Abstract
Internal conical diffraction produces a superposition of orthogonally polarised zero- and first-order Bessel like beams from an incident circularly polarised Gaussian beam. For right-circularly polarised light, the first-order beam has an optical vortex of charge -1. Upon propagation of the first-order beam through a second biaxial crystal, a process which is termed cascade conical refraction, the generated beam is a superposition of orthogonally polarised fields of charge 0 and -1 or 0 and -2. This spin to orbital angular momentum conversion provides a new method for the generation and annihilation of optical vortices in an all-optical arrangement that is solely dependent on the incident polarisation and vortex handedness.
Highlights
The total angular momentum of a paraxial beam of light consists of a spin component associated with polarisation and an orbital component due to the presence of a helical phase structure [1]
We show that a cascade of two biaxial crystals, with intervening polarisers, can be used to generate beams with = ±1 or ±2
In this paper we report the measurement of the phase profiles resulting from internal conical diffraction (ICD) in a two-crystal cascade, explicitly showing the generation of a doubly charged vortex
Summary
The total angular momentum of a paraxial beam of light consists of a spin component associated with polarisation and an orbital component due to the presence of a helical phase structure [1]. Common devices include spatial light modulators (SLM) [4], spiral phase plates (SPP) [5] and computer generated holograms (CGH) [6] They are all widely tuneable, enabling access to integer or non-integer OAM values, with non-integer values corresponding to superpositions of beams of different vortex charge. These devices have their associated problems such as low mode conversion efficiency (SLM, CGH), cost (SLM), and mode quality (SPP, CGH). The approach can be generalized to an arbitrary number of crystals, providing a polarisationtunable system for creating a wide variety of high-order vortex beams Such beams may find applications in quantum information processing, and in studies of the propagation of optical singularities. This work did not consider the effect of changing the state of polarisation between crystals, which is one of the topics considered in our work
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