Why is polarization not desirable

Polarized light can be produced from the common physical processes that deviate light beams, including absorption, refraction, reflection, diffraction or scattering , and the process known as birefringence the property of double refraction.

Light that is reflected from the flat surface of a dielectric or insulating material is often partially polarized, with the electric vectors of the reflected light vibrating in a plane that is parallel to the surface of the material. Common examples of surfaces that reflect polarized light are undisturbed water, glass, sheet plastics, and highways. In these instances, light waves that have the electric field vectors parallel to the surface are reflected to a greater degree than those with different orientations.

The optical properties of the insulating surface determine the exact amount of reflected light that is polarized. Mirrors are not good polarizers, although a wide spectrum of transparent materials act as very good polarizers, but only if the incident light angle is oriented within certain limits.

An important property of reflected polarized light is that the degree of polarization is dependent upon the incident angle of the light, with the increasing amounts of polarization being observed for decreasing incident angles.

When considering the incidence of non-polarized light on a flat insulating surface, there is a unique angle at which the reflected light waves are all polarized into a single plane. This angle is commonly referred to as Brewster's angle , and can be easily calculated utilizing the following equation for a beam of light traveling through air:.

By examining the equation, it becomes obvious that the refractive index of an unknown specimen can be determined by the Brewster angle.

This feature is particularly useful in the case of opaque materials that have high absorption coefficients for transmitted light, rendering the usual Snell's Law formula inapplicable.

Determining the amount of polarization through reflection techniques also eases the search for the polarizing axis on a sheet of polarizing film that is not marked. The principle behind Brewster's angle is illustrated Figure 3 for a single ray of light reflecting from the flat surface of a transparent medium having a higher refractive index than air.

The incident ray is drawn with only two electric vector vibration planes, but is intended to represent light having vibrations in all planes perpendicular to the direction of propagation. The incidence plane is defined by the incident, refracted, and reflected waves. The refracted ray is oriented at a degree angle from the reflected ray and is only partially polarized.

For water refractive index of 1. Light reflected from a highway surface at the Brewster angle often produces annoying and distracting glare , which can be demonstrated quite easily by viewing the distant part of a highway or the surface of a swimming pool on a hot, sunny day.

Modern lasers commonly take advantage of Brewster's angle to produce linearly polarized light from reflections at the mirrored surfaces positioned near the ends of the laser cavity. As discussed above, bright reflections originating from horizontal surfaces, such as the highway or the water in a pool, are partially polarized with the electric field vectors vibrating in a direction that is parallel to the ground. This light can be blocked by polarizing filters oriented in a vertical direction, as illustrated in Figure 4, with a pair of polarized sunglasses.

The lenses of the sunglasses have polarizing filters that are oriented vertically with respect to the frames. In the figure, the blue light waves have their electric field vectors oriented in the same direction as the polarizing lenses and, thus, are passed through. In contrast, the red light wave vibration orientation is perpendicular to the filter orientation and is blocked by the lenses.

Polarizing sunglasses are very useful when driving in the sun or at the beach where sunlight is reflected from the surface of the road or water, leading to glare that can be almost blinding. Polarizing filters are also quite useful in photography, where they can be attached to the front of a camera lens to reduce glare and increase overall image contrast in photographs or digital images.

Polarizers utilized on cameras are generally designed with a mounting ring that allows them to be rotated in use to achieve the desired effect under various lighting conditions.

Arago investigated the polarity of light originating from various sources in the sky and proposed a theory that predicted the velocity of light should decrease as it passes into a denser medium. He also worked with Augustin Fresnel to investigate interference in polarized light and discovered that two beams of light polarized with their vibration directions oriented perpendicular to each other will not undergo interference.

Arago's polarizing filters, designed and built in , were made from a stack of glass sheets pressed together. A majority of the polarizing materials used today are derived from synthetic films invented by Dr. Edwin H. Land in , which soon overtook all other materials as the medium of choice for production of plane-polarized light.

To produce the films, tiny crystallites of iodoquinine sulfate, oriented in the same direction, are embedded in a transparent polymeric film to prevent migration and reorientation of the crystals. Land developed sheets containing polarizing films that are marketed under the trade name of Polaroid a registered trademark , which has become the accepted generic term for these sheets.

