|
Schlieren
Schlieren ( ; , ) are optical inhomogeneities in transparent media that are not necessarily visible to the human eye. Schlieren physics developed out of the need to produce high-quality lenses devoid of such inhomogeneities. These inhomogeneities are localized differences in optical path length that cause deviations of light rays, especially by refraction. This light deviation can produce localized brightening, darkening, or even color changes in an image, depending on the directions the rays deviate. History Schlieren were first observed by Robert HookeHooke, R. (1665), "Of a New Property in the Air," ''Micrographia'', Observation LVIII, pp. 217–219, London. in 1665 using a large concave lens and two candles. One candle served as a light source. The warm air rising from the second candle provided the schliere. The conventional schlieren system is credited mostly to German physicist August Toepler, though Jean Bernard Léon Foucault invented the method in 1859 that To ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Background-oriented Schlieren Technique
Schlieren photography is a process for photographing fluid flow. Invented by the German physicist August Toepler in 1864 to study supersonic motion, it is widely used in aeronautical engineering to photograph the flow of air around objects. Classical optical system The classical implementation of an optical schlieren system uses light from a single collimated source shining on, or from behind, a target object. Variations in refractive index caused by density gradients in the fluid distort the collimated light beam. This distortion creates a spatial variation in the intensity of the light, which can be visualised directly with a shadowgraph system. Classical schlieren imaging systems appear in two configurations, using either one or two mirrors. In each case, a transparent object is illuminated with collimated or nearly-collimated light. Rays that are not deflected by the object proceed to their focal point, where they are blocked by a knife edge. Rays that are deflected by ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Schlieren Photography
Schlieren photography is a process for photographing fluid flow. Invented by the German physicist August Toepler in 1864 to study supersonic motion, it is widely used in aeronautical engineering to photograph the flow of air around objects. Classical optical system The classical implementation of an optical schlieren system uses light from a single collimated source shining on, or from behind, a target object. Variations in refractive index caused by density gradients in the fluid distort the collimated light beam. This distortion creates a spatial variation in the intensity of the light, which can be visualised directly with a shadowgraph system. Classical schlieren imaging systems appear in two configurations, using either one or two mirrors. In each case, a transparent object is illuminated with collimated or nearly-collimated light. Rays that are not deflected by the object proceed to their focal point, where they are blocked by a knife edge. Rays that are de ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Schlieren Video Of A Handgun
Schlieren ( ; , ) are optical inhomogeneities in transparent media that are not necessarily visible to the human eye. Schlieren physics developed out of the need to produce high-quality lenses devoid of such inhomogeneities. These inhomogeneities are localized differences in optical path length that cause deviations of light rays, especially by refraction. This light deviation can produce localized brightening, darkening, or even color changes in an image, depending on the directions the rays deviate. History Schlieren were first observed by Robert HookeHooke, R. (1665), "Of a New Property in the Air," '' Micrographia'', Observation LVIII, pp. 217–219, London. in 1665 using a large concave lens and two candles. One candle served as a light source. The warm air rising from the second candle provided the schliere. The conventional schlieren system is credited mostly to German physicist August Toepler, though Jean Bernard Léon Foucault invented the method in 1859 that ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Schlieren Imaging
Schlieren imaging is a method to visualize density variations in transparent media. The term "schlieren imaging" is commonly used as a synonym for schlieren photography, though this article particularly treats visualization of the pressure field produced by ultrasonic transducers, generally in water or tissue-mimicking media. The method provides a two-dimensional (2D) projection image of the acoustic beam in real-time ("live video"). The unique properties of the method enable the investigation of specific features of the acoustic field (e.g. focal point in HIFU transducers), detection of acoustic beam-profile irregularities (e.g. due to defects in transducer) and on-line identification of time-dependent phenomena (e.g. in phased array transducers). Some researchers say that schlieren imaging is equivalent to an X-ray radiograph of the acoustic field. Setup The optical setup of a schlieren imaging system may comprise the following main sections: Parallel beam, focusing eleme ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
August Toepler
August Joseph Ignaz Toepler (7 September 1836 – 6 March 1912) was a German chemist and physicist known for his experiments in electrostatics. Biography August Toepler was born on 7 September 1836. He studied chemistry at the Gewerbe-Institut Berlin (1855–1858) and graduated from the University of Jena in 1860. Later Toepler turned to experimental physics. August Toepler was a lecturer of chemistry and physics at the Academy Poppelsdorf (1859-1864). He received a chair of chemistry and chemical technology at the Polytechnic Institute of Riga and he hold this position between 1864 and 1868. In 1864, he applied Foucault's knife-edge test for telescope mirrors to the analysis of fluid flow and the shock wave. He named this new method schlieren photography, for which he is justifiably famous. He also developed the Toepler machine, an electrostatic influence machine (high voltage generator) in 1865, which would one day find use in early medical x-ray machines. Improved v ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Shadowgraph
