DESIGN OF A COMPACT SETUP TO GENERATE AND DETECT OPTICAL VORTEX BEAMS

D. PAVON; G. F. QUINTEIRO; S. LEDESMA; M. G. CAPELUTO

Pucón

Conferencia; IX Reunión Iberoamericana de Óptica y XII Reunión Iberoamericana de Óptica, Láseres y Aplicaciones (RIAO/OPTILAS); 2016

Sociedad Española de Optica

An optical vortex (OV), often referred to as ?twisted light?, is a beam of light whose phase varies in a corkscrew-like manner along the beam?s direction of propagation. Therefore, it has an helical wavefront, meaning that its phase is changing in such a way that describes an helix. The OV carries a phase singularity or a phase defect were both, real and imaginary values of optical field, go to zero. Each photon of an OV carries an orbital angular momentum which is an integer multiple of ℏ. Because of such unique properties OV have been used in a wide variety of applications like optical communications, LADAR (laser detection and ranging) system, optical tweezers, optical trapping and laser beam shaping. There are many ways to generate an OV which include spiral phase plates, synthetic holograms or computer generated holograms (CGH), double cylindrical lens phase converters, etc. In this work we present a compact design to generate and detect optical vortex beams. The device is based on a Spatial Light Modulator (SLM), where CGH are displayed. The SLM screen is divided in two halves. In one of them, we represent a binary fork-like hologram and in the other half, a Fresnel lens is displayed. The SLM is placed in a typical set-up for reconstruction of Fourier holograms. An expanded and collimated laser beam illuminates the SLM and the intensity distribution is observed in the focal plane of a convergent lens. The fork-like hologram is used to produce a diffraction pattern containing an optical vortex of a controlled topological charge, i. e. with a controlled angular momentum. The Fresnel lens is used to produce a spherical wavefront. When the Fresnel lens is blocked, each diffraction order in the fork-like hologram has the typical donut shape intensity distribution. The reconstruction of the hologram is made by uncovering the Fresnel lens, which produces the interference of the spherical wave and the diffraction orders in the Fourier plane. In that case, we see fork like patterns in the position of the orders. We show that the device allows as to generate and detect optical vortex of different charge at real time. In other region of the electromagnetic spectrum all materials are strongly absorbent, as it is in X rays. In that region of the spectrum all optical elements are made of diffractive optics and mirrors. The obtained results for this test experiment are the promising initial step for a future generation of OV in the Xray region.