We recently switched to a 405 nm laser diode which has a terrible beam profile -- it is a well-defined rectangle with an aspect ratio of about 10:1. The image below shows the collimated beam which has been expanded slightly for easier viewing. We would like to convert this to a ~ 5 mm Gaussian or tophat beam profile with minimal power losses. What options do we have? A few things we have investigated include
- Using a anamorphic prism pair. Previously we had a 678 nm laser with a nice elliptical profile which we easily corrected using a 2.5:1 prism pair, but this doesn't work very well for a rectangular beam.
- Using an engineered diffuser. We picked up a 1" 20 degree tophat diffuser from Thor, which is constructed from dark optical magics. We are able to get a nice ~12 mm collimated tophat from this, but further expanding or condensing the beam screws it up because, uh, magic.
- Using a normal diffuser (similar to half of the configuration in the photo here or with one of these.) I don't know of any easy way to estimate the losses in this case but may be less than ~60%.
- Running the beam through a pinhole to get a Gaussian profile, but this would mean ~90% lost power.
- Over-expanding and cropping the beam, but this would mean ~80% lost power.
Is there any other way to do this that we missed, or is there any sort of standard approach to emission patterns like this?