Cascaded frequency conversion under nonlinear stimulated Raman adiabatic passage.

Area of Science:

• Nonlinear Optics
• Quantum Optics
• Laser Physics

Background:

• Simultaneous three-wave mixing processes, including second harmonic generation (SHG) and difference frequency generation (DFG), are fundamental in nonlinear optics.
• Stimulated Raman adiabatic passage (STIRAP) is a quantum control technique typically used for atomic population transfer, offering precise state manipulation.

Purpose of the Study:

• To investigate the simultaneous occurrence of SHG and DFG under nonlinear STIRAP conditions.
• To explore the potential for complete pump-to-signal-and-idler conversion without exciting the second harmonic.
• To establish an analytical framework for understanding nonlinear adiabatic passage dynamics.

Main Methods:

• Theoretical analysis of coupled nonlinear wave equations governing the three-wave mixing processes.
• Development of an analogy between atomic population transfer in STIRAP and nonlinear optical dynamics.
• Linearization of the nonlinear dynamics by exploiting the dark state concept for analytical solutions.
• Derivation of the adiabaticity condition for achieving complete conversion.

Main Results:

• Demonstration of a nonlinear STIRAP process enabling simultaneous SHG and DFG.
• Achieved complete conversion from the input pump to the signal and idler frequencies via a counterintuitive adiabatic passage.
• Observed a large operational bandwidth of approximately 380 nm for the nonlinear STIRAP process.
• The second harmonic state remained unexcited throughout the process.

Conclusions:

• Nonlinear STIRAP provides a robust mechanism for efficient frequency conversion in optical systems.
• The analogy to atomic STIRAP successfully linearizes the nonlinear dynamics, enabling analytical predictions.
• This technique offers a pathway to broadband, high-efficiency light generation through controlled nonlinear interactions.