Schlieren systems with coherent illumination for quantitative measurements

Area of Science:

• Optics
• Image Processing

Background:

• Schlieren systems are used for visualizing phase objects.
• Coherent light sources offer potential for enhanced imaging but require careful analysis.

Purpose of the Study:

• Investigate coherent schlieren imaging properties with various cutoff filters.
• Evaluate the performance of different filters for phase object measurement.
• Introduce and validate a new schlieren point-spread function.

Main Methods:

• Fourier optics technique applied to coherent schlieren systems.
• Analysis of systems with piecewise linear and Gaussian step function convolution filters.
• Development and simulation of a modified Lopez cutoff filter.

Main Results:

• Image formation approximated by geometrical-optics theory for graded filters.
• Nonlinear phase contribution estimation enables strong phase object measurement.
• Proposed modified Lopez filter outperforms other tested filters.

Conclusions:

• Coherent schlieren imaging can be effectively analyzed using Fourier optics.
• The modified Lopez cutoff filter offers superior performance for phase derivative measurements.
• The schlieren point-spread function provides a framework for linear approximation analysis.