420 nm Rb optical frequency standard with short-term frequency stability below 2 × 10^-13

Area of Science:

• Atomic, Molecular, and Optical Physics
• Quantum Optics
• Metrology

Background:

• Miniature atomic cells are crucial for developing compact and portable frequency standards.
• Saturated Absorption Spectroscopy (SAS) is a key technique for laser frequency stabilization.

Purpose of the Study:

• To investigate the saturated absorption spectroscopy (SAS) characteristics of the ⁸⁷Rb 5S_1/2→6P_3/2 transition at 420 nm.
• To determine optimal laser intensity and cell temperature for a compact stabilized frequency standard.
• To analyze noise contributions and assess the feasibility of high-performance miniaturized optical frequency standards.

Main Methods:

• Experimental study of SAS in a miniature (3x3x3 mm³) cubic glass cell containing ⁸⁷Rb.
• Systematic investigation of laser intensity and cell temperature effects on the SAS signal.
• Laser frequency stabilization to the optimized SAS signal and measurement of beatnote stability.

Main Results:

• A beatnote stability of 2.4×10^-13 at 1 s was achieved between two identical SAS systems.
• This corresponds to a single-laser stability of 1.7×10^-13 at 1 s.
• Identified intermodulation and FM-AM conversion as primary sources of short-term frequency instability.

Conclusions:

• The study demonstrates a promising approach for high-performance miniaturized optical frequency standards using high-lying excited-state transitions in ⁸⁷Rb.
• Optimized SAS in miniature cells offers a viable path toward compact and stable atomic clocks.
• Understanding noise sources is critical for further improving the stability of these miniaturized systems.