Oolite - Oolite, a light gray rock composed of siliceous oolites cemented in compact silica, is formed in the sea. The mineral's name is derived from its structural similarity to fish roe, better known as caviar. Oolite forms in the sea when sand grains are rolled by gentle currents over beds of calcium carbonate or other minerals. These minerals build up around the sand grains and subsequent cementation transforms the grains into coherent rock. The thin sections show the original quartz nuclei (Figure 9(a-c)) on which the buildup of carbonate mineral occurred.

A circular specimen with an actual diameter of 0.01 mm (1 × 10-5 m), far smaller than a period on a printed page, would appear 400 times larger using this level of magnification, making it look like a 4-cm-wide object (about 1.6-inch wide) from the same distance.

Beck, Kevin. "Definition Of Magnification In Microscopy" sciencing.com, https://www.sciencing.com/definition-magnification-microscopy-5639922/. 9 November 2019.

The wave model of light describes light waves vibrating at right angles to the direction of propagation with all vibration directions being equally probable. This is referred to as "common" or "non-polarized" white light. In plane-polarized light there is only one vibration direction (Figure 1). The human eye-brain system has no sensitivity to the vibration directions of light, and plane-polarized light can only be detected by an intensity or color effect, for example, by reduced glare when wearing polarized sun glasses.

One magnification definition is "the process of making large," which is taken almost straight from the Latin; an idea that more properly captures magnification's meaning is "appearing to make something larger without actually doing so." But apart from magnification's specific definition as used in microscopy, the various instruments that classify as microscopes today feature combinations of lenses that allow users to achieve the necessary visualization.

During the solidification of polymer melts there may be some organization of the polymer chains, a process that is often dependent upon the annealing conditions. When nucleation occurs, the synthetic polymer chains often arrange themselves tangentially and the solidified regions grow radially. These can be seen in crossed polarized illumination as white regions, termed spherulites, with the distinct black extinction crosses. When these spherulites impinge, their boundaries become polygonal. This can be clearly seen in crossed polarizers but not under plane-polarized light.

The eyepiece lens is usually 10x, and there are often no other options. The total magnification gained in a compound microscope is just the product of the objective and eyepiece lens magnification values. So if you were looking at a specimen with an objective lens of 40x using a 10x eyepiece, the total magnification of the object would therefore be 10 times 40, or 400x.

There are two polarizing filters in a polarizing microscope - termed the polarizer and analyzer (see Figure 1). The polarizer is positioned beneath the specimen stage usually with its vibration azimuth fixed in the left-to-right, or East-West direction, although most of these elements can be rotated through 360 degrees. The analyzer, usually aligned with a vibration direction oriented North-South, but again rotatable on some microscopes, is placed above the objectives and can be moved in and out of the light path as required. When both the analyzer and polarizer are inserted into the optical path, their vibration azimuths are positioned at right angles to each other. In this configuration, the polarizer and analyzer are said to be crossed, with no light passing through the system and a dark viewfield present in the eyepieces.

What is polarized lightcalled

Resolution refers to the ability to discriminate between (i.e., visually separate) two adjacent objects. A resolution level in optics refers to the number of distinct pixels (picture elements) in a given area, such as dots per square inch.

In a compound microscope, one of the lens systems forms an enlarged image of the object; the second lens system magnifies the image formed by the first lens. In the modern compound microscope, the two lens systems are the objective lens and the ocular (eyepiece) lens.

Asbestos is a generic name for a group of naturally occurring mineral fibers, which have been widely used as insulating materials, brake pads, and to reinforce concrete. These materials can be harmful to the health when inhaled and it is important that their presence in the environment be easily identified. Specimens are commonly screened using scanning electron microscopy and x-ray microanalysis, but polarizing microscopy provides a quicker and easier alternative that can be utilized to distinguish between asbestos and other fibers and between the major types asbestos, including chrysotile, crocidolite, and amosite. From a health care point of view, it is believed that the amphibole asbestos derivatives (crocidolite and amosite) are more harmful than the serpentine, chrysotile.

