The second harmonic generation (SHG) tuning curves with temperature and angle of incidence were measured in periodically poled KTiOPO4 for narrow fundamental beams at intensities typical of quadratic soliton generation. Mutual self-focusing of the fundamental and harmonic, cascading, and walk-off for light incidence away from the poling axis drastically distorted the SHG response curves, in good agreement with theory.
Katz, M., Eger, D., Kim, H., Jankovic, L., Stegeman, G., Carrasco, S., Torner, L. Second harmonic generation tuning curves in quasiphase-matched potassium titanyl phosphate with narrow, high-intensity beams. "Journal of applied physics", Juny 2003, vol. 93, núm. 11, p. 8852-8861.