Malta-cross pattern, extinction ratio, contrast ratio and other scope pattern, if any more which one is the best to check the optical quality of electrooptical material and
The best measure is directly measuring the elctro-optic coefficient (EOC). One method is using the Pockel's law that relates the EOC (r33) parameter to the refractive index (RI). So, one could measure the RI of an EO crystal before and after poling and use the difference of the RI to calculate the EOC. Higher the EOC, better the EO crystal.