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We develop a theory describing two-beam energy exchange in a cholesteric liquid crystal (CLC) stabilized in the planar state by a helicoidal polymer network. The CLC layer is placed between photorefractive and non-photorefractive substrates and illuminated by two intersecting coherent light beams. An interference pattern created by the incident beams induces a spatially periodic space-charge electric field in the photorefractive substrate. The field penetrates into the adjacent CLC layer and interacts with the charges trapped on the polymer fibrils forcing the fibrils to move along the helicoidal axis. At new positions, the fibrils reorient the CLC director and, therefore, induce a director grating. The light beams propagating across the cell couple within the grating. We calculate the energy exchange between the coupled beams and the gain of the weak light beam. We analyze the dependence of the gain coefficient on the parameters of the polymer network and the CLC and show that it can reach values greater than those obtained in typical solid photorefractive crystals. [ABSTRACT FROM AUTHOR]

We report measurements of optically detected ferromagnetic resonance (ODFMR) in thin films using nitrogen-vacancy (NV) centers in diamond, whose fluorescence intensity changes in response to the ferromagnetic resonance (FMR) excitation of a proximal ferromagnet. Here, we extend the study of the off-resonant and broadband detection of FMR, first observed in the magnetic insulator YIG to a diverse set of ferromagnetic materials. We measure ODFMR signals from several technologically relevant metallic ferromagnetic materials including Py, Co, Co 2 (Mn 0.6 Fe 0.4 )Ge, and an insulating NiZnAl ferrite. These results show the generality of the spin-relaxation based coupling of the NV spins to the ferromagnetic dynamics that enables this detection. The observable field-frequency range of the ODFMR signal is dependent on material parameters such as saturation magnetization and damping. These results imply that NV-based ODFMR can give insights into nanoscale ferromagnetic dynamics and its damping processes, especially for samples with low magnetization and in the low field-frequency regime, which is important for several technologies. [ABSTRACT FROM AUTHOR]

A structure consisting of the 2d black phosphorus (BP) film and a rugate filter (RF) divided by a liquid crystal (LC) layer is theoretically studied as a system in which Tamm plasmon-polaritons (TPP) can be excited. The spectral distribution of the reflection coefficient of the system in the RF band gap region is calculated for the cases when the band gap is in the regions of 1 and 10 THz. It is shown that, in both cases, the reflection coefficient dip associated with TPP excitation near the 2d BP film appears in the RF band gap region. The spectral position and magnitude of the reflection coefficient dip depend on the harmonic profile parameters of the RF refractive index, concentration and effective mass of the 2d BP charge carriers, and the LC layer thickness and refractive index. It was found that the TPP wavelength is a periodic function of the LC layer thickness and its refractive index, and with their increase, two or more TPP can appear at wavelengths within the RF band gap. The possibility of controlling the TPP spectral position using an external electric field is noted. [ABSTRACT FROM AUTHOR]

Uniform growth of pristine two dimensional (2D) materials over large areas at lower temperatures without sacrifice of their unique physical properties is a critical pre-requisite for seamless integration of next-generation van der Waals heterostructures into functional devices. This Letter describes a vapor phase growth technique for precisely controlled synthesis of continuous, uniform molecular layers of MoS2 on silicon dioxide and highly oriented pyrolitic graphite substrates of over several square centimeters at 350°C. Synthesis of few-layer MoS2 in this ultra-high vacuum physical vapor deposition process yields materials with key optical and electronic properties identical to exfoliated layers. The films are composed of nano-scale domains with strong chemical binding between domain boundaries, allowing lift-off from the substrate and electronic transport measurements from contacts with separation on the order of centimeters. [ABSTRACT FROM AUTHOR]