Optics testing
The optics on Diamond beamlines are required to deliver the brightness from the electron beam source to the sample. This places high demands on individual optical elements in the beamlines. Once installed on a beamline it is difficult to characterise the operation of the individual optical elements. The Test beamline will allow measurements to be made on critical optical components in order to understand their operation, diagnose problems and develop more advanced optics.
The testing of monochromator optics is a major area of interest for Diamond. The Test beamline can be used to test monochromators that will be used on the high power insertion device beamlines, for example by investigating mounting or pressure induced strain in the diffracting surface. Measurements in triple crystal mode will allow crystal strain to be directly measured. The beamline will also allow a variety of measurement geometries to be used allowing measurements that could not be performed if the monochromator was installed on the insertion device beamline (for example double crystal mode). Diamond crystals can be used as monochromators or as quarter or half wave plates for polarisation control. Commercially available diamonds do not achieve the perfection of silicon. They show broadening of the Darwin curve caused by strain and impurities particularly near zone sector boundaries. Rocking curve mapping of diamond crystals will allow diamonds to be selected according to their perfection and will even allow the most perfect region of single diamonds to be located. Focusing monochromators such as sagitally bent double crystal monochromators need to be made to a high standard in order to focus the beam to the smallest spot size. X-ray measurements can be used to determine accurately the slope variation in bent crystal monochromators.
The Test beamline will also be used for testing of mirrors. This is required, not only for synchrotron radiation use (which is of increasing importance to British industry) but also for space telescopes, where the performance of mirrors must be verified before flight. It is precisely this technology that has pushed (and continues to push) mirror technology in performance. For instance, the slope errors have evolved over the last few years from several µradians to less than a µradian. As a first step to this improvement, the properties have to be measured and the Test beamline can provide tests on mirror slope error and roughness.
An important area for Diamond is the development of micro- and nano-focusing optics. X-ray focusing is a fast evolving field and significant developments have taken place in recent years. Complementary technologies are being applied based on reflection, refraction and diffraction to achieve smaller and smaller focused beams. The Test beamline will provide the necessary infrastructure to test such micro- and nano-focusing optics.
The Test beamline will enable the development of other X-ray optics such as waveguides, zone plate optics, phase plates, adaptive optics, refractive optics, etc.