Phase Analysis for Frequency Standards in the Microwave and Optical Domains

Area of Science:

• Atomic physics
• Precision spectroscopy
• Frequency standards

Background:

• Coherent manipulation of atomic states is crucial for high-precision spectroscopy.
• Cyclic processes in atomic standards can cause phase excursions, leading to frequency shifts.
• Accurate measurement of these phase variations is essential for improving frequency standard performance.

Purpose of the Study:

• To investigate cycle-synchronous phase excursions in atomic frequency standards.
• To quantify the impact of phase variations on frequency output.
• To develop and utilize a novel FPGA-based phase analyzer for precise measurements.

Main Methods:

• Construction of a field-programmable gate array (FPGA)-based phase analyzer.
• Measurements conducted on caesium fountain atomic clocks (PTB-CSF1 and PTB-CSF2).
• Investigation of phase variations in an Ytterbium ion (Yb+) optical frequency standard, including acousto-optic modulator (AOM) chirp analysis.

Main Results:

• Phase variations of the microwave source in caesium fountains were limited to a few microradians, corresponding to relative frequency shifts below [Formula: see text].
• In the Yb+ optical standard, cycle-synchronous and long-term phase excursions were found to not exceed [Formula: see text].
• Detailed measurements of AOM chirps and their dependence on duty cycle and driving power were performed.

Conclusions:

• The developed FPGA phase analyzer effectively measures and constrains phase variations in atomic frequency standards.
• The study demonstrates that phase excursions in both caesium fountain and Yb+ optical standards are below critical thresholds, ensuring high frequency stability.
• These findings contribute to the advancement of high-precision spectroscopy and the development of next-generation atomic clocks.