Diffraction-limited dark laser spot produced by a hollow optical fiber

By using the diffracted field of the ${\mathrm{LP}}_{11}$ mode of a hollow-core optical fiber, we have produced a micrometer-sized, focused dark laser spot in the near field of the fiber. The minimum half-width of the dark spot is less than $1 \mu \mathrm{m}$. In particular, by masking the hollow core and metal coating the cladding with a microsphere, we blocked the light propagating in the cladding and obtained a clean dark spot, which may be useful in atom-optical experiments such as with atomic lenses, atom traps, and atom switches.