
363Introduction to Optical Coatings and Thin Film Production
Chapter 13
at g = 1.0, it is just possible to insert it at every interface without altering the pitch of the
index variation. e resulting structure with its sinusoidal or cosinusoidal variation of
index is known as rugate. Such rugate structures exhibit the fundamental reection peak
but lack the higher orders and are much used in applications such as laser protection.
We have already alluded to a useful shorthand notation that helps in specifying
designs where quarter-wave optical thicknesses at λ
0
are indicated by a capital letter.
When only two materials are involved, it is usef