Efficient multilevel phase holograms for CO_2 lasers

Multilevel phase holograms for monochromatic radiation at a wavelength of 10.6 microm are recorded as surface relief gratings with multilevel discrete binary steps. Our experiments show that diffraction efficiencies close to 90% can be achieved both for transmissive and reflective elements. The reduction of efficiency due to errors in the depth and the width of the step levels is considered.