Phase retrieval in x-ray lensless holography by reference beam tuning

Area of Science:

• Coherent imaging
• Phase retrieval algorithms
• Soft X-ray microscopy

Background:

• Phase retrieval is crucial for reconstructing images in coherent imaging techniques.
• Traditional methods often require well-defined reference structures, limiting their applicability.
• Uniqueness and convergence issues can hinder the accuracy of phase retrieval.

Purpose of the Study:

• To develop a robust phase retrieval algorithm that does not rely on precisely defined reference structures.
• To enable accurate determination of the relative phase between an object and a reference scatterer.
• To improve the speed and reliability of image reconstruction in coherent imaging.

Main Methods:

• A reference-guided phase retrieval algorithm was developed, utilizing the relative phase as a constraint.
• The algorithm iteratively reconstructs both the object and the reference simultaneously.
• The method was demonstrated using a soft X-ray coherent imaging experiment with a switchable micrometer-sized reference structure.

Main Results:

• The algorithm successfully determined the relative phase by tuning the reference wave's intensity and phase.
• Rapid and reliable convergence was achieved, overcoming the uniqueness problem inherent in phase retrieval.
• A high-resolution object image, with resolution near the 21 nm pixel size, was obtained.

Conclusions:

• The proposed reference-guided phase retrieval algorithm offers a versatile and effective approach for high-resolution imaging.
• This method eliminates the need for precisely defined reference structures, broadening its potential applications.
• The demonstrated soft X-ray imaging experiment validates the algorithm's performance and resolution capabilities.