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."
This story is reprinted from material from Catalyst Communications, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier.