J.-J. Zondy, D. Touahri, and O. Acef 
  Absolute value of the d 36 nonlinear coefficient of AgGaS 2 : prospect for a low-threshold doubly resonant oscillator-based 3:1 frequency divider  
  Vol. 14, No. 10 / October 1997 / J. Opt. Soc. Am. B 2481