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abcrelativity
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I have a question. If you have two light beams of different frequencies, would you observe interference fringes?
abcrelativity said:Hi Cortiver, you seem to answer my question. This is for two light beams so frequency difference is really small (much less than 10 Hz). It is a difference of frequency of 1 part per 10'000 with respect to the average frequency of daylight. What I am not sure to understand is what would be the beat frequency?
cortiver said:Then when adding these two light beams you have a beat frequency fb = f1 - f2.
abcrelativity said:Hi Cortiver, you seem to answer my question. This is for two light beams so frequency difference is really small (much less than 10 Hz). It is a difference of frequency of 1 part per 10'000 with respect to the average frequency of daylight.
abcrelativity said:Is there a way to quantify the beat frequency? Maybe if you have a reference of a book with this problem would be usefull..
cortiver said:This is an interesting question. It turns out that the answer is no. This is pretty straightforward to see mathematically, but for the benefit of intuition it's instructive to consider the case when the light beams have two frequencies f1 and f2 which are very close, but not quite equal. Then when adding these two light beams you have a beat frequency fb = f1 - f2. If the two light beams are in phase at time t = 0 (so you have constructive interference), then at time t = pi/fb the light beams will be 180 degrees out of phase (so you have destructive interference). However, unless f1 and f2 are really close (say within 10Hz of each other), then the beat frequency will be too fast the human eye to resolve. In that case the light intensity that we will see is the average of constructive interference and destructive interference, which amounts to no interference at all.
e.bar.goum said:I think you're mixing up sound and light. The ear can resolve beat frequencies at 10Hz seperation. Visible light is many orders of magnitude higher in frequency (THz). In addition, considering that a linewidth of 10 Hz is an extremely good laser, such a restriction would mean that in practice we would never see interference fringes. (And certainly not before a decade or so ago).
An interference fringe is a pattern of light and dark bands that appears when two or more light waves interact with each other. It is caused by the superposition of the waves, where the peaks and troughs of the waves either reinforce or cancel each other out.
Interference fringes are created when two or more light waves of different frequencies overlap and interfere with each other. This can occur naturally, such as with sunlight passing through a thin film of oil, or it can be artificially created in a laboratory setting using specialized equipment.
The frequencies of the light waves determine the spacing and visibility of the interference fringes. Light waves with similar frequencies will produce closely spaced and distinct fringes, while waves with very different frequencies will produce wider and less defined fringes.
Interference fringes are used in many scientific experiments as a way to measure and analyze the properties of light, such as its wavelength, frequency, and polarization. By studying the patterns and behavior of interference fringes, scientists can gain a deeper understanding of light and its interactions with matter.
Interference fringes have many practical applications, including in microscopy, spectroscopy, and interferometry. They are also used in the construction of devices such as lasers, optical filters, and interferometers. In addition, the study of interference fringes has led to advancements in fields such as astronomy, telecommunications, and medical imaging.