Directional Random Lasing in Liquid Crystal Infiltrated Metasurfaces

Abstract

Random lasers (RL) emit light through multiple scattering in disordered gain media, typically resulting in isotropic emission with limited directionality control. Controlling RL emission direction in compact systems remains a challenge. Here we report directional random lasing achieved by infiltrating dye-doped nematic liquid crystals into a nanostructured silica metasurface. By adjusting pump energy, we induce a transition from uniform angular photoluminescence to a strongly directional emission peak at large angles in the amplified spontaneous emission and RL regimes. This directionality arises from enhanced spatial coherence in the strong scattering regime, enabling coupling of guided random-laser modes to high-angle diffraction through the metasurface grating. Our system demonstrates wide-angle RL beam steering at submicron scale without complex external components. These results provide a straightforward method to control RL emission directionality, advancing tunable coherent light sources and metasurface-based photonic applications.

Figures (5)

• Figure 1: Schematic illustration of random lasing in a LC-infiltrated metasurface. A fused-silica metasurface (area = 0.785 cm$^2$) comprising 140 million nanopillars is infiltrated with dye-doped LC via hemiwicking. Under optical excitation, the random laser emits directionally at large angles relative to the surface normal.
• Figure 2: Infiltrated SiO2 metasurface. (a) Full scale fabricated metasurface with 1 cm diameter. (b), (c) Uninfiltrated metasurface under co-polarization with concentric rings at the center (edge). (e), (f) Metasurface infiltrated with dye doped LC at the center (edge) under co-polarization and (h), (i) cross-polarization. (d) Nanopillars of the metasurface taken with a x100 objective near the center of the metasurface. (g) Infiltration height profile as a function of metasurface radius.
• Figure 3: ASE and RL temporal characteristics and threshold behavior. (a) The random-lasing setup, including the metasurface and spectrometer, was mounted on a rotation stage to measure the angular emission profile. BS: beam splitter, LP: linear polarizer, QWP: quarter wave plate, PCL: planar convex lens, IC: integrating cube. (b) Lasing characteristics of PM567 in LC infiltrated metasurfaces with threshold behavior. (c) Integrated variance at various pump energies calculated over the spectrum and averages over multiple pump shots. (d) Emission spectra versus pump energy.
• Figure 4: Temporal and angular characteristics of random lasing. (a) Pulse-to-pulse variation. (b) ASE, RL, and PL spectra. (c) Spectral variance. (d) Angular emission profiles of RL at different metasurface radii. (e) Comparison of angular emission for RL and PL
• Figure 5: Numerical modeling of metasurface-assisted emission. (a) Target and simulated phase profiles for metsurface operation, with and without LC infiltration. (b) Far-field radiation from y-oriented dipoles (top) and metasurface structure showing FZ patterning (bottom) (inset infiltrated metasurface with FZ zones and empty rings). (c) Angular emission spectra for dipole ensembles with different orientational order parameters (S = 0.9 and 0).