Deterministic Relation between Optical Polarization and Lattice Symmetry Revealed in Ion-Doped Single Microcrystals.

Rare-earth ion doped crystals are of great significance for microsensing and quantum information, while the ions in the crystals emit light with spontaneous partial polarization, which is, though believed to be originated from the crystal lattice structure, still lacking a deterministic explanation that can be tested with quantitative accuracy. We report experimental evidence showing the profound physical relation between the polarization degree of light emitted by the doped ion and the lattice symmetry by demonstrating, with high precision, that the lattice constant ratio c/a directly quantifies the macroscopic effective polar angle of the electric and magnetic dipoles, which essentially determines the linear polarization degree of the emission. Based on this result, we further propose a pure optical technology to identify the three-dimensional orientation of a rod-shaped single microcrystal using the polarization-resolved microspectroscopy. Our results, demonstrating the physical origin of light polarization in ion-doped crystals, allow work toward on-demand polarization control with crystallography and provide a versatile platform for polarization-based microscale sensing in dynamical systems.

Temporal and spectral hybrid bound state in continuum and its reliance on the correlation.

We study the hybrid bound states in continuum (BIC) in time and spectral domain obtained from Eu3+/Pr3+ doped YPO4 and BiPO4 crystals. The spectral and time domain BIC originates from the interference between broadband fluorescence (FL) and narrowband super-florescence (SP-FWM) due to the dressing effect and crystal phase transition. We present a relationship between BIC and correlation and investigate two-mode and three-mode noise correlation/squeezing when the wavelength of the applied field is fixed at the bright state and dark state. In contrast to the BIC peak, we observe a switch and anti-bunching-like phenomenon at the BIC dip. We realize at the BIC peak point that correlation exhibits multi-oscillations and long coherence time in Pr3+:YPO4 in contrast with Eu3+:YPO4. Further, our two-mode intensity noise correlation experimental results suggest a controllable bandstop filter with an 80% bandwidth contrast and a dual-channel amplifier with an 89% amplitude contrast.