Improving directivity of laser beams by employing the effect of conical refraction in biaxial crystals

The far-field pattern of Gaussian beams transformed by conical refraction in biaxial crystal is analyzed. It is shown that one of the two outgoing beam components acquires, under certain conditions, a profile with a dominating central peak. The width of this peak can be made significantly smaller than the width of the parent diffraction-limited Gaussian beam at the same propagation distance. The formation of such structurally-stable sub-diffraction beam core improves the beam directivity. Another component is a charge-one optical vortex, that forms the annular shell of the beam and carries the rest of the beam power. (C) 2010 Optical Society of America