Third order non-linear optical, diffractional, electrical, laser damage threshold, elemental and surface studies of l-methionine potassium hydrogen phthalate (LMKHP) single crystals

In this study, semi-organic non-linear optical (NLO) crystal l -methionine potassium hydrogen phthalate (LMKHP) was prepared via the solvent evaporation approach. Single-crystal XRD result shows that LMKHP is crystallized in the P2 1 ab space group of orthorhombic system with cell parameter a = 6.60 Ǻ, b = 9.87 Ǻ, c = 13.50 Ǻ, volume V = 880Ǻ 3 . Zwitterionic effects of l -methionine were authenticated by the existence of NH 3 + and COO − in the crystal. FT-Raman and FT-IR measurements were employed to reveal different functional groups in this crystal. To identify the surface morphology, the as-grown crystal was subjected to the SEM technique. The chemical composition of the grown crystal was estimated by Energy dispersive X-ray analysis. According to Vickers microhardness indentation, the LMKHP crystal exposed reverse indentation size effect behaviour and belongs to soft material. The study of dielectric constant (ε′′) and loss (ε′′) at high frequencies clearly indicates the high optical quality with low flaw crystals. Linear optical studies indicated that LMKHP crystal exhibits a short cut-off wavelength of 280 nm, and higher transmittance efficiency over a broad optical window of 300–1100 nm and a wide energy gap of 4.75 eV. Emission peaks are observed at 360 nm, 377 nm, 490 nm, and 537 nm and they are caused by transitions in COOH and NH 2 and indicate the luminescence nature of LMKHP. In the comparison to KDP, the LMKHP sample has an SHG efficiency that is 1.59 times higher. A multiple shot laser damage threshold was estimated to be 23.12 GW/cm 2 . Open aperture Z-scan measurements so that LMKPH exhibits sequential two-photon absorption (TPA) with ESA coefficient of 1.33 × 10 –11 m/W when excited with Nd: YAG laser (532 nm, 5 ns). LMKHP exhibits optical limiting behaviour attributed to excited state absorption (ESA) with lower onset optical threshold of 1.45 × 10 13 W/m 2 . Thus, the grown LMKHP crystal exhibits interesting second-order and third-order NLO characteristics, making it suitable for harmonic generation, optical limiting applications, and frequency conversion.