How Can Thin Film Interference Cause Complete Destructive Interference?

[maccha]

I've learned that when a wave is partially transmitted and partially reflected, it loses some of it's amplitude in order to conserve energy. How then, in thin film interference, can one wave produce complete destructive interference with the other if it has been partially transmitted? Wouldn't the two waves have different amplitudes?

 

[ehild]

For complete destructive interference, the two waves need to have equal amplitudes. Such complete destructive interference can happen in the reflected light when a thin film of appropriate thickness and refractive index covers a substrate. One ray is reflected directly from the front surface of the film. The remaining light is transmitted into the layer, and partly reflected at the back surface. This ray travels back, and partially transmitted at the film-air interface. This ray interferes with the first one.

ehild

 

[kerimek]

Thin film interference is a phenomenon that occurs when a wave passes through a thin film and reflects off of multiple surfaces, resulting in constructive and destructive interference. While it is true that a wave loses some of its amplitude when it is partially transmitted and partially reflected, this does not necessarily mean that the two interfering waves will have different amplitudes.

In thin film interference, the two interfering waves are typically very close in amplitude, as they are both derived from the same incident wave. The key factor that determines whether the interference will be constructive or destructive is the phase difference between the two waves. If the two waves have a phase difference of 180 degrees, they will interfere destructively and cancel each other out. This does not necessarily require the two waves to have different amplitudes.

Additionally, in thin film interference, the thickness of the film also plays a crucial role in determining the phase difference between the interfering waves. As the thickness of the film changes, so does the phase difference, resulting in varying degrees of constructive and destructive interference.

In summary, thin film interference is a complex phenomenon that involves not only the amplitude of the interfering waves, but also their phase difference and the thickness of the film. It is possible for two waves to have different amplitudes and still produce complete destructive interference, as long as they have a phase difference of 180 degrees.