Sample interview questions: Can you discuss your knowledge of the principles behind optical vortex beams and their properties?
Sample answer:
- Optical Vortex Beams:
— Intense light beams with a helical phase front, resulting in a phase singularity around the beam’s center.
— Phase singularity leads to a zero-intensity region and a characteristic spiral phase structure.
- Principle and Properties:
— Phase Structure:
— The phase of an optical vortex beam varies helically around the beam’s axis.
— The phase singularity at the beam’s center creates a zero-intensity region.
— Topological Charge:
— Characterized by an integer known as the topological charge (l).
— Topological charge quantifies the number of twists in the phase structure.
— Positive (negative) values indicate right-handed (left-handed) helicity.
— Orbital Angular Momentum:
— Possess orbital angular momentum (OAM) due to their helical phase structure.
— OAM is a conserved quantity, leading to unique properties and applications.
— Paraxial Approximation:
— Under paraxial approximation, the complex electric field of an optical vortex beam is described by:
E(r, θ, z) = E0 exp(ilθ) exp(-ikz) exp(-r²/w0²)
- Generation Methods:
— Intracavity Techniques:
— Inside a laser cavity, using elements like spiral phase plates or diffractive optical elements.
— Spatial Light Modulators:
— Using computer-generated holograms displayed on spatial light modulators.