Electrothermally tunable cholesteric liquid crystal laser achieving 130 nm range with high circular polarization purity (|g| ≥ 1.4)

Abstract

Circularly polarized light lasers are attracting growing attention for quantum optics, spin-optoelectronics, and next-generation display technologies. However, despite many demonstrations of cholesteric liquid crystal (CLC) lasers, two challenges remain: achieving broadband and continuous wavelength tunability and quantitatively determining the dissymmetry factor (g) under realistic conditions. Here, we present an actively tunable cholesteric laser based on supersaturated CLC (SCLC) cells driven by electrothermal control. In parallel SCLC cells, lasing wavelengths can be tuned about 130 nm (553-682 nm), but the spectral shift occurs discontinuously due to boundary constraints. In contrast, wedge-shaped SCLC cells form an electrothermally induced pitch gradient that enables rapid and continuous spectral tuning across similar to 100-126 nm. To rigorously quantify the polarization state, we employed the Stokes-Mueller analysis with three circular analyzers, correcting for non-ideal transmission and leakage. Across the full 130-nm tuning range, the generated laser maintained a consistently high degree of circular polarization purity, with the dissymmetry factor g quantified as 1.633 at 600-620 nm and 1.40 at 630-650 nm ranges. These results verify that the circular polarization performance of the SCLC-based tunable laser remains robust throughout the entire visible lasing spectrum. Differential scanning calorimetry further revealed second-order SmA-CLC-isotropic phase transitions, clarifying dynamic asymmetries between heating and cooling and guiding optimal voltage-sweep strategies. Together, these findings demonstrate a reliable pathway toward broadband, color-tunable, and spin-selective CLC lasers, bridging photonic bandgap engineering with practical applications in nanophotonics, spin-optoelectronics, and advanced display technologies.