Borate-Based Ultraviolet and Deep-Ultraviolet Nonlinear Optical Crystals

Abstract

Abstract:Borates have long been recognized as a very important family of nonlinear optical (NLO) crystals, and have been widely used in the laser frequency-converting technology in ultraviolet (UV) and deep-ultraviolet (DUV) regions. In this work, the borate-based UV and DUV NLO crystals discovered in the recent decade are reviewed, and the structure-property relationship in the representative borate-based UV and DUV NLO crystals is analyzed. It is concluded that the optical properties of these crystals can be well explained directly from the types and spatial arrangements of B-O groups. The deduced mechanism understanding has significant implications for the exploration and design of new borate-based crystals with excellent UV and DUV NLO performance.

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

“…In analogy to genetic fragments in biology, the FBBs can be inherited, altered and rationally re‐constructed to obtain new crystal structures by molecular design . The BO 3 unit is the mostly preferred FBB since the successful synthesis of KBBF, while other FBBs, such as the B 3 O 6 unit, were often overlooked. It is known that the planar B 3 O 6 FBB with delocalized π bonds possesses much larger microscopic second‐order susceptibility than that of BO 3 .…”

High-Power, Solid-State, Deep Ultraviolet Laser Generation

“…One is by SHG directly from a longer wavelength; the other one is by stages of SFG. T. Thao Tran et al and Y. Yang et al, respectively, summarized the nonlinear optical materials for DUV generation from 5th to 7th harmonics of Nd:YAG laser at 1064 nm [35,36] by SHG and SFG including CLBO, KBBF, LBO, BBO, K 2 Al 2 B 2 O 7 (KABO) etc. Recently, coherent radiation in the vacuum ultraviolet (VUV) region was generated with a wavelength as short as 121 nm in strontium tetra borate (SBO) by "random quasi-phase matching" (RQPM), which was the shortest wavelength generated by second-order nonlinear optical process in a solid-state material [37].…”

“…Table 2 summarizes the typical results of the solid-state DUV laser at 193 nm by use of the different nonlinear crystals. Among the above crystals, the KBBF crystal is currently known as the only one, enabling high power and short wavelength directly by SHG [28][29][30]36,38,39]. For the application of seeding the hybrid ArF excimer laser, the DUV laser should be at the wavelength of 193 nm.…”

“…However, the KBBF should be packed in a prism coupling device (PCD) consisting of CaF 2 or SiO 2 prisms to achieve the phase-matching condition [14,29]. Moreover, KBBF is significantly difficult to be grown into single crystal because of the weak interaction of alkali metal and fluorine cations [35,36], which limit its potential to be grown into large dimension and to be applied in generating a higher power 193-nm laser for seeding the hybrid ArF laser. Hence, the SFG process in other crystals is the practical method for high-power 193-nm laser generation.…”

Recent advances in ultraviolet and deep-ultraviolet second-order nonlinear optical crystals

“…a wide bandgap), large SHG coefficients, moderate birefringence, chemical stability and facile growth of large single crystals [29,30]. The planar [BO3] 3and isoelectronic anions such as [NO3]and [CO3] 2-, which possess moderate birefringence and large microscopic second-order hyperpolarizabilities β, are believed to be the most favorable anionic units for UV and deep-UV candidates [31,32]. Phosphates have attracted attention as potential UV and deep-UV NLO candidates in recent years due to their wide UV transparency and the ease with which one can grow bulk crystals [33].…”