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.

Subhertz-linewidth Nd:YAG laser

Abstract: Light from a Nd:YAG laser at 1064 nm is independently stabilized to two Fabry–Perot etalons situated on separate vibration-isolation platforms. A heterodyne beat measurement shows their relative frequency stability to be at the part-in-1015 level at 5 s and the relative linewidth to be less than 1 Hz.

Growth and characterization of L-lysine monohydrochloride dihydrate (L-LMHCl) single crystal

Abstract: A nonlinear optical crystal of L-lysine monohydrochloride dihydrate (L-LMHCl) was grown by slow evaporation solution growth technique using deionised water and mixed solvents of deionised water and ethanol. The functional groups and vibrational frequencies were identified using FTIR and FT-RAMAN spectra analyses. Also, the presence of hydrogen and carbon atoms in the grown sample was confirmed using proton and carbon NMR spectra analyses. Using TG-DTA analyses, the decomposition temperature was obtained. Transmittance of the grown crystals was analysed using UV-visible spectrum. The mechanical strength of the grown crystals was found using Vicker's microhardness tester.

An Experimental Investigation of the Interaction between Shock Waves and Boundary Layers

Abstract: An account is given of an investigation into the interaction between the boundary layer on a flat plate and a shock wave produced either externally, by a wedge in the supersonic main-stream, or from within the boundary layer, by a wedge held in contact with the plate. A wide range of free-stream Mach numbers, boundary-layer Reynolds numbers, and shock strengths has been covered, shock strength being defined as the ratio of the static pressure downstream of the shock to the static pressure upstream of it. Variations in these parameters can have large effects on the interaction, and there are also large differences between cases with externally generated shocks and cases where the shock is generated from within the boundary layer. The investigation has thrown light on the physical mechanisms involved. It is found that many of the major features of the interaction arise because the boundary layer separates from the surface ahead of the shock wave. The conditions under which separation occurs and the behaviour of the separated boundary layer thus have important effects, in terms of which, for example, the differences between the interactions observed with laminar and with turbulent boundary layers may be explained.

Raman spectroscopy as an advanced structural nanoprobe for conjugated molecular semiconductors.

Abstract: Raman spectroscopy has emerged as a powerful and important characterisation tool for probing molecular semiconducting materials. The useful optoelectronic properties of these materials arise from the delocalised ?-electron density in the conjugated core of the molecule, which also results in large Raman scattering cross-sections and a strong coupling between its electronic states and vibrational modes. For this reason, Raman spectroscopy offers a unique insight into the properties of molecular semiconductors, including: chemical structure, molecular conformation, molecular orientation, and fundamental photo- and electro-chemical processes - all of which are critically important to the performance of a wide range of optical and electronic organic semiconductor devices. Experimentally, Raman spectroscopy is non-intrusive, non-destructive, and requires no special sample preparation, and so is suitable for a wide range of in situ measurements, which are particularly relevant to issues of thermal, and photochemical stability. Here we review the development of the family of Raman spectroscopic techniques, which have been applied to the study of conjugated molecular semiconductors. We consider the suitability of each technique for particular circumstances, and the unique insights which it can offer, with a particular focus on the significance of these measurements for the continuing development of stable, high performance organic electronic devices.