Polarized Light
By: Thomas Lee Abshier, ND
- The photons approaching the reflecting interface have an E field which can be oriented
at any angle from parallel to vertical in reference to the reflecting surface. The
polarization angle of light is named according to the normal (perpendicular) to any
chosen reference surface, but having noted that, in this discussion, horizontally
polarized will refer to photonic E fields that are parallel to the horizon, or the
surface of the material. Likewise, photonic E fields that are vertically polarized
are oriented parallel to the vertical/normal of the surface.
o Non-metallic substances reflect light polarized parallel to their surfaces more
than light polarized vertically.
§ This may be because the vertically oriented electric vector engages the bulk of
the material more than the parallel E field vector. In other words, a portion of
the E field vector penetrates into the non-metallic substance and has the potential
to engage a surface or point for reflection. Whereas, a horizontally polarized photon
is skimming the top of the surface along its entire breadth.
- The key observation that can be inferred from this experimental data is that photons
do not engage reflective collisions only by their forward directed kinetic energy
field. The transverse E fields of the photon are in some way engaged in polarizing
the media and producing capture or reflection.
§ The reflectivity of metallic substances is dependent upon the angle of incidence,
just non-metallic substances. But, the reflectivity may be so much higher because
of the large numbers of concentration of conduction band orbitals.
§ Metallic substances absorb photons for the same reason that non metals do, the
photons penetrate, and are captured. The evidence of photonic absorption is obvious
to the person who has touched a quarter that has been sitting in the sun – it got
hot. There were photons that penetrated, transmitted their energy to electrons,
electrons that collided with nuclei and shook the lattice, raising the heat of the
metal.
o Reflection: Photons approach the reflective interface with two components of velocity,
1) perpendicular, and 2) parallel to the interface.
§ The perpendicular component of the photon attempts to compresses the electron cloud
into the nucleus, and the parallel component of the photon’s energy moves the electron
cloud tangential to its orbit.
§ The energy directed perpendicular to the interface will produce a rebound of energy
that reverses the perpendicular component of the photon’s velocity.
§ The energy directed parallel to the interface will either not interact with the
reflective substance, or simply conduct forward in the metallic media for a short
distance, and then disengage as the photon continues on in its original direction
after re-forming.
§ When the photon reflects, the horizontal velocity retains its direction, while
the vertical velocity of the photon has reversed itself. This causes a phase reversal
when the photon goes from medium of low refraction to a medium of high refraction.
There is no reversal when the photon reflects off a medium transition from high
to low Index of Refraction.
§ The net effect of reflection is to produce a reflected photon that makes an equal
angle, incident and exit, compared to a line drawn normal (perpendicular) to the
reflecting surface.
o A small increment of energy from the reflected photon is retained by the metal/mirror.
The amount of energy retained by the mirror upon reflecting the photon is held at
first by the forward velocity of the electrons the photon has encountered in its
collision. Then as those electrons collide with the nuclei and lattice of the bulk
material, the energy is dispersed as thermal energy.
o The amount of energy given to the electrons by the portion of the photon traveling
the normal (perpendicular) to the surface of the medium is:
§ Enormal = (Ephoton sinè).
§ But, in the rebound, that amount of energy will accelerate the mirror to a certain
velocity dependent upon its mass. E = ½ mv².
§ The velocity of a large mass will be small, but that amount of kinetic energy given
to the mirror must be considered in the conservation of energy of the total system.
§ Thus, the rebounded photon will have a lower frequency, and lower energy so as
to balance the amount of energy transferred to the mirror.
§ Considering this problem from a conservation of momentum perspective: The photon
has rebounded normal to its original direction, and according to the conservation
of momentum, the mirror is given an increment of momentum double the magnitude of
the momentum of the incoming photon.
- Note the discussion of the problem in www.physicsforms.com re: the problem of conservation
of momentum and conservation of energy. http://www.physicsforums.com/archive/index.php/t-64812.html
- Summary of essay: The energy and momentum must both be conserved when a photon is
reflected. The momentum of the mirror (or solar sail in the physics forum discussion
above) corresponds to a particular velocity and kinetic energy that the mirror acquired
by the collision.
