surfaces (in mid air) of constant OPL (optical path length)
In a perfect optical system or a first order optical system all wavefronts are either planar or spherical.
Wavefronts stay after reflection perpendicular to the propagation direction of the light.
number of wavelengths per cm
[table caption=”sample wavenumbers” width=”300″ colwidth=”100|100|100″ colalign=”left|left|left”]
wavenumber (cm^-1),wavelength (um),frequency (THz)