Hochstabiler optischer Resonator im Fallturmbetrieb für Präzisionsmessungen in Schwerelosigkeit

Abstract

The development of optical clocks has made a great progress in the past years. Optical atomic clocks have demonstrated higher accuracies and stabilities than state of the art microwave oscillators and show their potential to target fractional frequency inaccuracies below 10a 17. This has led to a proposal to redefine the SI second using an optical transition of an atom clock. Possible candidates are evaluated and within the next year one should be elected. Not only for such fundamental definitions of the metric system, but also for tests of the fundamental theories have these clocks provided an astonishing tool. Reaching into the atto-scale of fractional frequency inaccuracy the gravitational redshift is readily measurable within the laboratory. Prospects for tests of the Einstein equivalence principle both earth and space bound will open new boundaries for alternative theories of gravitation. Even the recently observed gravitational waves can be a research target of satellite missions with optical atomic clocks on board. In this work, a highly stable optical local oscillator for the use in the drop tower Bremen was developed. The drop tower Bremen allows the experimentalist for the use of 4,7 s free fall in microgravity. It is a first step in the evolution of experiments outside the laboratory and in terms of technology readiness this presents a first demonstration of an operation of an optical cavity in a relevant environment. Stringent requirements for weight, space and power consumption make it difficult to achieve the worlda s best performance. In this work the measured frequency stability was found to be I y(3,5 s) 7,2 A 10a 15 in the Allan deviation. The optical cavity used in the apparatus is a spherical ULE spacer with fused-silica mirrors. It shows a finesse of F a 480.000 for the reference cavity and F a 330.000 for the dropped cavity. We can report successful drops in the drop tower Bremen with no degeneracy in the performance. A detailed description of both apparatus is given and the special steps taken for the capsule integration are explained. Another part of this work is the detailed discussion of the mathematical framework for the electric signals of a photo detector, if two laser fields are detected simultaneously. The heterodyne measurement is explained and applied to the case, where the linewidth is to be measure by a self-referencing scheme. This includes both the long known delayed self-heterodyne interferometers as well as the discussion of the possibility for short-delayed self-heterodyne interferometers. A published work is disproved and discussed.