The photographic layers must be be sensitive to the wavelength of the laser.
Also the recording material must be suitable for high Spatial frequencies
which require a very fine grain. The carrier frequency of the microscopic
interference pattern is dependent on the wavelength and on the angles Bo 0f
the object and [Jr of the reference beam measured from the perpendicular of
the hologram plate. According to Fig. 4.4 it can be calculated by: