High Power Fiber Lasers Based On Homemade Components

Fiber lasers have found of high conversion efficiency, excel beam quality, simplicity in thermal management, and compact configuration. Their great potentialities in high-energy laser systems draw many an interest from militarists and researchers. The application of large-mode-area double-clad (LMA) rare-earth ion-doped fibers is speeding up the power scaling of high-energy fiber lasers. However, it is not so easy to obtain high beam quality laser output with an increasing size of fiber core diameter. Many researchers have put great effort on the optimization and design of LMA single mode fibers. However, no attentions of researchers are paid to the probability of realizing high power high beam quality laser output with small-core-diameter fibers all the meanwhile. This dissertation performs a theoretical and experimental study focusing on implementation of high power laser output with small core diameter fiber. Furthermore, the necessity, feasibility, and realization of lasers with small core fiber are analyzed.The dissertation reviews a series of achievements on domestic and overseas high power fiber lasers in the near decade. Then the current development state domestic high power fiber lasers and its internal driving causes of are summarized. Later we give out the analytic results of probability and feasibility of the localization of high power fiber laser. After synthesizing several classical proposals of high power fiber lasers, it is recommended that high power fiber laser system built with master oscillator power amplifier (MOPA) structure is of great feasibility at present.An experimental platform for MOPA structural high power polarization maintained fiber laser is established. In the experiment, a 5/130μm ytterbium doped double clad fiber is employed, and a 67-watt continuous wave high power polarization-maintained fiber laser with optical-to-optical conversion efficiency of 76% is obtained. Laser power density in core of the ytterbium-doped fiber is calculated to be 3.4 W/μm2. It is reasonably deduced that fiber lasers with 30-μm core diameter ytterbium doped double clad fiber can support laser output of even 2.4 kW power. Furthermore, a 126-watt continuous wave high power fiber laser output is achieved with double clad fiber of 11-μm diameter. What should be noted is that both high power fiber lasers are of strict single transverse mode. Due to their natural superiority in beam quality control and availability of high power lasing, small core diameter fibers are extremely promising in high beam quality high power fiber laser systems.The basic principle and technical proposals of single-frequency fiber laser are generalized, and the MOPA proposal for high power single-frequency fiber laser is figured out. Some single-frequency seed laser proposals are brought up, such as short cavity, longitudinal mode selection with Fabry-Perot etalon, and saturable absorber et al., and then their merits and demerits are discussed as well. Eventually the short cavity method is optimally selected as a suitable seed laser. The physical mechanism of stimulated Brillouin scattering and its impact on single-frequency amplifier are investigated, by numerically simulating the SBS suppression process of gain competition between two wide interval wavelength lasers on the ground of rate equations. The result shows that appropriately injected non-monochromatic signal laser helps to reduce increasing the SBS power threshold, which can suppress the SBS to a certain extent.The high power single-frequency fiber laser platform is established. For the sake of protecting previous system from damage by SBS yielded in single-frequency signal amplification, we furnish the system with aid device to monitor and control the backward light. When an 11/130μm double clad ytterbium doped fiber is used, 29.2 W single-frequency fiber laser of 20 kHz linewidth is achieved, with an optical to optical conversion efficiency of 78% and ASE suppression ratio of about 40 dB. Furthermore, a 30-μm core diameter large-mode-area fiber is used and an all-fiber single-frequency fiber laser of 122-W power is obtained.It is generally reported the efficiency of amplifier with WDM and single-clad Yb3+-doped fiber is around 40%. A single frequency fiber laser with a 1012 nm laser as the tandem pump source is preliminarily studied. At the low level, power amplification with slop efficiency of 63% is carried out. Because the quantum defect of tandem pump is less than that direct pump with 976 nm laser diode, and the fiber laser at like- 1012 nm wavelength is far brighter than LD, as a novel high bright pump source, tandem pump fiber laser is much potential in high power fiber laser field.On the base of tandem pump, a novel MOPA amplifier with super high magnification factor is constructed at low power level, and the limit of amplification is studied meanwhile. Seeded with 1012 nm auxiliary laser, 300-microwatt 1064 nm single-frequency fiber laser is amplified to 65 mW by a 216 times amplification factor. Due to the accompany amplification effect and tandem pump effect of 1012 nm fiber laser, the easily-arising ASE in weak signal light amplifier is effectively suppressed.