The reflectivity of rocks depends on the mineralogical composition, material composition, genetic nature and, accordingly, is their diagnostic feature in DME.
This image of Bathurst Island in Canada was captured by RADARSAT on March 21, 1996. The most striking feature in this image is the striking display of geological features. Dark spot in the center of the image (A) is Bracebridge, which borders the Arctic Ocean in the west of the area under consideration. From this bay to the east stretches a wide valley called the Polar Bear Pass.
The geology of Bathurst Island is characterized by the remarkable meandering of the gorges. The upper several kilometers of multi-level cliffs are deformed into a series of depressions, which are clearly visible in the RADARSAT image.
The light tones in this image (C) represent deposits of limestone, and the dark tones (B) represent deposits of stones. The boundaries between these two environments can be accurately and easily identified from a snapshot.
Among the first works in which the spectral brightness of rock surfaces are given and the importance of their selective measurements for the interpretation of aerial photographs is proved, is the publication of Ray and Fisher. On the basis of experiments, they found that the lithofacies differences between rocks in a certain landscape region are not always contrasting and therefore they cannot always be re-identified with confidence in an aerial photograph taken on a normal black-and-white panchromatic film. These researchers were looking for imaging and processing techniques that would make better use of the reflectivity and absorbency of different rock types and thereby obtain contrast-enhanced secondary data for specific rock differences in black and white aerial photographs. Ray and Fischer were looking for a spectral channel, respectively, a range of wavelengths in which the reflectivity of certain types of rocks would be most different. Using a colorimeter, they examined the reflectivity of weathered and fresh samples of shale, limestone, and sandstone from New Mexico. They established how the reflectivity of an individual rock surface changes, and plotted reflectance across the spectrum from this data. The shape and position of the curve on it show how many percent of the light flux energy is reflected from the rock surface in a certain wavelength interval (Fig. 6 and 7).
Rice. 6. Spectral reflectivity of four types of rocks: light brown sandstone (A), gray limestone (B), red siltstone (C) and gray sandstone (D)
In general, the reflectivity of the studied rocks decreases with decreasing wavelength (Fig. 6).
If we compare the position of the individual spectral curves of this graph, then we can determine:
1.the regions of the spectrum in which the curves come close to each other or intersect;
2. spectral regions or, spectral regions in which the reflectivity of the studied rocks is clearly similar;
3. Areas of the spectrum in which the reflection curves of different rocks clearly diverge from each other. In this spectral zone, the studied rock types reflect the incident luminous flux with the greatest difference.
This is seen even better in Fig. 7, which shows the reflection curves of red siltstone (A) and weathered gray limestone (B). In the 0.45-0.5 micron spectrum zone, as well as in the 0.65-0.7 kmc zone, the difference in the reflectivity of both types of rocks is especially pronounced. In the zone of 0.45-0.5 microns (blue) limestone (5) reflects the luminous flux incident on it much stronger than red siltstone (A). On the contrary, in the zone of 0.65-0.7 microns (red), the reflection of red siltstone (A) is much greater than that of limestone (B). In the zone of 0.575 microns, the reflectivity of both rocks is the same; here their spectral curves intersect.
Rice. 7. Spectral reflectivity of two types of rocks: red siltstone (A) and weathered gray limestone (B (Ray R.G., Fisher W.A., 1960)
This example shows that: a) the difference in the reflectivity of the two types of rocks in a certain wavelength interval or part of the spectrum is more pronounced than in others; b) the ratio of the reflectivity of the two types of rocks in the range of visible radiation can be reversed; c) spectral characteristics of various rocks in a certain wavelength interval may be similar or the same.
From the analysis of the graphs (Fig. 6) it follows that the differences in the reflectivity of two or more types of rocks in the visible range of electromagnetic radiation can more or less change. Thus, in the short-wavelength part of the spectrum, the spectral brightness curves of light brown sandstone (A), gray limestone (B), and gray sandstone (D) are close to each other. Rocks with different color, mineral composition and grain size have similar shapes of spectral brightness curves. On the other hand, these three varieties of rocks reflect the luminous flux incident on them in the blue part of the spectrum more strongly than red siltstone (C). In the red part of the spectrum (about 0.65-0.7 microns), light brown sandstone (A) reflects the luminous flux incident on it more strongly than gray limestone (B), red siltstone (S) and gray sandstone (D), which in this part of the spectrum, similar spectral characteristics are found.
