Political polarization

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Linear polarization

George Nomarski invented the method of differential interference contrast for the microscopic observation of phase objects in 1953. The features on a phase object typically modulate the phase of an incident beam without significantly affecting the beam's amplitude. Examples include unstained biological samples having differing refractive indices from their surroundings, and reflective (as well as transmissive) surfaces containing digs, scratches, bumps, pits, or other surface-relief features that are smooth enough to reflect specularly the incident rays of light. A conventional microscope image of a phase object is usually faint, showing at best the effects of diffraction near the corners and sharp edges but revealing little information about the detailed structure of the sample.

The Nomarski microscope uses a Wollaston prism in the illumination path to produce two orthogonally polarized, slightly shifted bright spots at the sample's surface. Upon reflection from (or transmission through) the sample, the two beams are collected by the objective lens, then sent through the same (or, in the case of a transmission microscope, a similar) Wollaston prism, which recombines the two beams by sliding them back over each other.

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Polarization

P-polarized light can be preferentially transmitted or reflected by certain optical components, such as beamsplitters or polarizers. The reflection of p-polarized light at nonmetallic surfaces can be minimized at a certain angle of incidence known as Brewster's angle.

S-polarized light is reflected differently compared to p-polarized light, especially at angles far from normal incidence. These differences are exploited in various applications where the polarization of light is critical, such as in polarimetry or in reducing glare in imaging systems.

Nomarski's method creates two slightly shifted, overlapping images of the same surface. The two images, being temporally coherent with respect to one another, optically interfere, producing contrast variations that contain useful information about the phase gradients across the sample's surface. In particular, a feature that has a slope in the direction of the imposed shear appears with a specific level of brightness that is distinct from other, differently sloping regions of the same sample.

S-polarization, short for senkrecht polarization or perpendicular polarization, occurs when the electric field vector is perpendicular to the plane of incidence. This orientation tends to have higher reflection coefficients at surfaces when compared to p-polarization.

S-polarization

In practical use, one can manipulate the polarization state of laser light using polarizing optics, such as waveplates, to convert one polarization state to another or using polarizers to select a particular polarization state.

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Electric polarization

Whether a laser is p-polarized or s-polarized depends on the laser design and the components in the laser cavity. Some lasers may emit light with a random polarization state, while others, by design, may produce a specific polarization. Diode lasers, for example, often emit naturally polarized light due to the geometric shape of the gain region and cavity design.

Circularly polarized light

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P-polarization, short for parallel polarization, refers to light waves with the electric field polarized parallel to the plane of incidence. The plane of incidence is defined as the plane that spans the incident, reflected, and refracted rays. When the electric field component is parallel to this plane, it is p-polarized.

Laser light can be either p-polarized (parallel) or s-polarized (senkrecht/perpendicular), depending on the orientation of the electric field vector with respect to the plane of incidence, when the light is incident upon a reflective surface.