One of the most common medical applications for polarized light microscopy is the identification of gout crystals (monosodium urate) with a first order retardation plate. This practice is so common that many microscope manufacturers offer a gout kit attachment for their laboratory brightfield microscopes that can be purchased by physicians. Gout is an acute, recurrent disease caused by precipitation of urate crystals and characterized by painful inflammation of the joints, primarily in the feet and hands. In practice, several drops of fresh synovial fluid are sandwiched between a microscope slide and cover glass and sealed with nail polish to prevent drying. After the specimen has been prepared, it is examined between crossed polarizers with a first order retardation plate inserted into the optical path.

There are two basic kinds of light microscopes, the name given to microscopes that possess their own illumination source (most modern units do). Simple microscopes were the first microscopes manufactured, and these consist of a single, usually hand-held lens that curved outward on one or both sides. A compound microscope makes use of two lenses (or lens systems).

What isunpolarizedlight

The two orthogonal components of light (ordinary and extraordinary waves) travel at different speeds through the specimen and experience different refractive indices, a phenomena known as birefringence. A quantitative measurement of birefringence is the numerical difference between the wavefront refractive indices. The faster beam emerges first from the specimen with an optical path difference (OPD), which may be regarded as a "winning margin" over the slower one. The analyzer recombines only components of the two beams traveling in the same direction and vibrating in the same plane. The polarizer ensures that the two beams have the same amplitude at the time of recombination for maximum contrast.

Polarized light is most commonly produced by absorption of light having a set of specific vibration directions in a dichroic medium. Certain natural minerals, such as tourmaline, possess this property, but synthetic films invented by Dr. Edwin H. Land in 1932 soon overtook all other materials as the medium of choice for production of plane-polarized light. 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 were marketed under the trade name of Polaroid®, which has become the accepted generic term for these sheets. Any device capable of selecting plane-polarized light from natural (unpolarized) white light is now referred to as a polar or polarizer, a name first introduced in 1948 by A. F. Hallimond. Today, polarizers are widely used in liquid crystal displays (LCDs), sunglasses, photography, microscopy, and for a myriad of scientific and medical purposes.

Discover how specimen birefringence is affected by the angle of polarizer when observed in a polarized light microscope.

World-class Nikon objectives, including renowned CFI60 infinity optics, deliver brilliant images of breathtaking sharpness and clarity, from ultra-low to the highest magnifications.

The polarized light microscope is designed to observe and photograph specimens that are visible primarily due to their optically anisotropic character. 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; see Figure 1), 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 each polarized in mutually perpendicular planes. The velocities of these components, which are termed the ordinary and the extraordinary wavefronts (Figure 1), are different and vary with the propagation direction through the specimen. After exiting the specimen, the light components become out of phase, but are recombined with constructive and destructive interference when they pass through the analyzer. These concepts are outlined in Figure 1 for the wavefront field generated by a hypothetical birefringent specimen. In addition, the critical optical and mechanical components of a modern polarized light microscope are illustrated in the figure.

Polarization oflightnotes PDF

Nylon Fibers - Observations under plane-polarized light (Figure 11(a)) reveal refractive index differences between a nylon fiber and the mounting medium, and the presence of opacifying titanium dioxide particles. The image under crossed polarizers (Figure 11(b)) reveals second and third order polarization colors and their distribution across the fibers indicate that this is a cylindrical and not a lobate fiber useful in predicting mechanical strength. The use of the quartz wedge (Figure 11(c)) enables the determination of optical path differences for birefringence measurements.

Phyllite - As well as providing information on component minerals, an examination of geological thin sections using polarizing microscopy can reveal a great deal about how the rock was formed. Phyllite, a metamorphic rock, clearly shows the alignment of crystals under the effects of heat and stress. Small-scale folds are visible in the plane-polarized image (Figure 8(a)) and more clearly defined under crossed polarizers (Figure 8(b)) with and without the first order retardation plate. The crossed polarizers image reveals that there are several minerals present, including quartz in gray and whites and micas in higher order colors. The alignment of the micas is clearly apparent. Addition of the first order retardation plate (Figure 8(c)) improves contrast for clear definition in the image.

