Patent ID: 8917398

Claim:
An apparatus arranged to analyze a multi-layer optical material structure, the apparatus comprising: a control unit, a light source arranged to irradiate a target structure; and a light receiver in communication with said control unit and arranged to receive said irradiated light from said light source after interaction with the target structure, said control unit comprising a processor and a memory, said memory storing machine readable instructions which cause said processor to: receive a planned composition of the target multi-layer structure; detect, in cooperation with said light receiver, an amplitude of the received light as a function of wavelength; perform a transform of a function of said detected amplitudes to an optical thickness domain; determine, responsive to the received planned composition of the target multi-layer structure, at least one of optical thickness and amplitude of expected peaks of said performed transform to the optical thickness domain which correspond with interactions with single interface between layers; identify spurious peaks which do not correspond with interfaces between layers; identify, responsive to said expected peaks, actual peaks of said performed transform to the optical thickness domain which correspond with interfaces between layers; and determine at least one physical characteristic of the target structure responsive to said identified actual peaks while not utilizing said identified spurious peaks in said determining, wherein said function of said detected amplitudes is performed as B ( N ) = B 0 ⁡ ( 1 + ∑ k = 1 N ⁢ ⁢ ∑ p = 1 N - k + 1 ⁢ ⁢ B p k ⁢ cos ⁢ ⁢ 4 ⁢ ⁢ π ⁢ ∑ m = p p + k - 1 ⁢ n m ⁢ d m ⁢ ⁢ w ) , where B p k = 4 ⁢ ⁢ r p - 1 , p · r p + k - 1 , p + k ∏ q = p p + k ⁢ ⁢ ( 1 + r q - 1 , q 2 ) , ⁢ B 0 = ∏ q = 1 N + 1 ⁢ 1 + r q - 1 , q 2 ⁢ 1 - r q - 1 , q 2 , r q - 1 , q = n q - 1 - n q n q - 1 + n q and where, utilizing the received planned composition of the target multi-layer structure, n m is the refractive index of layer m, n q is the refractive index of layer q, d m is the thickness of layer m, w represents the wave number, the k-superscript indicates groups of k adjacent layers of the received planned composition, and the p subscript indicates the starting layer for each group.