Extending the use of commercial Q-plates for the generation of high-order and hybrid vector beams

Abstract

Commercial non-tunable q-plates have become popular optical elements to generate vector beams at the design wavelength where the device exhibits half-wave (HW) retardance. However, their use is restricted since both the topological charge and the operating wavelength are set in fabrication. In this work, we report how to make such commercial q-plates more versatile for generating vector beams of higher topological charge and in different wavelength ranges. First, we show how to add, subtract or change the sign of the charge, by combining q-plates with HW plates. Second, we perform a broadband spectral characterization of the <i>q</i>-plate retardance, and identify the wavelengths with retardance values relevant for vector beam generation &pi;, ±&pi;/2). The wavelength is then used as a tuning parameter to change the device performance from a HW q-plate to a QW <i>q</i>-plate. The vector beams expected at these QW wavelengths are obtained as a superposition of the input polarization state and the output state of a HW <i>q</i>-plate. Experimental results are shown using the red and blue lines of an Ar-Kr laser. For input linearly polarized light of 488 nm the device generates hybrid vector beams (where the ellipticity varies with the azimuthal angle), while for 647 nm pure radial vector beams with constant ellipticity are obtained. These results could extend the use of commercial <i>q</i>-plates for multicolor vector beam applications.