The Anisotropic Thermal Expansion of Non-linear Optical Crystal BaAlBO3F2 Below Room Temperature

Xingxing Jiang,Rongjin Huang,Maxim S Molokeev,Wei Wang,Shibin Guo,Zhanggui Hu,Zheshuai Lin,Naizheng Wang,Laifeng Li

doi:10.3389/fchem.2018.00252

Abstract

Thermal expansion is a crucial factor for the performance of laser devices, since the induced thermal stress by laser irradiation would strongly affect the optical beam quality. For BaAlBO3F2 (BABF), a good non-linear optical (NLO) crystal, due to the highly anisotropic thermal expansion its practical applications are strongly affected by the “tearing” stress with the presence of local overheating area around the laser spot. Recently, the strategy to place the optical crystals in low-temperature environment to alleviate the influence of the thermal effect has been proposed. In order to understand the prospect of BABF for this application, in this work, we investigated its thermal expansion behavior below room temperature. The variable-temperature XRD showed that the ratio of thermal expansion coefficient between along c- and along a(b)- axis is high as 4.5:1 in BABF. The Raman spectrum combined with first-principles phonon analysis revealed that this high thermal expansion anisotropy mainly ascribe to progressive stimulation of the respective vibration phonon modes related with the thermal expansion along a(b)- and c-axis. The good NLO performance in BABF can be kept below room temperature. The work presented in this paper provides an in-depth sight into the thermal expansion behavior in BABF, which, we believe, would has significant implication to the manipulation in atomic scale on the thermal expansion of the materials adopted in strong-field optical facility.

Highlights

Thermal expansion behavior is a crucial performance factor for materials used in lasers, due to its affinity with the ability of the optical outputting (Wynne et al, 1999; Wang et al, 2007; Mangin et al, 2011; Ito et al, 2017; Fang et al, 2018)
As for the practical application of BABF, the optical spot with high-power is usually focused on one point of the crystal, and “tearing” stress resulted from anisotropic thermal expansion would severely affect the beam quality and outputting power
It is revealed that the BABF exhibit relatively high anisotropic thermal expansion, and the near-zero thermal expansion behavior along a(b)-axis below 100K was observed

Summary

INTRODUCTION

Thermal expansion behavior is a crucial performance factor for materials used in lasers, due to its affinity with the ability of the optical outputting (Wynne et al, 1999; Wang et al, 2007; Mangin et al, 2011; Ito et al, 2017; Fang et al, 2018). The previous study about the thermal property of BABF revealed that above room temperature, its thermal expansion coefficient along c-axis is about eight times of that along a(b)-axis, and the strongly anisotropic thermal expansion has been the major disadvantage to restrict its practical application (Yue et al, 2011). The thermal expansion behavior of BABF under low temperature has not been investigated yet, and its performance index below room temperature remain unclear. It is desirable to perform a study about the thermal expansion to give a comprehensive evaluation on the application prospect below room temperature and elaborate the structureproperty relationship of the anisotropic thermal expansion of BABF. The optical performance is slightly improved under low temperature These result indicates that the performance below room temperature for the laser generation is superior than that above room temperature, and BABF is a potential NLO crystals in cryogenic system

METHOD

AND DISCUSSION

CONCLUSION