: « I have long been interested in how the laser image stabilization system of telescopes works. Telescopes with such a system look very beautiful in photographs.”
Let's try to figure it out now.
The atmosphere, essential for humans and other life forms on Earth, is almost universally cursed by astronomers. It's great for breathing, but when it comes to astronomical observations of faint objects, the atmosphere constantly tends to ruin the image.
This problem was known to Isaac Newton, in 1704 he realized that atmospheric turbulence affects image formation. Just as heat waves hovering over a heated patch of earth can ruin our view of it, a telescope's image of a distant object is distorted by temperature changes in the layer of atmosphere separating us. Therefore, light entering the telescope reaches it along different trajectories and hits different points at the entrance aperture. Image size and quality depend on a statistical characteristic of the spatial frequency of the turbulence called the coherence length, or r0, typically equal to 10 cm at a good location. Therefore, even for a good location, the resolution of a large telescope (4 or 8 meters in diameter) is comparable to that of a 10 cm telescope; the image will not be sharper than the atmosphere allows.
Atmospheric turbulence acts as if one large telescope aperture were replaced by many small telescope apertures of size r0 and each telescope was shaken independently of the others and so that the individual image points would almost never coincide. The degree of this shaking is determined by another statistical parameter - the coherence time, which is usually on the order of 1 ms.
As a result, the image becomes blurry due to shaking, similar to the shaking of a hand, but with a frequency reaching a thousand hertz!
So what should we do?
One solution to this problem, proposed by Newton, was to mount telescopes as high as possible. This solution explains why modern astronomical telescopes are mounted on mountaintops, placed on hot air balloons and airplanes, or, like the Hubble Space Telescope, placed in low-Earth orbit. Since the space telescope is located beyond the
mi the earth's atmosphere, it realizes the full resolving power of its 2.4-m aperture and makes it possible to obtain revolutionary results in astrophysics. However, there is only one such telescope and it allows only a limited number of observations. If the resolving power of such large apertures could be realized, it would be a major advance in astronomy. Fortunately, there is technology that allows you to do this.
In 1953, Horace Babcock proposed an instrument that could measure atmospheric distortions in real time and correct them using rapidly tunable, shape-shifting optical components. The technologies available at that time did not allow this problem to be solved, but the basic proposed concept, supported by modern technologies, evolved over time into what is now the subject of adaptive optics.
Adaptive optics is an automatic optical-mechanical system designed to correct in real time atmospheric distortions in the image produced by a telescope. Adaptive optics systems are used in ground-based optical and infrared telescopes to improve image clarity. They are also necessary for the operation of astronomical interferometers, used to measure the sizes of stars and search for their close satellites, especially planets. Adaptive optics systems also have non-astronomical applications: for example, when it is necessary to observe the shape of artificial Earth satellites in order to identify them. The development of adaptive optics systems began in the 1970s and gained momentum in the 1980s in connection with the Star Wars program, which included the development of ground-based laser anti-satellite weapons. The first standard active optics systems began operating on large astronomical telescopes around 2000.
Rays of light coming from cosmic sources, passing through the heterogeneous atmosphere of the Earth, experience strong distortions. For example, the wavefront of light coming from a distant star (which can be considered a point at infinity) has a perfectly flat shape at the outer boundary of the atmosphere. But after passing through the turbulent air shell and reaching the Earth's surface, the flat wave front loses its shape and becomes like a wavy sea surface. This leads to the fact that the image of the star turns from a “dot” into a continuously trembling and seething blot. When observed with the naked eye, we perceive this as the rapid blinking and shaking of stars. When observing through a telescope, instead of a “point” star, we see a trembling and iridescent spot; images of stars close to each other merge and become indistinguishable individually; extended objects - the Moon and the Sun, planets, nebulae and galaxies - lose sharpness, their small details disappear.
Typically, in photographs taken by telescopes, the angular size of the smallest details is 2-3I; at the best observatories it is occasionally 0.5I. It should be borne in mind that in the absence of atmospheric distortions, a telescope with a lens with a diameter of 1 m gives an angular resolution of about 0.1I, and with a lens of 5 m it gives a resolution of 0.02I. In fact, such high image quality is never realized with conventional ground-based telescopes due to atmospheric influences.
A passive method of combating atmospheric distortions is that observatories are built on mountain tops, usually at an altitude of 2-3 km, choosing places with the most transparent and calm atmosphere (see ASTROCLIMATE). But it is almost impossible to build observatories and operate at an altitude of more than 4.5 km. Therefore, even at the best high-altitude observatories, most of the atmosphere is still located above the telescope and significantly spoils the images.