Any device capable of selecting plane-polarized light from natural non-polarized white light is now referred to as a polar or polarizer , a name first introduced in by A. Because these filters are capable of differentially transmitting light rays, depending upon their orientation with respect to the polarizer axis, they exhibit a form of dichroism , and are often termed dichroic filters. Polarized light microscopy was first introduced during the nineteenth century, but instead of employing transmission-polarizing materials, light was polarized by reflection from a stack of glass plates set at a degree angle to the plane of incidence.

Later, more advanced instruments relied on a crystal of doubly refracting material such as calcite specially cut and cemented together to form a prism. A beam of white non-polarized light entering a crystal of this type is separated into two components that are polarized in mutually perpendicular orthogonal directions.

One of the light rays emerging from a birefringent crystal is termed the ordinary ray , while the other is called the extraordinary ray. The ordinary ray is refracted to a greater degree by electrostatic forces in the crystal and impacts the cemented surface at the critical angle of total internal reflection. As a result, this ray is reflected out of the prism and eliminated by absorption in the optical mount.

The extraordinary ray traverses the prism and emerges as a beam of linearly-polarized light that is passed directly through the condenser and to the specimen positioned on the microscope stage. Several versions of prism-based polarizing devices were once widely available, and these were usually named after their designers. The most common polarizing prism illustrated in Figure 5 was named after William Nicol, who first cleaved and cemented together two crystals of Iceland spar with Canada balsam in Nicol prisms were first used to measure the polarization angle of birefringent compounds, leading to new developments in the understanding of interactions between polarized light and crystalline substances.

Presented in Figure 5 is an illustration of the construction of a typical Nicol prism. A crystal of doubly refracting birefringent material, usually calcite, is cut along the plane labeled a-b-c-d and the two halves are then cemented together to reproduce the original crystal shape.

A beam of non-polarized white light enters the crystal from the left and is split into two components that are polarized in mutually perpendicular directions. One of these beams labeled the ordinary ray is refracted to a greater degree and impacts the cemented boundary at an angle that results in its total reflection out of the prism through the uppermost crystal face.

The other beam extraordinary ray is refracted to a lesser degree and passes through the prism to exit as a plane-polarized beam of light. Other prism configurations were suggested and constructed during the nineteenth and early twentieth centuries, but are currently no longer utilized for producing polarized light in modern applications. Nicol prisms are very expensive and bulky, and have a very limited aperture, which restricts their use at high magnifications.

Instead, polarized light is now most commonly produced by absorption of light having a set of specific vibration directions in a filter medium such as polarizing sheets where the transmission axis of the filter is perpendicular to the orientation of the linear polymers and crystals that comprise the polarizing material. In modern polarizers, incident light waves having electric vector vibrations that are parallel to the crystal axis of the polarizer are absorbed.

Many of the incident waves will have a vector orientation that is oblique, but not perpendicular to the crystal axis, and will only be partially absorbed. The degree of absorption for oblique light waves is dependent upon the vibration angle at which they impact the polarizer. Those rays that have angles close to parallel with respect to the crystal axis will be adsorbed to a much greater degree than those having angles close to the perpendicular. The most common Polaroid filters termed the H-series transmit only about 25 percent of the incident light beam, but the degree of polarization of the transmitted rays exceeds 99 percent.

A number of applications, most notably polarized optical microscopy, rely on crossed polarizers to examine birefringent or doubly refracting specimens. When two polarizers are crossed, their transmission axes are oriented perpendicular to each other and light passing through the first polarizer is completely extinguished, or absorbed, by the second polarizer, which is typically termed an analyzer. The light-absorbing quality of a dichroic polarizing filter determines exactly how much random light is extinguished when the polarizer is utilized in a crossed pair, and is referred to as the extinction factor of the polarizer.

But if the surface is smooth, as with calm water or a flat piece of sheet metal, light reflects at one angle. When this light reflects right in your eyes, this is what we know as glare. Polarized sunglasses reduce glare and solve this problem. Polarized lenses have a special chemical applied to them to filter light.

