Pulsed lasers in speckle photography: error owing to pulse width

Area of Science:

• Optical Metrology
• Laser Speckle Velocimetry
• Vibration Analysis

Background:

• Speckle velocimetry and transient vibration analysis utilize pulsed lasers.
• Object motion during laser exposure introduces errors in fringe analysis.

Purpose of the Study:

• To investigate the effect of pulsed laser width on speckle velocimetry and vibration analysis.
• To propose a method to mitigate errors caused by object motion.

Main Methods:

• Pointwise filtering method to analyze the effect of object motion.
• Development of a novel aperture geometry for autocorrelation halo.
• Derivation of a closed-form solution for fringe shift.

Main Results:

• Object motion during exposure modulates Young's fringes with a sinc function.
• High object velocities lead to increased errors in fringe position calculation.
• The proposed aperture geometry maintains a constant autocorrelation halo, isolating sinc function effects.

Conclusions:

• The study provides a method to reduce errors in pulsed laser-based velocimetry and vibration analysis.
• A closed-form solution is obtained for fringe shift under specific conditions.
• Experimental validation confirms the proposed approach.