3) what is the difference between the polarizer and the analyzer

The light waves from different directions other than the selected direction are absorbed or sent to a different direction in order to remove the interference. Figure 1: A Wire Grid Polarizer. However, polarizers cannot convert light waves coming from any direction into the desired direction.

Polarizers can only remove the unwanted light waves. There are several types of polarizers such as circular polarizers, crystalline polarizers, and linear polarizers.

For low-power applications, sheet polarizers are used. These sheets are made out of polymer materials which have been stretched into one direction. There, light waves of unwanted directions are strongly absorbed by polymers. Much higher optical powers can be handled by polarizing beam splitters. Here, other than absorbing, the light waves of unwanted directions are sent to other directions rather than the desired direction.

Wire grid polarizers are another type of polarizers. These are made by fabricating very narrow metal strips on a glass substrate. The analyzer is a device used to determine whether the light is plane polarized or not. It acts as a second polarizer. In microscopy, the analyzer is placed in the optical pathway between the specimen and the observation tubes.

It is made up of a polarizing plate. The height of the polarizing plate height from the specimen can be adjusted. Figure 2: Analyzer in Microscopy.

Analyzer can be removed at will. B 17 10 Liang, X. Xiao, J. Li, B. Zhu, J. Zhu, H. Bao, L. Zhou, and Y. Wu Opt. Express 23 9 Belotelov, D. Bykov, L. Doskolovich, A. Kalish, and A. Zvezdin J. B 26 8 Demidenko, D. Makarov, O. Schmidt, and V. Lozovski J. B 30 8 You do not have subscription access to this journal.

Citation lists with outbound citation links are available to subscribers only. You may subscribe either as an Optica member, or as an authorized user of your institution. This concept is illustrated in Figure 8 , where the resultant electric vector does not vibrate in a single plane, but progressively rotates around the axis of light wave propagation, sweeping out an elliptical trajectory that appears as a spiral when the wave is viewed at an angle. The size of the phase difference between the ordinary and extraordinary waves of equal amplitude determines whether the vector sweeps an elliptical or circular pathway when the wave is viewed end-on from the direction of propagation.

If the phase shift is either one-quarter or three-quarters of a wavelength, then a circular spiral is scribed by the resultant vector. However, phase shifts of one-half or a full wavelength produce linearly polarized light, and all other phase shifts produce sweeps having various degrees of ellipticity. When the ordinary and extraordinary waves emerge from a birefringent crystal, they are vibrating in mutually perpendicular planes having a total intensity that is the sum of their individual intensities.

Because the polarized waves have electric vectors that vibrate in perpendicular planes, the waves are not capable of undergoing interference.

This fact has consequences in the ability of birefringent substances to produce an image. Interference can only occur when the electric vectors of two waves vibrate in the same plane during intersection to produce a change in amplitude of the resultant wave a requirement for image formation. Therefore, transparent specimens that are birefringent will remain invisible unless they are examined between crossed polarizers, which pass only the components of the elliptically and circularly polarized waves that are parallel to the axis of the polarizer closest to the observer.

These components are able to produce amplitude fluctuations to generate contrast and emerge from the polarizer as linearly polarized light. One of the most common and practical applications of polarization is the liquid crystal display LCD used in numerous devices including wristwatches, computer screens, timers, clocks, and a host of others. These display systems are based upon the interaction of rod-like liquid crystalline molecules with an electric field and polarized light waves.

The liquid crystalline phase exists in a ground state that is termed cholesteric , in which the molecules are oriented in layers, and each successive layer is slightly twisted to form a spiral pattern Figure 9. When polarized light waves interact with the liquid crystalline phase the wave is "twisted" by an angle of approximately 90 degrees with respect to the incident wave.

The exact magnitude of this angle is a function of the helical pitch of the cholesteric liquid crystalline phase, which is dependent upon the chemical composition of the molecules it can be fine-tuned by small changes to the molecular structure. An excellent example of the basic application of liquid crystals to display devices can be found in the seven-segment liquid crystal numerical display illustrated in Figure 9. Here, the liquid crystalline phase is sandwiched between two glass plates that have electrodes attached, similar to those depicted in the illustration.

In Figure 9 , the glass plates are configured with seven black electrodes that can be individually charged these electrodes are transparent to light in real devices. Light passing through polarizer 1 is polarized in the vertical direction and, when no current is applied to the electrodes, the liquid crystalline phase induces a 90 degree "twist" of the light that enables it to pass through polarizer 2, which is polarized horizontally and is oriented perpendicular to polarizer 1.

This light can then form one of the seven segments on the display. When current is applied to the electrodes, the liquid crystalline phase aligns with the current and loses the cholesteric spiral pattern. Light passing through a charged electrode is not twisted and is blocked by polarizer 2.

