Positive lens pair produces uniform Gaussian beam

The Gaussian intensity distribution of a TEM00 laser beam is undesirable for applications that require uniform illumination.

The Gaussian intensity distribution of a TEM00 laser beam is undesirable for applications that require uniform illumination. One possible solution, intensity redistribution by a pair of aspheric lenses, has been known for more than 30 years and consists of one lens with a negative aspheric shape and another with a positive aspheric shape. The first lens redirects light from an incoming Gaussian collimated beam so that it is uniform as it strikes the second lens, which then recollimates the beam. One problem with this setup is the difficulty in fabrication of the negative aspheric lens; another is the unwanted diffraction occurring as a result of apodization.

Researchers at the IBM Almaden Research Center (San Jose, CA) have solved both these problems in a Gaussian-to-flat-top design containing two positive aspheres with an intermediate focus. The monotonic form of the lenses eases fabrication. The design allows for acceptance of 99.7% of the beam, virtually eliminating undesired diffraction. Using magnetorheological finishing, lens pairs were fabricated for both broadband visible and narrowband ultraviolet use. The visible pair produced a flat-top beam with less than 5% root-mean-square nonuniformity from a Gaussian beam emitted by an argon-ion laser. Contact John Hoffnagle at hoffnagl@almaden.ibm.com.

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