通过振动和热补偿的ULE法布里-珀罗腔稳定化的亚赫兹线宽二极管激光器
Sub-Hz line width diode lasers by stabilization to vibrationally and thermally compensated ULE Fabry-Perot cavities
摘要：
在两个独立稳定于两个垂直安装的法布里-珀罗（FP）参考腔的外腔二极管激光器之间，我们在972 nm处实现了0.5 Hz的光学拍音线宽，频率漂移约为0.1 Hz/s。垂直FP参考腔悬挂在中间平面中，使得垂直振动对镜分离的影响被显著抑制。这使得该装置几乎不受垂直振动的影响，而垂直振动比水平振动更难隔离。为了补偿热漂移，FP垫片由具有零线性膨胀系数的超低膨胀（ULE）玻璃制成。在真空中使用Peltier元件的新设计允许在最佳温度下操作，其中ULE的二次温度膨胀也可以被消除。这种ULE FP腔测得的63 mHz/s的线性漂移是由于材料老化，并且在16小时的测量期间，残余频率波动小于40 Hz。温度引起的漂移的一部分归因于反射镜涂层的热膨胀。引起镜面振动的高频热波动限制了设计良好的参考腔的稳定性。通过比较两个相似的激光系统，我们得到了2*10-15的阿伦不稳定性的平均时间为0.1和10秒，这是接近理论的热噪声限制。
英文摘要：
We achieved a 0.5 Hz optical beat note line width with ~ 0.1 Hz/s frequency drift at 972 nm between two external cavity diode lasers independently stabilized to two vertically mounted Fabry-Perot (FP) reference cavities. Vertical FP reference cavities are suspended in mid-plane such that the influence of vertical vibrations to the mirror separation is significantly suppressed. This makes the setup virtually immune for vertical vibrations that are more difficult to isolate than the horizontal vibrations. To compensate for thermal drifts the FP spacers are made from Ultra-Low-Expansion (ULE) glass which possesses a zero linear expansion coefficient. A new design using Peltier elements in vacuum allows operation at an optimal temperature where the quadratic temperature expansion of the ULE could be eliminated as well. The measured linear drift of such ULE FP cavity of 63 mHz/s was due to material aging and the residual frequency fluctuations were less than 40 Hz during 16 hours of measurement. Some part of the temperature-caused drift is attributed to the thermal expansion of the mirror coatings. High-frequency thermal fluctuations that cause vibrations of the mirror surfaces limit the stability of a well designed reference cavity. By comparing two similar laser systems we obtain an Allan instability of 2*10-15 between 0.1 and 10 s averaging time, which is close to the theoretical thermal noise limit.
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