-width fiber laser amplifier. Function signal generator and acoustic optical modulator were used to do an outside cavity modulation for the seed resource of single frequency fiber laser. A stable nanosecond pulse laser at 1064 nm, with an output power of 0.27 m W, repetition frequency in 50 k Hz, and the pulse width in 330 ns. Master oscillator power amplifier(MOPA) structure was used for the narrow line-width fiber laser amplifier, and the modulated pulse laser was amplified in four-staged. In order to achieve high power output, we reduce the nonlinear effect by the enlarging the mode field area of gain fiber, decreasing the length of gain fiber, controlling the pressure and temperature of gain fiber during the amplified process. Finally we obtained a narrow line-width laser at 1064 nm, with an output average power of 1.95 W, repetition frequency in 50 k Hz, and the pulse width in 330 ns.