Low speckle line generation using a semiconductor laser source

In this contribution we show that we can design a low speckle line generator based on the reduced spatial coherence of a broad-area vertical-cavity surface-emitting laser (BA-VCSEL). This type of semiconductor laser can be driven into a special operation regime, a regime of low spatial coherence, which has already been shown to have a speckle reducing effect for image projection applications. However, the effectiveness of reducing speckle strongly depends on the line generating optics. Therefore we compare different line generating optical systems on their potential to use spatially incoherent laser emission for speckle reduction. These systems are: a single cylindrical lens, a tandem cylindrical lens array or a diffuser based line generator. We also compare these results with the speckle occurring if we replace the partial spatially coherent VCSEL with a single mode laser or with a multi-mode VCSEL. We finally draw conclusions on the design of the most optimal optical system. The results of our study are also valid for other sources of partial spatially coherent emission.