Comb-locked Lamb-dip spectrometer.

Area of Science:

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

Background:

• Doppler broadening limits precision spectroscopy.
• Achieving Doppler-free conditions requires high field intensities and signal-to-noise ratios, which are often difficult to attain.
• Detecting weak absorption features like Lamb dips is challenging.

Purpose of the Study:

• To develop a novel spectrometer capable of overcoming Doppler broadening for precision spectroscopy.
• To enable the study of transitions with extremely weak electric dipole moments.
• To achieve high sensitivity and frequency accuracy for spectroscopic measurements.

Main Methods:

• A novel comb-assisted spectrometer was developed, utilizing intra-cavity field enhancement.
• The spectrometer operates over a broad wavelength range (1.5 to 1.63 μm) with field enhancement up to 1.5 kW/cm².
• Referencing to an optical frequency comb and tight laser locking to an enhancement cavity were employed.

Main Results:

• The spectrometer achieves kHz-level frequency accuracy.
• An absorption sensitivity of 10⁻¹¹ cm⁻¹ was reached over 200 s in a direct-detection mode.
• Lamb-dip spectroscopy was demonstrated on a weak acetylene transition (P(15) line), revealing its extremely low line-strength and Einstein coefficient.

Conclusions:

• The developed comb-assisted spectrometer offers a simple, robust, and widely tunable platform for precision spectroscopy.
• It enables the exploration of thousands of molecular lines previously unobservable in a Doppler-free regime.
• The system's sensitivity and accuracy pave the way for new discoveries in molecular spectroscopy.