Carmine–PVA composites as optical limiters: effect of carmine concentration and the role of laser intensity in optical limiting

Abstract

As demand for optical limiters to protect sensors and eyes from laser harm rises, organic dye molecules are intriguing candidates. A carmine dye–polyvinyl alcohol (PVA) composite is introduced in this study to investigate its structural, morphological, linear, and nonlinear optical properties. This study pioneers a systematic investigation into the optical behavior of carmine, with a particular focus on its optical limiting properties. Carmine was strategically selected due to its robust green light absorption, exceptional photostability, and potential luminescence contributions. By systematically exploring the light-absorption characteristics of carmine–PVA composites across varying dye concentrations, this research fills a significant gap in the existing research. A PVA matrix was infused with carmine at various concentrations to make thin-film composites. Semicrystalline composites and PVA polymer chain–carmine molecule interactions were confirmed by XRD. A 1.7 μm average film thickness was observed using optical profiling, while SEM demonstrated constant film formation and carmine integration into the matrix. As the concentration of carmine grew, linear optical spectroscopy indicated enhanced green absorption and red emission. A Z-scan setup with a 532 nm Nd:YAG pulsed laser in the nanosecond regime revealed reverse saturable absorption (RSA) due to sequential two-photon absorption. Reverse saturable absorption increased as the carmine concentration increased from 0.3 to 1.2 mM. The non-linear absorption coefficient and optical limiting threshold of the carmine–PVA composite were 3.10 × 10⁻¹⁰ m W⁻¹ and 1.58 × 1012 W m⁻², respectively. However, at a higher concentration of 4.8 mM, dye aggregation completely suppressed the nonlinear response, emphasizing the critical importance of maintaining an optimal concentration range to achieve the desired optical performance. The results showed that the nonlinear absorption characteristics of the composites were affected by intensity. A deeper transmittance curve, indicative of improved nonlinear absorption, was observed as the laser intensity was raised. These results establish the carmine–PVA nanocomposite as a promising candidate for nonlinear optical applications, combining robust performance with tunable optical properties.