Dual-reference digital holographic interferometry for analyzing high-density gradients in fluid mechanics

Area of Science:

• * Optical Engineering
• * Fluid Dynamics
• * Aerodynamics

Background:

• * Analyzing high refractive index gradients in transonic and supersonic flows is crucial for understanding fluid dynamics.
• * Traditional interferometry methods face challenges with complex refractive index orientations.

Purpose of the Study:

• * To propose a novel dual-reference digital holographic interferometer for analyzing high refractive index phenomena.
• * To enable comprehensive analysis of transparent objects irrespective of refractive index gradient orientation.
• * To demonstrate the method's efficacy in visualizing shock waves in unsteady flow.

Main Methods:

• * A Wollaston prism is integrated into the reference arm to generate two orthogonally polarized reference waves.
• * Recorded interferograms yield two distinct interference patterns, separable in the Fourier spectrum.
• * Phase maps from two interference orders are reconstructed and fused, removing phase singularities.

Main Results:

• * The dual-reference interferometer successfully generates two separable interference patterns.
• * Reconstructed phase maps allow analysis independent of refractive index gradient orientation.
• * Experimental results validate the technique for analyzing shock waves around a circular cylinder at Mach 0.75.

Conclusions:

• * The proposed dual-reference digital holographic interferometer is suitable for high refractive index flow analysis.
• * The fusion of phase maps effectively eliminates phase singularities, enhancing data clarity.
• * This technique offers a robust solution for studying complex aerodynamic phenomena like shock waves.