Finite Reflections: Exploring Limitations of Parallel Mirrors

[Loren Booda]

Two state-of-the-art mirrors are mounted parallel and facing each other. What primarily prevents their reflections from traveling an infinite distance - less than perfect reflectivity, less than perfect flatness, the image of the observer or interference by intervening air?

 

[f95toli]

Impossible to tell.
What you are basically asking it what is limiting the Q value (or if you want, the finesse) of an optical cavity and there is no generic answer to that; it is a combination of many different factors.

Alhough I would expect a high-finesse cavity to be operated in a good vacuum, so I don't think the last reason you mention is actually relevant.

 

[astrokreng]

There are a few factors that contribute to the finite distance traveled by reflections in parallel mirrors. One of the main limitations is the reflectivity of the mirrors themselves. Even the most advanced mirrors are not perfectly reflective, meaning that some of the light that hits them will be absorbed or scattered rather than being reflected. This results in a decrease in the intensity of the reflected light as it travels back and forth between the mirrors, eventually becoming too weak to be seen by the observer.

In addition, the flatness of the mirrors also plays a role in limiting the distance of reflections. If the mirrors are not perfectly flat, the reflected light will become distorted and eventually too distorted to be recognized as a clear image. This can also contribute to the decrease in intensity of the reflections.

Another factor to consider is the position of the observer. As the observer moves further away from the mirrors, the angle at which they see the reflections changes, making it more difficult to see the reflections clearly. This can also contribute to the finite distance traveled by reflections.

Finally, the presence of intervening air can also interfere with the reflections. Air molecules can scatter and absorb light, leading to a decrease in the intensity of the reflections. This effect becomes more significant over longer distances, further limiting the distance that reflections can travel.

In conclusion, it is a combination of factors such as reflectivity, flatness, observer position, and intervening air that ultimately limit the distance traveled by reflections in parallel mirrors. While advancements in technology have allowed for highly reflective and flat mirrors, there will always be some limitations due to the nature of light and its interactions with the physical world.