Achromatic waveplate is similar to Zero-order
waveplate except that the two plates are made from
different materials, such as crystal quartz and magnesium
fluoride. Since the dispersion of the birefringence can be
different for the two materials, it is possible to specify the
retardation values at a wavelength range. Hence, the
retardation of the resulting waveplate can be made to
low sensitivity to wavelength change.
Etalon
is narrowband wavelength filter. An Etalon
consists of two partially transmission mirrors that are
separated by a specified distance. It's based on the
interference of multiple beams. It's widely used as
tunable filter, wavelength locker, etc.
2007-12
