A beam homogenizer is a device that smooths out the irregularities in a laser beam profile and creates a more uniform one. Most beam homogenizers use a multifaceted mirror with square facets. The mirror reflects light at different angles to create a beam with uniform power across the whole beam profile (a "top hat" profile).
The best results have been achieved with fly eye homogenizers which are composed of individually polished cylindrical lenses. The incoming laser beam is divided by an array of cylindrical lenses f_1 into several beamlets with size d. These beamlets match with the cylindrical lenses of a second array f_2. This second array and a condenser lens f_3 overlap all these beamlets in the focal plane of f_3. The homogenizer size D is proportional to the focal length of the collecting lens, the diameter and focal length of the micro-lens, and can be calculated using Equation:
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