Interference microscopy and Fourier fringe analysis applied to measuring the spatial refractive-index distribution

Area of Science:

• Crystallography
• Optical Physics
• Materials Science

Background:

• Microscopic interferometry is crucial for observing crystal growth dynamics.
• Fourier fringe analysis offers advanced methods for interpreting interferograms.
• Understanding crystal growth requires detailed analysis of surrounding solution properties.

Purpose of the Study:

• To apply Fourier fringe analysis to microscopic interferograms of growing needle crystals.
• To determine the 3D refractive index field around these crystals.
• To establish the phase shift sensitivity and spatial resolution of the technique.

Main Methods:

• Utilizing a differential technique comparing empty field and crystal-containing interferograms.
• Applying Fourier fringe analysis to two-dimensional interferogram data.
• Employing an iterative method to deduce the 3D refractive index field, assuming axial symmetry.

Main Results:

• Demonstrated a phase shift sensitivity of 0.01 fringe.
• Achieved a spatial resolution of approximately 1 µm (half a fringe spacing).
• Successfully deduced the 3D refractive index field around the growing crystals.

Conclusions:

• Fourier fringe analysis is a powerful tool for studying crystal growth.
• The method provides high sensitivity and resolution for analyzing microscopic phenomena.
• This technique enables detailed characterization of the 3D refractive index distribution during crystal formation.