Circular Polarization of Light, Circularly polarized Light

Hi Montec,

Thanks for your help.
Personally, RHCP or LHCP state of light can be two distinct states provided we are able to define what makes a Right circular polarizer and a Left Circular polarizer.
In the case of a linear polarizer, we can distinctly define the state of polarization depending on the orientation of the polarizer. In fact, there are many ways that light can be linearly polarized that you have brought up.
One of the peculiarity of linearly polarized light is the way it behaves when passing through another linear polarizer.
If we draw a line across a linear polarizer and designate it as the polarizing axis of the linear polarizer, then the photons that passes through can be said to be polarized in say, the x-state.
If we rotate the linear polarizer by 90 degree or 270 degree, what we will obtain for light passing through the same linear polarizer is the y-state.
If we next place two identical linear polarizers sequentially, we will obtain the following results(see my posting on 2 Mar 06):
2.1) l ψ> --> [Px] --> lx>
2.2) l ψ> --> [Py] --> ly>
2.5) l x> --> [Px] --> lx>
2.6) l y> --> [Py] --> ly>
2.7) l x> --> [Py] --> 0
2.8) l y> --> [Px] --> 0

Unfortunately, if you do an experiment using a commercial Right and Left Circular polarizers, you do not obtain the same result as predicted using Quantum Mechanics:

2.3) l ψ> --> [Pr] --> lR>
2.4) l ψ> --> [Pl] --> lL>
2.9) l R> --> [Pr] --> lR>
2.10) l L> --> [Pl] --> lL>
2.11) l R> --> [Pl] --> 0
2.12) l L> --> [Pr] --> 0

It is my failure to observe the result as predicted using Quantum Mechanics that led me to ask the questions whether there is a DISTINCT Right and Left Circularly Polarized state of light.

Confused2 (citing from Schneibster) had brought up PHASE as a possible explanation on why I do not observe the total cancellation of light when passing through the filters as shown in the Optografix diagram. On this subject, I have done two experiments using two sets of filters:

1) l ψ> --> [Px1] --> [Q1] --> [M(mirror)] --> [Q2] --> [Px2] --> l Lb>
2) l ψ> --> [Px1] --> [Q1] --> [M(mirror)] --> [Q1] --> [Px1] --> l La> (Original Optografix set up)

The intensity of lLb> is the same as lLa> notwithstanding that the distance between the the first and the second sets of circular polarizers is varied.

I hope both you and Confused2 could now appreciate why I disagree with the explanations put up by Schneibster.

I look forward to your help, Confused2 , Schneibster or anybody who has an intimate knowledge on this subject to shed more light.

Cheers

Hi hexa

What is the angle of the light to the mirror? Metallic reflection will cause a phase change between the two component electrical fields p and s. Where p is a component parallel to the surface and s is 90 deg to the surface. Silver has a 90 deg phase difference at an angle of incidence at 75 deg 35 min( to the normal). A 90 deg phase change should keep the light circularly polarized. A 0 deg incidence for the light will give a 0 deg phase angle.

Any other angle will result in elliptical polarization which will not be stopped by your set up.

Hope this helps.

Hi hexa
Another thing about the mirror, if it is a metal backed mirror your set up will not work. The glass will change the phase between the p and s field components at around 59 deg incidence angle. The only angle that will work is a 0 deg incidence. IE the light is perpendicular to the mirror.

Hi Hexa, Montec,

Many thanks to Montec..
I hope I haven't missed hexa's point ..
Are LHCP and RHCP utterly and physically the 'same' thing?

.. circular dichroism..
http://www.answers.com/main/ntquery;jsessi...lar%20dichroism

This last bit could lead us into discussion about what the meaning of 'same thing'.. interesting..

---------------

It seems there are ways to 'enhance' a quarter wave plate to increase the effective bandwidth .. this may make it better 'photographically' but worse 'optically'. Hexa doesn't state he is using monochromatic light and if so then how it is generated. (Sodium light, laser, dichroic filter ??) . How the light has been matched to the centre frequency of the QWP is also undefined. Assuming the filter is calcite .. I would expect this to have a bit of 'fog' in it which would make it less than perfect.

