Affiliation:
1. Research School of Physics Australian National University Canberra 2601 Australia
2. Department of Physics University of Otago Dunedin 9016 New Zealand
3. Laboratory for Quantum Magnetism Institute of Physics École Polytechnique Fédérale de Lausanne CH‐1015 Lausanne Switzerland
4. School of Electrical Engineering and Telecommunications UNSW Sydney Sydney 2052 Australia
Abstract
AbstractDouble‐negative refractive index materials have attracted sustained experimental and theoretical interest because they can display a range of surprising optical phenomena, including negative Doppler shifts and perfect lensing. Double‐negative indexes have been achieved experimentally in engineered metamaterials; however, these materials become increasingly challenging to fabricate at shorter wavelengths, and at optical wavelengths only 2D negative index materials have been achieved. Here, it is shown that a double‐negative index can occur in a natural material, near narrow optical transitions of dielectric crystals stoichiometric in a rare‐earth ion. Optical measurements of two candidate materials, the magnetically‐ordered erbium crystals, ErCl3 ·6H2O and 7LiErF4, which have ultra‐narrow optical linewidths of 3 GHz and 250 MHz, respectively, in the telecom band are presented. It is shown that the spectral density of 7LiErF4 is sufficient to achieve a negative index at 1530 nm. This material can enable the exploration of negative refractive index effects at optical wavelengths in a truly 3D, natural medium.
Funder
Australian Research Council
Subject
Atomic and Molecular Physics, and Optics,Electronic, Optical and Magnetic Materials