High-power Diode Laser Array Beam Shaping

As the high-power diode lasers have many strong points, such as small size, light weight, long work-life, low cost and high coupling efficiency, etc, they are widely used in materials processing, biomedicine, military defense, and as a solid-state laser pump sources. But the beam which is emitted by the diode laser has great asymmetries between the fast axial and the slow axial:first, the positions of the beam waists are different; Secondly, the beam sizes have big disparity; Finally, the beam divergence angles of the two directions have great difference. These asymmetries severely limit the applications of semiconductor lasers, in order to apply them better, we have to shape the beam.The shaping methods designed in this article toke a specific diode laser bar and a specific stack diode laser as examples:first, we use orthogonal cylindrical lens to collimate the beam, and at the same time to eliminate astigmatism; then according to the theory that when the beam pass through a parallel glass, the beam will have a offset, we use the parallel glass to shape the beam. Finally, we get a rectangular beam with a balance beam quality.The main contents of the paper include the following aspects:First, we analyzed the background and significance of the beam shaping, describes the existing shaping methods at home and abroad, and summed up the advantages and disadvantages of various methods. Through analysis, we proposed to use parallel glass to shape the beam.Secondly, we introduced many theories which could be used in diode laser beam shaping, including the nature of the Gaussian beam, the spatial pattern of the semiconductor laser, ABCD law, and methods to evaluate beam quality. After comparison, we preferred to use beam parameter product as the standard in this article.The focus of the paper is to collimate and shape the beam of diode laser bar, we use HTOE's LDAC1-0808-040W diode laser bar as the prototype. Collimating devices are consisted of orthogonal cylindrical lens arrays, through parameter calculation and ZEMAX optimization, we get the collimating lens parameters. Passed the collimating system, beam divergence angle changed from 68°(1/e2) to 1.459mrad in the fast axis, and from 17°(1/e2) to 8.194mrad in the slow axis, which can be seem as a parallel beam. According to parallel glass can shift beam, we designed the shaping system, which were composed of beam-split devices and beam-rearrangement devices. Simulated by the ZEMAX software, passed the shaping system, the beam parameter products of fast axis and slow axis were very closed, the beam quality had been balanced.Finally, we use HTOE's LDAC2-0808-320W diode laser as the stack diode laser prototype. Through extending and improving the shaping system of diode laser bar, we got the shaping system of stack diode laser.