Sharp focusing of light using a planar gradient microlens

It is shown numerically that using planar gradient microlenses, the coherent radiation can be focused in a narrow line of width $\lambda/38$ and length $\lambda/5.5$. The efficiency of focusing is $22\%$. A slitted photonic-crystal lens retains the properties of sharp focusing of light characteristic of a gradient lens. Substitution of the gradient lens by a photonic-crystal analogue synthesized in a silicon was found not to degrade the characteristics of the lens substantially. In this case, we observed a reduction of side lobes near the focal spot and a $30.2\%$ increase of the focusing efficiency.