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A novel beam homogenisation system based on a micro-lens array and beam expansion structure is proposed to convert a Gaussian-distributed circular beam to a flat-top-distributed square beam of size 2–5 mm and a homogeneity degree exceeding 95%. The novel micro-lens array based on a cylindrical lens element can potentially be widely applied in practice because of the absence of the preparative limitations of size and focal length. By employing this beam homogenisation system, laser shock processing experiments were performed on 7050 titanium alloy. The laser shock processing parameters were optimised. When the laser repetition frequency was 1 Hz, pulse width was 15 ns, and laser energy was 20 J, a residual stress of > 400 MPa was achieved on the titanium alloy. The experimental results demonstrate the ability of this beam-homogenisation system to perform laser shock processing. [ABSTRACT FROM AUTHOR]

A diode-pumped alkali metal vapor laser (DPAL) combines the advantages of a solid laser and a gas laser. DPAL is useful in the industrial, medical, aerospace and military fields and can yield high output power while maintaining excellent beam quality. However, applications in many fields are limited due to the narrow absorption spectrum of the alkali metal vapor laser. In this study, a novel linewidth narrowing structure of the high-power diode laser based on volume Bragg gratings (VBGs) is proposed to match the absorption spectrum of the alkali metal vapor laser. With the combination of fast-axis collimating lens, beam transformation systems, slow-axis collimating lens, VBGs and metal ceramic heaters, the divergence angles of both fast and slow axis are compressed within 10 mrad. A high-power narrow linewidth diode laser source with a central wavelength of 780.044 nm, a spectral width of 0.138 nm, and an output power of 1090 W is achieved at an operating current of 50 A. Experimental results show that the effect of external cavity feedback based on VBG is improved and the multi-channel spectral linewidth is narrowed effectively by such a structure. The diode laser source based on this structure can be applied for pumping the rubidium alkali metal vapor laser. [ABSTRACT FROM AUTHOR]