Introducing the Imaging and Coherence Beamline
Meera - This month we are taking you to the cutting edge of synchrotron science as we explore Diamond’s Imaging and Coherence Beamline where x-rays will soon allow scientists to see, with greater clarity than ever before. The beamline goes into operation in October for use across a wide range of scientific disciplines. Graham Morrison chaired the User Meeting Group for the beamline, and he explained just why the imaging offered is so unique.
Graeme – There are 3 ways in which images can be formed and x-ray imaging has been a long-established technique of ours since Röntgen discovered x-rays at the end of the 19th century. The 3 principle ways are; to form a shadow projection, you know like a hospital radiogram, where you simply have a parallel beam of x-rays going through the sample and you get absorption by certain areas – you get areas of light and dark. A more sophisticated method is to use some form of lens and with x-rays that is already a challenge because x-rays through lenses are quite difficult to fabrigate. With a lens in place in the beam path, effectively you can get magnification. Instead of just getting a life-sized image, a one-to-one image the way you would with projection, you can get a magnified image of the object you are looking at.
And the 3rd way which is newly being developed and explored over the last few years is a process known as coherent diffraction imaging where essentially you don’t try and form an image directly, what you record is the diffraction pattern from the object then use computer algorithms to try a reconstruct the image from the diffraction data that you’ve recorded. Now because that doesn’t involve any form of lens in the beam path, it means you are not limited in the same way that you are if you are using lenses and the technical capabilities of the lens. So in principal, you can get much better resolution from those reconstructions, but it does depend on the reliability of the algorithms that are used for that process.
Meera - And this latter process then, using diffraction patterning, that’s what the new Imaging and Coherence beamline at Diamond will be taking on board?
Graham – Well the Imaging and Coherence branch is intended to do both conventional imaging and to use this new approach of coherent diffraction imaging, as it’s called. So there are 2 branches on the beamline I13, one branch, the imaging branch obviously, will do the shadow projection imaging, which is a very straightforward technique and can yield very useful information. It allows us to look at samples with a big field of view, so that means you can look at perhaps millimetre sized objects.
Meera - But this new beamline, it does have 2 branches, it has the imaging and the coherence, what is different or unique about the coherence side of things.
Graeme – The coherent diffraction imaging branch, which is the, er, if you can record the diffraction pattern successfully and then use these computer algorithms to reconstruct the image, that will take you down to about 5 nanometres which is much higher than you can achieve with any focussing optic. So again, it allows you to address a new range of samples, or get you information about samples that is not currently readily achievable. But traditionally until now, until very recently, that’s been limited, but a new method that’s been developed in the last few years, known as Ptychography, developed principally by John Rodenburg at the University of Sheffield, has allowed the coherent diffraction method to be extended to look at much larger areas of sample and the idea is that you illuminate, produce a spot of x-rays on the sample, you’ve recorded the diffraction pattern from that area and then you step the spot over the sample so that each successive diffraction pattern comes from an overlapping area of the sample. And it turns out that if you do that, then the methods of reconstructing the image data from the diffraction pattern works much better and converges more quickly to a reliable answer. So this allows you to get lens-less imaging of samples at very high special resolution and also to look at extended areas of sample. So I think the application of this sort of an approach on the coherent diffraction imaging beamline will be a very important development.
Meera - How would you then just summarise the main benefits of this new beamline and the fact that it has these 2 branches?
Graeme – In a sense, it’s covering such a huge range of length scales, from the millimetre scale with the projection technique, right down to the nanometre scale with the coherent diffraction, and imaging and ptychography, as a result, it’s also going to cover a huge range of different types of sample from engineering materials down to nano-materials. I think it is actually a beamline that is attractive to the whole range of users.
Meera - Graeme Morrison, Chair of the User Working Group for Diamond’s Imaging and Coherence Beamline.