Tunable generation of Bessel beams with a fluidic axicon

Abstract

This paper describes a tunable fluidic conical lens, or axicon, for the generation and dynamic reconfiguration of Bessel beams. When illuminated with a Gaussian laser beam, our fluidic axicon generates a diverging beam with an annular cross section. By varying the refractive index of the solution that fills our device, we can vary easily the spatial properties of the resulting Bessel beam.

Figure 1

(a) When illuminated with a coaxial Gaussian beam, an axicon produces a characteristic interference pattern, known as a Bessel beam. (b) Theoretical cross-sectional profile taken at z^′ in (a). (Inset) Experimental Bessel beam generated by a γ=1° axicon.

Figure 2

(a) Photograph of our fluidic axicon prototype. (b) Fluidic axicon with n_ax>n_PDMS. (c) Fluidic axicon with n_ax<n_PDMS. z_max indicates the approximate propagation distance of the beam core in each case.

Figure 3

(a) Bessel beam cross sections, taken 5 cm after lens f₂, for a range of sucrose concentrations. In the last case (55%, n_ax≈n_PDMS), the axicon’s effect is negligible and we recover a Gaussian beam profile. (b) A plot of the measured Bessel beam core widths against the refractive indices of the fluidic medium in the axicon cavity. For our theoretical calculations, we assumed n_PDMS=1.43±.005. The theoretical curve is asymptotic as n_ax→n_PDMS, but in reality at this point the beam reverts back to a Gaussian beam and the concept of the Bessel beam core becomes redundant.