If a filter-film combination was used to survey the terrain with type A and B outcrops, in which rays of a certain color would fall through the light filter on the film, i.e. wavelengths, for example, blue (0.4-0.5 microns) or red (0.6-0.7 microns), then one would expect that in such a spectrozonal (narrow-gap) photograph, red mudstones (A) and gray limestones (B). In such an image, taken in the blue zone of the spectrum, dark gray limestones would stand out lighter, and red mudstones - darker shades. On an aerial photograph taken in the red zone of the spectrum, the phototones would be reversed, but the contrast between them would be preserved.
If an area with four identified types of rocks (Fig. 6) is photographed in the rays of the blue spectral zone, then on the aerial photograph, outcrops of rocks of type C will stand out as the darkest shade of gray among more light shades corresponding to more highly reflective outcrops of other rock types (A, B and D). With appropriate transmission of red rays, the filter-film combination in the narrow-zone image of the type A outcrops will be highlighted by the lightest tones among the darker outcrops of type B or C / D this time. Based on this knowledge and using suitable filter-film combinations, Ray and Fisher achieved the most contrasting images of various rock types in aerial photographs. Their research showed, first of all, how important is the technology of shooting, the spectral range in which the area is surveyed and which is determined by the spectral characteristics (each time by its own) of materials or environments - the surfaces of natural and anthropogenic objects of survey. The research methodology and the use of experimental data applied by Ray and Fisher laid the most important foundations for the development, which began several years later, in the development of multispectral surveys and methods of processing and data for remote sensing.
To select the optimal spectral channel or shooting range and obtain the optimal image when processing remote sensing data, first of all, it is necessary to know the reflective and absorption capacities of the materials of interest (survey objects) in the assumed wavelength range. In 1960-1970. the study of these patterns was devoted to measuring the reflectivity (albedo) of the most important minerals and rocks in laboratories, on the ground, as well as from aircraft and satellites. Investigations were initially limited to measurements in the visible and near infrared ranges of electromagnetic radiation. Later, they began to study the spectral brightness of minerals and rocks in the mid-IR range, as well as their emissivity (or thermal radiation coefficients) in the temperature, or thermal, range of infrared radiation.
The reflectivity of critical minerals and rocks in the visible and near infrared ranges in laboratory conditions has been extensively studied by Hunt and his colleagues. The results of their research served the most important start for all subsequent measurements of the spectral characteristics of rocks.
In natural conditions, the reflectivity, or albedo, of natural surfaces is determined by the influence of a number of variable parameters, which only partially depend on the surface material, and are partially related to the influence of the environment. More precisely, a comparison of laboratory and field measurements showed that the spectral brightness of the same types of rocks changes depending on the size of the window or slit of the spectrometer or radiometer, i.e. measurement field in which the spectral brightness coefficient of the object is determined. If laboratory measurements cover an area of several square millimeters, then for a field spectrometer or radiometer, the measurement field can vary from square decimeters to square meters, which depends on the technical data of the device and the measurement technique. The multispectral scanner installed on board the Landsat satellite covers a minimum area of about 6,000 square meters. In addition, the surfaces of the samples measured in the laboratory are homogeneous. Natural natural surfaces that fall into the field of measurements of a spectrometer, radiometer or scanner installed on board an aircraft or satellite are almost always heterogeneous, heterogeneous, due to possible differences in surface structure, variations in mineral composition, etc. the content of ferruginous minerals, the spectral brightness of the rock surface can change, since the soil formation, the type and composition of vegetation on it change. Spectral brightness of rock surfaces, which were obtained in different time, in different areas and with the help of different measuring and survey systems, depending on the purpose of the survey, it is hardly necessary to directly compare and contrast with each other. Despite this, the available data from previous spectral measurements show that the relative differences in the reflectivity, absorption and emissivity of the most important types of rocks can be used in landscape studies and in the compilation of thematic maps.
Results of some fundamental studies of the spectral characteristics of minerals and rocks.
Watson conducted a study of four types of rocks in one of the valleys of the piece. Oklahoma in the laboratory and in the field. He selected fresh crushed samples of quartz sandstone and granite, samples of weathered limestone, granite and dolomite, as well as granites covered with a lichen crust. The spectral brightness of several samples was measured each time different types rocks. Based on the data of the measurements, graphs were built (Fig. 8a), which show the reflectivity of the rocks (in percent with respect to the reference surface, i.e. the reference white matte surface).
