Simulation of Diffraction on a Stepped Spiral Phase Plate with Radiation of Different Wavelengths in order to Form Optical Vortices of Different Orders

The diffraction of a Gaussian beam by a stepped spiral phase plate (SPP) is studied for different wavelengths of laser radiation. Numerically, using the finite difference time domain method, the formation of a vortex beam by a SPP with different number of uniform sectors is shown. The diffraction of laser radiation with a wavelength in the range from 0.5 to 1.5 μm by a SPP with 20 sectors was calculated and the transformation of a Gaussian beam into a vortex beam with different topological charges due to variations in wavelength was shown. To determine the value of the orbital angular momentum (OAM) of the formed vortex beam, the weight spectrum is calculated on the basis of angular harmonics (AH). We estimated the vortex beam quality of an integer order using a multichannel diffractive optical element (DOE), which implements the optical decomposition of the light field according to the AH basis. The detection of vortex beams with 1st, 2nd and 3rd order is shown numerically by matched filtering.