Intensity control of the focal spot by vectorial beam shaping

A vectorial beam shaping algorithm is presented for the design of a phase-only diffractive optical element to achieve a given target intensity profile in the focal plane under tight focusing conditions. The underlying iterative optimization scheme is based on the Richards–Wolf vectorial diffraction theory and the Gerchberg–Saxton method, and is suitable for an arbitrary incoming polarization distribution, since only the magnitudes of the field vectors in the focal plane are reshaped. The efficiency of the method is numerically demonstrated for flat-top beam shaping examples of linear and circular incoming beam polarizations and square and circular flat-top region shape. A diffraction efficiency of 97.1% and a uniformity error of 4.8% were achieved in the case of focusing a Gaussian input beam onto a 50λ × 50λ square flat-top region with a 1.4-NA lens.