Rice. 8a. Spectral reflectivity of fresh and weathered surfaces of various rocks. (Spectral reflectance and photometric properties of selected rocks, by R. Watson, Remote Sensing of Environment, Vol. 2, 1972, pp. 95-100.)
1 - standard surface; 2 - quartz sandstone (fresh cleavage); 3 - granite (fresh cleavage); 4 - granite covered with green lichen; 5 - weathered limestone; 6 - weathered granite; 7 - weathered dolomite.
In most cases, in the visible part of the spectrum, fresh, unweathered surfaces of granites reflect radiation more strongly than surfaces of the same rocks, but weathered or covered with lichens. Weathered rough surfaces reflect poorly at all wavelength ranges.
In the visible range of electromagnetic waves, the surfaces of weathered limestones reflect most of the incident radiation always stronger than the surfaces of weathered dolomites (Fig.8a). Fresh fractured quartz sandstone, due to its clean and uniform surface, reflects the incident flow much more strongly than other rock types (Fig.8a).
Watson emphasizes that a comparison of the reflection values measured in the laboratory and in the field can only be approximate. First of all, let us recall that the spectrometer in the laboratory and on the ground measures areas of different sizes. For this reason alone, large differences in the measured reflection values are possible. In addition, the angle of illumination in the laboratory is constant or adjustable, and in natural conditions, in nature, the angle of incidence of the sun's rays changes depending on the time of day and year, which leads to variable illumination of the object. Different values of natural illumination change the intensity of the spectral reflection of the same surfaces during the day and at different times of the year. Therefore, the values of spectral brightness obtained at different times by ground-based measurements or as a result of fly-overs of test sites are not comparable or conditionally comparable with each other.
Thus, secondary geological processes (hydrothermal changes in rocks, weathering, etc.), which may be associated with the formation of mineral deposits, or the development of modern phenomena complicating the geoecological situation (areas unfavorable for the construction of engineering structures, etc.), significantly change spectral characteristics of rocks
It is widely used in DMY. The spectral characteristics of rocks change especially strongly during the development of clay-mica, carbonate and hydroxyl-containing minerals, and iron hydroxides.
Numerous positive examples are known ( former USSR, USA, France, etc.) of the use of DMI in air and space variants as direct methods of prospecting for deposits of copper, uranium, gold and other minerals.
Another comparison of the reflectivity of weathered and fresh surfaces of rocks: rhyolite, basalt, and tuff (Fig.8b) indicates a decrease in the value of the reflection coefficient on weathered surfaces. As can be seen from the graph, the shape of the characteristic curves remains almost unchanged, which can be explained by the stability of the spectral features of certain types of rocks.
Rice. 8b. Spectral reflectivity of fresh and weathered rock surface on the example of rhyolite (K), basalt and tuff. (The multiband approach to geological mapping from orbiting satellites: is it redundant or vital? By R. J. Lyon, Remote Sensing of Environment, Vol. 1, 1970, pp. 237-244.
A - rhyolite; B - hydrothermally altered basalt; VT - tuff with amethyst; index W weathered samples.
Let us now consider the quantitative dependence of the spectral brightness of surfaces of different types of rocks on the density of the vegetation covering them. These measurements were carried out in the field with a spectrometer with a measurement range from 0.45 to 2.4 μm, i.e., from visible to average (reflected) infrared radiation, from a height of about 1.3 m with a measurement area of about 200 cm2. Surfaces of andesite, basalt, rhyolite, lava (red-orange), quartz, trachyandesite (latite), limestone, red shale, limonitized and argilized rubble and soil, silicified limestone and marbled dolomite with limonite were selected as objects. The surfaces of each type of rocks were covered with a cover of green meadow grasses and pine seed, which was not uniform in density, as well as bearberry and wilted sage bushes.
The influence of the vegetation cover density on the value of the spectral reflection of andesite, limestone, and alumina limonitized weathered soils is shown in Fig. 10. These graphs compare the brightness of non-vegetated and overgrown rock surfaces (the density of vegetation in the spectrometer measurement field is expressed as a percentage). As expected, the effect of vegetation in the spectrum of the reflected energy flux is clearly pronounced only for rocks with a negligible albedo. Even at 10% of meadow grasses, the spectral characteristics of andesite and limestone are masked by the spectral signal of meadow vegetation (Fig. 10, a). Even with an insignificant vegetation cover, it was difficult to identify the spectral signals of these two types of rocks.
