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Development of ultra-stable cryogenic silicon optical resonators for laser frequency stabilization

开发用于激光频率稳定的超稳定低温硅光学谐振器

基本信息

批准号：
279028307
负责人：
Professor Stephan Schiller, Ph.D.
金额：
--
依托单位：
Institut für Experimentalphysik
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2015
资助国家：
德国
起止时间：
2014-12-31 至 2018-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/279028307?language=en
关键词：
Development ultra stable cryogenic silicon

项目摘要

Optical resonators with low sensitivity to temperature and mechanical forces are of great importance for precision measurements in the optical and microwave frequency domains. In the optical domain, they serve to stabilize the frequencies of lasers for spectroscopic applications, notably for optical atomic clocks, and for probing fundamental physics concepts such as the properties of space-time. Also, by conversion of ultra-stable optical frequencies to the radio-frequency domain via an optical frequency comb, radio-frequency sources with ultralow phase noise can be realized, applicable to, e.g., radar measurements with improved sensitivity. The conventional approach for ultra-stable optical resonators is the use of ULE (ultra-low expansion glass) material, operated at temperatures near room temperature. This necessarily leads to a level of Brownian length fluctuations which imposes a fundamental limit to the achievable frequency stability. Cryogenic operation of a resonator provides one avenue towards reduction of these Brownian fluctuations. This offers the possibility of reduction of laser frequency instability more than one order of magnitude lower than with ULE resonators. Crystalline cryogenic optical resonators are furthermore characterized by the near-absence of length drift thanks to the near-perfect lattice structure. Silicon optical resonators have recently been studied in two configurations: first, at 124 K, a silicon resonator has been used to stabilize a laser frequency to the fractional instability level of 1E-16 on short time scales. Second, in our own work, detailed characterizations of a silicon resonator at cryogenic temperature (1.5 K) were performed, which confirmed the potential of eventually leading to 1E-17 frequency instability. Based on these important proof-of-principle studies, we propose here to perform further developments on cryogenic silicon resonators at 1.5 K, with the goal of the first 2 years being to reach a frequency instability on the level of < 5E-17 for medium-long integration times 1E2 s - 1E4 s (with drift removal). This is an intermediate goal towards eventually reaching the 1E-17 level on both short and medium-long timescales, 1 s - 1E4 s To demonstrate the performance aimed for in our 2-year goal, a second cryogenic resonator system needs to be developed, since no reference having 5E-17 instability is available. It will be operated in the same cryostat as the first, existing resonator, and will allow intercomparisons via beat frequency measurements. Moreover, several key issues, previously identified, will be taken care of by implementing suitable subsystems: reduction or residual laser amplitude modulation, installation of an active vibration isolation to reduce cryostat vibrations, implementation of optical breadboards inside the cryostat, prestabilization of the laser to a room-temperature ULE resonator in order to achieve Hz-level linewidth.

对温度和机械力敏感度低的光学谐振腔对于光学和微波频域的精密测量具有重要意义。在光学领域，它们用于稳定光谱应用的激光频率，特别是光学原子钟，以及探测基本物理概念，如时空特性。此外，通过经由光频梳将超稳定的光频率转换到射频域，可以实现具有超低相位噪声的射频源，其适用于例如，提高雷达测量灵敏度。超稳定光学谐振器的常规方法是使用ULE（超低膨胀玻璃）材料，在接近室温的温度下操作。这必然导致布朗长度波动的水平，这对可实现的频率稳定性施加了基本限制。谐振器的低温操作提供了减少这些布朗波动的一种途径。这提供了比ULE谐振器低一个数量级以上的激光频率不稳定性降低的可能性。此外，由于近乎完美的晶格结构，晶体低温光学谐振器的特征在于几乎不存在长度漂移。硅光学谐振器最近已被研究在两种配置：首先，在124 K，硅谐振器已被用来稳定的激光频率的分数不稳定性水平的1E-16在短时间尺度上。其次，在我们自己的工作中，在低温（1.5 K）下对硅谐振器进行了详细的表征，这证实了最终导致1E-17频率不稳定的可能性。基于这些重要的原理验证研究，我们建议在1.5 K下对低温硅谐振器进行进一步开发，前两年的目标是在中长积分时间1E2 s-1E4 s（漂移消除）下达到<5E-17的频率不稳定性水平。这是一个中期目标，最终达到1E-17水平的短期和中长期的时间尺度，1 s-1E4 s为了证明我们的2年目标的性能，第二个低温谐振器系统需要开发，因为没有参考5E-17不稳定性。它将在与第一个现有谐振器相同的低温恒温器中运行，并将允许通过拍频测量进行相互比较。此外，几个关键的问题，以前确定的，将照顾到通过实施合适的子系统：减少或残留的激光振幅调制，安装一个主动隔振，以减少低温振动，实施低温内的光学试验板，预稳定的激光器到室温ULE谐振器，以实现Hz级的线宽。