Constraint-free wavelength conversion supported by giant optical refraction in a 3D perovskite supercrystal

Nonlinear response in a material increases with its index of refraction as n4. Commonly, n ~ 1 so that diffraction, dispersion, and chromatic walk-off limit nonlinear scattering. Ferroelectric crystals with a periodic 3D polarization structure overcome some of these constraints through versatile Cherenkov and quasi-phase-matching mechanisms. Three-dimensional self-structuring can also lead to a giant optical refraction. Here, we perform second-harmonic-generation experiments in KTN:Li in conditions of giant broadband refraction. Enhanced response causes wavelength conversion to occur in the form of bulk Cherenkov radiation without diffraction and chromatic walk-off, even in the presence of strong wave-vector mismatch and highly focused beams. The process occurs with a wide spectral acceptance of more than 100 nm in the near infrared spectrum, an ultra-wide angular acceptance of up to ±40∘, with no polarization selectivity, and can be tuned to allow bulk supercontinuum generation. Results pave the way to highly efficient and adaptable nonlinear optical devices with the promise of single-photon-to-single-photon nonlinear optics.

Theoretical analysis of terahertz generation in periodically inverted nonlinear crystals based on cascaded difference frequency generation process

The characteristics of terahertz (THz) generation based on cascaded difference frequency generation (DFG) process in periodically inverted gallium arsenide ( GaAs ) and gallium phosphide ( GaP ) is calculated from coupled wave equations, in which the output enhancement factors are 5.4 and 3.9 in the two crystals, respectively, compared with DFG without cascading. The optimal interaction length, influence of crystal absorption, wave vector mismatch and pump intensity are analyzed. A short discussion on wavelength tuning is also given. The calculated optimal operating parameters and conclusions can provide good directions for the experimental design.

INVESTIGATION ON THE PUMP ACCEPTANCE BANDWIDTH FOR COLLINEAR QUASI-PHASE-MATCHING OPTICAL PARAMETRIC AMPLIFICATION

We investigated the issue of parametric bandwidth for a collinear quasi-phase-matching (QPM) optical parametric amplification (OPA). Mathematical model for evaluating the parametric bandwidth tolerance of the OPA was derived by expanding the wave-vector mismatch in Taylor series and taking the first two terms into consideration for accuracy. Based on the model, the variation of pump acceptance spectral bandwidth with parametric wavelength was discussed. The correlating curve of the pump wavelength and the parametric wavelength was obtained for the largest pump acceptance spectral bandwidth. These results were compared to that obtained by numerically calculating the parametric gain curves of OPA when pumped with different Gauss bandwidths by means of three-wave mixing equations directly, and were found to be in good accordance. The results presented are helpful for specifying the optimal pump wavelength of the parametric amplification and oscillation.