A waveguide segment with two sub-segments including a first sub-segment with a first wall and a second wall, each having an inner face by which laser light can be reflected. The inner faces are opposite to each other and a depth of the sub-segment is defined by a distance between the first and the second inner face. Further, each wall has an exit side, and an opposite entry side, a height defined by the distance between the exit and the entry side and a width. At least part of the entry side of each wall extends in an angle to the height, for which applies: 0°