Influence of gadolinium doping on low- and high-order nonlinear optical properties and transient absorption dynamics of ZnO nanomaterials

Doping of materials by suitable additives can dramatically modify the physical characteristics of the complex systems. In this paper, we investigate the role of gadolinium concentration on the linear, nonlinear optical properties and transient absorption dynamics of ZnO and Al-doped ZnO. The characteristics of the mentioned materials with different dopant concentrations are evaluated using absorption spectroscopy, Z-scan and pump-probe technique with femtosecond laser pulses at 800 and 400 nm wavelengths. The nonlinear absorption is increased in Al-doped ZnO compared to pure ZnO at 800 nm wavelength. Gadolinium dopant demonstrated a significant reduction in nonlinear refractive index and absorption of Al-doped ZnO but could not influence pure ZnO. The transient absorption dynamics of ZnO and Al-doped ZnO illustrated the decrease of response time with dopant concentration. We also generated high-order harmonics using nanosecond heating pulses to generate laser plasmas and femtosecond driving pulses propagating through the plasmas. Laser plasma was generated from an ablated Gd-doped ZnO and the high-order harmonics were studied by varying the delay between heating and driving pulses.