Method and apparatus for measuring the absolute thickness of dust defocus layers
First Claim
1. Apparatus for measuring the distance between upper and lower surfaces of a transparent coating upon a planar surface, comprising:
- means for producing a beam of light;
means, optically coupled to said light-producing means, for collimating said beam, wherein said collimating means is a cylindrical telescope;
lens means coupled to receive said collimated beam for focusing said collimated beam, at a point proximate to the coating, thereby forming a converging beam which is directed towards the coating at a predetermined angle of incidence defined by an angular spread centered about said angle of incidence, wherein said converging beam is reflected from the upper and lower surfaces, thereby forming a pair of diverging beams with an interference pattern having a fringe density which is proportional to the distance between the upper and lower surfaces; and
solid-state image sensing means coupled to receive said interference pattern for counting the number of fringes between said angular spread.
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Abstract
A method and apparatus for measuring the absolute thickness of dust defocus layers upon spinning optical disks utilizes a collimated, expanded beam of light from a helium-neon laser which is focused into a converging beam and directed towards the layer at a predetermined angle of incidence defined by an angular spread centered about the angle of incidence. A pair of divergent beams reflecting from the upper and lower surfaces of the layer are received by a collecting mirror and are recollimated by a collimating lens to be incident upon a self-scanning photodiode array. The divergent beams form a monotonic interference pattern having a fringe density which is proportional to the distance between the upper and lower surfaces, and which is determined by the photodiode array.
55 Citations
7 Claims
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1. Apparatus for measuring the distance between upper and lower surfaces of a transparent coating upon a planar surface, comprising:
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means for producing a beam of light; means, optically coupled to said light-producing means, for collimating said beam, wherein said collimating means is a cylindrical telescope; lens means coupled to receive said collimated beam for focusing said collimated beam, at a point proximate to the coating, thereby forming a converging beam which is directed towards the coating at a predetermined angle of incidence defined by an angular spread centered about said angle of incidence, wherein said converging beam is reflected from the upper and lower surfaces, thereby forming a pair of diverging beams with an interference pattern having a fringe density which is proportional to the distance between the upper and lower surfaces; and solid-state image sensing means coupled to receive said interference pattern for counting the number of fringes between said angular spread.
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2. A method for determining the distance between upper and lower surfaces of a transparent coating upon a planar surface, comprising the steps of:
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producing a beam of light; collimating said beam; focusing said collimated beam to produce a converging beam having a predetermined angular spread; reflecting said converging beam from the upper and lower surfaces to produce a pair of diverging beams having an interference pattern formed therebetween, wherein said interference pattern consists of a plurality of alternating nulls and peaks forming a plurality of fringe cycles; counting the number of fringe cycles within said predetermined angular spread, wherein said counting step consists of the steps of; setting a threshold value indicative of a midpoint between each respective null-peak pair; pulsing said sensing means at a predetermined clock rate corresponding to a preselected number of sensing elements within said sensing means; counting said clock pulses and a number indicative of the total times said threshold value is exceeded; multiplying said number, minus one, by the number of said sensing elements; and dividing the result from said multiplying step by said count of clock pulses encompassing the (n-1) fringes to yield a fringe count that is proportional to the distance between the upper and lower surfaces of the transparent coating.
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3. Apparatus for measuring the absolute thickness of a dust defocus layer upon a spinning optical disk, comprising;
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a source of light; means, coupled to said source, for collimating a beam of light received therefrom, wherein said collimating means is a cylindrical telescope; lens means coupled to receive said collimated beam for focusing said collimated beam to produce a converging beam which is directed towards the layer at a predetermined angle of incidence defined by an angular spread centered about said angle of incidence; collection means for receiving a first and second diverging beam reflected respectively from an upper and lower surface of the layer, wherein said first and second diverging beams form an interference pattern having a fringe density which is proportional to the absolute thickness; and a self-scanning linear diode array receiving said interference pattern, said array adapted to count the fringes therein and determine said fringe density.
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4. A method for measuring the absolute thickness of a dust defocus layer with upper and lower surfaces situated upon a spinning optical disk, comprising the steps of:
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producing a beam of light; collimating said beam; shaped said collimated beam to produce a converging beam having a predetermined angular spread; reflecting said converging beam from the upper and lower surfaces to produce a pair of diverging beams having an interference pattern formed therebetween, said interference pattern having a plurality of fringes with a fringe density that is proportional to the absolute thickness; receiving said pair of diverging beams with said interference pattern formed therebetween with collection means; disposing a self-scanning linear diode array relative to said collection means so as to project said interference pattern upon said self-scanning linear diode array; and counting said plurality of fringes in said interference pattern with said self-scanning linear diode array, thereby determining said fringe density and the absolute thickness. - View Dependent Claims (5, 6, 7)
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Specification