Figure 4-32. Light ray striking coated surface (coating one-half wave length in thickness).

TM 9-258

c. If, however, the film were only one-quarter of a

each other (fig 4-33). The radiant energy, which is light,

wavelength in thickness, the reflected waves would

is not lost when the reflected waves are canceled;

follow paths which would cause them to interfere with

instead, this energy is contributed to the refracted light.

each other and the reflected waves would cancel

Figure 4-33. Light ray striking coated surface (coating one-quarter wavelength in thickness).

top surface so that the two are 180ƒ out of phase. The

d. Another way to understand the action of coated

optics is to consider two incident light waves: ray 1 and

vibrations of these two coincident reflected waves then

next oncoming wave, ray 2. With a film of one-quarter

are in opposite directions and cancel each other, the

wavelength in thickness, the time required for a wave in

same as two matched teams in a tug of war, pulling with

ray 1 (fig 4-34) to travel from the top of the film to the

equal force, remain stationary. Because of the 180

bottom and return results in a one-half wavelength lag

relative to the reflected wave from the next oncoming

wave, or to the coincident reflected wave in ray 2 at the

4-33