Improve Beam Quality of High-power Laser Diode Array Stacks by External-cavity Technique

Because of its own structure's limitation, the beam divergence angle of the semiconductor laser is very large. In the fast-axis direction, the beam plays good quality and can be collimated less than 1 by using cylindrical micro-lens. However, in the slow-axis direction, the beam quality is too poor to be collimated to a small pattern. This could limit its application in the fields which need high beam quality. For high-power laser diode array (LDA), external-cavity technique can make all the emitters working in the same wavelength, and can improve their beam quality. In this paper, direct feedback method was employed to achieve cross-injection between 25 emitters of a LD bar by using a stripe mirror. At a certain cavity length, after the reflection of the external-cavity mirror's reflective stripe, the beam with large slow-axis divergence angle will feedback to the spacer region between the emitters and lose its energy, or would exactly feedback to the neighbor emitter. Simultaneously, the beam with small divergence angle would output from the transparent stripe of the external-cavity mirror. The slow-axis divergence of the stacks with two bars was suppressed from 6 degrees to 2 degrees by using this technique.