Refocus criterion for both phase and amplitude objects in digital holographic microscopy

Area of Science:

• Optics and Photonics
• Microscopy Techniques
• Digital Holography

Background:

• Traditional focus criteria in digital holographic microscopy often yield different results for phase and amplitude objects.
• Existing methods may require object-specific adjustments, limiting their universal applicability.

Purpose of the Study:

• To develop a universal focus criterion for digital holographic microscopy.
• To enable focus detection irrespective of whether the object is phase- or amplitude-based.

Main Methods:

• Modification of the focus criterion by integrating the amplitude modulus.
• Application of the criterion to high-pass filtered complex amplitudes from holographic data.
• Validation through simulations and experimental results on real samples.

Main Results:

• The proposed focus criterion consistently yields a minimum at the focus plane for both phase and amplitude objects.
• Demonstrated efficiency and potential of the method in practical digital holographic microscopy scenarios.

Conclusions:

• The modified focus criterion offers a robust and universal approach for automated focusing in digital holographic microscopy.
• This advancement simplifies the analysis of holographic data from diverse sample types.