Reconstruction and modeling of the complex refractive index of nonlinear glasses from terahertz to optical frequencies.

The linear complex refractive index of a set of borosilicate and tellurite as well as heavy metal oxide silicate, germanate and fluoride glasses has been determined using the Kramers-Kronig analysis on combined data from terahertz time domain (THz-TD) and Fourier transform infrared (FTIR) spectrometers in the ultrabroadband range of 0.15 THz to 200 THz. Debye, Lorentz and shape language modeling (SLM) approaches are applied. Far-infrared absorption power-law model parameters are determined via searching for the largest frequency range that minimizes the root mean squared error (RMSE) of a linear least squares fit for the set of glasses and other glass literature data. Relationships between the absorption parameters, glass properties and compositions are explored.

Rigorous broadband study of the intrinsic ferromagnetic linewidth of monocrystalline garnet spheres.

This work demonstrates the first application of direct broadband (1 GHz-30 GHz) quality (Q) factor measurements of the uniform precession mode in magnetised garnet spheres for the accurate determination of the room-temperature intrinsic ferromagnetic linewidth (ΔH). The spheres were enclosed in a subwavelength cavity, so that the measured Q-factor depended mainly on their magnetic losses and the conduction losses of the cavity walls. The contribution of the latter is assessed by means of the recently proposed magnetic plasmon resonance model and has been found to be negligible. A total of 10 samples made from commercially available pure yttrium iron garnet (YIG) and gallium-substituted YIG have been measured, differing in diameter and/or saturation magnetisation Ms. The dependence of the intrinsic ΔH on the internal magnetic field is found to have near-perfect linear dependence, which cannot be said about the typically studied extrinsic ΔH even at high frequencies. It is found that the difference between the two linewidths, which becomes significant at low frequencies, can be attributed to a geometric effect. Due to its fundamental nature, this work is applicable not only to magnetic material characterization, but also to the study of the origins of losses in magnetic materials.

Ferromagnetic Resonance Revised - Electrodynamic Approach.

Resonance in a ferromagnetic sphere, known in the body of literature as the mode of uniform precession, has recently been proven to be magnetic plasmon resonance (MPR). This finding has prompted research which is presented in this paper on the relation between the Q-factor at the MPR and the ferromagnetic resonance (FMR) linewidth ΔH, which is a parameter of magnetized gyromagnetic materials. It is proven in this paper that ΔH can be unequivocally determined from the Q-factor measured at the MPR, if all losses in the resonance system are properly accounted for. It can be undertaken through a rigorous but simple electrodynamic study involving the transcendental equation, as proposed in this paper. The present study also reveals that electric losses have a substantially reduced impact on ΔH due to the large magnetic to electric energy storage ratio at the MPR. Theoretical results are supported by measurements of the Q-factors on a monocrystalline yttrium iron garnet (YIG) sphere.