Apparatus and methods for scanning phase profilometry

Claim 2

For use with a coherent input light beam, a scanning phase profilometer for detecting minute phase variations across a specimen, comprising: means including an acousto-optic Bragg cell and associated sound wave generating apparatus for producing from the input beam by diffraction a pair of mutually coherent interrogating beams having different optical frequencies, for focusing the interrogating beams on the specimen, for collecting and recombining said interrogating beams after interrogation of the specimen, and for causing said pair of interrogating beams to scan the specimen in unison and with constant angular displacement; phase demodulating means including light-responsive means in the path of the recombined interrogating beams for detecting phase variations between said interrogating beams caused by optical path length variations as said beams are scanned across the specimen and for producing an electrical phase differential signal characterizing said variations; and electrical integrating means responsive to said phase demodulating means for integrating said phase differential signal to produce a signal characterizing the phase profile of the scansion across the specimen.

Claim 3

The apparatus defined by claim 1 wherein said sound wave generating means includes oscillator means for generating a selectable fixed audio frequency continuous wave carrier signal fm, a frequency ramp generator for generating a ramp signal fs sweeping through a range of megahertz frequencies, a mixer for mixing said carrier signal and said ramp signal to produce continuous wave signals having together-sweeping frequencies fs+fm and fs-fm and transducer means coupled to said Bragg cell for converting the output signal from said mixer into sound waves in said cell.

Claim 4

The apparatus defined by claim 1 wherein the specimen is light-reflective and wherein said Bragg cell means comprises a single cell which diffracts the input beam and which receives and acts on the interrogating beams after reflection from the specimen.

Claim 5

For use with a coherent input light beam having an optical center frequency f0, a scanning phase profilometer for detecting minute phase variations across a specimen, comprising: means including acousto-optic Bragg cell means and associated sound wave generating means for diffracting from the input beam a pair of interrogating beams having different optical frequencies f1 and f2 and for recombining said interrogating beams after interrogation of the specimen, and for causing said interrogating beams to scan across the specimen in unison and with constant angular displacement, the frequency separation of f1 and f2 from f0 and from each other being very small relative to f0, said sound wave generating means comprising oscillator means for generating a selectable fixed audio frequency continuous wave carrier signal fm, a frequency ramp generator for generating a ramp signal fs sweeping through a range of megahertz frequencies, a mixer for mixing said carrier signal and said ramp signal to produce continuous wave signals having together-sweeping frequencies fs+fm and fs-fm, and transducer means coupled to said Bragg cell means for converting said continuous wave signals from said mixer into sound waves iN said cell which produce by diffraction said optical beams of optical frequencies f1 and f2, respectively; optical lens means for focusing the interrogating beams on the specimen and for collecting and recombining said beams after interaction with the specimen; phase demodulating means including light-responsive means in the path of the recombined interrogating beams coupled to said oscillator means for detecting phase variations between said interrogating beams caused by optical path length variations as said beams are scanned across the specimen and for producing an electrical phase differential signal characterizing said variations; and electrical integrating means responsive to said phase demodulating means for integrating said phase differential signal to produce a signal characterizing the phase profile of the scansion across the specimen.

Claim 6

For use with a coherent input light beam having an optical center frequency f0, a scanning phase profilometer for detecting minute phase variations across a specimen, comprising: means including acousto-optic Bragg cell means and associated sound wave generating means for diffracting from the input beam a pair of interrogating beams having different optical frequencies f1 and f2 and for recombining said interrogating beams after interrogation of the specimen, and for causing said interrogating beams to scan across the specimen in unison and with constant angular displacement, the frequency separation of f1 and f2 from f0 and from each other being very small relative to f0, said sound wave generating means comprising oscillator means for generating a selectable fixed audio frequency continuous wave carrier signal fm, a frequency ramp generator for generating a ramp signal fs sweeping through a range of megahertz frequencies, a mixer for mixing said carrier signal and said ramp signal to produce continuous wave signals having together-sweeping frequencies fs+fm and fs-fm, and transducer means coupled to said Bragg cell means for converting said continuous wave signals from said mixer into sound waves iN said cell which produce by diffraction said optical beams of optical frequencies f1 and f2, respectively; optical lens means for focusing the interrogating beams on the specimen and for collecting and recombining said beams after interaction with the specimen; phase demodulating means including light-responsive means in the path of the recombined interrogating beams coupled to said oscillator means for detecting phase variations between said interrogating beams caused by optical path length variations as said beams are scanned across the specimen and for producing an electrical phase differential signal characterizing said variations; and electrical integrating means responsive to said phase demodulating means for integrating said phase differential signal to produce a signal characterizing the phase profile of the scansion across the specimen.

Claim 7

The apparatus defined by claim 4 including means for effecting relative movement between said pair of interrogating beams and the specimen in a direction transverse to the direction of relative movement introduced by said sound wave generating means, and further including means coupled to said integrating means for producing a two-dimensional display in the form of a spatial succession of phase profile traces representing the phase profiles of a corresponding spatial succession of scansions across the specimen.

Claim 8

The system defined by claim 5 wherein the specimen is light-reflective and wherein said Bragg cell means comprises a single cell which diffracts the input beam and which receives and acts on the interrogating beams after reflection from the specimen.