Shadowgraph is an optical method that reveals non-uniformities in transparent media like air, water, or glass. It is related to, but simpler than, the schlieren and schlieren photography methods that perform a similar function. Shadowgraph is a type of flow visualisation. In principle, a difference in temperature, a different gas, or a shock wave in the transparent air cannot be seen by the human eye or cameras. However, all these disturbances refract light rays, so they can cast shadows. The plume of hot air rising from a fire, for example, can be seen by way of its shadow cast upon a nearby surface by the uniform sunlight. Sunlight shadowgraph Some aquatic predators detect their transparent prey by way of their shadows cast upon the ocean floor. It was Robert Hooke who first scientifically demonstrated the sunlight shadowgraph and Jean-Paul Marat who first used it to study fire. A modern account of shadowgraphy is given by Gary S. Settles. Applications Applicat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Laser Schlieren Deflectometry
Laser schlieren deflectometry (LSD) is a method for a high-speed measurement of the gas temperature in microscopic dimensions, in particular for temperature peaks under dynamic conditions at atmospheric pressure. The principle of LSD is derived from schlieren photography: a narrow laser beam is used to scan an area in a gas where changes in properties are associated with characteristic changes of refractive index. Laser schlieren deflectometry is claimed to overcome limitations of other methods regarding temporal and spatial resolution. The theory of the method is analogous to the scattering experiment of Ernest Rutherford from 1911. However, instead of alpha particles scattered by gold atoms, here an optical ray is deflected by hot spots with unknown temperature. A general equation of LSD describes the dependence of the measured maximum deflection of the ray ''δ''1 on the local maximum of the neutral gas temperature in the hot spot ''T''1: : \frac + \frac = 1, where ''T' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Synthetic Schlieren
Synthetic schlieren is a process that is used to visualize the flow of a fluid of variable refractive index. Named after the schlieren method of visualization, it consists of a digital camera or video camera pointing at the flow in question, with an illuminated target pattern behind. The method was first proposed in 1999.{{citation , doi=10.1017/S0022112099005017 , first1=B. R. , last1=Sutherland , first2=S. B. , last2=Dalziel , first3=G. O. , last3=Hughes , first4=P. F. , last4=Linden , title=Visualization and measurement of internal waves by "synthetic schlieren". Part 1: Vertically oscillating cylinder , journal=Journal of Fluid Mechanics , volume=390 , issue=1 , pages=93–126 , year=1999 , bibcode=1999JFM...390...93S Variations in refractive index cause the light from the target to refract as it passes through the fluid, which causes a distortion of the pattern in the image seen by the camera. Pattern matching algorithms can measure this distortion and calcu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Liquid Crystal
Liquid crystal (LC) is a state of matter whose properties are between those of conventional liquids and those of solid crystals. For example, a liquid crystal may flow like a liquid, but its molecules may be oriented in a crystal-like way. There are many types of LC phases, which can be distinguished by their optical properties (such as textures). The contrasting textures arise due to molecules within one area of material ("domain") being oriented in the same direction but different areas having different orientations. LC materials may not always be in a LC state of matter (just as water may be ice or water vapor). Liquid crystals can be divided into 3 main types: * thermotropic, *lyotropic, and * metallotropic. Thermotropic and lyotropic liquid crystals consist mostly of organic molecules, although a few minerals are also known. Thermotropic LCs exhibit a phase transition into the LC phase as temperature changes. Lyotropic LCs exhibit phase transitions as a function of both ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Refraction
In physics, refraction is the redirection of a wave as it passes from one medium to another. The redirection can be caused by the wave's change in speed or by a change in the medium. Refraction of light is the most commonly observed phenomenon, but other waves such as sound waves and water waves also experience refraction. How much a wave is refracted is determined by the change in wave speed and the initial direction of wave propagation relative to the direction of change in speed. For light, refraction follows Snell's law, which states that, for a given pair of media, the ratio of the sines of the angle of incidence ''θ1'' and angle of refraction ''θ2'' is equal to the ratio of phase velocities (''v''1 / ''v''2) in the two media, or equivalently, to the refractive indices (''n''2 / ''n''1) of the two media. :\frac =\frac=\frac Optical prisms and lenses use refraction to redirect light, as does the human eye. The refractive index of materials varies with the wa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Léon Foucault
Jean Bernard Léon Foucault (, ; ; 18 September 1819 – 11 February 1868) was a French physicist best known for his demonstration of the Foucault pendulum, a device demonstrating the effect of Earth's rotation. He also made an early measurement of the speed of light, discovered eddy currents, and is credited with naming the gyroscope. Early years The son of a publisher, Foucault was born in Paris on 18 September 1819. After an education received chiefly at home, he studied medicine, which he abandoned in favour of physics due to a blood phobia. He first directed his attention to the improvement of Louis Daguerre's photographic processes. For three years he was experimental assistant to Alfred Donné (1801–1878) in his course of lectures on microscopic anatomy. With Hippolyte Fizeau he carried out a series of investigations on the intensity of the light of the sun, as compared with that of carbon in the arc lamp, and of lime in the flame of the oxyhydrogen blowpipe; on th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mach–Zehnder Interferometer
The Mach–Zehnder interferometer is a device used to determine the relative phase shift variations between two collimated beams derived by splitting light from a single source. The interferometer has been used, among other things, to measure phase shifts between the two beams caused by a sample or a change in length of one of the paths. The apparatus is named after the physicists Ludwig Mach (the son of Ernst Mach) and Ludwig Zehnder; Zehnder's proposal in an 1891 article was refined by Mach in an 1892 article. Demonstrations of Mach–Zehnder interferometry with particles other than photons (particles of light) had been demonstrated as well in multiple experiments. The versatility of the Mach–Zehnder configuration has led to its being used in a wide range of fundamental research topics in quantum mechanics, including studies on counterfactual definiteness, quantum entanglement, quantum computation, quantum cryptography, quantum logic, Elitzur–Vaidman bomb tester, the q ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
