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We consider the transformation of a Gaussian laser beam into a flat-top intensity profile or into an optical bottle beam (OBB) by resorting to a diffractive or an interferometric method. The diffractive technique is based on the use of a diffractive optical element consisting in a π-plate, while the interferometric technique uses a Michelson interferometer (MI). The coaxial superposition of two coherent Gaussian beams yields to a flat-top or a OBB in the focal plane of a lens depending on the geometric characteristics of the MI. The performances of the two techniques are compared.

We have demonstrated that a simple diaphragm can play the role of a very cheap reconfigurable diffractive optical element allowing the generation of interesting laser beam patterns. For instance, a truncated Laguerre-Gauss LG 10 beam (one peak surrounded by one ring) can be transformed in the focal plane of a lens into an optical bottle beam (OBB) which consists to a dark (or minimal intensity) region surrounded by higher intensity light in the three principal directions. Depending on the beam truncation, one can also observe a flat-top intensity profile.

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