โ Scribed by S.K. Das; S. Mukhopadhyay; N. Sinha; A. Saha; P.K. Datta; S.M. Saltiel; L.C. Andreani
No coin nor oath required. For personal study only.
We report the first, according to our knowledge, experiment for direct third harmonic (TH) generation in periodically poled quadratic crystals. TH radiation of a diode array pumped and acousto-optically Q-switched Nd:YVO 4 laser is generated in a 25 mm long periodically poled lithium niobate (PPLN) crystal of period 7.0 lm. A theoretical model is developed that explains the experimental results. It predicts that the efficient phase-matched direct TH generation in periodically poled structures with duty factor 0.5 requires even order quasi-phase matching. In contrast to the similar experiments in bulk birefringence crystals, where direct phase matched TH signal is the sum of the contribution of both intrinsic and cascaded cubic nonlinearities, in periodically poled quadratic crystals only cascaded cubic nonlinearity contributes to the direct phase-matched TH signal.
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