Measuring extinction with digital holography: noisy holograms.

Area of Science:

• Optical Physics
• Particle Characterization
• Metrology

Background:

• Digital in-line holography (DIH) enables lens-less imaging of microparticles (several to >100 microns).
• DIH can determine particle extinction cross-sections, but noise compromises accuracy.
• Accurate cross-section measurement is crucial for aerosol science and material analysis.

Purpose of the Study:

• To develop and validate a noise reduction method for digital holograms of single particles.
• To enhance the accuracy of extinction cross-section estimation from noisy holographic data.
• To demonstrate the method's effectiveness across different particle types and wavelengths.

Main Methods:

• A noise reduction technique involving masking the complex-valued particle image-amplitude.
• Application of a Fresnel transformation to the masked amplitude to generate a noise-reduced hologram.
• Validation using micro-sphere and non-spherical particles at 440 nm and 1040 nm.

Main Results:

• Successfully reduced noise in digital holograms of single microparticles.
• Achieved more effective estimation of extinction cross-sections compared to standard methods.
• Demonstrated robustness for both spherical and non-spherical particles.

Conclusions:

• The proposed noise reduction method significantly improves the accuracy of extinction cross-section determination from digital holograms.
• This technique enhances the utility of DIH for quantitative particle analysis, particularly in noisy environments.
• The method offers a practical solution for more reliable characterization of microparticles using holography.