Wednesday 12 August 2015

quantum mechanics - Polarized Filtering Frequency Shift?


A polarized filter is exposed to a unpolarized light source. The output of the filter should be of lower intensity, hence lower energy.


Should not the filtered light be of a lower frequency to account for the lower energy ( E = h v) ?



Answer



Light is quantized so the energy $E = n h \nu$, where $n$ is the number of photons in the optical pulse. (If you don't like to think in terms of pulses, then $P = n h \nu$ denotes the optical power of the beam, with $n$ here being the number of photons per unit time). The polarizing filter absorbs or reflects some of the photons in the light beam, which is why the energy/power measured after the polarizer is reduced. But the frequency remains intact.


You may now like to think of what would happen if a single photon (i.e. $n = 1$) was subjected to this experiment. The answer is that either a photon with energy equal to that of the photon emitted by the source will be found, or nothing will be measured.



No comments:

Post a Comment

Understanding Stagnation point in pitot fluid

What is stagnation point in fluid mechanics. At the open end of the pitot tube the velocity of the fluid becomes zero.But that should result...