Fig. 2
From: Sequential and non-sequential simulation of volume holographic gratings
Example for transmission and reflection HOE a HOE that works in transmission. b HOE that works in reflection. kR, kO and kG denote the wave vector of the reference and object beam and the grating vector, respectively. d is the thickness of the HOE. The light hits the HOE from the left hand side (red, dashed), interacting with the VHG. Thereby, some part of the reference wave is diffracted into the first order, which is called the object wave (green, solid). The non-diffracted part propagates in the same direction as kR (blue, dotted)