Broad Area Semiconductor (BAS) lasers usually show poor beam quality, especially in a high power regime. The emitting region of this lasers has typical dimensions of 1 μm in the vertical direction (fast axis) and hundreds of μm in the horizontal direction (slow axis). Along the fast axis, the beam is tightly confined to single mode emission and can be collimated using a cylindrical micro-lens. The collimation problem arises in the slow axis, where the aperture size can range between 50-400 μm (Fig 1.a) and the light distribution over many spatial modes makes it difficult to collimate. The beam quality of these lasers is worse in terms of focusability and increased M2.
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