Handbook of Biomedical Optics

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2.1 Huygens’ Principle

According to Huygens, each point on a wave front serves as the

source of a spherical secondary wavelet with the same frequency

as the primary wave. e amplitude at any point is the super-

position of these wavelets. Note that Huygens’ principle con-

siders diraction as a summation of spherical waves, not as a

summation of plane waves, as we will consider in Section 2.7.

is theory gives a simple qualitative description of diraction

but needs to be adapted to give good agreement with more exact

formulations that will be shown later in Section 2.6.

Consider the propagation of a plane wave. Each point in the

wave