Frequency characteristics of far-detuned parametric four-wave mixing in Rb

Area of Science:

• Atomic Physics
• Nonlinear Optics
• Quantum Optics

Background:

• Four-wave mixing (FWM) is a nonlinear optical process where four waves interact within a medium.
• Parametric FWM can generate new frequencies, but controlling the output characteristics is crucial for applications.
• Rubidium vapor is a common medium for nonlinear optical experiments due to its accessible atomic transitions.

Purpose of the Study:

• To investigate the frequency characteristics of a coherent 420 nm beam generated by parametric four-wave mixing.
• To understand the relationship between the excitation laser frequency and the generated 420 nm beam frequency.
• To explore the potential of this process as a tunable photon source.

Main Methods:

• A single, high-power 778 nm laser was used as the excitation source.
• The laser beam was directed through a high-density rubidium cell.
• A detuning of 1 THz from the intermediate state was employed to induce parametric FWM.
• The frequency shift of the 420 nm light was measured as the excitation laser was tuned.

Main Results:

• The frequency of the 420 nm light was observed to shift with changes in the excitation laser frequency.
• A measured frequency shift ratio of 1.87±0.04 was determined.
• This shift is attributed to the selection of different atomic velocity classes within the rubidium cell.
• The generated 5.23 μm beam frequency is correspondingly shifted.
• The 420 nm light was tuned over a 1 GHz range.

Conclusions:

• The frequency of the 420 nm parametric FWM output is tunable by adjusting the excitation laser frequency.
• The observed frequency shift is explained by Doppler effects related to atomic velocity classes.
• This parametric FWM process offers potential as a tunable photon source for generating light at novel wavelengths.