标题： 为甚长基线干涉测量适应低温蓝宝石振荡器 显示英文标题

标题： Adapting a Cryogenic Sapphire Oscillator for Very Long Baseline Interferometry

摘要： 非常长基线干涉测量（VLBI）扩展到观测波长小于1.3mm提供了卓越的角分辨率（约20微角秒）并为研究天体物理现象提供了新的光谱区域。在这些波长下，为了在全球VLBI阵列中保持相位相干性，需要在所有参与的射电望远镜的外差接收器中使用超稳定的频率参考。氢原子钟传统上被用作VLBI参考，但大气湍流通常将亚毫米VLBI相干时间限制在约1-30秒。低温蓝宝石振荡器（CSO）在这些时间尺度上的稳定性优于氢原子钟，并且作为VLBI参考可能替代原子钟。在这里，我们描述了从CSO的微波（11.2 GHz）输出产生10 MHz VLBI频率标准的系统设计、实现和测试。为了提高新参考的长期稳定性，CSO被锁定到全球定位系统卫星的定时信号并校正了振荡器老化。通过与同一实验室中的氢原子钟进行比较来测量CSO的长期性能。出色的短期性能以及通过调节实现的改进的长期性能使CSO成为波长小于1.3mm的VLBI的合适参考。 显示英文摘要

摘要： Extension of very long baseline interferometry (VLBI) to observing wavelengths shorter than 1.3mm provides exceptional angular resolution (~20 micro arcsec) and access to new spectral regimes for the study of astrophysical phenomena. To maintain phase coherence across a global VLBI array at these wavelengths requires that ultrastable frequency references be used for the heterodyne receivers at all participating telescopes. Hydrogen masers have traditionally been used as VLBI references, but atmospheric turbulence typically limits (sub) millimeter VLBI coherence times to ~1-30 s. Cryogenic Sapphire Oscillators (CSO) have better stability than Hydrogen masers on these time scale and are potential alternatives to masers as VLBI references. Here, We describe the design, implementation and tests of a system to produce a 10 MHz VLBI frequency standard from the microwave (11.2 GHz) output of a CSO. To improve long-term stability of the new reference, the CSO was locked to the timing signal from the Global Positioning System satellites and corrected for the oscillator aging. The long-term performance of the CSO was measured by comparison against a hydrogen maser in the same laboratory. The superb short-term performance, along with the improved long-term performance achieved by conditioning, makes the CSO a suitable reference for VLBI at wavelengths less than 1.3mm.