By coordinating the voltage on the seven positive and negative electrodes, the display is capable of rendering the numbers 0 through 9. In this example the upper right and lower left electrodes are charged and block light passing through them, allowing formation of the number "2" by the display device seen reversed in the figure.

The phenomenon of optical activity in certain chemicals derives from their ability to rotate the plane of polarized light. Included in this category are many sugars, amino acids, organic natural products, certain crystals, and some drugs.

Rotation is measured by placing a solution of the target chemical between crossed polarizers in an instrument termed a polariscope. First observed in by French physicist Dominique Arago, optical activity plays an important role in a variety of biochemical processes where the structural geometry of molecules governs their interactions. Chemicals that rotate the vibrational plane of polarized light in a clockwise direction are termed dextrorotatory , while those that rotate the light in a counterclockwise direction are referred to as levorotatory.

Two chemicals having the same molecular formula but different optical properties are termed optical isomers , which rotate the plane of polarized light in different directions. Asymmetric crystals can be utilized to produce polarized light when an electric field is applied to the surface. A common scientific device that employs this concept is termed a Pockels cell , which can be utilized in conjunction with polarized light to change the polarization direction by 90 degrees.

Pockels cells can be switched on and off very rapidly by electrical currents and are often used as fast shutters that allow light to pass for very brief periods of time ranging in nanoseconds.

Presented in Figure 10 is a diagrammatic representation of polarized light passing through a Pockels cell yellow wave. The green and red sinusoidal light waves emanating from the central region of the cell represent light that is polarized either vertically or horizontally. When the cell is turned off, the polarized light is unaffected as it passes through green wave , but when activated or turned on, the electric vector of the light beam is shifted by degrees red wave. In situations where extremely large electric fields are available, molecules of certain liquids and gases can behave as anisotropic crystals and be aligned in the same manner.

A Kerr cell , designed to house liquids and gases instead of crystals, also operates to change the angle of polarized light. Other applications for polarized light include the Polaroid sunglasses discussed above, as well as the use of special polarizing filters for camera lenses.

A variety of scientific instruments utilize polarized light, either emitted by lasers, or through polarization of incandescent and fluorescent sources by a host of techniques. Polarizers are sometimes used in room and stage lighting to reduce glare and produce a more even degree of illumination, and are worn as glasses to bestow an apparent sense of depth to three-dimensional movies. Crossed polarizers are even utilized in space suits to dramatically reduce the chances of light from the sun entering the astronaut's eyes during naps.

Polarization of light is very useful in many aspects of optical microscopy. The polarized light microscope is designed to observe and photograph specimens that are visible primarily due to their optically anisotropic character. Anisotropic materials have optical properties that vary with the propagation direction of light passing through them.

In order to accomplish this task, the microscope must be equipped with both a polarizer, positioned in the light path somewhere before the specimen, and an analyzer a second polarizer , placed in the optical pathway between the objective rear aperture and the observation tubes or camera port. Image contrast arises from the interaction of plane-polarized light with a birefringent or doubly-refracting specimen to produce two individual wave components that are polarized in mutually perpendicular planes.

The velocities of these components are different and vary with the propagation direction through the specimen. After exiting the specimen, the light components are out of phase and sweep an elliptical geometry that is perpendicular to the direction of propagation, but are recombined through constructive and destructive interference when they pass through the analyzer.

Polarized light microscopy is a contrast-enhancing technique that improves the quality of the image obtained with birefringent materials when compared to other techniques such as darkfield and brightfield illumination, differential interference contrast, phase contrast, Hoffman modulation contrast, and fluorescence. In addition, use of polarized light allows the measurement of optical properties of minerals and similar materials and can aid in the classification and identification of unknown substances.

Douglas B. Michael W. World-class Nikon objectives, including renowned CFI60 infinity optics, deliver brilliant images of breathtaking sharpness and clarity, from ultra-low to the highest magnifications. Polarization of Scattered Light Gas and water molecules in the atmosphere scatter light from the sun in all directions, an effect that is responsible for blue skies, white clouds, red sunsets, and a phenomenon termed atmospheric polarization.

Elliptically and Circularly Polarized Light In linearly polarized light, the electric vector is vibrating in a plane that is perpendicular to the direction of propagation, as discussed above. Applications of Polarized Light One of the most common and practical applications of polarization is the liquid crystal display LCD used in numerous devices including wristwatches, computer screens, timers, clocks, and a host of others.

Contributing Authors Douglas B. Kenneth R. Spring - Scientific Consultant, Lusby, Maryland, Related Nikon Products Optics World-class Nikon objectives, including renowned CFI60 infinity optics, deliver brilliant images of breathtaking sharpness and clarity, from ultra-low to the highest magnifications. Objective Selector Filter, find, and compare microscope objective lenses with Nikon's Objective Selector tool. Share this article:.