Optical orbital angular momentum of evanescent Bessel waves

Area of Science:

• Optics and Photonics
• Electromagnetism
• Wave Phenomena

Background:

• Orbital angular momentum (OAM) is a key property of light.
• Evanescent waves are near-field phenomena with unique characteristics.
• Understanding OAM in evanescent fields is crucial for near-field optics.

Purpose of the Study:

• To investigate and quantify the orbital angular momentum (OAM) of evanescent light.
• To compare the OAM characteristics of evanescent Bessel waves with traveling waves.
• To analyze the impact of the evanescent decay rate on OAM.

Main Methods:

• Theoretical analysis of evanescent Bessel waves.
• Calculation of OAM for evanescent fields.
• Comparison with established results for traveling light waves.

Main Results:

• The paraxial contribution to OAM vanishes in evanescent Bessel waves when averaged azimuthally.
• OAM per unit energy is reduced by a factor of (1+κ²/k²) for evanescent Bessel fields compared to traveling fields.
• The reduction factor depends on the wave number (k) and evanescent decay rate (κ).

Conclusions:

• Evanescent light possesses distinct OAM properties compared to traveling light.
• The vanishing paraxial OAM component and reduced OAM per unit energy are significant findings for evanescent fields.
• These results have implications for near-field optical manipulation and microscopy.