Rice. 3.5. Influence of vegetation different types and different densities on the spectral brightness of andesite, limestone and limonitized clay soil with fragments of weathered rock (soil on the weathering crust): a - meadow grasses; b - thickets of bearberry; c - thickets of dried sage. Vegetation density is shown as a percentage on each graph (Kronberg, 1988)
Withering or withered vegetation gives almost no masking effect for the spectral signals of the underlying base. This is obvious from a comparison of the two considered groups of graphs (cf. Fig. 10, a, b). Even with a cover density of about 60%, the spectral features of the underlying soil are preserved. Of course, with an increase in the density of vegetation, the albedo of limestone and limonitized alumina soil decreases.
Dry and withering vegetation changes the nature of the spectrum of rocks and soils little. It only decreases the albedo value.
Thus, the presence (percentage of distribution), nature (live, dry) and type of vegetation (species) affect the spectral characteristics of rocks in different ways. The effect on rocks characterized by low albedo is especially strong: andesites, limestones, clays and products of their destruction.
The study of the spectral characteristics of natural objects contributed to the selection of the two most optimal wavelength intervals: 1.2-1.3 and 1.6-2.2 microns, in which it is possible to search for copper-porphyry mineralization in unaltered intrusive, volcanogenic and sedimentary rocks in secondary zones. minerals and rocks formed as a result of hydrothermal alteration.
As a result of laboratory measurements, it was found that certain minerals that are found in zones of hydrothermally altered rocks near deposits, for example, porphyry copper ores, have specific spectral features, especially in the wavelength range of 2.1-2.4 microns. These signs can be used for remote sensing. Thus, kaolinite, montmorillonite, alunite and calcite are recognized by their characteristic narrow and wide energy absorption bands in the mid-infrared (Fig. 12). Based on the assumption that using a ten-channel radiometer with a measuring range of 0.5-2.3 microns it will be possible to find at least kaolin or carbonate rocks by their spectral characteristics for a start, experimental surveys were carried out from the Space Shuttle Columbia reusable spacecraft ... Along with measurements in specific narrow zones of the spectrum, measurements in a certain combination of zones or channels have been proposed to prove the possibility of identifying minerals of interest. The studies carried out on the test site proved the effectiveness of the proposed combination of two channels; 1.6 and 2.2 microns. The first of these is very important for the detection of hydroxyl groups in minerals typical of hydrothermally altered zones of deposits. According to the measurements carried out in both of these channels, it was possible to distinguish limonitized, hydrothermally altered rocks and igneous rocks, in most cases, also with limonite, which is formed as a result of oxidation of iron-magnesium minerals and crystallization of glass. In addition, strongly clarified hydrothermally altered rocks without limonite were found if they contained minerals with a hydroxyl group OH-.
Rice. 12. Spectral reflectivity of some minerals found in areas of development of hydrothermal alteration in rocks (according to laboratory measurements). For the determination of minerals, the position of the spectral absorption bands turned out to be important, 1 - kaolinite; 2 - montmorillonite; 3 - alunite; 4 - calcite.
The use of the mid-infrared range has become possible only in last years thanks to the development of such receivers that made it possible to carry out these measurements. Thematic schematic images are obtained by the Landsat-4 multispectral scanner, which has a special 2.2 µm channel designed for mapping lithofacies or mineral facies.
Based on the results of one of the experiments carried out to solve geological problems by remote methods, a conclusion was made about the efficiency of spectrometry in the following spectral zones: 1.18-1.3; 4.0-4.75; 0.46-0.50; 1.52-1.73; 2.10-2.36 microns. This conclusion is based on the results of processing data from one test site per piece. Utah. The measurements were carried out with a multispectral scanner while flying around the territory of the site with outcrops of the main types of rocks - sedimentary and intrusive, as well as with zones of their secondary hydrothermal alteration. The size of the measurement field over the surface of the studied rock was about 0.24 km2. For all types of rocks, measurements were carried out in 15 channels with an interval of 0.34-0.75 μm between them. With the help of discriminant analysis, the zones were identified, in which the survey of all rock differences with the optimal contrast of specific rock differences in relation to other types was most often carried out. The recording of the selected zones was intended for re-study and mapping of lithofacies differences. The multispectral scanner used had a spectral resolution in the visible range of 0.04-0.06 µm, in the near-IR range of 0.05-0.26 µm and in the thermal range of 0.25-0.36 µm. Only one of the spectral channels of this scanner operated in the same spectral range as the scanners of the first Landsat satellites - from 0.4 to 1.1 μm, the other four optimal channels worked in the long-wave, infrared, radiation region, the significance of which was emphasized by the above examples.
