Abstract. Durable window materials with minimal optical loss are important for future high-energy laser (HEL) systems that will operate at or near the megawatt level. Sapphire is recognized as a promising HEL window candidate due to its outstanding optical transparency and mechanical properties. However, its weak scattering characteristics and absorption levels near the 1-μm wavelength region need to be lowered further for future HEL applications. In our study, the weak absorption and scattering of sapphire samples provided by three vendors were measured. Ultraviolet–visible spectroscopy measurements were made in the wavelength range 190 to 600 nm and several absorption bands due to vacancies and impurities were detected. The bulk absorption of several samples at wavelengths of 355, 532, and 1064 nm were measured using photothermal common-path interferometry and the absorption coefficient values obtained were in the range of 10 − 5 to 10 − 2 cm − 1 and increased as the wavelength decreased. An empirical weak absorption tail model was used to fit the measured data. In addition, scattering measurements on all samples were made at 405, 532, 633, 1064, and 1550 nm using an instrument developed to assess the bidirectional scatterance probability distribution function. The total integrated scatterance was in the range of 10 − 4 to 10 − 2 and increased for all samples as the wavelength decreased. Surface roughness was found to contribute insignificantly to the scattering loss, while bulk defects along with subsurface damage have major impact. A simple single-scatter model was developed and applied to the measured bulk scattering data. The model suggests that impurity particles, porosity, and other density variations exist with a range of sizes that contribute to scattering. Overall, the measurements indicate that both weak absorption and scattering losses are strongly related to defect structures such as lattice disorder and impurities that were introduced during crystal growth or postgrowth processing. Understanding these defects and their contributions to optical loss can lead to improved manufacturing and processing methods.

中文翻译：

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单晶蓝宝石材料从可见光到近红外的弱吸收和散射损失

摘要。具有最小光损耗的耐用窗口材料对于未来将在兆瓦级或接近兆瓦级运行的高能激光 (HEL) 系统非常重要。由于其出色的光学透明度和机械性能，蓝宝石被公认为有前途的 HEL 窗口候选者。然而，其在 1 微米波长区域附近的弱散射特性和吸收水平需要进一步降低，以用于未来的 HEL 应用。在我们的研究中，测量了三个供应商提供的蓝宝石样品的弱吸收和散射。在 190 到 600 nm 的波长范围内进行紫外-可见光谱测量，并检测到几个由于空位和杂质引起的吸收带。几个样品在 355、532、和 1064 nm 是使用光热共路径干涉法测量的，获得的吸收系数值在 10 - 5 到 10 - 2 cm - 1 的范围内，并且随着波长的减少而增加。使用经验弱吸收尾部模型来拟合测量数据。此外，使用为评估双向散射概率分布函数而开发的仪器在 405、532、633、1064 和 1550 nm 处对所有样品进行了散射测量。总积分散射率在 10 - 4 到 10 - 2 的范围内，并且随着波长的减少，所有样品的散射率都会增加。发现表面粗糙度对散射损失的贡献微不足道，而体缺陷和次表面损伤具有重大影响。开发了一个简单的单散射模型并将其应用于测量的体散射数据。该模型表明，杂质颗粒、孔隙率和其他密度变化存在，其尺寸范围会导致散射。总体而言，测量结果表明，弱吸收和散射损失都与晶体生长或生长后加工过程中引入的晶格无序和杂质等缺陷结构密切相关。了解这些缺陷及其对光损耗的影响可以改进制造和加工方法。测量结果表明，弱吸收和散射损失都与晶体生长或生长后加工过程中引入的晶格无序和杂质等缺陷结构密切相关。了解这些缺陷及其对光损耗的影响可以改进制造和加工方法。测量结果表明，弱吸收和散射损失都与晶体生长或生长后加工过程中引入的晶格无序和杂质等缺陷结构密切相关。了解这些缺陷及其对光损耗的影响可以改进制造和加工方法。