The role of spatial and temporal modes in pulsed parametric down-conversion

Area of Science:

• Quantum optics
• Nonlinear optics
• Solid-state physics

Background:

• Parametric down-conversion (PDC) is crucial for quantum light generation.
• Stimulated emission enhances PDC efficiency and influences spatial correlations.
• Understanding mode structure is key to controlling PDC output.

Purpose of the Study:

• To investigate spatial correlations from stimulated pair emission in frequency degenerate PDC.
• To determine the ratio of stimulated to spontaneous pairs and its relation to mode structure.
• To introduce and validate a universal curve for this ratio, considering pump focusing effects.

Main Methods:

• Utilizing periodically poled potassium titanyl phosphate (PPKTP) crystals.
• Employing ∼2 ps duration laser pulses for pumping.
• Measuring spatial correlations of PDC output light under varying focusing conditions.

Main Results:

• Achieved a stimulated-to-spontaneous pair ratio as high as 0.8.
• Identified a universal curve for the stimulated-to-spontaneous ratio, incorporating a coherence diameter r(0).
• Demonstrated the robustness of this universal curve, with breakdown only at very small pump beam waists (<40 μm).

Conclusions:

• The stimulated-to-spontaneous pair ratio is a direct measure of relevant modes in PDC.
• The coherence diameter r(0) effectively characterizes pump focusing effects on spatial correlations.
• The universal curve provides a robust model for PDC spatial correlations, applicable across various experimental regimes.