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We report here the generation of a three dimensional dark focus from a singlefocused monochromatic Gaussian beam that undergoes conical refraction when itpropagates along one of the optic axes of a biaxial crystal. We study theresulting ring intensity pattern behind the crystal as a function of the ratiobetween the ring radius and the beam waist and derive the particular parametervalues for which a three dimensional dark focus with null intensity at the ringcenter is formed. We have performed experiments with a ${\rm KGd(WO_4)_2}$biaxial crystal reporting the generation of a bottle beam in full agreementwith our theoretical investigations.

Generating a three dimensional dark focus from a single conically refracted light beam