The Composition and intensity-driven sign reversal of the nonlinear optical response of nanoparticle-doped liquid crystal glass

The combination of liquid crystals and nanotechnology has resulted in a variety of tunable multifunctional materials suitable for advanced nanophotonic applications, including miniature lasers, structured light, nonlinear optics, quantum technologies, sensing, imaging, communication, and soft robotics. The development of new nanocomposites made of liquid crystals and various types of nanoparticles is critical for future progress in this rapidly evolving field. Traditionally, conventional molecular liquid crystals are used as anisotropic hosts for nanomaterials to create advanced nonlinear optical materials. Recently, we proposed using glass-forming ionic liquid crystals made of metal alkanoates to produce glass nanocomposites exhibiting long-term stability and strong third-order nonlinear optical response. In this paper, we provide a comparative analysis of the nonlinear optical response of vitrified mesogenic cadmium octanoate containing gold, carbon, or both gold and carbon nanoparticles. Z-scan measurements, conducted using both nanosecond and femtosecond laser pulses, revealed an unusual nonlinear optical response in the studied materials. The measured values of the nonlinear absorption coefficients and nonlinear refractive indices are intensity-dependent. In addition, the excitation of the studied samples by nanosecond laser pulses can lead to the sign reversal of the nonlinear absorption coefficient, whereas the use of femtosecond laser pulses leads to sign reversal in the nonlinear refractive index. This sign reversal of nonlinear optical parameters depends on both light intensity and the composition of the studied nanocomposites. The obtained results can benefit the rapidly growing field of advanced nanophotonics, as they demonstrate different ways to control the effective nonlinear optical response of liquid crystal nanocomposites.