Controlling the water nonlinear refractive index in the THz frequency range via temperature variation

To create self-controlled radiation photonics systems, it is necessary to have complete information about the nonlinear properties of the materials used. In this paper, the vibrational mechanism of the giant low-inertia cubic nonlinearity of water in the terahertz frequency range is experimentally proven. Its dominance which manifests itself when the temperature of the liquid changes is demonstrated. The measured nonlinear refractive index in the THz frequency range for water jet at temperatures from 14$^{\circ}$C to 21$^{\circ}$C demonstrates a correlation with the theoretical approach, varies from 4 to 10$\cdot$10$^{-10}$ cm$^2$/W and is characterized by a inertial time constant of less than 1 ps.