@article{oai:kumadai.repo.nii.ac.jp:00027756,
 author = {黒田, 規敬 and 津川, 晃一 and 横井, 裕之 and Kuroda, Noritaka and Tsugawa, Koichi and Yokoi, Hiroyuki},
 issue = {11},
 journal = {Journal of the Physical Society of Japan},
 month = {Nov},
 note = {application/pdf, 論文(Article), The properties of refraction of extraordinary rays at principal surfaces of a uniaxial crystal having a strongly anisotropic dielectric dispersion are studied. Subject to optical nonabsorptivity of the crystal, the criteria for characterizing the refraction behavior are derived from Maxwell's equations. The criteria reveal that in sapphire a variety of specific oblique-incidence reflection spectra arise from negative refraction and counterposition in the infrared region of multimode polar optical phonons. The effects of light dissipation due to damping of the phonons are explored further to interpret the oblique-incidence reflection spectrum measured for the c-surface of a synthetic crystal of sapphire. We pay attention to the directions of wave-normal and Poynting vectors of the infrared light transmitted into the crystal. It turns out that the damping of phonons gives rise to a true negative refraction that the two vectors are simultaneously refracted or deflected negatively in a certain frequency range., http://jpsj.ipap.jp/link?JPSJ/81/114706/},
 title = {Negative Refraction of Infrared Waves and Rays in Sapphire α-Al2O3},
 volume = {81},
 year = {2012}
}