Other polymers may not be birefringent (evidenced by the polycarbonate specimen illustrated in Figure 10(b)), and do not display substantial secondary or tertiary structure. In other cases, both biological and synthetic polymers can undergo a series of lyotropic or thermotropic liquid crystalline phase transitions, which can often be observed and recorded in a polarized light microscope. Figure 10(c) illustrates a birefringent columnar-hexatic liquid crystalline phase exhibited by rod-like DNA molecules at very high aqueous solution concentrations (exceeding 300 milligrams/milliliter).

Beck, Kevin. Definition Of Magnification In Microscopy last modified March 24, 2022. https://www.sciencing.com/definition-magnification-microscopy-5639922/

Different levels of information can be obtained in plane-polarized light (analyzer removed from the optical path) or with crossed polarizers (analyzer inserted into the optical path). Observations in plane-polarized light reveal details of the optical relief of the specimen, which is manifested in the visibility of boundaries, and increases with refractive index. Differences in the refractive indices of the mounting adhesive and the specimen determine the extent to which light is scattered as it emerges from the uneven specimen surface. Materials with high relief, which appear to stand out from the image, have refractive indices that are appreciably different from the mounting medium. Immersion refractometry is used to measure substances having unknown refractive indices by comparison with oils of known refractive index.

Polarization colors result from the interference of the two components of light split by the anisotropic specimen and may be regarded as white light minus those colors that are interfering destructively. Figure 2 illustrates conoscopic images of uniaxial crystals observed at the objective rear focal plane. Interference patterns are formed by light rays traveling along different axes of the crystal being observed. Uniaxial crystals (Figure 2) display an interference pattern consisting of two intersecting black bars (termed isogyres) that form a Maltese cross-like pattern. When illuminated with white (polarized) light, birefringent specimens produce circular distributions of interference colors (Figure 2), with the inner circles, called isochromes, consisting of increasingly lower order colors (see the Michel-Levy interference color chart, Figure 4). A common center for both the black cross and the isochromes is termed the melatope, which denotes the origin of the light rays traveling along the optical axis of the crystal. Biaxial crystals display two melatopes (not illustrated) and a far more complex pattern of interference rings.

In plane-polarized light (Figure 9(a)), the quartz is virtually invisible having the same refractive index as the cement, while the carbonate mineral, with a different refractive index, shows high contrast. The crossed polarizer image (Figure 9(b)) reveals quartz grains in grays and whites and the calcium carbonate in the characteristic biscuit colored, high order whites. The groups of quartz grains in some of the cores reveal that these are polycrystalline and are metamorphic quartzite particles. When a first order retardation plate is inserted into the optical path (Figure 9(c)), optical path differences become apparent in the specimen, and contrast is enhanced.

Polarisation meaning in Physics

What isplanepolarized lightin Chemistry

Isotropic materials, which include a variety of gases, liquids, unstressed glasses and cubic crystals, demonstrate the same optical properties when probed in all directions. These materials have only one refractive index and no restriction on the vibration direction of light passing through them. In contrast, anisotropic materials, which include 90 percent of all solid substances, have optical properties that vary with the orientation of incident light with the crystallographic axes. They demonstrate a range of refractive indices depending both on the propagation direction of light through the substance and on the vibrational plane coordinates. More importantly, anisotropic materials act as beamsplitters and divide light rays into two orthogonal components (as illustrated in Figure 1). The technique of polarizing microscopy exploits the interference of the split light rays, as they are re-united along the same optical path to extract information about anisotropic materials.

Examinations of transparent or translucent materials in plane-polarized light will be similar to those seen in natural light until the specimen is rotated around the optical axis of the microscope. Then observers may see changes in the brightness and/or the color of the material being examined. This pleochroism (a term used to describe the variation of absorption color with vibration direction of the light) depends on the orientation of the material in the light path and is a characteristic of anisotropic materials only. An example of a material showing pleochroism is crocidolite, more commonly known as blue asbestos. The pleochroic effect helps in the identification of a wide variety of materials.

Magnification, instead, is about details, typically those you could never see with the unaided eye simply because your eye is so large compared to things like molecules, bacteria and viruses. Using a magnifying device is akin to walking closer and closer to a sign and being able to make out more of the words and pictures as you approach.

