Nonlinear optical materials are essential for the development of solid-state lasers. KBe2BO3F2 (KBBF) is a unique nonlinear optical material for generation of deep-ultraviolet coherent light; however, its industrial application is limited. Here, we report a new material NH4B4O6F, which exhibits a wide deep-ultraviolet transparent range and suitable birefringence that enables frequency doubling below 200 nm. NH4B4O6F possesses large nonlinear coefficients about 2.5 times that of KBBF. In addition, it is easy to grow bulk crystals and does not contain toxic elements.

Finding the Next Deep-Ultraviolet Nonlinear Optical Material: NH4B4O6F

Nonlinear Optical Crystals: A Complete Survey

The discovery of new nonlinear optical (NLO) materials for coherent light generation in the deep-ultraviolet (DUV, wavelength below 200 nm) region is essential for the development of laser technologies. Herein, we report a new material CsB4O6F (CBF), which combines the superior structural properties of two well-known NLO materials, beta-BaB2O4 (BBO) and KBe2BO3F2 (KBBF). CBF exhibits excellent DUV optical properties including a short cutoff edge (155 nm), a large SHG response (approximate to 1.9 X KDP), and a suitable birefringence that enables frequency doubling down to 171.6 nm. Remarkably, CBF melts congruently and shows an improved growth habit. In addition, our rational design strategy will contribute to the discovery of DUV NLO materials.

CsB4O6F: A Congruent-Melting Deep-Ultraviolet Nonlinear Optical Material by Combining Superior Functional Units

Deep-ultraviolet nonlinear optical (DUV NLO) crystals are the key materials to extend the output range of solid-state lasers to below 200 nm. The only practical material KBe2BO3F2 suffers high toxicity through beryllium and strong layered growth. Herein, we propose a beryllium-free material design and synthesis strategy for DUV NLO materials. Introducing the (BO3F)(4-),(BO2F2)(3-), and (BOF3)(2-) groups in borates could break through the fixed 3DB-O network that would produce a larger birefringence without layering and simultaneously keep a short cutoff edge down to DUV. The theoretical and experimental studies on a series of fluorooxoborates confirm this strategy. Li2B6O9F2 is identified as aDUV NLO material with a large second harmonic generation efficiency (0.9 x KDP) and a large predicted birefringence (0.07) without layering. This study provides a feasible way to break down the DUV wall for NLO materials.

Fluorooxoborates: Beryllium-Free Deep-Ultraviolet Nonlinear Optical Materials without Layered Growth.

This review introduces in detail the history of the discovery of the nonlinear optical crystal KBe2BO3F2 (KBBF), with a full description of its growth, space structure, optical properties, and capability to generate deep-ultraviolet (UV) harmonic generation. Several important applications developed recently using all-solid-state deep-UV light sources, such as super-high-resolution laser photoemission spectrograph and 193 nm photolithography, will be reviewed.

Deep-UV nonlinear optical crystal KBe2BO3F2―discovery, growth, optical properties and applications

Potassium fluoroboratoberyllate KBe2BO3F2 (KBBF) has been revealed theoretically and experimentally as a novel ultraviolet nonlinear optical crystal, but it is found to be very difficult to grow in a large size, because of the weak binding interaction between the (Be2BO3)∞ units, which leads to an apparent layer habit in the growth. By using a molecular engineering approach, oxygen bridges when brought in to strengthen the binding between the infinite units are found to be useful to overcome the above shortcoming of KBBF, and in the light of it another new ultraviolet nonlinear optical crystal—strontium boratoberyllate Sr2Be2B2O7 (SBBO) has been discovered. The linear optical properties of SBBO are similar to KBBF’s, but its nonlinear optical properties are better than that of the latter. d22(SBBO)≂d22(β‐BaB2O4), which is two times higher than d11 of KBBF. SBBO has very good mechanical properties, and it is also not deliquescent. So SBBO is expected to have great potential for the application in ultraviol...

New development of nonlinear optical crystals for the ultraviolet region with molecular engineering approach

MBe2BO3F2 (M=Na,K) have been discovered to be nonlinear optical (NLO) materials for UV applications. They have relatively large NLO coefficients: deff is about 2.5 times as large as that of KH2PO4 (λ=1079 nm, Nd:YAP laser), the UV cutoff wavelengths are as short as 155 nm, and they have a moderate birefringence of nearly 0.10. Their structures are characterized by an infinite sheet which is formed by six‐membered rings [Be2BO6F2] with Be‐O and B‐O edges in common. Such structures are favorable for good NLO properties. These NLO properties make MBe2BO3F2 promising candidates for vacuum UV NLO materials.

Linfeng Mei

Papers

New development of nonlinear optical crystals for the ultraviolet region with molecular engineering approach

Nonlinear optical materials based on MBe2BO3F2 (M=Na,K)