A laser-lock concept to reach cm s 1 -precision in Doppler experiments with Fabry-Pérot wavelength calibrators
A laser-lock concept to reach cm s 1 -precision in Doppler experiments with Fabry-Pérot wavelength calibrators
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DOI：
10.1051/0004-6361/201424099
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发表时间：
2014-08
影响因子：
6.5
通讯作者：
A. Reiners;R. Banyal;R. Ulbrich
中科院分区：
文献类型：
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作者：
A. Reiners;R. Banyal;R. Ulbrich
最先进的多普勒实验需要在厘米S−1级别进行精确的波长校准。低精度法布里-珀罗涉仪(FPI)可以提供天文实验所需的很大带宽的波长梳，但不可避免的光谱漂移是很难控制的。我们提出用87RbD2原子线被动稳定干涉仪，并跟踪腔外随时间变化的长度漂移，而不是主动控制腔。双精细腔允许在观察期间进行漂移跟踪。在低精细光谱范围内，该腔提供了为天文光谱仪量身定做的梳状透射谱。腔长的漂移被监测在相对于外部标准的高精细范围内：单个窄的透射峰被锁定到外腔二极管激光器，并与来自无多普勒跃迁的原子频率进行比较。遵循标准锁定方案，可以实现S−1亚毫米精度的跟踪。这比目前计划的高精度多普勒实验好了几个数量级，并允许自由设计，包括在某些条件下使用单一精细干涉仪。建议设置的所有组件都是现成的，这使得这种方法对即将到来的多普勒实验特别有趣。我们还表明，天文FPI中使用的大量干涉模式使我们能够明确地识别每个FPI传输峰值的干扰模式，定义其绝对波长解决方案。在激光概念的每次共振中达到的精度由腔长度定义，腔长度由一个锁定的峰值和群速度色散确定。后者可以在相关频率范围内变化几个100m的S−1，并严重限制单个峰值位置的精度，尽管它们的干扰模式是已知的。确定绝对峰值位置的一种可能方法是使用激光频率梳(LFC)从外部测量每个单独峰值的频率。因此，激光锁定FPI的概念可能有助于将LFC的绝对精度应用于天文光谱仪，而不需要在天文台使用LFC。
State-of-the-art Doppler experiments require wavelength calibration with precision at the cm s −1 level. A low-finesse Fabry-Perot interferometer (FPI) can provide a wavelength comb with a very large bandwidth as required for astronomical experiments, but unavoidable spectral drifts are difficult to control. Instead of actively controlling the FPI cavity, we propose to passively stabilize the interferometer and track the time-dependent cavity length drift externally using the 87 RbD2 atomic line. A dual-finesse cavity allows drift tracking during observation. In the low-finesse spectral range, the cavity provides a comb transmission spectrum tailored to the astronomical spectrograph. The drift of the cavity length is monitored in the high-finesse range relative to an external standard: a single narrow transmission peak is locked to an external cavity diode laser and compared to an atomic frequency from a Doppler-free transition. Following standard locking schemes, tracking at sub-mm s −1 precision can be achieved. This is several orders of magnitude better than currently planned high-precision Doppler experiments, and it allows freedom for relaxed designs including the use of a single-finesse interferometer under certain conditions. All components for the proposed setup are readily available, rendering this approach particularly interesting for upcoming Doppler experiments. We also show that the large number of interference modes used in an astronomical FPI allows us to unambiguously identify the interference mode of each FPI transmission peak defining its absolute wavelength solution. The accuracy reached in each resonance with the laser concept is then defined by the cavity length that is determined from the one locked peak and by the group velocity dispersion. The latter can vary by several 100 m s −1 over the relevant frequency range and severely limits the accuracy of individual peak locations, although their interference modes are known. A potential way to determine the absolute peak positions is to externally measure the frequency of each individual peak with a laser frequency comb (LFC). Thus, the concept of laser-locked FPIs may be useful for applying the absolute accuracy of an LFC to astronomical spectrographs without the need for an LFC at the observatory.