Vera M. Titze | Searcharxiv

arXiv2026

Purely equatorial lasing in spherical liquid crystal polymer microlasers with engineered refractive index gradient

Liquid crystal whispering gallery mode microlasers show high sensitivity to external stimuli and distinct spectral features, rendering them ideally suited for various sensing applications. They also offer intrinsic anisotropic optical properties, which can be used to shape and manipulate light even inside spatially highly symmetric structures. Here, we report the synthesis and detailed optical characterization of a spherical bipolar liquid crystal polymer microlaser that tightly confines the optical path of whispering gallery modes to the equatorial plane. By controlled anchoring of the liquid crystal mesogens followed by polymerization, a fixed refractive index gradient is formed within the spherical microcavity. Consequently, only transverse electric (TE) modes oscillating in the equatorial plane experience the high extraordinary refractive index, allowing to confine lasing into a single plane. Furthermore, we observe that the refractive index gradient causes a characteristic splitting of the TE modes. By combining hyperspectral imaging and analytical modeling, we demonstrate that the observed splitting is caused by lifting of the energy degeneracy of higher order azimuthal laser modes, enabling direct insights into the complex interplay of refractive index gradients and resulting whispering gallery mode confinement. In addition, the unique ability to confine lasing of a spherical microbead into only a single plane makes these microlasers independent of the exact position of the pump beam, which allows consistent localized sensing especially in combination with fast point scanning microscopes or inside highly dynamic biological environments.

physics.optics↗

arXiv2025

Monitoring microplastics in live reef-building corals with microscopic laser particles

Micro- and nanoplastics pose a growing threat to marine organisms, such as reef-building corals. Yet, our understanding of microplastic uptake, interaction with coral tissue, and incorporation into coral skeletons remains limited, mainly due to the invasiveness of existing methods for detecting microplastics. Here, we exploit optical resonances in polymer spheres to transform microplastic particles into microscopic lasers. The bright, distinctive, and stable spectral signatures emitted by the microscopic laser particles function as optical barcodes, allowing extended tracking of microplastics transport through optically opaque coral tissue. Simultaneously, the lasers provide real-time sensing of dynamic changes at the microplastic surface with nanoscale resolution. Using confocal hyperspectral imaging, we establish the technical and analytical framework to capture coral anatomy and combine tracking and surface sensing into an integrated, non-invasive approach. With this, we explore the transport and internalization of individual microplastics in live corals, opening new avenues for understanding their ecological impact.

physics.bio-ph↗