Nonlinear optical crystal is an important material of photoelectric information, which has wide application prospects in information, research, energy, industrial manufacturing and medical and health fields.With the rapid development of laser precision machinery processing, laser chemistry, ultraviolet laser spectroscopy and laser medicine, people urgently need to develop all solid-state deep UV coherent light sources.The key breakthrough is the development and application of nonlinear optical crystals with deep UV band (spectral range below 200nm).In recent years, in the newly developed deep UV nonlinear optical crystal materials, phosphate materials have become a hot research hotspot due to their advantages of short UV cutoff.However, the microsecond-order frequency coefficient of the PO4 functional groups in phosphate is only a tenth of the planar b-o oxygen group (B3O6 and BO3), which leads to the deficiency of the phosphate material with a smaller frequency multiplier.Therefore, it is necessary to effectively enhance the effect of the double frequency effect by reasonably designing the combination and arrangement of the functional groups.
In recent years, the research team of pan Shilie, a new photoelectric functional material laboratory of the Chinese academy of sciences in Xinjiang, has been working on the study of new nonlinear optical crystals.From the previous research results of composite alkali metal borate nonlinear optical crystal materials, through the introduction of ionic radius difference of alkali metal cations in the more phosphate, the research team successfully designed and synthesized a phosphate deep ultraviolet nonlinear optical crystal materials LiCs2PO4.The compound exhibits not only a short UV cutoff edge (174nm), but also a large frequency doubling effect (2.6 times KDP). This is the largest compound of SHG effect in the deep ultraviolet nonlinear optical crystal system. At the same time, LiCs2PO4 can realize phase matching under 1064nm, and the crystal is easy to grow. It is expected to be a new type of deep ultraviolet nonlinear optical crystal material.
In addition, the crystal glass is orthophosphate, and the source mechanism of its large frequency doubling effect is different from the gain doubling effect of polyphosphate group proposed by other research groups. The optical properties of the material have been theoretically calculated by first principles. It is found that the crystal structure of the material has LiO4-PO4 group common edge bonding.The special connection mode is beneficial to the directional alignment of O-2p non bonded orbitals, leading to the effective superposition of the microscopic nonlinear optical coefficients of the phosphorus oxygen structure elements. This makes the LiCs2PO4 display a greater frequency doubling effect. This work provides a new research idea for the design of nonlinear optical crystal materials with larger SHG effect in phosphate.