Inline mechano-vibration holography for simultaneous phase and elasticity mapping of soft samples

Area of Science:

• Biophysics
• Optical Metrology
• Materials Science

Background:

• Traditional holography methods like off-axis and in-line interferometry have limitations in spatial bandwidth, dynamic range, and simultaneous viscoelastic mapping.
• Accurate characterization of soft sample viscoelasticity and thickness is crucial for understanding cellular mechanics and material properties.

Purpose of the Study:

• To develop a novel holographic technique for simultaneous, high-resolution mapping of soft sample thickness and viscoelastic properties.
• To overcome the limitations of existing holographic methods for dynamic and multi-property measurements.

Main Methods:

• Vibration-encoded in-line Mach-Zehnder holography utilizing twelve holograms acquired over one vibration cycle.
• Analysis via Bessel-based harmonic inversion and robust regression to extract static phase, modulation depth, and phase lag.
• Quantification of Kelvin-Voigt storage modulus (E') and loss modulus (E'') from recovered phase information.

Main Results:

• Simulations demonstrate accurate recovery of E' and E'' (within ~2%) across a broad range of viscoelastic ratios.
• Sub-micron thickness error achieved for simulated micro-beads (20-45 μm).
• Experimental validation on polyacrylamide beads shows sub-micron thickness repeatability (median ~0.57 μm) and stiffness estimates within 10% of ground truth.

Conclusions:

• Vibration-encoded in-line Mach-Zehnder holography provides a robust platform for simultaneous thickness and viscoelasticity mapping of soft materials.
• The method demonstrates high accuracy, repeatability, and applicability to biological samples, as shown with MCF-7 cells.
• This technique advances holographic metrology for quantitative characterization of soft matter.