Selection rules for the orbital angular momentum of optically produced THz radiation

Area of Science:

• Optics and Photonics
• Quantum Optics
• Terahertz Science

Background:

• Orbital angular momentum (OAM) in light offers unique properties for advanced applications.
• Efficiently converting OAM from infrared lasers to terahertz (THz) frequencies is crucial for novel THz technologies.

Purpose of the Study:

• To theoretically investigate the transduction mechanisms of OAM from infrared pump lasers into the THz domain.
• To analyze the selection rules governing OAM transfer in different nonlinear optical processes.

Main Methods:

• Theoretical analysis of optical rectification (OR) and difference frequency generation (DFG).
• Examination of OAM selection rules under various pump polarizations (linear, circular, radial, azimuthal).
• Investigation of the influence of pump beam focusing on OAM transduction.

Main Results:

• In OR, OAM transduction is mediated by spin-orbit interaction, with a strict OAM selection rule of l=0.
• In DFG, OAM selection rules depend on pump polarization: l=Δl for linear/circular, and l ranging from Δl-2 to Δl+2 for radial/azimuthal polarization.
• For tightly focused pumps in DFG, OAM tends towards Δl±2, while large pump beams result in OAM tending to zero.

Conclusions:

• The study elucidates distinct OAM transduction pathways and selection rules for OR and DFG.
• Understanding these rules is vital for controlling and optimizing THz wave generation with tailored OAM properties.