Demonstration of a HeNe/CH4-based optical molecular clock

Area of Science:

• Atomic, Molecular, and Optical Physics
• Metrology
• Spectroscopy

Background:

• Optical clocks offer high precision for timekeeping.
• Methane's optical transitions are promising for frequency standards.
• Frequency combs enable precise optical-to-microwave frequency links.

Purpose of the Study:

• To implement a simple optical clock utilizing the methane F2(2) [P(7), v3] transition.
• To establish a phase-coherent link between an optical reference and an RF repetition rate using a femtosecond laser frequency comb.
• To evaluate the instability and phase noise of the developed optical clock.

Main Methods:

• A femtosecond laser's frequency comb was used for difference frequency generation to create an infrared (IR) comb at 3.39 micrometers.
• The IR comb established a phase-coherent link between an 88-THz optical reference and the radio frequency (RF) repetition rate.
• The repetition rate signal was compared with a second femtosecond comb stabilized to molecular iodine.

Main Results:

• An instability of 1.2 x 10^-13 at 1 second was achieved, limited by microwave detection.
• The single-sideband phase noise of the microwave signal was below -93 dBc/Hz at a 1-Hz offset (normalized to 1 GHz carrier frequency).

Conclusions:

• A simple and effective optical clock based on methane has been demonstrated.
• The frequency comb technology provides a robust method for linking optical and RF frequencies.
• The achieved performance indicates the potential for high-precision timekeeping applications.