What happens to the emergent ray in a glass slab with parallel refracting surfaces, and how is it related to the incident ray?

In a glass slab with parallel refracting surfaces, when light enters the slab at an angle, it undergoes refraction at both surfaces. The emergent ray is parallel to the incident ray, maintaining the same angle of deviation. However, the emergent ray shifts laterally, or undergoes a lateral displacement, relative to the incident ray. This displacement is due to the parallel surfaces causing the light to change direction twice. The lateral shift is proportional to the thickness of the slab and the angle of incidence. This phenomenon is known as lateral displacement or lateral shift in the context of ray optics.