Studies of the spectral characteristics of unchanged and altered rocks near uranium deposits have established a number of spectral zones: 1.25; 0.95; 2.20; 2.15; 1.75; 2.45; 2.10; 1.60; 1.55 and 0.75 microns, measurements in which, carried out in the indicated sequence, are most effective for separating lithofacies in areas of uranium deposits. This example emphasizes the importance of spectral surveys in strictly limited narrow areas of the spectrum, in which remote sensing methods can be more or less effectively used in prospecting and exploration.
The spectral characteristic brightness of rocks strongly depends on the size of the window or slit of the spectrometer or radiometer, i.e., the field of measurement (vision). The narrower the field, the higher the contrast in spectral brightness, the better the resolution in the area. This is due to the fact that the effect of scattered radiation decreases.
Spatial resolution is a quantity that characterizes the size of the smallest objects distinguishable in the image. (find examples of pictures of rocks).
It is important to perform DMI in different parts of the spectrum, where various properties rocks have contrasting spectral characteristics. This is achieved by using multispectral scanners, which have a spectral resolution: in the visible range - 0.04-0.06 microns; in the near infrared range - 0.05-0.26 microns; in the thermal range - 0.25-0.36 microns. In this case, shooting is simultaneously performed in five or more ranges (examples of pictures).
Secondary thermal radiation of rocks (emission)
Along with the characteristics of the spectral reflection of surfaces of rocks and soils in the visible and near-IR ranges, in the 1960s, some geologists were also interested in the secondary thermal radiation of rocks, which they hoped to use in remote sensing.
As a result of studies carried out since the end of the 50s, it was found that the shape of the curves on the graphs of the secondary thermal radiation of rocks is closely related to the mineral composition of the rocks, that silicate and non-silicate rocks can be distinguished by the spectra of their secondary thermal radiation in the range 8-13 μm and that, finally, silicate rocks of different mineral composition can be divided according to the same spectra. In all cases, the position of the minima on the graphs of the secondary thermal radiation of rocks served as a feature for recognition.
Consider a group of heat radiation energy plots obtained from measurements of some coarse fresh crushed granite samples from New England. Individual samples vary in color from dark gray to brown, pink, or bluish. But the difference in color, according to Lyon and Green, does not affect the intensity of the emitter radiation. The measurement of the position of the energy minimum on the graphs (Fig. 14) is caused by changes in the mineral composition of the samples (chemical modulus) of quartz granites (D and E) and alkaline feldspar granites (F). For comparison, both minima in the emission spectrum of quartz (Q) are shown.
Rice. 14. Spectral emissivity of a fresh surface of coarse granite from New England. Q is the emission minimum of quartz, for comparison. The vertical arrows show where the emission is 1.
In principle, the spectral characteristics of the surface of a rock or soil are influenced by numerous factors, both dependent on the properties of the surface of the measurement object, and not depending on them, but related to its environment and atmosphere. However, for regions in which vast areas of the territory are devoid of vegetation cover, for example, in arid regions, in high-mountainous regions, etc., large areas of exposed rocks are covered by the scanner during thermal imaging. Here, one can use the minima on the plots of the secondary thermal radiation of objects, which are naturally associated with their mineral composition, to interpret certain lithofacies differences of rocks or their complexes. This hypothesis has been proven by airplane thermal imaging: areas of exposed rocks of different composition the most contrasting shades of gray were conveyed in two ranges: 8-9 and 9-11 microns. The smallest values of this ratio are found in rocks or soils, which include quartz or plagioclases. Higher values of this ratio indicate the poverty of rocks or soils in quartz and feldspars... But finally, the question of the optimality (and efficiency) of using these two spectral ranges for studying the lithofacies features of regions according to thermal survey data and the effect of atmospheric and other interference on them when a signal passes to a receiver installed on board a carrier - an aircraft or a satellite - has not been resolved on the current stage of research.
