Nonlinear optical measurements using a 4f coherent imaging system with phase objects

We report a one-laser-shot measurement technique using a phase object at the entry of a 4f coherent imaging system to characterize the value of the nonlinear refractive index of materials placed in the Fourier plane of the setup. Experimental and simulated images are presented here in order to validate our approach. We show that the use of a quarter-wavelength dephasing object maximizes the transmission variations in the detected image. We show also that the use of phase objects increases significantly the sensitivity of the measurement compared to top-hat beams (by a factor of 6). Moreover, by adding this type of object at the entry of our imaging system it is possible to determine the sign of the refractive nonlinearity.