Quantitative phase imaging in flows with high resolution holographic diffraction grating.

Area of Science:

• Optical Physics
• Fluid Dynamics
• Metrology

Background:

• Quantitative phase imaging (QPI) is crucial for non-invasive analysis of transparent objects.
• Traditional QPI methods can be limited by resolution, accuracy, or complexity.
• Holographic techniques offer potential for high-resolution phase retrieval.

Purpose of the Study:

• To propose and demonstrate a new QPI method using a high-resolution holographic grating.
• To enable accurate reconstruction of phase gradients and optical thickness.
• To validate the technique for analyzing dynamic fluid phenomena.

Main Methods:

• A high-resolution holographic grating in a 'kite' configuration was designed to generate a four-wave shearing interferogram.
• Parasitic mixing of diffraction orders was avoided through the grating's specific design.
• Phase gradients were reconstructed by selecting specific diffraction orders and performing spectral analysis; integration yielded phase and optical thickness.

Main Results:

• The method successfully reconstructed phase gradients along defined directions.
• Derivative axes were precisely determined irrespective of experimental configuration.
• The technique was demonstrated on a supersonic jet (5.56mm diameter), showing excellent agreement with digital holography results.

Conclusions:

• The proposed quantitative phase imaging technique using a kite-configured holographic grating is effective and accurate.
• It provides a robust method for phase and optical thickness reconstruction.
• The approach is suitable for analyzing complex phenomena like supersonic flows.