Think of it like a miniblind hanging in front of a window. On polarized sunglasses , the filter creates vertical openings for light. Only light rays that approach your eyes vertically can fit through those openings. The lenses block all the horizontal light waves bouncing off a smooth pond or a shiny car hood, for instance. As a result of this filtering, the image you see with polarized lenses is a bit darker than usual. But objects look crisper and clearer with polarized lenses, and details are easier to see.

People who use polarized sunglasses often say they are less tired than usual after hours of battling sun glare. Polarized sunglasses can be a good choice for most everyday situations. These are some specific situations when polarized sunglasses may be especially helpful:. Polarized lenses will have a label saying so.

To learn more about the benefits and drawbacks of polarized lenses, talk with your eye care provider. It is a quantitative procedure that scores the ideological positions of legislators on the basis of roll call votes information regarding who votes with whom.

A legislator that votes with two colleagues more frequently than these colleagues vote together is positioned as a moderate, in between his or her more extreme two colleagues. For a more detailed explanation, see Keith T. These measures are also not able to exactly capture ideological distances between legislators and between parties. Fiorina and Samuel J. The true reason that party polarization in the United States is worrisome is not the extent of ideological polarization, but rather the particular issues parties are polarized about.

Most accounts on polarization, similar to Poole and Rosenthal cited above, assume that polarization concerns divides over policy issues, either economic, cultural, or both.

In contrast, recent polarization in the US Congress includes party differences about the rules of the game, or essentially about conceptions of democracy. The recent behavior of some politicians can serve as a clear example of these worrisome divisions over the rules of the game. The following examples specifically depict visible transgressions of the norms of liberal democracy, such as open disrespect of key institutions. More than two weeks after the December 12, , special election, he not only still failed to concede but also doubled-down on the voter fraud claims which were widely perceived as questionable and unfounded by bringing a lawsuit.

The subtext of such attacks reveals a fundamental division over conceptions of democracy. To be sure, criticism of liberal democracy is not recent. What is new and significant is that individual transgressions of the rules of the game receive widespread support from large numbers of bystanders who play active roles in the political system, and who either openly cheer or silently support this behavior. What is also new is that these transgressions have come to be structured as party political stances.

While supporters of the Republican Party tend to promote this vision of democracy, it is contradicted by their Democratic counterparts who continue to subscribe to the liberal procedural creed of democracy. Fiorina, Samuel J. Abrams, and Jeremy C. Pope, Culture War? The Myth of a Polarized America , 3rd ed. New York: Longman, Zingher and Michael E. In this vein, opposing views are not perceived as a different side in a political debate, but rather as a morally wrong choice.

The argument made here does not consider the substance of current debates to be the only worrisome aspect of polarization for US politics. Contradicting earlier accounts on the desirability of responsible party government in the United States, some authors rightly point out that party polarization necessarily will result in gridlock given how the US system of checks and balances 14 For example, see Frances E.

However, what is truly significant about the concerning features of party polarization stressed in this essay is that they are not confined to US politics but are also present in the established democracies of Europe, which have seen the rise of populist parties.

According to Zsolt Enyedi, new democracies in Eastern Europe are plagued by populist forms of polarization, which he claims pose a more acute danger to democracy than the much-feared under-institutionalization and fragmented configurations of party politics in these countries. The gravity of the situation results from the fact that populist parties and elites in countries such as Hungary or Poland have come to question the fundamental rules of the game, such as the independence of the judicial system, freedom of the press, and checks and balances as key elements of democracy.

Similar developments can be seen in established Western European democracies where populist parties, of the left and right, promote the need to reclaim power from corrupt and detached elites and to revamp key features of democracy. So far, the difference between European and US developments lies in the pattern that this form of party polarization takes. In Europe, antagonistic debates pitch new populist parties against established mainstream parties.

In the United States, one of the two established parties has been significantly affected by populist trends and now functions as an anti-establishment voice in this debate.

This suggests that polarization over the rules of the game is gaining ground and will certainly affect the future of democratic governance, which is at a crucial juncture today on both sides of the Atlantic.