Recently, increasing attention has been devoted to mastering a new technique of optical delivery of micro-objects tractor-beam’1, 2, 3, 4, 5, 6, 7, 8, 9. Such beams have uniform intensity profiles along their propagation direction and can exert a negative force that, in contrast to the familiar pushing force associated with radiation pressure, pulls the scatterer toward the light source. It was experimentally observed that under certain circumstances, the pulling force can be significantly enhanced6 if a non-spherical scatterer, for example, a linear chain of optically bound objects10, 11, 12, is optically transported. Here we demonstrate that motion of two optically bound objects in a tractor beam strongly depends on theirs mutual distance and spatial orientation. Such configuration-dependent optical forces add extra flexibility to our ability to control matter with light. Understanding these interactions opens the door to new applications involving the formation, sorting or delivery of colloidal self-organized structures.

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The purpose of this work is the study of the correlation between the thickness of tantalum pentoxide thin films and their three-dimensional (3D) micromorphology. The samples were prepared on silicon substrates by electron beam evaporation. The differences in surface structure of the processed and reference samples were investigated. Compositional studies were performed by energy-dispersive X-ray spectroscopy. Stereometric analysis was carried out on the basis of atomic force microscopy (AFM) data, for tantalum pentoxide samples with 20 nm, 40 nm, 60 nm, 80 nm and 100 nm thicknesses. These methods are frequently used in describing experimental data of surface nanomorphology of Ta2O5. The results can be used to validate theoretical models for prediction or correlation of nanotexture surface parameters.

In scanning probe microscopy laser interferometers are usually used for measuring the position of the probe tip with a metrological traceability. As the most of the AFM setups are designed to work under standard atmospheric conditions the changes of the refractive index of air have an influence to measured values of the length with 1.0 × 10 −4 relatively. In order to achieve better accuracies the refractive index of air has to be monitored continuously and its instantaneous value has to be used for compensating the lengths measured by all of the interferometric axes. In the presented work we developed a new concept of an electronic unit which is able to monitor the refractive index of air on basis of measurement of ambient atmospheric conditions: temperature, humidity, pressure of the air and the CO2 concentration. The data processing is based on Ciddor equation for calculating the refractive index of air. The important advantage of the unit is a very low power consumption of the electronics so the unit causes only negligible temperature effects to the measured environment. The accuracy of the indirect measuring method employed by the unit was verified. We tested the accuracy in comparison with a direct method of measuring refractive index of air based on an evacuatable cell placed at the measuring arm of a laser interferometer. An experimental setup used for verification is presented together with a set of measurements describing the performance. The resulting accuracy of the electronic unit falls to the 4.1 × 10 −7 relatively.

We present techniques oriented to improvement of precision in incremental interferometric measurements of displacements over a limited displacement range. The wavelength of the coherent laser source is here directly stabilized to a mechanical reference and not to a reference of any optical frequency. This may represent a reduction of uncertainty linking the laser wavelength not to indirectly evaluated refractive index but to the setup mechanics which cannot be completely eliminated. Here we suggest an approach where the traditional interferometers are replaced by a passive Fabry-Perot cavity with position sensing using an intracavity transparent photodetector.