National Physical Laboratory

About: National Physical Laboratory is a facility organization based out in London, United Kingdom. It is known for research contribution in the topics: Dielectric & Thin film. The organization has 7615 authors who have published 13327 publications receiving 319381 citations.

Imaging properties of the Gabor superlens

Abstract: A superlens is an optical system consisting of a pair of microlens arrays in which there is a slight difference in pitch. The relative displacement of one lens with respect to its partner causes the bundle of light passing through a pair of lenses to be deviated in such a way that all bundles converge to a common point and the system behaves like a lens. The focal properties are very different from those of a conventional lens and were originally described by Gabor in 1940. We have extended his analysis and have taken advantage of modern technology to assemble superlenses and confirm their properties experimentally.

Effect of cadmium telluride quantum dots on the dielectric and electro-optical properties of ferroelectric liquid crystals.

Abstract: We present here the dielectric and electro-optical studies of cadmium telluride quantum dots (CdTe QDs) doped ferroelectric liquid crystals (FLCs). It has been observed that the doping of CdTe QDs not only induced a pronounced memory effect but also affected the physical parameters of FLC material (LAHS19). The modifications in the physical parameters and memory effect of LAHS19 are found to depend on the concentration ratio of CdTe QDs. The lower concentration of CdTe QDs (1--3 wt%) enhanced the values of spontaneous polarization and rotational viscosity of LAHS19 material but did not favor the memory effect, whereas a higher concentration of CdTe QDs (g5 wt%) degraded the alignment of LAHS19 material. The doping of \ensuremath{\sim}5 wt% of CdTe QDs is found to be the most suitable for achieving good memory effect without significantly affecting the material parameters.

Pseudorandom signals for the dynamic analysis of multivariable systems

Abstract: The extension of the input/output-crosscorrelation method of system dynamic identification, using a pseudorandom input signal, to multi-input/multioutput systems is considered. The system impulse responses may be obtained directly from the measured crosscorrelation functions (in a similar manner to the single-input/single-output case), provided that the system-input signals have autocorrelation functions of delta-function form and are uncorrelated with each other, it is found that it is not possible to meet both these requirements without resorting to a very prolonged integration time. Methods of overcoming this difficulty by using signals of practicable lengths, the properties of which approximate to those required, are therefore proposed. Both 2- and 3-level signals are considered.

Determination of the transfer function for optical surface topography measuring instruments—a review

Abstract: A significant number of areal surface topography measuring instruments, largely based on optical techniques, are commercially available. However,implementation of optical instrumentation into production is currently difficult dueto the lack of understanding of the complex interaction between the light and the component surface. Studying the optical transfer function of the instrument can help address this issue. Herea review is given of techniques for the measurement of optical transfer functions. Starting from the basis of a spatially coherent, monochromatic confocal scanning imaging system, the theory of optical transfer functions in three-dimensional (3D) imaging is presented. Further generalizations are reviewed allowing the extension of the theory to the description of conventional and interferometric 3D imaging systems. Polychromatic transfer functions and surface topography measurements are also discussed. Following presentation of theoretical results, experimental methods to measure the optical transfer function of each class of system are presented, with a focus on suitable methods for the establishment of calibration standards in 3D imaging and surface topography measurements.