Parametric wave interaction in quadratic crystal with randomized   distribution of ferroelectric domains
  We study the parametric wave interaction in qua- dratic nonlinear media with randomized distribution of the ferroelectric domains. In particular, we discuss properties of second and cascaded third harmonic generation.   We derive analytical formulas describing emission properties of the second and third harmonics in the presence of domain disorder and show that the latter process is governed by the characteristics of the constituent processes, i.e. second harmonic generation and sum frequency mixing. We demonstrate the role of randomness on various second and third harmonic generation regimes such as Raman-Nath and \v{C}erenkov nonlinear diffraction. We show that the randomness-induced incoherence in the wave interaction leads to deterioration of conversion efficiency and angular spreading of harmonic generated in the processes relying on transverse phase matching such as Raman-Nath. On the other hand forward and \v{C}erenkov frequency generation are basically insensitive to the domain randomness. 
Ksawery Kalinowski, Vito Roppo, Tadeusz {\L}ukasiewicz, Marek   \'Swirkowicz, Yan Sheng, Wieslaw Krolikowski
physics.optics