Measurement of the nonlinear refractive index in ZnSe crystal by modified methodof Z-scan in the terahertz spectral range

We report the measurement of the intensity-dependent refractive index m of ZnSe crystal at THz frequencies. We used a modified Z-scan method with an intense THz beam of maximum intensity 0.8×10⁹W/cm². We measured an extremely large m value of the order of 10^-11 cm²/W, which is significantly larger than the m value of ZnSe in the near infrared.