Glass-Forming Ionic Liquid Crystal Gold–Carbon Nanocomposites with Ultrafast Optical Nonlinearity Sign Reversal

The development of new types of nanocomposites capable of manipulating light is critical for various modern photonics applications. Recently, we proposed the use of overlooked glass-forming ionic liquid crystals made of cadmium octanoate containing gold, carbon, or both carbon and gold nanoparticles as promising optical and nonlinear optical materials. These were characterized using nanosecond laser pulses at a wavelength of 532 nm. In this paper, femtosecond radiation at different wavelengths (600 nm and 800 nm) is employed to study ultrafast electronic nonlinear optical processes in mesomorphic glass nanocomposites. The observed nonlinear optical response probed at the femtosecond time scale dramatically differs from that at the nanosecond time scale reported previously. The intensity-dependent effective nonlinear absorption coefficient of all studied samples remains positive due to the dominant reverse saturable absorption effect, while the nonlinear refractive index exhibits a sign reversal depending on the intensity and wavelength of laser pulses. The strategy for producing glass-forming ionic liquid crystal gold–carbon nanocomposites with an ultrafast nonlinear optical response is of high interest for modern applications in advanced photonics, and it can also be applied to other types of glass-forming metal alkanoates and nanomaterials.