BFU physicists suggested a new model of a variable focus lens called a mini transfocator. It may be used in microscopic research that requires compact and mobile optical systems. The development was supported by the Ministry of Education and Science with a grant (No. 14. Y26.31.0002). The results were published in the Microscopy and Microanalysis journal.
Lens optical systems and X-ray lenses are currently used in microscopy, for making high-resolution X-ray images, and for focusing X-rays to submicron scale. To focus X-rays one may change the number or the combination of lenses. To do so, scientists use variable focus lenses or transfocators. These are systems with adjustable lenses that can be removed or added to an X-ray beam to regulate the focus distance. The configuration of a transfocator is easily changeable, therefore it is used for initial focusing in combination with other focusing elements, and also as an independent focusing device in a beam.
"These are the methods we suggested and successfully promoted at the ESRF synchrotron in France and at the German PETRA-III synchrotron at DESY. But for them to work, we need light and mobile transfocators. They should be easy to install and to adjust in the direction of a scattered or diffracted beam," says Anatoly Snigirev, the supervisor of the "Coherent Optics" specialization and the head of the X-ray optics laboratory at the Immanuel Kant Baltic Federal University.
Traditional transfocators are quite heavy and cannot be used for X-ray visualization on site or for introscopy (non-invasive study of the structure and internal processes of biological objects). Moreover, gaps can occur between their cartridges. In such cases it becomes difficult to gradually change the focus distance as the lenses that are located close to each other and those spread along the beam will have different focus positioning. Mobile mini transfocators help to study the internal structure and peculiarities of biological samples and track changes in them. They are also used in the new area of studies called hard X-rays microscopy. The lens is used as an objective and shows the details of the sample with submicron or even nanometer resolution. This is especially relevant for studies carried out in extreme conditions (under high pressure or temperature) as well as for nondestructive studies of biological objects.
In the new transfocator model the lenses are attached individually on stacks and are located close to each other. Therefore, one lens can be easily removed or added, and the focus distance would change gradually. This type of construction is more compact and mobile. The length of the transfocator is 150 mm, the width - 100 mm, and the height - 90 mm, while its weight is less than 2 kg. Traditional transfocators depending on their function may be 0.5 to 1.5 m long and weigh from 20 to 100 kg. All materials and components are vacuum compatible and are manufactured using high-precision equipment. 50 independent lenses that stand in the way of the beam are moved by an electric engine.
The participants of the experimental studies also represented the European Molecular and Biological Laboratory in Hamburg (Germany) and the Research Accelerator Complex ESRF (European Synchrotron Radiation Facility) in Grenoble (France).