The overwhelming majority of past and present imaging systems use a lens to focus the subject of interest, even today's super-resolution light microscopes that breach the diffraction limit through ingenious experimental methods. Lensless imaging offers the prospect of a radical improvement in resolution by reconstructing a high-resolution image of an object from one or more diffraction patterns.
One downside of lensless imaging is that samples typically need to fulfil very specific geometric constraints and illuminated with a narrow, stable and accurately defined spectrum. These technical limitations have been overcome recently by a team from LaserLaB Amsterdam at the VU University in Amsterdam. Writing in the new nature.com journal 'Light: Science and Applications', they describe a general approach to lensless imaging without spectral bandwidth limitations or sample requirements, capturing the faint images with an ultrahigh sensitivity Andor iKon-L SO high-energy detection camera.
According to Dr. Stefan Witte, "We used the fully-coherent radiation from a bench-top, high-harmonic generation (HHG) soft-X-ray source but, rather than trying to filter the ultra-broadband spectrum and suffering very large losses in the already very low HHG flux, developed our 'two-pulse imaging' method. By scanning between two time-delayed coherent light pulses, we were able to reconstruct diffraction-limited images for all spectral components in the pulse. We also developed an iterative phase retrieval algorithm, which uses these spectrally resolved Fresnel diffraction patterns to obtain high-resolution images of complex extended objects without any support requirements.
"Due to the low flux of our source, detection sensitivity was a very important consideration and we chose the Andor iKon-L SO digital CCD camera for its ultra high sensitivity throughout the XUV down to the soft-X-ray spectral range. The numerical aperture of our imaging system was determined by the size of the camera, so the large 2048 x 2048 pixel CCD chip was also an advantage. Furthermore, the high pixel count allows fine sampling of the diffraction patterns and image reconstruction over a large field of view."
"For such a complex and sensitive piece of equipment, handling and operation of the Andor iKon-L was very convenient. We found the comprehensive software supplied with the camera intuitive to operate and quick and easy to integrate into our experiment set-up."
"Dr. Witte's breakthrough arose from the team's research aims of developing soft-X-ray imaging for biological applications," says Colin Duncan, product specialist at Andor. "Radiation in the so-called 'water-window' (2 - 4 nm wavelength) promises both strong intrinsic contrast and ultra-high resolution for carbon-based structures, such as cells, and their use of a compact, bench-top HHG source, rather than a much larger synchrotron or free electron laser, holds out the promise of widespread high-resolution lensless imaging use in life science laboratories worldwide."
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