Diffraction patterns with mth order symmetry generated by sectional spiral phase plates

The possibility of generating diffraction patterns with mth order symmetry when laser beams of different wavelengths illuminate sectional spiral phase plates (SPPs) is investigated analytically, numerically and experimentally. Such distributions are generated by a SPP with m sections in which the phase increases from 0 to 2p for the base wavelength. If the wavelength of laser light is changed, we get a decomposition of the mth order vortex beam into m off-axis vortices of the first order. We show that generating array of first-order optical vortices by the sectional SPPs can be dynamically controlled by the laser wavelength. Numerical simulation and experimental results are in a good agreement with the analytical calculations.