Philip C. Robinson - Department of Ceramic Technology, Staffordshire Polytechnic, College Road, Stroke-on-Trent, ST4 2DE United Kingdom.

Consider a very tiny yet extremely bright object, like an atom glowing at its maximum fluorescence (light that results from collisions with high-energy electromagnetic waves). You might be able to see it in some sense under a microscope, but you would not be able to make out any features or even necessarily place it precisely in space.

Monosodium urate crystals grow in elongated prisms that have a negative optical sign of birefringence, which generates a yellow (subtraction) interference color when the long axis of the crystal is oriented parallel to the slow axis of the first order retardation plate (Figure 6(a)). Rotating the crystals through 90 degrees changes the interference color to blue (addition color; Figure 6(b)). In contrast, pseudo-gout pyrophosphate crystals, which have similar elongated growth characteristics, exhibit a blue interference color (Figure 6(c)) when oriented parallel to the slow axis of the retardation plate and a yellow color (Figure 6(d)) when perpendicular. The sign of birefringence can be employed to differentiate between gout crystals and those consisting of pyrophosphate. Gout can also be identified with polarized light microscopy in thin sections of human tissue prepared from the extremities. Polarized light is also useful in the medical field to identify amyloid, a protein created by metabolic deficiencies and subsequently deposited in several organs (spleen, liver, kidneys, brain), but not observed in normal tissues.

Explore how birefringent anisotropic crystals interact with polarized light in an optical microscope as the circular stage is rotated through 360 degrees.

Constructive and destructive interference of light passing through the analyzer occurs between the orthogonal components, depending on the optical path difference of the specimen and the wavelength of the light, which can be determined from the order of polarization colors. This effect relies on the properties of the specimen, including the thickness difference between the refractive index and the birefringence of the two mutually perpendicular beams, which has a maximum value dependent on the specimen and on the direction of light propagation through the specimen. Optical path differences can be used to extract valuable "tilt" information from the specimen.

The addition of the first order retardation plate (Figure 10(a)) confirms the tangential arrangement of the polymer chains. The banding occurring in these spherulites indicates slow cooling of the melt allowing the polymer chains to grow out in spirals. This information on thermal history is almost impossible to collect by any other technique. Nucleation in polymer melts can take place as the result of accidental contamination or contact with a nucleating surface and can lead to substantial weakening of the product. Identification of nucleation can be a valuable aid for quality control.

The strengths of polarizing microscopy can best be illustrated by examining particular case studies and their associated images. All images illustrated in this section were recorded with a Nikon Eclipse E600 microscope equipped with polarizing accessories, a research grade microscope designed for analytical investigations.

A microscope has one basic purpose: to make objects that are very tiny in relation to the human eye appear larger, usually for the purpose of learning more about whatever is being studied or teaching others to do the same. (A telescope has a similar purpose in that it makes objects that look very tiny or can't be seen at all appear bigger; they do so, however, by in effect making large, very distant objects appear to be closer to you instead of magnifying objects in the same physical space.)

Polarized light microscopy is capable of providing information on absorption color and optical path boundaries between minerals of differing refractive indices, in a manner similar to brightfield illumination, but the technique can also distinguish between isotropic and anisotropic substances. Furthermore, the contrast-enhancing technique exploits the optical properties specific to anisotropy and reveals detailed information concerning the structure and composition of materials that are invaluable for identification and diagnostic purposes.

Polarizedand unpolarizedlight

For incident light polarized microscopy, the polarizer is positioned in the vertical illuminator and the analyzer is placed above the half mirror. Most rotatable polarizers are graduated to indicate the rotation angle of the transmission azimuth, while analyzers are usually fixed into position (although advanced models can be rotated either 90 or 360 degrees). The polarizer and analyzer are the essential components of the polarizing microscope, but other desirable features include:

