We determine the absolute phase and amplitude of four dominant components of the susceptibility tensor that governs second-harmonic generation (SHG) from $\mathrm{Si}\left(001\right)$ interfaces, including both bulk and surface contributions. Measurements of crystal-orientation-dependent SHG intensity with linearly polarized excitation alone yield two possible values of the relative phase of bulk and surface SHG, corresponding to dual solutions of quadratic equations. We resolve this ambiguity by measuring the handedness difference of SHG with circularly polarized excitation. Then, using frequency-domain interferometric SHG calibrated to a quartz crystal, we obtain the following absolute phases and amplitudes at the fundamental wavelength $745\mathrm{nm}$ for a $\mathrm{Si}\left(001\right)$/dielectric sample: surface dipole susceptibility components $d_{15}=1.2\times {10}^{-18}\exp \left(i0.46\pi \right){\mathrm{m}}^2∕\mathrm{V}$, $d_{31}+\gamma ∕ϵ=4.3\times {10}^{-20}\exp (-i0.53\pi ){\mathrm{m}}^2∕\mathrm{V}$, and $d_{33}-d_{31}\approx d_{33}=5.8\times {10}^{-18}\exp \left(i0.38\pi \right){\mathrm{m}}^2∕\mathrm{V}$; anisotropic bulk quadrupole susceptibility component $\zeta =4.4\times {10}^{-18}\exp (-i0.62\pi ){\mathrm{m}}^2∕\mathrm{V}$. Here, $\gamma$ is an undetermined isotropic bulk quadrupole susceptibility component and $ϵ$ the dielectric function of Si. If $\gamma ∕ϵ$ is negligible, all contributions are determined. The estimated error in each amplitude and phase is a single unit of the last significant digit.

Terahertz imaging is unlocking unique capabilities for the analysis of cultural heritage artifacts. This paper uses terahertz time-domain imaging for the study of a gilded wooden artifact, providing a means to perform stratigraphic analysis, yielding information about the composition of the artifact, presence of certain materials identifiable through their THz spectral fingerprint, as well as alterations that have been performed over time. Due to the limited information that is available for many historic artifacts, the data that can be obtained through the presented technique can guide proper stewardship of the artifact, informing its long-term preservation.

Capsaicin is a chemical compound found in pungent chili peppers (Capsicum spp.). In biotechnology, capsaicin has been proposed as a pathogen control; however, its low solubility in water and high instability limits its uses. The aim of this work was to study the effect of high concentrations of capsaicin on the synthesis of nanoparticles and to evaluate their inhibitory effect on the growth of Rhodotorula mucilaginosa yeast. Bovine serum albumin (BSA)-capsaicin nanoparticles were formulated at 0, 16.2, 32.5, 48.7 and 65.0 µg of capsaicin per mg of BSA. Nanoparticle properties were evaluated and they were added to cultures of R. mucilaginosa to quantify their effect on cell viability. We found that increased capsaicin levels caused several changes to the physicochemical parameters, probably due to changes in the hydrophobicity sites of the albumin during the nanostructuration. The administration of nanoparticles to cultures of R. mucilaginosa produced a maximal viability with nanoparticles at 16.2 µg/mg; on the contrary, nanoparticles at 65.0 µg/mg caused maximal cell death. R. mucilaginosa cells displayed a hormesis effect in response to the nanoparticle dose concentration. The nanoparticles showed different responses during the uptake process, probably as a consequence of the nanostructural properties of capsaicin in the BSA molecules.

Light emission properties of a fluorene cross-conjugated polymer (PF–1) based on the monomer 4,7-bis[2-(9,9-dimethyl)fluorenyl] benzo[1,2,5]thiadiazole are reported. This polymer exhibits solubility at high concentrations, good processability into thin solid films of good quality and a broad emission band with a fluorescence quantum yield of approximately 1. Based on these features, in this paper we implemented the use of PF–1 as an active layer in polymer light-emitting diodes (PLEDs) and as a laser gain medium in solution. To get insight on the conducting properties of PF–1, two different electron injectors, poly [(9,9-bis(3′-(N,N-dimethylamino) propyl)-2,7-fluorene)-alt-2,7-(9,9–dioctylfluorene)] (PFN) and lithium fluoride (LiF), were used in a simple PLED architecture. PLEDs with the PFN film were found to exhibit better performance with a maximum luminous efficiency of 40 cd/A, a turn-on voltage (V_on) of approximately 4.5 V and a luminance maximum of 878 cd/m² at 5.5 V, with a current density of 20 A/m². For the lasing properties of PF–1, we found a lasing threshold of around 75 μJ and a tunability of 20 nm. These values are comparable with those of rhodamine 6G, a well-known laser dye.

Spectra of the degenerate two-photon absorption coefficient $\beta (\omega )$ , anisotropy parameter $\sigma (\omega )$ , and dichroism parameter $\delta (\omega )=[\sigma (\omega )+2\eta (\omega )]/2$ of crystalline 110-cut GaAs, GaP, and Si, at 300 K were measured using femtosecond pump–probe modulation spectroscopy over an excitation range in the vicinity of each material’s half-bandgap $E_g/2$ (overall $0.62<\hslash \omega <1.91$ eV or $2000>\lambda >650$ nm). Together, these three parameters completely characterize the three independent components of the imaginary part of the degenerate third-order nonlinear optical susceptibility tensor $\mathrm{Im}\{{\chi }_{abcd}^{(3)}(\omega )\}$ . In direct-gap GaAs, these components peak at $\hslash \omega \approx 0.78E_g$ , which is close to the peak at $\hslash \omega =0.71E_g$ predicted by the Jones–Reiss phenomenological model. The dispersion is comparable with ab initio calculations. In indirect-gap GaP and Si, these components tend to increase with $\hslash \omega$ over our tuning range. In Si, the dispersion differs significantly from predictions of semi-empirical models, and ab initio calculations do not account for transitions below the two-photon direct bandgap, motivating further investigation. Kleinman symmetry was observed to be broken in all three materials. We also note anomalies observed and their possible origins, emphasizing the advantages of a 2-beam experiment in identifying the contribution of various nonlinear effects.