| The background of this paper is to promote the directly application of high power diode laser (HPDL) in laser manufacturing, and its investigated subjects are improve the the beam quality of the HPDLs. Against the problems result in bad beam quality of high power diode laser array, we use three methods to solving it. They are fiber coupled external cavity; volume holographic gratings coupled external cavity; and polarization coupling method. Theoretical and experimental analyse has adopted to this three methods, and their feasibility is discussed.High power diode laser array is consists of emitters that electrically and optically separated, the radiation beam of this emitters is incoherent, so the beam quality of whale array is poor. External cavity phase-locking of the HPDL is an interesting technique; it formed an external resonator to locking the phase of each emitter, in order to obtain the coherent beams of nearly diffraction-limited. External cavity phase-locking offers the greatest potential for high spatial and spectral brightness of all beam combining techniques. Currently,phase-locking of an HPDL has been achieved by using a simple external cavity, it consist of high reflectivity mirror or grating or phase conjugate mirror as the feedback mirror. In this method, emitters are coupled only with its two nearest neighbors. This is so called series coupling, a weak coupling among whale array.In the paper,reshaping laser beams through fiber arrays is applied to enlarge the locking scale in the diode laser array. This method establish strong coupling in the laser array, emitters are rearranged from one dimension to two dimensions. Optical fiber has the characteristic of flexibleness and low dissipation in transmission, we named the fiber array as fiber beam reshaper. Using this method, the spectrum width is narrowed from 2.6nm to 0.23nm. The matrix of coupling coefficient is obtained, and the supermode of the fiber external cavity is analysis.For reducing the self-coupling coefficient from the external cavity, we use the plan-concave cylinder mirror as the external cavity and locate the semi-confocal cavity with the theory analysis and experimental studies. The spectral width of diode laser narrowed from 2.5nm to 0.5nm. Improve the coherent characteristic greatly. Besides, for stabilize the wavelength of diode laser array, first use the volume holographic gratings to improve the spectral properties in our country, and experimental study have been carried out, spectral width was narrowed to 0.22nm, wavelength shift with the temperature is reduced to 0.01 nm/℃. At last, we combine the VHG and the plan-concave mirror to make up of an external complexes cavity, gained the dualwavelength emitting, central wavelength is 1.8nm all the time, and the spectrum width narrowed to 0.2nm. We also developed a directly application high power diode laser by two diode laser stack with polarization coupling method, the highest output power is 1kW. Output laser beam of high power quantum well structure diode laser is linearly polarized, and Gran-Tayor prism can distinguish two laser beams in vertical polarizing direction by its characteristic of birefringent. If the input beams have vertical polarizing direction oppositely of the Gran-Tayor prism, they will be coupled in one beam. Measuring with the UFF100 laser beam diagnostics meter, the focal spot is rectangular, the area is 0.55×5.0mm2, and BPP is Kf=26.1mm·mrad. At the operation current 130A, the efficiency of electrical-optical alternation is 43%. All of the laser system works stably.It is important to improve the beam quality of high power diode laser. High beam quality is the key of high focusing power density, which is needed in the aera such as deep penetration welding. In this paper, we improve the light intensity and brightness, so that the power density is increased. The narrowed spectrum got in this paper is also usable in the area such as diode pumped solid stste laser. And, the theory about parallel coupling taken in this paper is usful for the external cavity of array or stacks aftertime.
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