- The result of the mirror moving away from the photon with a velocity causes the emitted/reflected
photon to generate with a lower frequency, which of course corresponds to a lower
energy. Thus, the total kinetic energy of the system of the system remains the same
before the reflection as after.
o Non-Metallic reflection: A photon striking a non-metallic substance can be absorbed
and captured by the orbital electron system, or some other mode of energy containment
such as molecular vibration, atomic rotation, or atomic translation.
§ If the non-metallic substances do not absorb the incident photons, they will reflect
or refract the remaining photons.
§ When refracted or absorbed, both parallel and perpendicular energy components of
the photon penetrate the medium. In the case of non-metallic reflection, the surface
atoms do not absorb or transmit the incoming photon.
- The other consideration in reflection vs. refraction is the question of how big an
area the photon impacts. The size of a visible light photon (400-700nm) is too large
to be reflected by a single metallic atom (.1-.2 nm). Thus, the photon’s energy
would be spread out over an area significantly larger than a single atom. Thus,
the reflection and refraction type of phenomenon would be mediated by a collision
that was distributed over an area, and participated in by many atoms.
- In photon scattering, the photon energy may increase, decrease, or stay the same.
An irregular molecular surface or fine particles in the air will scatter photons.
Scattering is the phenomenon that creates the blue sky on the horizon, the white
color of clouds and fog, and the whitish area of sky around the sun. There are many
types of scattering, each one associated with a particular configuration of photon-mass
interaction.
- In photon polarization, the direction of the E field determines the nomenclature
of the polarization of a photon. Horizontal polarization refers to an E field aligned
with the horizon, and vertical polarization refers to polarization perpendicular
to the horizon. The more general terminology for the polarized light is parallel
and perpendicular to the plane of incidence. The plane of incidence is the plane
perpendicular to the reflecting surface and perpendicular to the incoming photon.
Light emitted from the sun, incandescent lights, fluorescent lights, chemical reactions,
nuclear reactions, and most other radiant sources (prior to some special processing)
is randomly polarized.
o At all angles, horizontally polarized light reflects to some extent off of a non-metallic,
visible light-transparent air-glass or air-water interface.
o But, vertically polarized light does not reflect at all at the Brewster angle.
Thus, there is some effect in play, some aspect of the photon, which is contributing
to reflection that is not operating when the photon is incident with only horizontally
polarized light.
o At the Brewster angle (around 60 from vertical for water), vertically polarized
light transmits fully/totally/completely into the refracting media. Possibly this
is because the photon is polarizing the media and penetrating into it with the vertically
polarized aspect of the photon. Thus, an aspect of the photon-media interaction
that produces a reflection appears to be how deeply the photon polarizes the substance
below its surface layer, angle of the polarization of the media, and the angle of
the bonds at the surface of the media.
o The metallic media is populated with conduction band electrons, which are in general
capable of reacting against the photon-applied accelerating force. And, because
there are no gaps in the conduction band, there is no significant transmission, or
absorption at any frequency. Thus, the metal will reflect all frequencies of visible
photons, and in general reflect a higher percentage of those photons at all angles.
o When randomly polarized light hits the interface at the Brewster angle, at about
60 from vertical, all the vertically polarized light is refracted into the water.
This leaves only horizontally polarized light as the constituent of the reflected
light beam. Thus, sunglasses that block horizontally polarized light will reveal
a glare-free view of the surface of the water at that angle.
o Polaroid material is composed of plastic with long molecules drawn so that the
molecules are arranged side by side, all pointing in one direction. When the E field
of the photon vibrates in the same direction as the molecule in the Polaroid film,
the energy of the photon is absorbed and does not transmit through that Polaroid
material. Thus, when the Polaroid film, and its constituent long molecules are oriented
horizontally, it will block horizontally polarized photons. Vertically polarized
photons will pass through these molecules because there is no current induced that
can flow a distance and dissipate the energy by the collision of the electrons.
o Thus, Polaroid sunglasses will block horizontally polarized photons that reflect
off the water at the Brewster angle, and there will be no glare/reflection off the
water at that angle. At he Brewster angle, the vertically polarized photons do not
reflect because they are refracted into the water, and the Polaroid film of the sunglasses
will block the horizontal photons. The randomly polarized photons (other than vertical
and horizontal) will still be reflected and transmit through the sunglasses.
http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/polar.html#c2