The diagnostic features of rocks are, first of all, the position of the minima and other characteristics of the graphs, as well as the ratio of spectral signals of different ranges (8-9 and 9-11 µm, Fig. 3.6).
Rice. 3.6. Spectral emissivity of basalts (A and B), quartz monzonite (E and F) and granodiorite (I). Vertical arrows show where emission is 1, and horizontal - 0.9. (Ljon, Green, 1975.)
Thus, the ability to simultaneously carry out spectrometry over many critical (characteristic) spectral ranges, i.e. the possibility of carrying out a multi-zone thermal scanner survey from airplanes or satellites, as well as the possibility of computer processing of its results and presentation of data in the form of contrast-optimized images.
Thus, the secondary thermal radiation of rocks is determined by their physical properties: - thermal conductivity, density, specific heat, thermal diffusivity, heat transfer (temperature inertia). In turn, these properties depend on the material, mineralogical and chemical composition. The ratio of dark-colored (iron-magnesium) and light-colored minerals is especially strongly influenced.
Contrastingly, this can be seen from the change in the coefficient of secondary thermal radiation (emission coefficient) in the daytime and at night (Fig. 2.5). Some objects "look brighter" in daytime others - at night. The timing of filming is important. The most preferred hours are before dawn and noon.
Surface temperatures various materials during the day (Lowe, 1969). 1 - water in a puddle; 2 - gravel; 3 - mowed lawn; 4 - concrete; 5 - lawn; 6 - roof of the house
Computer processing of thermal scanner data and their visualization (shades gray or color coloration) produce high-contrast thermal images.
Thermal scanner survey is performed, as a rule, over several of the most informative (characteristic) spectral ranges. Infrared surveys are usually performed in conjunction with the visible range to account for the strong influence of shadow areas (during daytime) on infrared results.
Quantitative processing of data from multispectral surveys, including thermal scanners and radiometers, is becoming more and more important every day. Already now, remote sensing is based on the temperature characteristics of soils, plant communities or rocks when solving operational problems of environmental monitoring. Different thermal properties of rocks (Table 1a) and different coefficients of secondary thermal radiation or emission coefficients (Table 1 b) lead to their different heating during the day and cooling at night, which is determined by temperature contrasts in the diurnal temperature course, which is used for remote sensing. ...
It is important to emphasize here that even information about the relative difference in the radiation temperatures of the surface of objects can be decisive in the geological interpretation of images, since additional evaluation criteria are possible that cannot be obtained by surveys in the visible range of electromagnetic waves.
Table 1a. Thermal properties of various rocks and water at a temperature of 20 ° C.
- Reflectivity is a value that describes the ability of any surface or interface between two media to reflect the incident electromagnetic radiation flux. It is widely used in optics, quantitatively characterized by the reflection coefficient. A quantity called albedo is used to characterize diffuse reflection.
The ability of materials to reflect radiation depends on the angle of incidence, on the polarization of the incident radiation, as well as on its spectrum. The dependence of the reflectivity of the body surface on the wavelength of light in the region of visible light is perceived by the human eye as body color.
The dependence of the reflectivity of materials on the wavelength is important in the construction of optical systems. To obtain the required properties of materials for the reflection and transmission of light, sometimes optical antireflection is used, for example, in the production of dielectric mirrors or interference filters.
Related concepts
Refraction (refraction) is a change in the direction of a ray (wave) that occurs at the boundary of two media through which this ray passes or in one medium, but with varying properties, in which the speed of wave propagation is not the same.
A fiber Bragg grating (FBG) is a distributed Bragg reflector (a type of diffraction grating) formed in the light-carrying core of an optical fiber. FBGs have a narrow reflection spectrum, are used in fiber lasers, fiber-optic sensors, for stabilization and change of the wavelength of lasers and laser diodes, etc.
Photometry (ancient Greek φῶς, genitive φωτός - light and μετρέω - I measure) is a scientific discipline common to all branches of applied optics, on the basis of which quantitative measurements of the energy characteristics of the radiation field are made.
Photoluminescence spectroscopy is a type of optical spectroscopy based on the measurement of the spectrum of electromagnetic radiation emitted as a result of the photoluminescence phenomenon caused in the sample under study, by means of its excitation with light. One of the main experimental research methods optical properties materials, and in particular semiconductor micro- and nanostructures.
