WAVELENGTH MISMATCH CORRECTING ELEMENTS FOR VOLUME HOLOGRAMS WRITTEN ON A LASER PATTERN GENERATOR

Holographic optical lenses based on volume gratings commonly suffer fr om severe aberrations due to wavelength mismatch between recording (bl ue-sensitive material) and application (often employing diode lasers). Here, methods are described for the precompensation of the aberration s at the recording. Both, aberrations in the phase of the reconstructe d wave from the desired wave ('wave aberration'), as well as aberratio ns in intensity resulting from deviations from the Bragg condition dur ing reconstruction ('Bragg aberration') need to be compensated for. Th e design method for generating the computer generated holograms is des cribed which are used as precompensating elements in the recording ste p of the interferometrically produced holographic optical elements. Th e computer generated holograms are written on a laser pattern generato r. Test results of our laser pattern generator are shown to demonstrat e its capability for this process. The measurement of the aberrations at the design wavelength in the near infrared is a very important step because it allows to eliminate in a second recording process misadjus tment errors which will occur during the first recording step. By modi fication of at least one of the computer generated holograms the conve rgence of the procedure can be achieved.