Design of phase only DOEs with a high signal-to-noise ratio

We report on the design of phase only diffractive optical elements (DOES) with a locally improved signal to noise ratio. The formation of low noise regions is particularly useful for designs where it is difficult to achieve low background noise throughout the entire reconstruction. Such a case may arise in highly quantized elements or elements with a small spatial bandwidth. The DOE design is achieved by a direct search algorithm which allows for the definition of arbitrary low-noise areas in the reconstruction plane. However, the method is not restricted to direct search and should work with all direct schemes. While the local suppression of noise works rather well other performance criteria like diffraction efficiency and reconstruction error do, in practice, not suffer much from the additional constraints. This is due to the advantage that amplitude freedom and phase freedom can be maintained in large areas of the reconstruction. It is shown how this approach may be used in the design of beam sputters to prevent the formation of unwanted repeated spot patterns.