A potential application of dual-mode metafilm for enhanced second harmonic generation in refractive index and angle...

Second harmonic generation (SHG) is a nonlinear phenomenon in which incident electromagnetic wave signals are converted into harmonic signals with doubled frequency. In this paper, a method has been proposed to enhance the SHG using metafilm, enabling the measurement of refractive index and incident angle. Metafilm refers to artificially constructed layered structures. Nonlinear frequency conversion within metafilms yields dual-mode harmonics, which can effectively distinguish the refractive index of sample layers. When the sample layer is composed of biomedical materials, the fundamental mode can distinguish enamel from dentin, while the second harmonic mode can effectively distinguish normal cells from cancerous cells. Finally, we consider the influences of thickness errors and material losses on detection performance and find that the system has good stability. This non-contact measurement method with extended range shows broad application prospects in the fields of biological tissue composition analysis and medical diagnosis.