To assist in the identification of fast and slow wavefronts, or to improve contrast when polarization colors are of low order (such as dark gray), accessory retardation plates or compensators can be inserted in the optical path. These will cause color changes in the specimen, which can be interpreted with the help of a polarization color chart (Michel-Levy chart; see Figure 4). These charts illustrate the polarization colors provided by optical path differences from 0 to 1800-3100 nanometers together with birefringence and thickness values. The wave plate produces its own optical path difference, which is added or subtracted from that of the specimen. When the light passes first through the specimen and then the accessory plate, the optical path differences of the wave plate and the specimen are either added together or subtracted from one another in the way that "winning margins" of two races run in succession are calculated. They are added when the slow vibration directions of the specimen and retardation plate are parallel, and subtracted when the fast vibration direction of the specimen coincides with the slow vibration direction of the accessory plate. If the slow and fast directions are known for the retardation plate (they are usually marked on the mount of commercially available plates), then those of the specimen can be deduced. Since these directions are characteristic for different media, they are well worth determining and are essential for orientation and stress studies.

What is polarized lightin physics

Plane-polarized light provides information about gross fiber morphology, color, pleochroism, and refractive index. Glass fibers and others that are isotropic will be unaffected by rotation under plane-polarized light while asbestos fibers will display some pleochroism. Chrysotile asbestos fibrils may appear crinkled, like permed or damaged hair, under plane-polarized light, whereas crocidolite and amosite asbestos are straight or slightly curved. Chrysotile has a refractive index of about 1.550, while that of amosite is 1.692, and crocidolite has the highest, with a value of 1.695. Note that the refractive index value of the amphibole asbestos products is much higher than chrysotile.

Polarized light microscopy is perhaps best known for its applications in the geological sciences, which focus primarily on the study of minerals in rock thin sections. However, a wide variety of other materials can readily be examined in polarized light, including both natural and industrial minerals, cement composites, ceramics, mineral fibers, polymers, starch, wood, urea, and a host of biological macromolecules and structural assemblies. The technique can be used both qualitatively and quantitatively with success, and is an outstanding tool for the materials sciences, geology, chemistry, biology, metallurgy, and even medicine.

Michael W. Davidson - National High Magnetic Field Laboratory, 1800 East Paul Dirac Dr., The Florida State University, Tallahassee, Florida, 32310.

Illustrated in Figure 3 is a series of reflected polarized light photomicrographs of typical specimens imaged utilizing this technique. On the left (Figure 3(a)) is a digital image revealing surface features of a microprocessor integrated circuit. Birefringent elements employed in the fabrication of the circuit are clearly visible in the image, which displays a portion of the chip's arithmetic logic unit. The blemished surface of a ceramic superconducting crystal (bismuth base) is presented in Figure 3(b), which shows birefringent crystalline areas with interference colors interspersed with grain boundaries. Metallic thin films are also visible with reflected polarized light. Figure 3(c) illustrates blisters that form imperfections in an otherwise confluent thin film of copper (about 0.1 micron thick) sandwiched over a nickel/sodium chloride substrate to form a metallic superlattice assembly.

Careful specimen preparation is essential for good results in polarized light microscopy. The method chosen will depend on the type of material studied. In geological applications, the standard thickness for rock thin sections is 25-30 micrometers. Specimens can be ground down with diamond impregnated wheels and then hand finished to the correct thickness using abrasive powders of successively decreasing grit size. The final specimen should have a cover glass cemented with an optically transparent adhesive. Softer materials can be prepared in a manner similar to biological samples using a microtome. Slices between one and 40 micrometers thick are used for transmitted light observations. These should be strain-free and free from any knife marks. Biological and other soft specimens are mounted between the slide and the cover glass using a mounting medium whose composition will depend on the chemical and physical nature of the specimen. This is particularly significant in the study of synthetic polymers where some media can chemically react with the material being studied and cause degrading structural changes (artifacts).

Whenever the specimen is in extinction, the permitted vibration directions of light passing through are parallel with those of either the polarizer or analyzer. This fact can be related to geometrical features of the specimen, such as fiber length, film extrusion direction, and crystal facets. In crossed polarized illumination, isotropic materials can be easily distinguished from anisotropic materials as they remain permanently in extinction (remain dark) when the stage is rotated through 360 degrees.

