氧化铝和蓝宝石上毫米波亚波长结构的皮秒Laser烧蚀
Picosecond Laser Ablation of Millimeter-Wave Subwavelength Structures on Alumina and Sapphire
摘要：
我们使用一个1030 nm的激光与7 ps的脉冲宽度和平均功率高达100 W的烧蚀氧化铝和蓝宝石上的形亚波长结构（SWS）。SWS在毫米波段提供了一种有效的和低温鲁棒的减反射涂层。我们证明了氧化铝和蓝宝石上的结构高度分别为900 $μ$ m和750 $μ$ m时，平均烧蚀速率高达34 mm $^3$ /min和20 mm $^3$ /min。这些比率分别比以前报告的类似结构高出34倍和9倍。我们提出了一个模型，涉及结构高度的累积激光能量密度。该模型依赖于吸收长度$δ$，它被假定为取决于峰值通量，并对阈值通量$ϕ_{th}$。使用最佳拟合程序，我们发现氧化铝和蓝宝石的平均$δ= 630$ nm和650 nm，以及$ϕ_{th} = 2.0^{+0.5}_{-0.5}$ J/cm $^2$和$2.3^{+0.1}_{-0.1}$ J/cm $^2$，峰值通量值在30和70 J/cm $^{2}$之间。在最佳拟合值的情况下，累积通量的模型和数据值在10%以内一致。给定$δ$和$ϕ_{th}$的输入，该模型用于预测作为SWS高度和平均激光功率的函数的平均消融速率。
英文摘要：
We use a 1030 nm laser with 7 ps pulse duration and average power up to 100 W to ablate pyramid-shape subwavelength structures (SWS) on alumina and sapphire. The SWS give an effective and cryogenically robust anti-reflection coating in the millimeter-wave band. We demonstrate average ablation rate of up to 34 mm$^3$/min and 20 mm$^3$/min for structure heights of 900 $μ$m and 750 $μ$m on alumina and sapphire, respectively. These rates are a factor of 34 and 9 higher than reported previously on similar structures. We propose a model that relates structure height to cumulative laser fluence. The model depends on the absorption length $δ$, which is assumed to depend on peak fluence, and on the threshold fluence $ϕ_{th}$. Using a best-fit procedure we find an average $δ= 630$ nm and 650 nm, and $ϕ_{th} = 2.0^{+0.5}_{-0.5}$ J/cm$^2$ and $2.3^{+0.1}_{-0.1}$ J/cm$^2$ for alumina and sapphire, respectively, for peak fluence values between 30 and 70 J/cm$^{2}$. With the best fit values, the model and data values for cumulative fluence agree to within 10%. Given inputs for $δ$ and $ϕ_{th}$ the model is used to predict average ablation rates as a function of SWS height and average laser power.
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