Surface and Subsurface Quality Assessment of Polished Lu2O3 Single Crystal Using Quasi-Brewster Angle Technique

Chengyuan Yao,Wanfu Shen,Xiaodong Hu,Chunguang Hu

doi:10.3389/fphy.2021.795639

Abstract

The sesquioxide Lu2O3 single crystal has attracted tremendous attention as potential host material for high-power solid-state lasers. As polishing is the terminal process of conventional ultra-precision machining, the quality of polished crystal directly impacts the crucial performance indicators of optics. The high melting point of Lu2O3 single crystal makes crystal preparation difficult. Therefore, investigations on the surface/subsurface quality inspection of polished Lu2O3 single crystal are scarce. In this paper, we utilize the quasi-Brewster angle technique (qBAT) based on ellipsometry to inspect the quality of polished Lu2O3 single crystal, achieving fast, non-destructive, and high-sensitive surface/subsurface damage assessment. A systematic crystal processing scheme is designed and polished Lu2O3 crystal samples are obtained. To verify the results of qBAT, the surface and subsurface quality are tested using optical profilometer and transmission electron microscope, respectively. The consistency of the test results demonstrates the feasibility, high sensitivity, and accuracy of the qBAT. To our knowledge, this is the first time that the qBAT is applied to investigate the polished surface/subsurface quality of Lu2O3 single crystal. In conclusion, this method provides a powerful approach to the high-precision characterization of the surface/subsurface quality of Lu2O3 single crystal, and has significant potential for material property study and process optimization during ultra-precision machining.

Highlights

Lu2O3 single crystal as sesquioxide has proven to be prospective for high-power solid-state lasers, high-energy radiation detection, and semiconductors due to its high thermal conductivity, low phonon energy, high-density scintillators, high absorption efficiency, wide band gap, and robust thermal stability [1,2,3,4,5,6,7]
Surface/Subsurface Quality Measurement Based on Optical Profilometer and transmission electron microscopy (TEM)
Each sample was measured at three randomly selected locations in the center area, and the average of the three measurements was used as the final surface roughness (Sa)

Summary

Introduction

Lu2O3 single crystal as sesquioxide has proven to be prospective for high-power solid-state lasers, high-energy radiation detection, and semiconductors due to its high thermal conductivity, low phonon energy, high-density scintillators, high absorption efficiency, wide band gap, and robust thermal stability [1,2,3,4,5,6,7]. As the terminal process of traditional ultra-precision machining, can achieve high surface flatness and roughness, but inevitably produces surface and subsurface damage. Typical surface and subsurface damage include pits, scratches, subsurface cracks, residual stresses, dislocations, etc. Surface/subsurface damage directly diminishes the strength, lifetime, coating quality, imaging quality, and laser damage threshold of optics. Investigations on the surface/subsurface quality of polished Lu2O3 single crystals are scarce, which severely limits the Polished Lu2O3 Quality Using qBAT design, fabrication, and application of related devices. The prerequisite for effective suppression and removal of surface and subsurface damage is high precision inspection. The assessment of surface/subsurface damage on polished Lu2O3 has momentous theoretical research significance and practical value

Methods

Results

Conclusion