Linearlypolarized light

Beck, Kevin. (2019, November 9). Definition Of Magnification In Microscopy. sciencing.com. Retrieved from https://www.sciencing.com/definition-magnification-microscopy-5639922/

The strengths of polarizing microscopy can best be illustrated by examining particular case studies and their associated images. All of the images illustrated in this section were recorded with a microscope equipped with polarizing accessories, a research grade instrument designed for analytical investigations. As described above, polarized light microscopy is utilized in a broad range of disciplines, including medicine, biology, geology, materials science, and the food industry. The specimens that are readily examined between crossed polarizers originate from a variety of natural and synthetic sources and include gout crystals, amyloid, muscle tissue, teeth, minerals, solid crystals, liquid crystals, fibers, fats, glasses, ceramics, metals, alloys, among others.

Although an understanding of the analytical techniques of polarized microscopy may be perhaps more demanding than other forms of microscopy, it is well worth pursuing, simply for the enhanced information that can be obtained over brightfield imaging. An awareness of the basic principles underlying polarized light microscopy is also essential for the effective interpretation of differential interference contrast (DIC).

In summary, polarizing microscopy provides a vast amount of information about the composition and three-dimensional structure of a variety of samples. Virtually unlimited in its scope, the technique can reveal information about thermal history and the stresses and strains to which a specimen was subjected during formation. Useful in manufacturing and research, polarizing microscopy is a relatively inexpensive and accessible investigative and quality control tool, which can provide information unavailable with any other technique.

Crocidolite displays blue colors, pleochroism, and murky brown polarization colors. The fast vibration for this fiber is parallel with the long axis. In summary, identification of the three asbestos fiber types depends on shape, refractive indices, pleochroism, birefringence, and fast and slow vibration directions.

In most microscopes, the objective lens system offers more than one level of magnification. For example, by rotating a plate that puts different objective lenses on the user's viewing area, the objective magnification might be 4x, 10x or 100x. This simply means that the images created are 4, 10 and 100 times the size of the object itself.

With the use of crossed polarizers it is possible to deduce the permitted vibration direction of the light as it passes through the specimen, and with the first order retardation plate, a determination of the slow and fast vibration directions (Figure 7) can be ascertained. Under crossed polarizers, chrysotile displays pale interference colors, which are basically restricted to low order whites (Figure 7(a)). When a first order retardation plate is added (retardation value of one wavelength, or 530-560 nanometers), the colors of the fiber are transformed. If the fiber is aligned Northwest-Southeast, the retardation plate is additive (white arrow in Figure 7(b)) and produces primarily yellow subtractive interference colors in the fiber. When the fiber is aligned Northeast-Southwest (Figure 7(c)), the plate is additive to produce a higher order blue tint to the fiber with no yellow hues. From this evidence it is possible to deduce that the slow vibration direction of the retardation plate (denoted by the white arrows in Figures 7(b) and 7(c)) is parallel with the long axis of the fiber. Amosite is similar in this respect.

Polarized light microscopy can be used both with reflected (incident or epi) and transmitted light. Reflected light is useful for the study of opaque materials such as ceramics, mineral oxides and sulfides, metals, alloys, composites, and silicon wafers (see Figure 3). Reflected light techniques require a dedicated set of objectives that have not been corrected for viewing through the cover glass, and those for polarizing work should also be strain free.

Polarized light 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. Polarized light microscopes have a high degree of sensitivity and can be utilized for both quantitative and qualitative studies targeted at a wide range of anisotropic specimens. Qualitative polarizing microscopy is very popular in practice, with numerous volumes dedicated to the subject. In contrast, the quantitative aspects of polarized light microscopy, which is primarily employed in crystallography, represent a far more difficult subject that is usually restricted to geologists, mineralogists, and chemists. However, steady advances made over the past few years have enabled biologists to study the birefringent character of many anisotropic sub-cellular assemblies.

Superimposed on the polarization color information is an intensity component. As the specimen is rotated relative to the polarizers, the intensity of the polarization colors varies cyclically, from zero (extinction; Figure 5(d)) up to a maximum brightness at 45 degrees (Figure 5(a), and then back down to zero after a 90-degree rotation. That is why a rotating stage and centration are provided in a polarized light microscope, which are critical elements for determining quantitative aspects of the specimen. Centration of the objective and stage ensures that the center of the stage rotation coincides with the center of the field of view in order to maintain the specimen in the exact center when rotated.