In this work, a new strategy was proposed for active control of mm-thick liquid crystals (LC) cell to realize the polarization manipulation in terahertz (THz) regime, which through the electric field control and static magnetic field pre-anchoring. The LC cell was fabricated by a nematic 5CB LC and two silica substrates that were coated with the graphite layer as the transparent electrode. Under the pre-anchoring of the static magnetic field, the optical axis of LC can be precisely controlled by the variable electric field. By using a THz-TDS with a wire grid polarizer, the output THz polarization from the LC cell can be deduced from the amplitude and phase shift of ±45° components. Here, we systematically analyzed three different outfield configurations. Only if the ±45° components that output from the polarizer have phase shifts, can the polarization state conversion be realized. The results show that the linear to circular or the cross-polarization conversion were realized under the specific electric field. This work provides a new approach for the thick-LC layer anchoring and orientation control, and also the tunable polarization manipulation of THz LC devices.
Shaohua Liu,Li-Li Zhang,Ke Li,Xiaotian Ma,Xifa Long,Yun Yang
The capability of zero-order waveplates to manipulate the polarization of fundamental-frequency light has garnered significant attention in light of the rapid advancements in laser technology. In particular, zero-order waveplate materials in the deep-ultraviolet range (DUV; λ < 200 nm) are in urgent and short supply. In this study, three aluminum fluorides, AlF3 (P6/mmm), BaAlF5 (I4/m), and Li2KAl2F9 (C2/m), have been successfully designed and synthesized through a strategy that combines perfluorinated [AlF6] group with alkali and alkaline-earth metals. The results of experimental and theoretical calculations indicate that all three new aluminum fluorides have a short cutoff edge (λ < 200 nm) and small birefringence (0.0006 ~ 0.0056 @1064 nm). Theoretical calculations indicate that AlF3 (P6/mmm) has the shortest wavelength of 125 nm, which is comparable to the shortest wavelength of the commercially available MgF2. However, its birefringence of 0.0006 @1064 nm is about 20 times lower than that of the MgF2 (0.012 @546 nm), making it highly advantageous for fabricating deep-ultraviolet zero-order waveplate materials. Further microscopic analysis reveals that the [AlF6] group exhibits a substantial band gap of 9.17 eV and small polarizability anisotropy, indicating that the aluminum fluorides are potential candidates for designing suitable compounds for DUV zero-order waveplate materials.
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