Phase correlation between four-wave mixing and optical fields in double Λ-type atomic system.

Area of Science:

• Atomic physics
• Quantum optics
• Laser spectroscopy

Background:

• Four-wave mixing (FWM) is a nonlinear optical process involving the interaction of multiple light fields within a medium.
• Double Λ-type atomic systems offer unique pathways for coherent light-matter interactions.
• Phase-noise in optical fields can significantly influence nonlinear optical phenomena.

Purpose of the Study:

• To investigate the spectral features and phase of four-wave mixing (FWM) light.
• To understand the role of relative phase-noise in optical fields coupled to a double Λ-type atomic system.
• To elucidate the influence of two-photon coherence on the FWM process.

Main Methods:

• Utilized a double Λ-type atomic system based on the 5S_1/2-5P_1/2 transition of ⁸⁷Rb atoms.
• Studied spectral features and phase of FWM light under varying relative phase-noise conditions.
• Employed a beat interferometer to measure the relative linewidth of the FWM signal to probe and pump lasers.

Main Results:

• The FWM spectrum's shape was found to be identical to the two-photon absorption (TPA) spectrum, attributed to two-photon coherence.
• The spectral shape was independent of the relative phase-noise of the pump light.
• The FWM signal's phase was confirmed to be strongly correlated with the pump laser's phase when probe and coupling lasers were phase-locked for two-photon coherence.

Conclusions:

• Two-photon coherence plays a critical role in the FWM process, dictating spectral characteristics.
• The FWM process in this system is robust against pump light phase-noise due to underlying two-photon coherence.
• Phase-locking of lasers is essential for maintaining strong correlation between the FWM signal and pump laser phase.