Second-harmonic generation tensors from high-throughput density-functional perturbation theory

peer reviewedOptical materials play a key role in enabling modern optoelectronic technologies in a wide variety of domains such as the medical or the energy sector. Among them, nonlinear optical crystals are of primary importance to achieve a broader range of electromagnetic waves in the devices. However, numerous and contradicting requirements significantly limit the discovery of new potential candidates, which, in turn, hinders the technological development. In the present work, the static nonlinear susceptibility and dielectric tensor are computed via density-functional perturbation theory for a set of 579 inorganic semiconductors. The computational methodology is discussed and the provided database is described with respect to both its data distribution and its format. Several comparisons with both experimental and ab initio results from literature allow to confirm the reliability of our data. The aim of this work is to provide a relevant dataset to foster the identification of promising nonlinear optical crystals in order to motivate their subsequent experimental investigation

European Extremely Large Telescope Site Characterization II: High angular resolution parameters

This is the second article of a series devoted to European Extremely Large Telescope (E-ELT) site characterization. In this article we present the main properties of the parameters involved in high angular resolution observations from the data collected in the site testing campaign of the E-ELT during the Design Study (DS) phase. Observations were made in 2008 and 2009, in the four sites selected to shelter the future E-ELT (characterized under the ELT-DS contract): Aklim mountain in Morocco, Observatorio del Roque de los Muchachos (ORM) in Spain, Mac\'on range in Argentina, and Cerro Ventarrones in Chile. The same techniques, instruments and acquisition procedures were taken on each site. A Multiple Aperture Scintillation Sensor (MASS) and a Differential Image Motion Monitor (DIMM) were installed at each site. Global statistics of the integrated seeing, the free atmosphere seeing, the boundary layer seeing and the isoplanatic angle were studied for each site, and the results are presented here. In order to estimate other important parameters such as the coherence time of the wavefront and the overall parameter "coherence \'etendue" additional information of vertical profiles of the wind speed was needed. Data were retrieved from the National Oceanic and Atmospheric Administration (NOAA) archive. Ground wind speed was measured by Automatic Weather Stations (AWS). More aspects of the turbulence parameters such as their seasonal trend, their nightly evolution and their temporal stability were also obtained and analyzed.Comment: 46 pages and 17 figures. Accepted to be published in PAS

Computationally-driven discovery of second harmonic generation in EuBa3 (B3O6)3 through inversion symmetry breaking

Nonlinear optical (NLO) crystals with superior properties are significant for advancing laser technologies and applications. Introducing rare earth metals to borates is a promising and effective way to modify the electronic structure of a crystal to improve its optical properties in the visible and ultraviolet range. In this work, we computationally discover inversion symmetry breaking in EuBa3(B3O6)3, which was previously identified as centric, and demonstrate noncentrosymmetry via synthesizing single crystals for the first time by the floating zone method. We determine the correct space group to be P¯6. The material has a large direct bandgap of 5.56 eV and is transparent down to 250 nm. The complete anisotropic linear and nonlinear optical properties were also investigated with a d11 of ∼0.52 pm/V for optical second harmonic generation. Further, it is Type I and Type II phase matchable. This work suggests that rare earth metal borates are an excellent crystal family for exploring future deep ultraviolet (DUV) NLO crystals. It also highlights how first principles computations combined with experiments can be used to identify noncentrosymmetric materials that have been wrongly assigned to be centrosymmetric

MgSiP2: An Infrared Nonlinear Optical Crystal with a Large Non‐Resonant Phase‐Matchable Second Harmonic Coefficient and High Laser Damage Threshold

Superior infrared nonlinear optical (NLO) crystals are in urgent demand in thedevelopment of lasers and optical technologies for communications andcomputing. The critical challenge is to find a crystal with large non-resonantphase-matchable NLO coefficients and high laser damage threshold (LDTs)simultaneously, which however scale inversely. This work reports such amaterial, MgSiP2,that exhibits a large second harmonic generation (SHG)coefficient ofd14≈d36=89±5pmV−1at 1550 nm fundamental wavelength,surpassing the commercial NLO crystals AgGaS2, AgGaSe2, and ZnGeP2.First principles theory reveals the polarizability and geometric arrangement ofthe [SiP4] tetrahedral units as the origin of this large nonlinear response.Remarkably, it also exhibits a high LDT value of 684 GW cm−2, which is sixtimes larger than ZnGeP2and three times larger than CdSiP2. It has a widetransparency window of 0.53–10.35μm, allowing broadband tunability.Further, it is Type I and Type II phase-matchable with large effective SHGcoefficients ofdeff,I≈80.2 pm V−1anddeff,II≈73.4 pm V−1. The outstandingproperties of MgSiP2make it a highly attractive candidate for opticalfrequency conversion in the infrared