Integrating sphere port error in diffuse reflectance measurements.

The impact of a finite thickness integrating sphere port on the measurement of diffuse reflectance is addressed in a combined numerical and experimental study. It is shown that for a finite thickness port, additional light losses occur due to scattering between the sphere port wall and the test sample, causing the sample reflectance to be underestimated. Monte Carlo ray tracing is applied to obtain quantitative estimates of the resulting measurement error for the case of a diffusely reflecting sample. The effects of sample reflectance, port geometry, and illumination beam size on the measurement error are explored. Experimental data collected with a pair of integrating sphere reflectometers with different port geometries support the validity of the numerical results. It is argued that finite port thickness may be an important source of measurement error, even for a well-designed integrating sphere port, and a strategy for minimizing this error is discussed.

2022 Optical Interference Coatings Conference: Manufacturing Problem Contest [Invited].

Participants in the 2022 Manufacturing Problem Contest were challenged to fabricate an optical filter with a specified stepped transmittance spanning three orders of magnitude from 400 to 1100 nm. The problem required that contestants be versed in the design, deposition, and measurement of optical filters to achieve good results. Nine samples from five institutions were submitted with total thicknesses between 5.9 and 53.5 µm with between 68 and 1743 layers. The filter spectra were measured by three independent laboratories. The results were presented in June 2022 at the Optical Interference Coatings Conference in Whistler, B.C., Canada.

Modeling fluorescence reemission in the one-dimensional radiative transfer problem using the P3 approximation.

A model of radiative transport in fluorescent, scattering media that accounts for fluorescence reabsorption and reemission effects is discussed. The model is studied in a simplified one-dimensional geometry using the P3 approximation. An example calculation of a model system, sintered polytetrafluoroethylene doped with rhodamine 6G, is used to illustrate the features of the model.

Reflectance matrix approach to absolute photoluminescence measurements with integrating spheres.

Absolute measurements of photoluminescence are commonly performed using an integrating sphere setup, as this allows the collection of all emitted photons independent of the spatial characteristics of the emission. However, such measurements are plagued by multiple reflection effects occurring within the integrating sphere that make the sample illumination and sphere throughput sample dependent. To address this problem, we developed a matrix theory for integrating spheres with photoluminescent surfaces. In conjunction with a bispectral luminescence data set, this model allows for multiple reflection effects to be fully accounted for. The bispectral data is obtained by mounting both the sample and a non-luminescent reference on the sphere and permuting their positions in order to compare direct and diffuse sample illumination conditions. Experimental measurements of a photoluminescent standard confirm the validity of the method.

Charge-Spin Correlation in van der Waals Antiferromagnet NiPS_{3}.

Strong charge-spin coupling is found in a layered transition-metal trichalcogenide NiPS_{3}, a van der Waals antiferromagnet, from studies of the electronic structure using several experimental and theoretical tools: spectroscopic ellipsometry, x-ray absorption, photoemission spectroscopy, and density functional calculations. NiPS_{3} displays an anomalous shift in the optical spectral weight at the magnetic ordering temperature, reflecting strong coupling between the electronic and magnetic structures. X-ray absorption, photoemission, and optical spectra support a self-doped ground state in NiPS_{3}. Our work demonstrates that layered transition-metal trichalcogenide magnets are useful candidates for the study of correlated-electron physics in two-dimensional magnetic materials.

Author Correction: Two-magnon scattering in the 5d all-in-all-out pyrochlore magnet Cd2Os2O7.

A correction to this article has been published and is linked from the HTML version of this article.

Two-magnon scattering in the 5d all-in-all-out pyrochlore magnet Cd2Os2O7.

5d pyrochlore oxides with all-in-all-out magnetic order are prime candidates for realizing strongly correlated, topological phases of matter. Despite significant effort, a full understanding of all-in-all-out magnetism remains elusive as the associated magnetic excitations have proven difficult to access with conventional techniques. Here we report a Raman spectroscopy study of spin dynamics in the all-in-all-out magnetic state of the 5d pyrochlore Cd2Os2O7. Through a comparison between the two-magnon scattering and spin-wave theory, we confirm the large single ion anisotropy in this material and show that the Dzyaloshinskii-Moriya and exchange interactions play a significant role in the spin-wave dispersions. The Raman data also reveal complex spin-charge-lattice coupling and indicate that the metal-insulator transition in Cd2Os2O7 is Lifshitz-type. Our work establishes Raman scattering as a simple and powerful method for exploring the spin dynamics in 5d pyrochlore magnets.Pyrochlore 5d transition metal oxides are expected to have interesting forms of magnetic order but are hard to study with conventional probes. Here the authors show that Raman scattering can be used to measure magnetic excitations in Cd2Os2O7 and that it exhibits complex spin-charge-lattice coupling.

Spin-Orbit Coupling and Interband Transitions in the Optical Conductivity of Sr_{2}RhO_{4}.

The prototypical correlated metal Sr_{2}RhO_{4} was studied using optical and photoemission spectroscopy. At low energies and temperatures, the optical data reveal a complex, multicomponent response that on the surface points to an unconventional metallic state in this material. Via a comparison with photoemission, the anomalous optical response may be attributed to an unexpectedly strong interband transition near 180 meV between spin-orbit coupled bands that are nearly parallel along ΓX. This spin-orbit coupling effect is shown to occur in a number of related metallic ruthenates and explains the previously puzzling optical properties reported for these materials.

Scattering continuum and possible fractionalized excitations in α-RuCl(3).

The combination of electronic correlation and spin-orbit coupling is thought to precipitate a variety of highly unusual electronic phases in solids, including topological and quantum spin liquid states. We report a Raman scattering study that provides evidence for unconventional excitations in α-RuCl_{3}, a spin-orbit coupled Mott insulator on the honeycomb lattice. In particular, our measurements reveal unusual magnetic scattering, typified by a broad continuum. The temperature dependence of this continuum is evident over a large scale compared to the magnetic ordering temperature, suggestive of frustrated magnetic interactions. This is confirmed through an analysis of the phonon linewidths, which show a related anomaly due to spin-phonon coupling. These observations are in line with theoretical expectations for the Heisenberg-Kitaev model and suggest that α-RuCl_{3} may be close to a quantum spin liquid ground state.