The hologram is image focused making it possible to increase the efficiency of the optical reading

摘要

A focused-image hologram recorded in a thin phase medium having a high- frequency line spacing, such that the ratio of this line spacing to the wavelength of the readout light beam is greater than one but less than two, when read out with a light beam inclined at an angle greater than 30. degree. with respect to the normal to the plane of the focused image hologram, results in an optical readout efficiency approaching 50%, compared to the theoretical maximum optical readout efficiency of about 34% of a coarse sinusoidal phase grating having a line spacing much larger tha twice the wavelength of the readout light beam.