Methods for slow axis beam quality improvement of high power broad area diode lasers

Abstract

For high brightness direct diode laser systems, it is of fundamental importance to improve the slow axis beam quality of the incorporated laser diodes regardless what beam combining technology is applied. To further advance our products in terms of increased brightness at a high power level, we must optimize the slow axis beam quality despite the far field blooming at high current levels. The later is caused predominantly by the built-in index step in combination with the thermal lens effect. Most of the methods for beam quality improvements reported in publications sacrifice the device efficiency and reliable output power. In order to improve the beam quality as well as maintain the efficiency and reliable output power, we investigated methods of influencing local heat generation to reduce the thermal gradient across the slow axis direction, optimizing the built-in index step and discriminating high order modes. Based on our findings, we have combined different methods in our new device design. Subsequently, the beam parameter product (BPP) of a 10% fill factor bar has improved by approximately 30% at 7 W/emitter without efficiency penalty. This technology has enabled fiber coupled high brightness multi-kilowatt direct diode laser systems. In this paper, we will elaborate on the methods used as well as the results achieved.

Beam control of high-power broad-area photonic crystal lasers using ladderlike groove structure

“…19,20) In addition, the fabricated grooves (Regions III and V) will also increase the losses of high-order lateral modes and reduce the number of lasing modes. 14) As expected, a narrower range of NF intensity of the LLGS laser can be obtained, as shown in the inset of Fig. 2.…”

“…However, there is still much room for the improvement of both the lateral beam quality and the output power of PBC BA lasers. It had been demonstrated that the control of the lateral index difference 14) and the suppression of carrier accumulation at the device edges 15) play an important role in the improvement of lateral beam quality. In this work, a ladderlike groove structure (LLGS) was introduced to BA PBC lasers to improve both the beam quality and the output power by reducing current diffusion and modifying the lateral index difference.…”