During birefringence measurments, I have got some values which are too low (2.56X 10-2) and some of the single crystals show up to 9.52X10-2. Which of these is good for NLO applications?
However, if NLO crystal has large NLO coefficients but its birefringence is smaller than dispersion, and inversion of domains is impossible then there is no use of large NLO for bulk material.