Extended area diffractive subtractive color filters

Claim 1

A method for forming a subtractive color filter suitable for selective attenuation of predetermined wavelengths comprising (a) directing a pair of mutually coherent beams of radiation having a substantially constant intensity over a given area onto a surface of a photographic medium to form a latent image of a standing wave interference fringe field pattern in which the peak image intensity is substantially constant across an area greater than a square of 50 cm 2 , (b) processing said medium to form a permanent image of said field pattern as regions of uniformly varying optical density, (c) applying a transparent barrier layer to the exposed surface of said medium, (d) applying a positive photoresist material onto the exposed surface of the barrier layer to form thereon a photoresist layer having a substantially uniform thickness in the range of 0.50-2.00 μm±0.05 μm, (e) directing radiation through the processed medium to form in the photoresist layer a latent image of the optical density image in said medium, under controlled time and exposure conditions such that the total exposure in the photoresist layer results in an aspect ratio in exposed regions in the photoresist layer corresponding to adjacent regions of said optical density image ranging between 0.25 and 0.75, (f) processing said photoresist layer to remove substantially all of the exposed portions corresponding to the transmissive portions of said optical density image, forming therein a surface relief pattern, having a succession of peaks and valleys, the distance therebetween being substantially equal to the thickness of the layer, and (g) replicating said pattern into the surface of a polymeric web to form on a surface thereof an optically detectable, width controlled periodic surface relief pattern corresponding to said interference fringe field pattern and extending uniformly and free of discontinuities over a square area greater than 50 cm 2 .

Claim 2

A method for forming a subtractive color filter suitable for selective attenuation of predetermined wavelengths comprising (a) directing a pair of mutually coherent beams of radiation having a substantially constant intensity over a given area onto a surface of a photographic medium to form a latent image of a standing wave interference fringe field pattern in which the peak image intensity is substantially constant across an area greater than a square of 50 cm 2 , (b) processing said medium to form a permanent image of said field pattern as regions of uniformly varying optical density, (c) applying a transparent barrier layer to the exposed surface of said medium, (d) applying a positive photoresist material onto the exposed surface of the barrier layer to form thereon a photoresist layer having a substantially uniform thickness in the range of 0.50-2.00 μm±0.05 μm, (e) directing radiation through the processed medium to form in the photoresist layer a latent image of the optical density image in said medium, under controlled time and exposure conditions such that the total exposure in the photoresist layer results in an aspect ratio in exposed regions in the photoresist layer corresponding to adjacent regions of said optical density image ranging between 0.25 and 0.75, (f) processing said photoresist layer to remove substantially all of the exposed portions corresponding to the transmissive portions of said optical density image, forming therein a surface relief pattern, having a succession of peaks and valleys, the distance therebetween being substantially equal to the thickness of the layer, and (g) replicating said pattern into the surface of a polymeric web to form on a surface thereof an optically detectable, width controlled periodic surface relief pattern corresponding to said interference fringe field pattern and extending uniformly and free of discontinuities over a square area greater than 50 cm 2 .