Optical tweezers, sometimes "laser tweezers" or "optical traps", are an optical instrument that allows you to manipulate microscopic objects using laser light (usually emitted from a laser diode). It allows you to apply forces from femtonewtons to nanonewtons to dielectric objects and measure distances from a few nanometers to microns. In recent years, optical tweezers have begun to be used in biophysics to study the structure and operating principle ...
The pressure of electromagnetic radiation, the pressure of light - the pressure exerted by light (and generally electromagnetic) radiation falling on the surface of the body.
Optics lightening is the application of a thin film or several layers of films one on top of the other to the surface of lenses bordering on air. This allows you to increase the light transmission of the optical system and increase the contrast of the image by suppressing glare. The values of the refractive indices alternate in magnitude and are selected in such a way as to reduce (or completely eliminate) unwanted reflection due to interference.
Light interference - the interference of electromagnetic waves (in the narrow sense - first of all, visible light) - the redistribution of light intensity as a result of the superposition (superposition) of several light waves. This phenomenon is usually characterized by alternating maxima and minima of light intensity in space. The specific type of such distribution of light intensity in space or on a screen where light falls is called an interference pattern.
Luminescence (from Latin lumen, genus case luminis - light and -escent - suffix meaning weak action) is a non-thermal glow of a substance that occurs after it absorbs excitation energy. Luminescence was first described in the 18th century.
The Kerr effect, or the quadratic electro-optical effect, is the phenomenon of a change in the value of the refractive index of an optical material in proportion to the square of the applied electric field... It differs from the Pockels effect in that the change in the exponent is directly proportional to the square of the electric field, while the latter changes linearly. The Kerr effect can be observed in all substances, but some liquids exhibit it more strongly than other substances. Opened in 1875 by Scottish ...
Near-infrared spectroscopy (NIR spectroscopy, English near-infrared spectroscopy, NIR) is a section of spectroscopy that studies the interaction of near infrared radiation (from 780 to 2500 nm, or from 12 800 to 4000 cm-1) with substances. The near infrared region is located between visible light and the mid infrared region.
Dielectric mirror - a mirror, the reflective properties of which are formed due to the coating of several alternating thin layers of various dielectric materials. Used in a variety of optical devices. With the proper choice of materials and layer thicknesses, optical coatings can be created with the desired reflectivity at the selected wavelength. Dielectric mirrors can provide very high reflectivity, (called super mirrors), which provide reflection ...
A distributed Bragg reflector is a layered structure in which the refractive index of the material periodically changes in one spatial direction (perpendicular to the layers).
Polarimeter (polariscope, - for observation only) - a device designed to measure the angle of rotation of the plane of polarization caused by the optical activity of transparent media, solutions (saccharometry) and liquids. In a broad sense, a polarimeter is a device that measures the polarization parameters of partially polarized radiation (in this sense, the parameters of the Stokes vector, the degree of polarization, the parameters of the polarization ellipse of partially polarized radiation, etc.) can be measured.
Rayleigh scattering is coherent scattering of light without changing the wavelength (also called elastic scattering) on particles, inhomogeneities or other objects, when the frequency of the scattered light is significantly higher than the natural frequency of the scattering object or system. Equivalent formulation: scattering of light by objects smaller than its wavelength. Named after the British physicist Lord Rayleigh, who established the dependence of the intensity of scattered light on the wavelength in 1871 ...
An absolutely black body is a physical body that, at any temperature, absorbs all electromagnetic radiation falling on it in all ranges.
Infrared spectroscopy (vibrational spectroscopy, mid-infrared spectroscopy, IR spectroscopy, IR) is a section of spectroscopy that studies the interaction of infrared radiation with substances.
Disc darkening toward the edge is an optical effect when observing stars, including the Sun, in which the central part of the star's disk appears brighter than the edge or limb of the disk. Understanding this effect made it possible to create models of stellar atmospheres taking into account such a brightness gradient, which contributed to the development of the theory of radiation transfer.
The Michelson interferometer is a two-beam interferometer invented by Albert Michelson. This device made it possible for the first time to measure the wavelength of light. In Michelson's experiment, an interferometer was used by Michelson and Morley to test the hypothesis of luminiferous ether in 1887.