On the 'phase' front - I'm not sure what Schneibster intended .. I think it might have been a mistake.. I can only say my own references to phase (?) were probably unhelpful.
The 90 degree rotation (linear polarisation) after two QWPs doesn't help to answer whether it is + or - 90 degrees and therefore does not distinguish between RHCP and LHCP (despite what the Instagrafix diagram has written on it).

For the purposes of discussion can I suggest you might be able to turn RHCP into LHCP simply by looking at it the other way up .. and if not then why not.
Again this could lead us into discussion about the meaning of 'same thing'..

Hopefully the references to circular dichroism will help. On a good day I think this will finally clarify whether or not LHCP and RHCP are distinct.

-C2.

Hi Montec & Confused2,

Thanks for your help.

On Montec question:

about the experiment:

The angle of inclination for (2) is 0 degree but not in (1).
The source of light that I used for the experiment include ordinary white light, red and green laser. The results are identical.
I also vary the the distance between the two polarizers as well as the separation between the linear polarizer and the QWP, the results are identical.
Finally, I also vary the thickness of the QWP, the results are again identical.

The commercial photographer's circular polarizers are constructed as follows:
Right circular polarizer (RCP) = Linear polarizer + Quarter wave plate
Left circular polarizer (LCP) = Quarter wave plate + Linear polarizer.

Since the QWP is made of birefrigent materials, I think the light that passes through a RCP will tend to depolarize the linear polarized light after passing through the first linear polarizer. However, I must add that the depolarization may not be total as this is probably dependent on the surface characteristics of the QWP. If the two filters are bonded together, then the bonding may somewhat affect the degree that the depolarized light eventually emerged from the RCP.
In that sense, it may give rise to the mistaken belief that there is a circular and elliptical polarized states. As such I don't think it is correct for Richard Feynman to describe the circular and elliptically polarized state of light the way he did in his Lectures on Physics, Vol.I, pg 33-2.

In the case of a LCP, the light that gets through will take on the orientation of the linear polarizer. This can easily be confimed by placing another linear polarizer after the LCP to verify the state of light passing through the LCP.

In that sense I think many authors of Physics Text including the revered Nobel laureate, Richard Feynman also made the same mistake in perceiving that there is a distinct Circular Polarized States of Light similar to the linear polarized states.
This led Richard Feynman to draw the wrong conclusion with regards to the elegance of Quantum Mechanics to account for the quantum states of light, see Vol.III, pg.11-11.
The prediction using Quantum mechanics simply will not yield the result based on how we construct a Right and a Left circular polarizer.

I hope both of you could make an attempt to verify my assertion.

Cheers.

Hi hexa,

Interestingly this beetle seems to have mastered polarisation - LHCP and RHCP must be distinct for this beetle to work .

http://www.polarization.com/beetle/beetle.html

-C2.

Hi Confused2,

Thanks for providing this rather interesting website.
I was trying to see if they provide the construction details of a Right and a Left circular polarizer.
Unfortunately they do not provide anymore information than what Optografix had already given us.

Would you or Montec like to provide some insight on what is being observed in this website?

Cheers.

Hi Confused2, Montec, Schneibster, Maltida and others,

Let me make the following clarification pertaining to the chiral properties of material. The molecular structure may be right handed or left handed.
A right handed crystal may rotate light passing through it in one direction while a left handed crystal may rotate light in the other direction.

Notwithstanding these properties exhibited by the chiral properties of these crystals, it is incorrect to describe the light that is transmitted through it as having a Right circular polarized state or a left circular polarized state. It is also incorrect to assume that the light passing through a right handed crystal will be cut off by another left handed crystal or vice versa similar to what happen to linearly polarized light passing through another linear polarizer.

It is for this reason that I disagree with Richard Feynman when he tried to use Right and Left Circular Polarization of Light to illustrate the elegance of Quantum Mechanics. I could not see how a composite filter would yield the result that he claimed in his book, Feynman Lectures on Physics.

Cheers.

