We investigate the group velocity of light in a one-dimensional volume-index grating inside a photorefractive LiNbO><sub>3</sub> crystal. The slowdown of the group electromagnetic propagation is observed experimentally by tuning of the wave number of the optical beam close to the outside edge of the forbidden bandgap. We obtain a large group index of up to 7.5 in a 3.5-cm crystal sample. The group index is compared with the result of a theoretical derivation. The results are presented and discussed.
© 2000 Optical Society of America
(050.7330) Diffraction and gratings : Volume gratings
(160.3730) Materials : Lithium niobate
(190.5530) Nonlinear optics : Pulse propagation and temporal solitons
(260.2030) Physical optics : Dispersion
Shiuan Huei Lin, Ken Y. Hsu, and Pochi Yeh, "Experimental observation of the slowdown of optical beams by a volume-index grating in a photorefractive LiNbO3 crystal," Opt. Lett. 25, 1582-1584 (2000)