High-sensitivity measurement of surface optical nonlinearities

A novel single-shot method for the investigation of surface nonlinearity in materials with limited transparency is demonstrated. When a circular disk that blocks the beam is placed in the beam path before the detector in the conventional reflection 4F coherent imaging system, the surface nonlinear optical response of the sample can be determined by measuring the normalized reflectance under different conditions. The theoretical principle of the method is presented in detail and the influences of incidence-angle variation on the measurement sensitivity are analyzed using numerical simulation. This approach allows for sensitivity enhancement, one-laser-shot detection, determination of the nonlinear absorption coefficient and nonlinear refractive index simultaneously. The results show that the measurement sensitivity of this novel technique is two orders of magnitude larger than that of the original reflection Z-scan technique under the same condition.