Lensless Imaging MontageWhat is lensless imaging?

When you think of a microscope, you usually think of looking through lenses. The lenses magnify the object and focus on details within it.

We make transmission (and reflection) microscopes without using lenses. Instead, we record the intensity of the radiation scattered by the object (the diffraction pattern) and process this computationally to form the image. Unfortunately, the phase of the scattered wave (the time of arrival of the peaks and troughs of the waves) is lost when we measure intensity. To get this back (essential if we need to form an image), we need to undertake an elaborate inverse calculation.

We use this roundabout method because for short wavelength radiation (X-rays and electrons) it’s very hard to make a good quality lens. Lensless imaging disposes of all the problems associated with lenses. As it happens, a lensless image has more information in it than a conventional image taken with a good quality lens! So lensless imaging is useful even at optical wavelengths.

Ptychography

The particular method we work on is called ‘ptychography’. It processes many diffraction patterns taken from different areas of the object. The technique (originally developed by John Rodenburg in the Electronics and Electrical Engineering Department in the University of Sheffield) is by far the most effective lensless imaging approach. It has been adopted widely in the X-ray imaging community and is now available commercially at optical wavelengths. We are now actively developing the method at electron wavelengths. See:

Humphrey, M.J., Kraus, B., Hurst, A.C., Maiden, A.M., and Rodenburg, J.M.
Ptychographic electron microscopy using high-angle dark-field scattering for sub-nanometre resolution imaging'
Nature Communications 3, Art. No: 730 doi:10.1038/ncomms1733

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