Optimal vector phase-matching conditions in biaxial crystalline materials determined by the extreme surfaces method: the case of orthorhombic crystals.

The optimal geometries of vector phase matching are determined for the cases of second harmonic generation, sum frequency generation, and difference frequency generation in a number of orthorhombic nonlinear optical crystals: KTP, KTA, KB5, K N b O 3, LBO, CBO, and LRB4. The extreme surface method was used to define the wave vector directions of highest possible generation efficiency. As shown, in a significant number of cases vector phase matching ensures higher efficiencies than the scalar one.

Dynamic Kerr and Pockels electro-optics of liquid crystals in nanopores for active photonic metamaterials.

Photonic metamaterials with properties unattainable in base materials are already beginning to revolutionize optical component design. However, their exceptional characteristics are often static, as artificially engineered into the material during the fabrication process. This limits their application for in-operando adjustable optical devices and active optics in general. Here, for a hybrid material consisting of a liquid crystal-infused nanoporous solid, we demonstrate active and dynamic control of its meta-optics by applying alternating electric fields parallel to the long axes of its cylindrical pores. First-harmonic Pockels and second-harmonic Kerr birefringence responses, strongly depending on the excitation frequency and temperature, are observed in a frequency range from 50 Hz to 50 kHz. This peculiar behavior is quantitatively traced by a Landau-De Gennes free energy analysis to an order-disorder orientational transition of the rod-like mesogens and intimately related changes in the molecular mobilities and polar anchoring at the solid walls on the single-pore, meta-atomic scale. Thus, our study provides evidence that liquid crystal-infused nanopores exhibit integrated multi-physical couplings and reversible phase changes that make them particularly promising for the design of photonic metamaterials with thermo-electrically tunable birefringence in the emerging field of space-time metamaterials aiming at full spatio-temporal control of light.

LabVIEW-Based Automated Setup for Interferometric Refractive Index Probing.

In the paper, we explain an automated LabVIEW-controlled setup that enables interferometric measurement of refractive indices in crystalline materials using a laser light source. The setup combines a mechanical system, a microcomputer-controlled gearless drive, a Michelson interferometer, an optical detector, a data acquisition system, and a LabVIEW virtual instrument for an accurate nondestructive determination of the refractive index of given plane-parallel samples. We explain the concept, implementation, and hardware/software peculiarities of the developed system. Test experiments on different crystals yielded results that are in good agreement with available reference data. The range of potential applications of the proposed setup extends from fundamental optical research to biophotonics instrumentation, where efficient delivery of light is of crucial importance and reliable automated probing tools are needed for optical component characterization.

General method of extreme surfaces for geometry optimization of the linear electro-optic effect on an example of LiNbO3:MgO crystals.

A general method for determining the global maximum of the linear electro-optic effect in crystalline materials based on the construction and analysis of extreme surfaces obtained as a result of the optimization procedure is proposed. The electrically induced optical path length changes for ordinary and extraordinary waves as well as the optical path difference for orthogonally polarized waves were used as the objective functions in the optimization. The objective functions were determined for units of the electric field and crystal thickness in the light pass direction. In the example of LiNbO3:MgO, it is shown that the maximal achievable given values of the optical path length change (global maxima) for ordinary and extraordinary waves are 119 pm/V and 277 pm/V, respectively. The global maximum of the optical path difference for orthogonally polarized waves is 269 pm/V (for 632.8 nm wavelength and at room temperature). These global maxima are exceeded by ∼1.5, 1.7, and 2.3 times the respective maximum values on direct cut crystals of LiNbO3:MgO and are ∼5%, 9%, or 11% larger than the global maxima for undoped LiNbO3 crystal. This ensures a possibility to increase the energy efficiency by ∼2.9 or 5.3 times in the case of using of LiNbO3:MgO crystals with optimal cuts as sensitive elements of electro-optic devices.