Superimposed CGHs on metals using laser ablation of diffractive pixels

By direct interferometric laser ablation, the individual pixels of the CGH are generated in such a way that all pixels contain a diffractive substructure consisting of linear gratings of the same period, which diffracts incident light in defined directions. Each individual CGH is assigned a specific type of substructure. This can be a different period of the grid lines or in the simplest case a different orientation of the grid lines. The individual pixels of the CGH are arranged locally in such a way that they do not overlap. This can be done by dividing the targeted writing area into larger pixels, which in turn are subdivided into subpixels, each subpixel being assigned to a particular CGH. Alternatively, the individual CGHs can be written very close to each other so that they do not overlap but can still be illuminated with the same readout beam. This method has been successfully tested in practice. With the diffractive laser scanner developed at IFNANO, five different CGH were written close to each other in one process step. The pixels of the CGH had a diffractive substructure of linear gratings with a grating period of 1.5 µm. Each of these CGH generates an image in the focal plane of the illumination beam in the direction of the 0th order as well as in the +- 1st and higher diffraction orders of the diffractive substructure. If the orientation of the grating lines is varied for each CGH, all images of the CGH still overlap in the 0th order, but separate in the first and higher diffraction orders.