Take the 2-minute tour ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free, no registration required.

The book I'm reading about optics says at some point that "each color (wavelength) contained in the white light interferes only with itself". But why is this so?

Edit: I moved the rest of the question elsewhere.

share|improve this question
    

3 Answers 3

up vote 9 down vote accepted

Add any instant in time, light of different wavelengths can be said to interfere. However, because of the extreme frequencies of optical light, any cross interference will get time-averaged away very quickly unless the two waves are very close in frequency.

share|improve this answer
    
Very simple and clear. Just one thing: did you mean "At any instant"? Also, I was wondering if I should strip down the question and retain only the first sentence; the rest might be a bit messy or slightly off-topic. What do you think? –  waldyrious Jul 12 '11 at 17:09
    
I think it might be better if I moved the rest of it to another question. I'll do so now. –  waldyrious Jul 12 '11 at 17:19

Interference is not an instant phenomenon but a time-lasting one. The time should be sufficient to speak of certain frequencies. Two different frequencies can be easily distnguished with the corresponding resonators but this process takes time. It is in a long term condition that two frequencies are separated (resonators pumped). Instantly we cannot even speak of a frequency.

share|improve this answer

Imagine two light beam each of its own wavelength $L_1=720\text{ nm}$ and $L_2=719\text{ nm}$. One can show I suppose that every $720$ cycles of the $L_2$ beam the total constructive interference shall repeat.

In air the $L_1$ beam light frequency is $$F_1=\frac{C}{L_1}=417\times 10^{14}\text{ Hz}$$

and therefore the frequency of the interference effect is $$F_\text{int}=\frac{F_1}{720}=57.9*10^{12}\text{ Hz}$$

This frequency is rather high to be detectable. When two light beams are of identical wavelength however, the interference effect is time independent and therefore observed as an interference pattern. It is obvious that there is the interference between light beams of a different "color" albeit difficult to observe. Please read about the white light interferometry.

share|improve this answer

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.