Investigation of one of the most fundamental limits to parametric processes: two-photon absorption

Among almost all the work done on parametric processes in the past, two-photon absorption (TPA) has been intentionally avoided by properly choosing the pump wavelength. On the contrary, we have purposely explored how TPA sets the fundamental limit on the optical parametric generation (OPG) and oscillation (OPO) by using periodically poled LiNbO 3 (PPLN) as a testing nonlinear medium. Indeed, we have demonstrated that the TPA dramatically affects the characteristics of these two parametric processes. To our surprise, the OPO is actually not a preferred parametric process anymore compared with the OPG due to the presence of the strong TPA. In addition, the TPA can further be enhanced by self-focusing effect caused by accumulated thermal effect (ATE).