Bragg Selectivity
In the case of a simple Bragg reflector the wavelength selectivity can be roughly estimated by, where is the vacuum wavelength of the reading light, is the period length of the grating and is the thickness of the grating. The assumption is just that the grating is not too strong, i.e., that the full length of the grating is used for light diffraction. Considering that because of the Bragg condition the simple relation holds, where is the refractive index of the material at this wavelength, one sees that for typical values one gets
showing the extraordinary wavelength selectivity of such volume holograms.
In the case of a simple grating in the transmission geometry the angular selectivity can be estimated as well:, where is the thickness of the holographic grating. Here is given by 2). Using again typical numbers one ends up with
showing the impressive angular selectivity of volume holograms.
Read more about this topic: Volume Hologram
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—Melvyn Bragg (b. 1939)