High-precision nonlinear refractive index determination using high-repetition-laser and nonlinear ellipse rotation measurements

In order to achieve high-precision determination of the ultrafast nonlinear refractive index of optical materials, we propose using high-repetition-rate lasers (~MHz) and nonlinear-ellipse-rotation (NER) measurements in thick samples. Usually, a MHz repetition rate laser is not recommended for nonlinear material’s characterization since a strong cumulative thermal signal can disturb the ultrafast nonlinear refractive index determination. However, such a laser assures good pulse energy determination in comparison to low (< kHz) repetition lasers. Furthermore, the NER measurement is able to determine simultaneously the samples’ third-order nonlinearities and the pulses’ parameters, including the pulse width, being completely blind to undesired spurious thermal nonlinearity.