Long-term stable frequency standard

The DLR (German Aerospace Center) funded project “Entwicklung einer langzeitstabilen, auf einem Resonator basierenden optischen Frequenzreferenz bei 1064 nm (EBB mit EM-Design)“  (“Development of long-term stable frequency standard based on an optical resonator at 1064 nm (EBB with EM-Design)”) has the goal of the experimental realization of a laser setup stabilized on an optical resonator with a relative frequency instability below 1E-15 for long integration times of about 1000 s. Apart from this, the experimental setup will be optimized with respect to its mass, compactness, thermal and vibrational robustness for future space mission applications. For instance, the thermal stability of the resonator has to be below 10E-9 K, which can only be realized by a very advanced thermal control and shield design (Fig. 1) and has to be calculated before by means of finite-element analysis (FEM). To fulfil these ambitious goals cooperations with the Leibniz Universität Hannover (LUH)  for integration of the electronics and the DLR Institute for Space Systems in Bremen (DLR-RY) are in progress.

Fig. 1: Finite-element analysis of the thermal control system in a cylindrical shield design and cubic resonator (cavity).
Fig. 2: Simulation results for a full thermal radiation and conduction model with an outer periodical perturbation of +-1K.

Possible applications are future space missions focusing on the test of the violations of the boost invariance, e.g. mSTAR (mini Space-Time Asymmetry Research project) and BOOST (Boost Symmetry Test), which are investigated at ZARM as well. The basic experimental principle of these experiments (modern Kennedy-Thorndike experiment) is to compare a frequency standard where the frequency is depending on the optical pathway like an optical resonator with a molecular frequency standard (Iodine clock). This is a direct test of the Lorentz Boost Invariance and therefore the most accurate test of the independency of the speed of light. A violation of the Lorentz Boost Invariance would require new theories of physics, e.g. String Theory and Quantum-Loop-Gravitation. Both, the Iodine frequency standard as well as the optical resonator are under current development in the Metrology and AIVT group at DLR-RY and the Phase 0/A group at ZARM, respectively.

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