[Paper Review] Ultra-broadband extreme-ultraviolet lensless imaging of extended complex structures

Stefan Witte, Vasco T. Tenner+2 more|arXiv (Cornell University)|Feb 25, 2013

Advanced X-ray Imaging TechniquesPhysics and Astronomy39 references63 citations

TL;DR

This paper introduces a lensless imaging technique using two time-delayed coherent pulses to enable ultra-broadband extreme-ultraviolet imaging of complex, extended objects without spectral or sample support constraints. By scanning the pulse delay and applying an iterative phase retrieval algorithm to spectrally resolved Fresnel diffraction patterns, the method achieves diffraction-limited resolution across octave-spanning bandwidths, demonstrated in both visible and extreme-ultraviolet regimes using table-top sources.

ABSTRACT

Lensless imaging is an elegant approach to high-resolution microscopy, which is rapidly gaining popularity in applications where imaging optics are problematic. However, current lensless imaging methods require objects to be placed within a well-defined support structure, while the light source needs to have a narrow, stable, and accurately known spectrum. Here we introduce a general approach to lensless imaging without spectral bandwidth limitations or sample requirements. We use two time-delayed coherent light pulses, and show that scanning the pulse-to-pulse time delay allows the reconstruction of diffraction-limited images for all spectral components in the pulse. Moreover, an iterative phase retrieval algorithm is introduced, which uses these spectrally resolved Fresnel diffraction patterns to obtain high-resolution images of complex extended objects without any support requirements. We demonstrate this two-pulse imaging method with octave-spanning visible light sources (in both transmission and reflection geometries), and with broadband extreme-ultraviolet radiation from a high-harmonic source. This demonstrates that our approach enables effective use of low-flux ultra-broadband sources, such as table-top soft-X-ray systems, for high-resolution imaging.

Motivation & Objective

• To overcome spectral and sample support limitations in lensless imaging.
• To enable high-resolution imaging using ultra-broadband, low-flux sources such as table-top high-harmonic generation systems.
• To develop a method that does not require predefined object support or narrowband light sources.
• To demonstrate applicability across extended, complex objects in both transmission and reflection geometries.
• To enable effective use of extreme-ultraviolet radiation for high-resolution microscopy.

Proposed method

• The method employs two time-delayed coherent light pulses to generate spectrally resolved Fresnel diffraction patterns.
• Scanning the pulse-to-pulse time delay allows acquisition of diffraction data across the entire spectral bandwidth of the source.
• An iterative phase retrieval algorithm reconstructs high-resolution images from the spectrally resolved diffraction patterns.
• The approach is independent of object support, enabling imaging of complex, extended structures without prior constraints.
• The technique is validated using octave-spanning visible light and broadband extreme-ultraviolet radiation from a high-harmonic source.
• The method is applicable in both transmission and reflection geometries, enhancing experimental flexibility.

Experimental results

Research questions

• RQ1 Can lensless imaging be extended to ultra-broadband sources without requiring narrowband or stable spectra?
• RQ2 Can high-resolution imaging of complex, extended objects be achieved without predefined object support?
• RQ3 Can time-delayed coherent pulses enable spectrally resolved diffraction pattern acquisition for phase retrieval?
• RQ4 Is the method effective for extreme-ultraviolet radiation from compact, low-flux sources?
• RQ5 Can the technique be applied in both transmission and reflection imaging geometries?

Key findings

• The method achieves diffraction-limited imaging resolution across octave-spanning bandwidths in both visible and extreme-ultraviolet regimes.
• The technique successfully reconstructs high-resolution images of complex, extended objects without requiring object support constraints.
• Spectrally resolved Fresnel diffraction patterns were acquired using time-delayed pulses, enabling full spectral utilization.
• The iterative phase retrieval algorithm effectively reconstructs images from broadband, low-flux sources such as high-harmonic generation systems.
• The method was experimentally demonstrated in both transmission and reflection geometries, confirming robustness and versatility.
• The approach enables effective use of table-top extreme-ultraviolet sources for high-resolution lensless imaging.