Sustainable nonlinear optical properties of green Cumin extract: Cuminaldehyde as a natural bio-chromophore for green photonic applications

This study investigates the linear and nonlinear optical (NLO) properties of essential oils extracted from several ecotypes of green cumin ( Cuminum cyminum L.) differing in cuminaldehyde content. The plants were cultivated under two irrigation regimes: normal irrigation and terminal drought stress. Essential oils were extracted from mature seeds via hydrodistillation, followed by quantification of cuminaldehyde levels. Ultraviolet–visible (UV–Vis) absorption spectra were recorded to evaluate the optical behavior and band gap energies of the samples. Changes in cuminaldehyde concentration as a new bioresource influenced the degree of electron delocalization and molecular perturbation, resulting in measurable shifts in absorption spectra. The NLO properties were characterized using the Z-scan technique (open and closed aperture) with continuous-wave laser excitation at 532 nm. Nonlinear refractive indices (NLR-n 2 ) and nonlinear absorption (NLA) coefficients (β) were determined, revealing significant third-order nonlinearities in the essential oils. The NLA of samples was evaluated relating to the reverse saturation absorption (RSA) mechanism. All samples exhibited a positive NLR index referring to the self-focusing effect. The order of the NLR index value, depending on the different concentration of cuminaldehyde is about 10 −8 (cm 2 /W) and the NLA coefficients of specimens are in the order of 10 −3 (cm/W). Cuminaldehyde's enhanced NLO response arises from a synergy of structural features: aromatic π-conjugation, resonance stabilization, a strong donor–acceptor system, and the potential for intermolecular π–π interactions. These findings demonstrate the potential of green cumin essential oil as a natural, low-cost nonlinear optical material, with possible applications in photonic devices and sustainable optical technologies.