Owing to their vital role in creating and controlling polarized light, birefringent materials are used extensively in various advanced optical systems which in turn impact a large, rapidly increasing range of applications in science and technology. Currently, the fairly small birefringence of MgF 2 and the low transmittance of α-BaB 2 O 4 (α-BBO) hinder their efficient application for wavelength below 200 nm. For example, deepultraviolet (DUV) birefringent materials for light polarization are urgently needed for DUV lithography. Here we demonstrate based on computational and experimental results that parallel chains of corner-connected planar sp 2 -hybridized BO 3 groups found in Ca(BO 2 ) 2 effectively produce large birefringence. Ca(BO 2 ) 2 achieves three vital "best" properties including the shortest UV cutoff edge, the largest birefringence, and the highest laser-induced damage threshold (LIDT) compared to all the reported borate birefringent materials. On the basis of a Ca(BO 2 ) 2 single crystal, a DUV Glan polarizer has been realized and is more efficient than one constructed with commercially available MgF 2 .

If a bucket is to hold more water, its shortest plank must be made longer. This guideline also applies to the exploration of ultraviolet (UV) and deep-UV (DUV) nonlinear optical (NLO) materials that are limited by multiple criteria. Phosphates are one kind of promising candidate for new NLO materials. Unfortunately, the small birefringence, as the shortest plank, severely restricts the phase-matching of second harmonic generation (SHG) in the UV/DUV region. In this work, fluorophosphates are rationally proposed as substitutes for phosphates to break down the limitation of birefringence and simultaneously enhance SHG response and retain wide UV transmittance. The (PO3F)2– and (PO2F2)− groups are confirmed as superior material genomes to achieve the discussed combination properties. Accordingly, (NH4)2PO3F was screened out by density functional theory calculation, and single crystals with centimeter size have been grown. It possesses a powder SHG efficiency of 1 × KH2PO4 (KDP) and is phase-matchable with output of SHG wavelength at 266 nm. To the best of our knowledge, it is the first time that fluorophosphates are identified and developed as new and ideal candidates to new UV/DUV NLO materials by combining theories and experiments.

Birefringent materials, the key components in modulating the polarization of light, are of great importance in optical communication and the laser industry. Limited by their transparency range, few birefringent materials can be practically used in the deep ultraviolet (DUV, λ < 200 nm) region. Different from the traditional BO3- or B3O6-based DUV birefringent crystals, we propose a new functional gene, the B2O5 unit, for designing birefringent materials. Excitingly, the synergistic combination of Li4B2O5 and Na4B2O5 generates a new compound, Li2Na2B2O5, with enhanced optical properties. The Li2Na2B2O5 crystal with a size of up to 35 × 15 × 5 mm3 was grown by the top-seeded solution growth (TSSG) method, and its physicochemical properties were systematically characterized. Li2Na2B2O5 features a large amount of birefringence (0.095@532 nm), a short DUV cutoff edge (181 nm) with a high laser-induced damage threshold (LDT, 7.5 GW/cm2 @1064 nm, 10 ns), favorable anisotropic thermal expansion (αa/αb = 5.6), and the lowest crystal growth temperature (<609 °C) among the commercial birefringent crystals. Moreover, the influences of the B2O5 structural configurations on the optical anisotropy were explored. The fascinating experimental results will provide a prominent DUV birefringent crystal and an effective synthesis strategy, which can facilitate the design of DUV birefringent materials.

To design high-performance mid-infrared (mid-IR) nonlinear optical (NLO) materials,w eh ave focused on the combination of aheavy metal lone pair cation, Pb 2+ and mixed oxyhalides.Asystematic investigation in PbO-PbCl 2 -PbBr 2 system led us to discover the first examples of NLO lead mixed oxyhalides,n amely,P b 13 O 6 Cl 4 Br 10 ,P b 13 O 6 Cl 7 Br 7 ,a nd Pb 13 O 6 Cl 9 Br 5 .A ll the reported materials have remarkably comprehensive properties including broad IR transparency (up to 14.0 mm), qualified second harmonic generation (SHG) responses (0.6-0.9 AgGaS 2 ), wide band gaps (3.05-3.21 eV), and ease of crystal growth. Interestingly,acentimeter-sized single crystal (2.9 1.3 0.5 cm 3 )o fP b 13 O 6 Cl 9 Br 5 revealing aw ide transparent range (0.384-14.0 mm) and high laser damage threshold (LDT) (14.6 AgGaS 2 )h as been successfully grown in an open system. The study suggests that all the reported mixed oxyhalides are outstanding candidates for mid-IR NLO materials.

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As important materials in modulating the polarization of light, birefringent crystals have attracted considerable attention and played crucial roles in the field of optical communication and the laser industry. Limited by the transparency range, few birefringent crystals can be used in the deep-ultraviolet (DUV) region, except for α-BaBO (α-BBO). However, the application of α-BBO in the DUV range is restricted by the relatively high cutoff edge and low transmittance rate below 200 nm. In this paper, we design and synthesize a new fluoroborate, NaBOF, by introducing fluorine into borate system. It possesses a short cutoff edge of 169 nm and birefringence larger than 0.080 at 589.3 nm. The NaBOF crystals with sizes up to 3.0 mm × 1.5 mm × 0.2 mm have been grown with good quality by a high-temperature solution method in the open system. First-principles calculations were carried out to understand the optical properties.

Birefringent materials play indispensable roles in modulating the polarization of light and are vital in the laser science and technology. Currently, the design of birefringent materials operating in the deep-ultraviolet region (DUV, λ ≤200 nm) is still a great challenge. In this work, we developed a new DUV birefringent crystal LiBO2 based on [BO2]∞ infinite chains in the Li-B-O system, which simultaneously achieves the shortest UV cutoff edge (164 nm) and the largest birefringence (≥0.168 at 266 nm) among all the reported borate-based DUV birefringent materials. Single crystals of LiBO2 with dimensions up to Ø55 × 34 mm3 were grown by the Czochralski method, providing access to large-sized single crystal with low cost. Moreover, it has a high laser damage threshold and stable physicochemical properties. These outstanding characters unambiguously support that LiBO2 can be an excellent birefringent material for DUV application.

Second-order nonlinear optical (NLO) materials have drawn enormous academic and technological attention attributable to their indispensable role in laser frequency conversion and other greatly facilitated applications. The explorations of new...