High-speed dynamic speckle interferometry: phase errors due to intensity, velocity, and speckle decorrelation

Area of Science:

• Optical Metrology
• Experimental Mechanics
• Non-Destructive Testing

Background:

• High-speed phase-shifting speckle interferometry (HSPS) with temporal phase unwrapping enables dynamic displacement measurement.
• HSPS is effective for objects with discontinuities like cracks.
• Local speckle averaging can introduce phase errors that accumulate over time, dependent on the speckle rereferencing rate.

Purpose of the Study:

• To analyze phase errors in HSPS introduced by intensity, velocity, and speckle decorrelation.
• To investigate the combined and independent effects of these error sources.
• To provide guidance on optimizing the speckle rereferencing rate for practical applications.

Main Methods:

• Computer-generated speckle patterns were used to simulate errors.
• Analysis of phase errors for common phase-shifting algorithms.
• Evaluation of errors under controlled out-of-plane geometry.

Main Results:

• Speckle decorrelation errors increase with the time between rereferencing events.
• Intensity and velocity errors decrease as the time between rereferencing events increases.
• Speckle decorrelation errors are generally more significant than intensity and velocity errors.

Conclusions:

• Understanding error sources is crucial for accurate dynamic displacement measurements using HSPS.
• The speckle rereferencing rate significantly influences the magnitude of phase errors.
• Optimizing the rereferencing rate can mitigate errors and improve measurement reliability.