Hi Hexa,

I too have the same problem in trying to comprehend the topic on Circular Polarization of Light. I have come to realise that your account of Circular Polarization of Light provide the best explanation so far. It would be great if you could share with us your account of Malus Law which you claim is based on another novel particle approach that does not violate Causality and Locality. In short, Local Reality is maintained.

From your account of the Double Slits Experiment involving electrons, you have suggested a novel approach to account for the observation done by the Hitachic scientists ( http://www.hqrd.hitachi.co.jp/em/doubleslit.cfm ). From the video clips provided by Hitachi, I cannot but form the conclusion that the only reality of the electron is that they are pure particles and not some particle-wave enigma that contemporary science has painted itself into a corner.

I find the explanation using the Copenhagen Interpretation or the Aharonov-Bohm Effect or the Many Worlds Hypothesis to account for the Double Slits Experiment irrelevant in the light of your novel proposal of electron pairs. Your electron pair is not inconceivable and is based on simple common sense logic that do not require us to invoke some ridiculous postulates.

I would appreciate if you could further elaborate on how the electron pairs could account for the observation as seen in this Hitachi website.

Yours hopefully,

Maltida

03 21 06

Hey there:
I am late to these very interesting discussions, so will be brief. I am happy to have seen the discussion between Schneibster and Hexa on quantum entanglement. I like your invocation of Noether's theorem in this discussion, Schneibster.

Hexa: I think you are thinking of entanglement in a very classical sense. And your appeal to the polarization of light and Malus's law reflects this. To give you a classical example of a concept in entanglement, think of the double coupled pendulum. The set of differential equations needed to describe the double pendulum system contain terms that couple the pendulums to one another. We cannot perturb pendulum 1 without affecting the motion of pendulum 2. These terms reflect the physicality of the actual pendulum coupling. When we look at two entangled particles, their wavefunctions must have terms that couple their entangled operators together. One cannot describe an entangled property of one particle without referencing that property in the other. No need to be redundent here, but I was thinking that this example might be helpful. [B]

And quantum mechanically, whenever we measure some property of a system, we are disturbing it and forcing it into an eigenstate of whatever operator we wish to measure. Until the measurement, the system is said to be in a superposition of its eigenstates. So Schneibster's analysis was spot on. Very good discussion. I shall come back from time to tome.

Hi Mandisa,

One of the joys of a public site is you never know what (or who) is going to turn up..

I was impressed (understatement) by Schneibster's entanglement explanation.. I'm not sure he knows/knew about Noether's Theorum .. I certainly don't .. I get tantalising glimpses of it on the web.. would you (or anyone) be kind enough to help me find more about it?

To Hexa,

I fear that we may not, in this lifetime, be able to sort out whether or not the device you have labelled as a Left Hand Circular Polarising Filter .. isn't. My conclusion is that they do exist and I suggest they are no more than a linear polariser with the QWP rotated through 90 degrees to bring the 'extraordinary wave' ahead/behind of the 'ordinary wave', the rotation thereby being (whichever) the 'other way'.

-C2.

03 30 06

Hey there C2:
Sure, I just refound this link! Schneibster's explanation invoked Neother's Theorem and set of a flurry of thought and recent research on my part. Typically physics students aren't exposed to the theorem until a first term in a Quantum Field Theory Course. However, whenver you take E &M and look at fields that can be written in terms of a scalar potential, or you do Hamiltonian and Lagrangian formalism, you are invoking Noether's theorem. Noether's theorem states that whenever we have a conservation law, there is a correlated symmetry=>quantity left invariant under a certain symmetry operation. It sounds simplistic, but it is one of the singlemost important theorems in physics! So, whenever a system is invariant under rotations, angular momentum is a conserved quantity, and whenever the system is invariant under translations the system has momentum conservation. When you take your quantum mechanics courses, you will see that indeed, angular momentum generates rotations and translations generate linear momentum. I don't want to get into the time energy uncertainty relation and what that means, because I don't think I or many texts do that relation justice, and hence I have ommitted the energy conservation example from the discussion.

If you would like a deeper classically motivated discussion, see Herbert Goldstein's Classical Mechanics Second Ed, Chapter 9 sections 1-5. This is because he covers The Symplectic Approach to Canonical Transformations, while Noether's Theorem is specifically interested in what happens along symplectic manifolds.