Small angle X-ray scattering abbr., MPP (English small angle X-ray scattering abbr., SAXS) - elastic scattering of X-ray radiation on inhomogeneities of a substance, the dimensions of which significantly exceed the radiation wavelength, which is λ = 0.1–1 nm; the directions of the scattered rays in this case only slightly (at small angles) deviate from the direction of the incident ray.
X-ray optics is a branch of applied optics that studies the propagation of X-rays in media and develops elements for X-ray devices. X-ray optics, in contrast to conventional optics, considers electromagnetic waves in the X-ray wavelength range of 10-4 to 100 Å (from 10-14 to 10-8 m) and gamma radiation
The geometrical factor (also étendue, from the French étendue géométrique) is a physical quantity that characterizes how much light in an optical system is "expanded" in size and direction. This value corresponds to the beam quality parameter (BPP) in Gaussian beam physics.
X-ray mirror - an optical device used to control X-ray radiation (reflection of X-rays, focusing and scattering). Technologies are now making it possible to create X-ray mirrors and extreme UV parts with wavelengths ranging from 2 to 45-55 nanometers. An X-ray mirror consists of many layers of special materials (up to several hundred layers).
A diffraction grating is an optical device, the operation of which is based on the use of the phenomenon of light diffraction. It is a collection of a large number of regularly spaced strokes (slots, protrusions) applied to a certain surface. The first description of the phenomenon was made by James Gregory, who used bird feathers as a lattice.
The Sadovsky effect is the appearance of a mechanical torque that acts on a body irradiated with light elliptically or circularly polarized.
Any object that emits electromagnetic energy in the visible region of the spectrum. By their nature, they are divided into artificial and natural.
Dynamic light scattering is a combination of such phenomena as a change in frequency (Doppler shift), intensity and direction of movement of light passing through a medium of moving (Brownian) particles.
Light is one of the effects of self-action of light, consisting in the concentration of the energy of a light beam in a nonlinear medium, the refractive index of which increases with increasing light intensity. The phenomenon of self-focusing was predicted by the Soviet theoretical physicist G.A.Askar'yan in 1961 and was first observed by N.F.Pilipetskiy and A.R. Rustamov in 1965. The foundations of a mathematically rigorous description of the theory were laid by VI Talanov.
A two-photo laser microscope is a laser microscope that allows you to observe living tissues at a depth of more than one millimeter, using the phenomenon of fluorescence. A two-photon microscope is a kind of multi-photon fluorescence microscope. Its advantages over a confocal microscope are its high penetrating power and low degree of phototoxicity.
Infrared radiation - electromagnetic radiation occupying the spectral region between the red end of visible light (with a wavelength λ = 0.74 μm and a frequency of 430 THz) and microwave radio emission (λ ~ 1-2 mm, frequency 300 GHz).
Birefringence or birefringence is the effect of splitting a light beam into two components in anisotropic media. If a ray of light falls perpendicular to the surface of the crystal, then on this surface it is split into two rays. The first ray continues to propagate directly, and is called ordinary (o - ordinary), the second deviates to the side, and is called extraordinary (e - extraordinary).
The Vavilov - Cherenkov effect, the Cherenkov effect, the Vavilov - Cherenkov radiation, the Cherenkov radiation - the glow caused in a transparent medium by a charged particle moving at a speed exceeding the phase velocity of light propagation in this medium.
Electromagnetic waves / electromagnetic radiation is a perturbation (change in state) of an electromagnetic field propagating in space. Among the electromagnetic fields generated by electric charges and their movement, it is customary to refer to radiation as that part of alternating electromagnetic fields that is capable of propagating farthest from their sources - moving charges, fading out most slowly with distance.
The spectral absorption line or dark spectral line is a feature of the spectrum, which consists in a decrease in the radiation intensity near a certain energy.
Microscope (ancient Greek μικρός "small" + σκοπέω "look") is a device designed to obtain enlarged images, as well as to measure objects or structure details that are invisible or poorly visible to the naked eye.
Visible radiation - electromagnetic waves perceived by the human eye. The sensitivity of the human eye to electromagnetic radiation depends on the wavelength (frequency) of the radiation, with the maximum sensitivity being at 555 nm (540 THz), in the green part of the spectrum. Since the sensitivity gradually decreases to zero with distance from the maximum point, it is impossible to specify the exact boundaries of the spectral range of visible radiation. Usually, the shortwave boundary is taken ...
Fourier spectrometer is an optical device used for quantitative and qualitative analysis of the content of substances in a gas sample.
