We used a binary coding scheme based on optical density inside a basic cell to produce a smooth multilevel phase pattern on a photoresist film. This technique, which is as simple as a contact copy, is very easy to control for our type of computer-generated holograms. Preliminary results show that a good blazed profile can be obtained with minimum equipment at low cost. Specialized transmission holograms produced with this technique showed a 40% diffraction efficiency and good quality for 632.8-nm radiation.
Roger A. Lessard,
"New coding technique to obtain multilevel computer-generated holograms in one step," Optical Engineering 32(9), (1 September 1993). https://doi.org/10.1117/12.145065