Nearly-degenerate twin signals generated by optical parametric oscillator in inverted KTA twin crystals

Summary form only given. Consider an optical parametric oscillator (OPO) in a single (KTiOPO₄) KTP crystal where type-II non-critical phase-matching condition based on birefringence is satisfied. A pair of the signal and idler is generated. It was demonstrated previously that each signal is split into the twin signals whereas each idler is split into the twin idlers in periodically-inverted KTP stack composite. The wavelengths of the twin signals and twin idlers are dictated by the quasi-phase-matching (QPM) condition: Δkl = ±π. The twin signals or twin idlers were used for the efficient THz generation, with the THz wave exhibiting the significantly-reduced quantum noise. Moreover, they can be used to restore the blurred images caused by the phase distortion in the beam path. Furthermore, through periodic inversion of the crystal plates, the spatial walk-off effect for extraordinary waves can be mitigated, resulting in the significant reduction of OPO threshold and significant increase in the OPO conversion efficiency. In this presentation, the generation of eye-safe nearly-degenerate twin signals at the wavelength of about 1.57 11m in an OPO based on twin (KTiOAsO₄) KTA crystals was demonstrated.