Spatial Manipulation of a Supercontinuum Beam for the Study of Vortex Interference Effects

Abstract

In this work, we generate optical vortices from the supercontinuum output of an ultrafast laser interacting with a micro-structured fiber. Using a segmented spatial light modulator, multiple vortices are designed and dynamically generated and shifted in order to observe their superposition in the image plane. It is shown that single-color patterns of exquisite complexity can be generated across a wide frequency range. Multi-color interference patterns are experimentally generated and compared to the results of computer simulations. Multiple vortices of varying colors are also generated and independently controlled, demonstrating that no spatial interference occurs. Experimental results are compared with theoretical and numerical simulations, showing excellent agreement.

Topological Charge of Multi-Color Optical Vortices

“…Since the angular derivative of Equation ( 7) is ∂E(r, ϕ, z)/∂ϕ = inE(r, ϕ, z), then, according to Equation (3), the TC of the superposition (7) with arbitrary colors is equal to the TC of each beam: TC = n. This result is simple, but practical generation of the superposition (7) is challenging, since it requires that, in the waist planes of each colored Gaussian beam, different SPPs be placed, the maximal relief depth h s of which is matched with the wavelength λ s of the incident light: 2πh s (n 0 − 1) = nλ s , with n 0 being the refractive index of the SPP material (we suppose that there is no dispersion of the refractive index). However, if an amplitude fork grating is used, as in [9,18], then all spectral components of the beam have the same TC. However, due to diffraction by the grating, monochromatic beam components diffract by different angles.…”

“…However, due to diffraction by the grating, monochromatic beam components diffract by different angles. Therefore, in [18], light rings of different colors are shifted relative to each other. This shift can be compensated by a prism.…”

“…Thus, only an instantaneous phase value can be visualized, i.e., the phase in a specific moment of time. The TC of a multi-color beam can be determined not only by the instantaneous phase distribution, but also by counting the number of fork teeth in the interference pattern obtained by coherent addition with a tilted plane wave [11] or by addition of the beam with itself but with a conjugate phase [18].…”

“…The white vortex was obtained in [16] (as in [9]) by adding a prism into the optical setup, which compensated the dispersion of the grating in the modulator. In works [17,18], supercontinuum optical vortex pulses were studied experimentally (bandwidth from 500 nm to 800 nm). As in [9], the optical vortex in [17,18] was generated by forked diffraction grating, synthesized on a reflective SLM.…”

“…In works [17,18], supercontinuum optical vortex pulses were studied experimentally (bandwidth from 500 nm to 800 nm). As in [9], the optical vortex in [17,18] was generated by forked diffraction grating, synthesized on a reflective SLM.…”