Refraction close refractionProcess by which a wave changes speed and sometimes direction upon entering a denser or less dense medium, eg a light ray changes direction when refracted by a lens.

A ray diagram showing refraction at the boundary between air and glass Refraction can cause optical illusions as the light waves appear ... causes the wave to change direction.

Researchers at the University of California, Los Angeles (UCLA) have unveiled a new optical technology that enables precise focusing of light ... the THz radiation in the forward direction ...