Apparatus and method for automatic cross correlation interferometry

Claim 2

Interferometric apparatus for determining a physical parameter of a product comprising a source of broadband radiation emitting within a predetermined spectrum, a broadband radiation detector responsive to propagated radiation emitted by said source and forming a signal proportional to the radiation detected, a multiple reflection interferometer interposed with the product in the path of the propagated radiation detected by said detector and modifying such radiation, said interferometer having two relatively opposed optical surfaces, one of which surfaces being partially transmissive and the other being at least partially reflective of the radiation and including means coupled therewith for varying the physical spacing between said surfaces, and electrical circuit means interconnected with said radiation detector and said interferometer responsive to the detector signal for varying the spacing of said optical surfaces by a periodic signal superimposed on a variable steady state signal to provide an output proportional to the cross correlation between interferometric properties of the product and said interferometer and indicative of the product parameter.

Claim 3

Interferometric apparatus according to claim 1 wherein said interferometer is disposed in the path of radiation transmitted through the product.

Claim 4

Interferometer apparatus according to claim 1 wherein said interferometer is disposed in the path of radiation reflected from the product.

Claim 5

Interferometer apparatus according to claim 1 in which said interferometer is of the Fabry-Perot type.

Claim 6

Interferometer apparatus according to claim 1 in which said interferometer is of the Fizeau type.

Claim 7

Interferometric apparatus according to claim 1 wherein said electrical circuit means varies the steady state spacing of said interferometer optical surfaces to optically coincide with the effect of the physical parameter of the product and equivalent to said steady state signal, said periodic signal effecting a variation of the optical surface spacing to a predetermined maximum relative to the steady state spacing.

Claim 8

Interferometric apparatus according to claim 1 which includes process control means responsive to the steady state signal and operable to modify the process producing the product in accordance with deviation of the steady state signal from a predetermined value to thereby control said physical parameter.

Claim 9

Interferometric apparatus according to claim 7 which includes reference means selectively interconnected therewith and which provides a standard reference input, said apparatus responsive to said input to maintain said predetermined value steady state signal.

Claim 10

An interferometric method for determining a physical parameter of a product consisting of directing broad spectral band radiation at least partially transmitted by the product into incident relationship to the product producing reflected radiation spectrally modified in accordance with principles of interference, further spectrally modifying the radiation incident to the product by a multiple reflection interferometer having two relatively opposed optical surfaces, one of which surfaces being partially transmissive and the other being at least partially reflective of the radiation with the steady state physical spacing between said surfaces selectively controlled and periodically varied relative to the steady state spacing, detecting the radiation thus modified by the product and the interferometer and forming a signal related to the radiation thus detected, and applying tHe signal thus formed to vary the steady state spacing of said interferometer optical surfaces to obtain a spacing therof optically equivalent to the physical parameter of the product thereby maximizing the signal thus formed and which is proportionally related to the product''s physical parameter.

Claim 11

An interferometric method for determining a physical parameter of a product consisting of directing broad spectral band radiation at least partially transmitted by the product into incident relationship to the product producing reflected radiation spectrally modified in accordance with principles of interference, further spectrally modifying the radiation incident to the product by a multiple reflection interferometer having two relatively opposed optical surfaces, one of which surfaces being partially transmissive and the other being at least partially reflective of the radiation with the steady state physical spacing between said surfaces selectively controlled and periodically varied relative to the steady state spacing, detecting the radiation thus modified by the product and the interferometer and forming a signal related to the radiation thus detected, and applying tHe signal thus formed to vary the steady state spacing of said interferometer optical surfaces to obtain a spacing therof optically equivalent to the physical parameter of the product thereby maximizing the signal thus formed and which is proportionally related to the product''s physical parameter.

Claim 12

An interferometric method according to claim 9 including the step of controlling a process producing the product in accordance with the formed signal.

Claim 13

An interferometric method according to claim 9 in which a standard reference signal is selectively applied at periodic intervals for standardization.