Pushing periodic-disorder-induced phase matching into the deep-ultraviolet spectral region: theory and demonstration

摘要

Schematic graph of the birefringent phase-matching condition in a negative uniaxial crystal. is the phase-matching angle. Along this direction, ( ) =  (2 ) and Δ  = 0. Schematic graph of the quasi-phase-matching condition in a ferroelectric crystal. The up and down arrows represent positive and negative polarizations, respectively. The period length Λ is double the coherence length (Λ =   +  ). Schematic graph of the additional phase-matching condition in arbitrary nonlinear optical crystals. The white and gray regions represent the ordered crystal and the disordered amorphous state, respectively. The period length Λ equals the sum of the ordered width and disordered width (Λ =   +  ). Notably, and may be equivalent to or an integer multiple of . /0 and / represent the second-order nonlinear coefficient and refractive index of the ordered and disordered regions, respectively. The amplitude of the generated second-harmonic (SH) field under phase-mismatching and different phase-matching conditions. Equal interaction lengths of the nonlinear media and the same efficient nonlinear coefficients are assumed. The period length Λ for quasi-phase-matching and additional phase matching is 2 (Λ =   +  )