Cavity-free random Raman dye laser based on Rhodamine B dye and eco-friendly synthesized ZnO nanoparticles

In the paper, a cavity-free random Raman laser is proposed to be produced based on Rhodamine B (RhB) dye containing ZnO nanoparticles synthesized by a green route using walnut-husk extract. The ZnO nanoparticles serve as strong scattering centers, enabling diffuse feedback in a disordered gain medium and supporting multiple Raman-active modes without the need for well-defined resonators. Comprehensive characterization of the ZnO constituents reveals that nanoscale agglomerated spherical particles with sizes predominantly 20–25 nm (average 21.4 ± 4.1 nm), a Zn–O-rich composition with residual carbon from the walnut extract, with an amorphous structure. Optical analysis reveals refractive indices at 532 nm ranging from 2.07 to 2.20, as determined by Moss, Herve, and the wavelength-dependent methods, consistent with robust scattering, and a dielectric function characterized by a strong UV interband absorption signature. Lasing performance is demonstrated by pumping RhB/ZnO dispersions using a Nd: YAG laser at 532 nm. Results indicate the potential of green-synthesized ZnO nanoparticles as scattering centers for the development of eco-friendly random laser systems. The output power of the proposed random Raman laser exhibits multi-mode operation with ultra-narrow linewidths and high quality factors. Multimode random Raman laser operation in the 561–581 nm region is achieved using the proposed cavity-free laser. The proposed laser benefits from a sustainable synthesis route, straightforward solution processing, and potential for scalable, low-cost photonic devices.