Archives August 2025

congratulation to Our new paper in Journal of Optic

Temperature Dependent Random Laser Performance of Au@Cu and Cu@Au Core-Shell Nanoparticles in a Rhodamine 6G–PNIPAM Smart Polymer Matrix Medium

Mariam Kadhim Jawad, J. M. Jassim, S. F. Haddawi, S. M. Hamidi

Abstract:
This study aimed to investigate the temperature-dependent performance of random lasers using Rhodamine 6G (R6G) dye embedded in a thermoresponsive PNIPAM polymer matrix with Au, Cu, Au@Cu, and Cu@Au nanoparticles serving as scattering centers. At 25 °C, only fluorescence was observed due to the hydrophilic state of PNIPAM, resulting in high optical absorption and insufficient refractive index contrast for lasing. As temperature increased to 30–45 °C, PNIPAM became hydrophobic, enhancing index contrast and reducing absorption, which facilitated random lasing. Among the nanoparticles, Au showed the highest emission intensity (62618 a.u.) and narrowest FWHM (4.6 nm), followed by Cu@Au (59908 a.u., 5.3 nm), attributed to the strong plasmonic response of the Au shell. Conversely, Au@Cu and Cu exhibited weaker outputs due to higher damping and less effective plasmonic resonance. Temperature-dependent spectral analysis showed that Cu had the most pronounced bandwidth narrowing (7.5 nm to 3.4 nm), while Au@Cu demonstrated the highest intensity modulation (30913 a.u. to 65195 a.u.). A temperature-induced blue shift in peak emission was observed, most prominently in PNIPAM alone (6.2 nm), with smaller shifts in nanocomposite systems due to varied thermal coupling. These results highlight the pivotal role of PNIPAM’s thermal transition in controlling random laser behavior, offering new strategies for designing tunable or thermally stable laser systems.

Long-range hyperbolic polaritons on a non-hyperbolic crystal surface

Lu Liu, Langlang Xiong, Chongwu Wang, Yihua Bai, Weiliang Ma3, Yupeng Wang1, Peining Li, Guogang Li, Qi Jie Wang, Francisco J. Garcia-Vidal, Zhigao Dai & Guangwei Hu

Nature,Springer Nature

https://doi.org/10.1038/s41586-025-09288-1

Abstract:

Hybridized matter–photon excitations in hyperbolic crystals—anisotropic materials characterized by permittivity tensor components with opposite sign—have attracted substantial attention owing to their strong light–matter interactions in the form of hyperbolic polaritons. However, these phenomena have been restricted to hyperbolic crystals, whose optical responses are confined to fixed spectral regions and lack tunability, thereby limiting their broader applicability. Here we demonstrate the emergence of hyperbolic surface phonon polaritons in a non-hyperbolic yttrium vanadate (YVO₄) crystal. Using real-space nanoimaging combined with theoretical analyses, we visualize hyperbolic wavefronts of surface phonon polaritons on YVO₄ crystal surfaces within its non-hyperbolic frequency range, where the permittivity tensor components of the material have the same negative sign. Furthermore, by varying the temperature from room temperature to cryogenic levels, we realize in situ manipulation of polariton dispersions, enabling a topological transition from hyperbolic to canalization and eventually to the elliptic regime. This temperature-controlled dispersion engineering not only provides precise control over polariton topology but also modulates their wavelength and group velocity, showing remarkable sensitivity alongside low-loss, long-range propagation. These findings extend the realm of hyperbolic nano-optics by removing the reliance on hyperbolic crystals, unlocking opportunities for applications in negative refraction, superlensing, polaritonic chemistry ntegrated photonics and beyond.