COMPARISON OF METHODS FOR DETERMINING THE BIAS INDEX OF A DICHROMATEDGELATIN HOLOGRAM

Determination of the bias refractive index of a holographic emulsion b efore exposure and after development is an important factor in the des ign of holographic optical elements. Several experimental methods are discussed for determining the bias index of a volume hologram in dichr omated gelatin, and the results for each technique are presented. It i s shown experimentally that these measurement methods yield different results for the same hologram, and the cause of the differences is pro posed to be a variation of the bias index with depth in the hologram. An index measurement technique is also presented that accounts for var iation in the bias index and is shown to yield an accurate value for t he bias index.