Check this Wikipedia link:
http://en.wikipedia.org/wiki/Noether's_theorem

I hoped this made sense. Schneibster is a far better explainer of details than myself. And particularly his explanation of the entangled degrees of freedom made a lot of sense and partially solved the puzzle for me about how "information" is defined.
For more science talk, check out my blog at http://www.mrigmaiden.blogspot.com
Warmest Regards

Hi Confused2,

Sorry for taking so long to respond to your question.

First, I did not define a circular polarizer in the way I have described. This is the commercial specification from those people selling filters and lenses for cameras.
The way Schneibster defined circular polarised state of light as a clockwise or anti-clockwise rotation of electric vector of light is in accord with Maxwell definition of electromgnetic radiation prior to the introduction of quantum physics at the beginning of the 20th century. This is similar to that described by Richard Feynman in his Lectures on Physics in Vol.I. Personally, I don't think this description represent the Physical Reality of Circular Polarized Light.

If we have a QWP placed after the linear polarizer, then the light that emerges will be defined by the QWP (made of birefringent material). Conversely, if the Linear polarizer is placed after the QWP, then the light that emerges will be defined by the Linear Polarizer.
You can do an experiment to test this hypothesis or one based on the prediction of Quantum Mechanics.

Incidentally, the claim on quantum entanglement and the explanation which Schneibster had provided here is indeed very well crafted. Unfortunately, the claim that either Causality or Locality is violated is irrational to me. Some even claim that it is possible to have instantaneous communication based on Quantutm entanglement.

To me this is simply absurd. The Aspect Experiment that was based on the violation of Bell’s inequality was subsequently claimed as the confirmation of the Aharonov-Bohm Effect and that there is something magical about the Quantum effect. Finally it was also claimed that Locality is violated.

On closer examination of the experimental data and result, it shows nothing more than our inability to account for the observation of Malus Law (the probability of the intensity is based on the cosine square of the angle).

This is where I told Schneibster that I could account for Malus Law that is firmly rooted on Local Reality. It is stochastic and does not violate Causality or Locality. It assumes that the linear polarizers are atoms arranged with a certain orientation and that the photons are pure particles with orientation described by their electric vector.
I was very surprised that by adopting this method that assume photons as particles and the polarizers as atoms (that are aligned and can regulate the passage of photons with a certain orientation through it), I was able to obtain the result predicted by Malus Law.

Thereupon, I went on to investigate the nature of circular polarization of light. Unfortunately, all attempt could not yield the observation that was predicted by Quantum Mechanics.

It is for this reason I raised this topic in the Forum, hoping that some expert could provide me the answer to the nature of Circular Polarization of Light.
In this respect, I must thank Schneibster for the patience and the explanation that he has given me. I must also thank you, Maltida, Montec, KTWong, etc for helping to shed some light on this topic.
With regards to Noether's theorem, I am curious to hear more from Mahndisa on whether the theorem could resolve the dilemma that I have mentioned in this thread?

Cheers.

Not sure if this subject is way beyond me but I thought I should post as I have a slightly differate viewpoint. I am a laser technician so I deal with a little more practice, than theory. However, I do work with a device that uses both left and right circular polarized light. We typically use the terms counter-clockwise and clockwise circular polarization. The device starts out with a laser beam horizontally polarized. It then passes through several optics which do not really matter to this subject but then passes through a beamspitter (bs3) (passing horizontally polarized light and reflecting vertical) then the beam hits a quarterwave plate (wp1) at this state the beam is ccw circular polarized it then reflects off of the target (patients fovea) then returns passes through wp1 again and becomes vertical polarized. The beam is now reflected by bs3 and completes the rest of its optical path which includes another waveplate putting it into cw circular and back to horizontal to be read by a CCD camera (camera that captures infared light with high detail)

Hope this is the kind of stuff your looking for if it is i can go into a little more detail on how this system works as the optical path is very intresting.

I apologize for any spelling/gramatical errors english was never my strong point.

Do we still wish to know if circular polarization exsists?