Three-photon and four-photon absorption in lithium niobate measured by the Z-scan technique

Benabdelghani, Imene and Tóth, György and Krizsán, Gergő and Bazsó, Gábor and Szaller, Zsuzsanna and Mbithi, Nelson and Rácz, Péter and Dombi, Péter and Polónyi, Gyula and Hebling, János (2024) Three-photon and four-photon absorption in lithium niobate measured by the Z-scan technique. OPTICS LETTERS, 32 (5). pp. 7030-7043. ISSN 0146-9592

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Abstract

In conclusion, our study employed open-aperture Z-scan measurements to explore the determination of three-photon (3 PA) and four-photon absorption (4 PA) coefficients in congruent and stoichiometric lithium niobate (cLN, sLN) with varying concentrations of Mg doping, utilizing laser pulses at 800 nm and 1030 nm wavelengths. Remarkably, we observed that the 3 PA and 4 PA coefficients exhibited distinctive variations at different Mg doping concentration with different intensities. Both cLN and sLN displayed minima in their absorption coefficients at a specific Mg doping concentration, corresponding to the point at which photo-refraction was effectively suppressed. This finding indicating the role of the interplay of second harmonic and the defect center related polarons, shedding light on the underlying mechanisms governing these nonlinear optical phenomena. Furthermore, our investigation revealed a difference in the nonlinear absorption behavior between 3 PA at 800 nm and 4 PA at 1030 nm, with the latter exhibiting greater absorption under similar intensity levels, the analysis of 3 PA and 4 PA coefficients in these lithium niobate crystals holds significant promise for selecting the most suitable crystal type for efficient terahertz (THz) generation and other nonlinear optical processes that demand high pump intensities.

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