Negative propagation effect in nonparaxial Airy beams

Area of Science:

• Optics and Photonics
• Electromagnetism

Background:

• Negative propagation is an unusual optical phenomenon where Poynting vector components change sign.
• Airy beams are known for their unique propagation-invariant and diffraction-free properties.

Purpose of the Study:

• To report and analyze negative propagation in finite-energy Airy beams within a subwavelength nonparaxial regime.
• To investigate the underlying mechanisms and implications of this effect in Airy beams.

Main Methods:

• Analysis of the spectral domain decomposition of Airy beams into propagating and evanescent plane waves.
• Demonstration of the effect for single TE or TM modes, contrasting with Bessel beams and X-waves.
• Theoretical investigation into the contribution of evanescent waves to energy flux.

Main Results:

• Negative propagation is observed in subwavelength nonparaxial Airy beams due to coupling between propagating and evanescent waves.
• Unlike vector Bessel beams and X-waves, Airy beams require only single TE or TM modes for this effect.
• Evanescent waves alone cannot sustain energy flux, meaning pure evanescent Airy beams are not physically realizable.
• The loss of shape-preserving and diffraction-free properties in nonparaxial Airy beams is solely due to propagating waves.

Conclusions:

• The negative propagation effect in subwavelength nonparaxial Airy beams is a distinct phenomenon driven by wave coupling.
• This effect offers potential applications in advanced optical technologies like optical traps, cloaking detection, and nanoparticle manipulation.
• Understanding the role of propagating waves is crucial for controlling Airy beam behavior in nonparaxial regimes.