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.

Sub-milliwatt-level microresonator solitons with extended access range using an auxiliary laser

Abstract: The recent demonstration of dissipative Kerr solitons in microresonators has opened a new pathway for the generation of ultrashort pulses and low-noise frequency combs with gigahertz to terahertz repetition rates, enabling applications in frequency metrology, astronomy, optical coherent communications, and laser-based ranging. A main challenge for soliton generation, in particular in ultra-high-Q resonators, is the sudden change in circulating intracavity power during the onset of soliton generation. This sudden power change requires precise control of the seed laser frequency and power or fast control of the resonator temperature. Here, we report a robust and simple way to increase the soliton access window by using an auxiliary laser that passively stabilizes intracavity power. In our experiments with fused silica resonators, we are able to extend the access range of microresonator solitons by two orders of magnitude, which enables soliton generation by slow and manual tuning of the pump laser into resonance and at unprecedented low power levels. Importantly, this scheme eliminates the sudden change in circulating power (“soliton step”) during transition into the soliton regime. Both single- and multi-soliton mode-locked states are generated in a 1.3-mm-diameter fused silica microrod resonator with a free spectral range of ∼50.6 GHz, at a 1554 nm pump wavelength at threshold powers <3 mW. Moreover, with a smaller 230-μm-diameter microrod, we demonstrate soliton generation at 780 μW threshold power. The passive enhancement of the soliton access range paves the way for robust and low-threshold microcomb systems and has the potential to be a practical tool for soliton microcomb generation.

Open-Ended Coaxial Dielectric Probe Effective Penetration Depth Determination

Abstract: We have performed a series of experiments, which demonstrate the effect of open-ended coaxial diameter on the depth of penetration. We used a two-layer configuration of a liquid and movable cylindrical piece of either Teflon or acrylic. The technique accurately demonstrates the depth in a sample for which a given probe diameter provides a reasonable measure of the bulk dielectric properties for a heterogeneous volume. In addition, we have developed a technique for determining the effective depth for a given probe diameter size. Using a set of simulations mimicking four 50- $\Omega $ coaxial cable diameters, we demonstrate that the penetration depth in both water and saline has a clear dependence on the probe diameter, but is remarkably uniform over frequency and with respect to the intervening liquid permittivity. Two different 50- $ \Omega $ commercial probes were similarly tested and confirm these observations. This result has significant implications to a range of dielectric measurements, most notably in the area of tissue property studies.

The optical and electron resonance spectra of SO3

Abstract: The ionic radical SO3 - has been identified in γ-irradiated single crystals of sodium dithionate, sulphamic acid, potassium sulphamate, potassium amine disulphonate and potassium methane disulphonate. The electron resonance spectrum is a single line with an isotropic g factor of 2·004. The principal values of the 33S hyperfine coupling tensor are 428, 314 and 316 Mc/s, from which the percentages of 3s and 3p character of the unpaired electron orbital are obtained, enabling a value of 111° for the O-S-O angle to be deduced. Ultra-violet transitions at 2700 a and 2400 a were found for SO3 -. A value of 104 for the extinction coefficient of the 2400 a band was measured. A comparison of spin populations between the isoelectronic species PO3 =, SO3 - and ClO3 is included.

Size dependence of core and valence binding energies in Pd nanoparticles: Interplay of quantum confinement and coordination reduction

Abstract: An analysis is given of the electronic structure of Pd nanoparticles synthesized by inert gas evaporation technique. A study of the effect of size on various core and valence electrons in Pd nanoparticles reveals a varied dependence of binding energy of electrons in different electronic levels. The shift in the Pd x-ray photoelectron spectroscopy 4d valence band centroid is more than the core level shift. The results of the present study provide a direct evidence of interplay of quantum confinement (a size effect) and coordination reduction (a surface effect).