EFFECTS OF PLATE THICKNESS AND STACK DISTRIBUTION OF QUASI-PHASE-MATCHED MATERIALS ON NONLINEAR FREQUENCY GENERATION

Analytical results indicate that tile plate-thickness tolerance of the GaAs prates in a quasi-phase-matched (QPM) stack with respect to the coherence length is not a critical parameter, Rather, proper placement order of the plates of different thicknesses that make up the stack i s essential for generating efficient nonlinear conversion; conversion efficiency approaching that from a stack of plates with plate thicknes s equal exactly to the coherence length can be obtained, In effect, su ch ordered stacking optimizes the relative phase of the nonlinear proc ess as it propagates down the stack and enhances the conversion effici ency, Furthermore, the analysis shea that random-order stacking of pla tes of different thicknesses produces a large variation in conversion efficiency, varying from one random stack to another, This may not be desirable in practice; one would normally prefer to have a process tha t produces QPM stacks with good and predictable performance, A single- pass three-wave coupled nonlinear frequency interaction model,vith tem poral and spatial pulse profiles is used to analyze the behavior of th e nonlinear conversion process in a quasi-phase-matched stack, second- harmonic generation of CO2 laser radiation in GaAs plates is used as a n example.