ANOMALOUS INDEX OF REFRACTION IN PHOTONIC BANDGAP MATERIALS

Near the gap in a photonic bandgap material the effective index of ;re fraction can become less than unity and in fact can approach zero at t he band edge itself-leading to ultra-refractive optical effects. We il lustrate this effect quantitatively in a simple one-dimensional Kronig -Penney model of a three-dimensional bandgap structure. As a complemen t to index-enhancing schemes involving lasing without inversion, ultra -refractive optics with photonic band materials has many applications, including laser accelerators and lenses of ultra-short focal lengths.