Patent ID: 8300313

Claim:
A method of making an optical bandpass filter for transmitting a band of ultraviolet light within the range of 230 nanometers to 320 nanometers and with extended out-of-band blocking comprising the steps of: providing a substrate having front-side and backside surfaces; forming a transmission filter on at least one of said surfaces, said transmission filter consisting of alternating layers of at least two hard coating materials of a higher refractive index and a lower refractive index respectively; wherein each individual layer of the alternating layers is deposited by a data processor controlled process comprising the steps of: calculating with the data processor, a theoretical transmission (T i ) of ultraviolet light through the individual layer, calculating with the data processor an expected deposition time (t i ) of the individual layer, measuring, during the deposition of the individual layer for a period of time less than (t i ), a measured transmission (T m ) of light through the layer, determining with the data processor when deposition of the individual layer is to terminate based upon the theoretical transmission (T i ) and the measured transmission (T m ); and wherein the calculation of (t i ) and (T i ) accounts for absorption of ultraviolet light by the layer by defining the transmission of UV light within the individual layer as T = 4 ⁢ n a ⁢ n s H where T is a level of a monitoring signal within the individual layer, where n a and n s are the refractive indices of the individual layer and substrate, respectively, where H is defined as H = [ β 1 ′ + β 2 ′ ⁢ cos ⁡ ( 2 ⁢ ⁢ θ m + 1 ) + β 3 ′ ⁢ sin ⁡ ( 2 ⁢ ⁢ θ m + 1 ) ] / [ 1 + D ⁢ ⁢ θ m + 1 ) with β 1 ′ = [ β 1 ⁢ δ + ( 1 - α ) 2 ⁢ R bR T b ] / ( 1 - α ) β 1 = n a 2 + n m + 1 2 2 ⁢ (  p  2 +  q  2 n m + 1 2 ) + 2 ⁢ n a ⁢ Re ( pq * ) β 2 ′ = β 2 ⁢ δ 1 - α β 2 = n a 2 - n m + 1 2 2 ⁢ (  p  2 +  q  2 n m + 1 2 ) β 3 ′ = β 3 ⁢ δ 1 - α β ⁢ ⁢ 3 = ( n a 2 n m + 1 - n m + 1 ) ⁢ Im ⁡ ( p * q ) δ = γ + ( 2 ⁢ α - α 2 ) ⁢ ( 1 - A fR ) ⁢ R bR T b γ = 1 + A fR ⁢ R bR + A bR T b where Re(pq*) is a real part of a product of a complex number p and a complex conjugate of a complex number q, defined as [ p q ] = ∏ l = 1 m ⁢ ⁢ [ cos ⁢ ⁢ θ l ( - i ⁢ ⁢ sin ⁢ ⁢ θ l n l ) - in l ⁢ sin ⁢ ⁢ θ l cos ⁢ ⁢ θ l ] ⁡ [ 1 n s ] where θ l is an accumulated phrase in an I th deposited layer, where D is an in-situ fitted parameter which models a decrease in transmission due to extinction in the UV spectrum for any previously-deposited layers on the front-side and backside surfaces and in the substrate, where T b is the transmittance through any previously deposited back-side layers, where R bR is the substrate to backside surface reflectance, where A fR is the absorption of any previously-deposited layers on the front-side surface of the substrate, where α is the substrate single-pass absorption value, and where A bR is the absorption of any previously-deposited layers on the backside surface of the substrate.