Patent ID: 7518764

Claim:
A scanning apparatus comprising: a light source for generating a light beam; and an angular prism coupled to a sample at a base interface; characterised in that the base angle θ p of the prism satisfies the equations: ( cos 2 ⁢ θ c - sin 2 ⁢ θ p ) ⁢ ( tan ⁢ ⁢ θ i ⁢ sin ⁢ ⁢ θ p + cos ⁢ ⁢ θ p ) = 1 cos ⁢ ⁢ θ c ⁢ cos ⁡ ( θ p ± θ c ) and n i sin θ i =n p sin(θ p −θ c ) wherein θ c is the coupling angle required for light incident at base interface of the prism, θ i is the incident angle of the light beam on the prism, n i is the refractive index of the medium at the interface where the light beam enters the prism and n p is the refractive index of the prism.