Project summary: Nonlinear optical (NLO) crystals play a crucial role in converting laser light from one color to another
using nonlinear optical processes, enabling a wide spectrum of applications such as optical communications, sensing, imaging, spectroscopy, aviation, and security. While they are mainly operational in the visible region, there are only a few crystals that work in the infrared. Discovering superior NLO crystals is challenging due to the need to balance various factors, including high nonlinearity, a large bandgap (which increases laser damage threshold), a broad transparency window, and phase-matchability. Unfortunately, materials with larger bandgaps tend to have lower nonlinear susceptibilities, making it a difficult task to enhance both nonlinearity and laser damage resistance simultaneously. Recently, Gopalan and Mao’s groups at Penn State discovered a NLO crystal MgSiP2, which can overcome all these problems. Their work demonstrated that this material has large non-resonant phase-matchable NLO coefficients which surpass the commercial NLO crystals AgGa(S/Se)2 and ZnGeP2. Furthermore, it also possesses a giant laser damage threshold value, about more than six times greater than the benchmark NLO crystal ZnGeP2. These distinct nonlinear optical properties of MgSiP2 make it a highly attractive candidate for optical frequency conversion in the infrared.
Publication: J. He, et al. Advanced Optical Materials 2301060 (2023). Patent application has been filed for this work.
2DCC Role: The high-quality MgSiP2 single crystals used in this study were synthesized using the 2DCC Bulk Growth facilities. The combination the 2DCC’s capacity of bulk crystal growth and the optical characterization by the Gopalan group enables this achievement.
What Has Been Achieved: This work demonstrated that MgSiP2 single crystal has large non-resonant phase-matchable nonlinear optical (NLO) coefficients and high laser damage threshold. Meanwhile, the type-I and type-II phase-matching conditions as well as the corresponding effective SHG coefficients were determined. Its SHG nonlinear coefficient of |d36| = 89 ± 5pm/V surpasses the commercial NLO crystals AgGa(S/Se)2 and ZnGeP2. Furthermore, this material possesses a giant laser damage threshold value, about more than six times greater than the benchmark crystal ZnGeP2.
Importance of Achievement: The outstanding nonlinear optical properties of MgSiP2 makes it a highly attractive candidate for optical frequency conversion in the infrared.
Unique Features of the MIP That Enabled Project: Although MgSiP2’s single crystal growth using the Sn/Sb flux growth method was previously reported, the grown crystals were small and contaminated by the Sn/Sb flux on its surface, which prevents its optical property characterization. The 2DCC bulk growth team successfully synthesized clean MgSiP2 crystals with dimension of a few mm using the Sb-flux method combined with centrifuging for the first time. This makes optical measurements on this material possible.
Publication: Jingyang He, Yingdong Guan, Victor Trinquet, Guillaume Brunin, Ke Wang, Robert Robinson, Rui Zu, Suguru Yoshida, Seng Huat Lee, Yu Wang, Yanglin Zhu, Gian-Marco Rignanese, Zhiqiang Mao, Venkatraman Gopalan, MgSiP2: An Infrared Nonlinear Optical Crystal with a Large Non-Resonant Phase-Matchable Second Harmonic Coefficient and High Laser Damage Threshold, Advanced Optical Materials 2301060 (2023). https://doi.org/10.1002/adom.202301060
Acknowledgments: J.H. and V.G. acknowledge primary support from NSF DMR-2210933 for work since September 2022. J.H. and V.G. also acknowledge partial support from the Air Force Office of Scientific Research Grant number FA9550-19-1-0243 for work prior to September 2022. Support for crystal growth and characterization was provided by the National Science Foundation through the Penn State 2D Crystal Consortium-Materials Innovation Platform (2DCC-MIP) under NSF cooperative agreement DMR-2039351. Partial crystal growth efforts made by a graduate student (Y.G.) are also supported by the U.S. Department of Energy under grants DE-SC0019068. Computational resources have been provided by the supercomputing facilities of the Université catholique de Louvain (CISM/UCL) and the Consortium des Équipements de Calcul Intensif en Fédération Wallonie Brux-elles (CÉCI) funded by the Fond de la Recherche Scientifique de Belgique (F.R.S.-FNRS) under convention 2.5020.11 and by the Walloon Region. The authors acknowledge U.S. Department of Energy, Office of Science, Basic Energy Sciences, Award No. DE-SC0020145 for supporting the development of Shaarp. The authors thank Peter Schunemann and Kevin Zawilski for the scientific discussions and for offering the ZnGeP2and CdSiP2crystals.