The role of the astronomer-observer. Generally speaking, the problem of “obtaining an image better than the atmosphere provides” is solved in astronomy by different means. Historically, in the era of visual observation through a telescope, astronomers have learned to carefully capture moments of good images. Due to the random nature of atmospheric distortions, at some moments they become insignificant, and fine details appear in the image. The most experienced and persistent observers spent hours watching these moments and were thus able to sketch very fine details of the surface of the Moon and planets, as well as detect and measure very close double stars. But the extreme bias of this method was clearly demonstrated in the story of the Martian canals: some observers saw them, others did not.
The use of photographic plates in astronomy has made it possible to identify many new objects that are inaccessible to the eye due to their low brightness. However, photographic emulsion in low light has very low sensitivity to light, so at the beginning of the 20th century. astronomical photography required many hours of exposure. During this time, atmospheric jitter noticeably reduces the image quality compared to the visual one.
Some astronomers tried to combat this phenomenon by independently playing the role of active and partly adaptive optical systems. Thus, American astronomers J.E. Keeler (Keeler J.E., 1857-1900) and W. Baade (Baade W., 1893-1960) adjusted the focus of the telescope during the exposure, observing with very high magnification (about 3000 times) the shape of the coma of the star at the edge of the field of view. And the famous telescope designer J.W. Ritchey G.W., 1864-1945 developed a special photographic cassette on a movable platform - the so-called “Ritchey cassette”; with its help, you can quickly remove the photographic plate from the focus of the telescope, replacing it with a focusing device (Foucault knife), and then return the cassette exactly to its previous position. During the exposure, Ritchie moved the tape back several times when he felt he needed to adjust the focus. In addition, by observing the image quality and its position through an eyepiece placed next to the cassette, Ritchie constantly adjusted the position of the cassette and learned to quickly close the shutter when images became poor. This work required a very high voltage from the astronomer, but Ritchie himself obtained in this way magnificent photographs of spiral galaxies, in which individual stars became visible for the first time; These beautiful photographs were reproduced in all textbooks of the 20th century. However, the Ritchie cassette was not widely used due to the great complexity of working with it.
The development of photographic and video technology has made it possible to quickly capture an image of an object in filming mode with the subsequent selection of the most successful images. More subtle methods of a posteriori image analysis have also been developed, for example, speckle interferometry methods, which make it possible to identify the location and brightness of objects with previously known properties, such as “point” stars, in a spot blurred by the atmosphere. Mathematical image restoration techniques can also enhance contrast and reveal fine details. But these methods are not applicable in the process of observation.
Principles of adaptive optics.
The launch of the 2.4 m diameter Hubble optical telescope into orbit in 1990 and its extremely efficient operation in subsequent years proved the great capabilities of telescopes unencumbered by atmospheric distortions. But the high cost of creating and operating the Space Telescope forced astronomers to look for ways to compensate for atmospheric interference near the Earth's surface. The advent of high-speed computers and, last but not least, the desire of the military to create a space weapons system with ground-based lasers have made it urgent to work on compensating for atmospheric image distortions in real time. The adaptive optics system makes it possible to align and stabilize the wavefront of radiation passing through the atmosphere, making it possible not only to obtain a clear image of a space object at the focus of a telescope, but also to launch a sharply focused laser beam from the Earth into space. Fortunately, military devices of this type were not realized, but the work done in this direction has enormously helped astronomers to almost completely realize the theoretical parameters of large telescopes in terms of image quality. In addition, the development of active optics has made it possible to build ground-based optical interferometers based on large-diameter telescopes: since the coherence length of light after passing through the atmosphere is only about 10 cm, a ground-based interferometer cannot operate without an adaptive optics system.
The task of adaptive optics is to neutralize in real time the distortions introduced by the atmosphere into the image of a space object. Typically, the adaptive system works in conjunction with an active optics system to maintain the telescope's structure and optical elements in "perfect" condition. Working together, active and adaptive optics systems bring image quality closer to extremely high, determined by fundamental physical effects (mainly the aberration of light on the telescope lens). In principle, active and adaptive optics systems are similar to each other. Both of them contain three main elements: 1) an image analyzer, 2) a computer with a program that generates correction signals, and 3) execution mechanisms that change the optical system of the telescope so that the image becomes “ideal”. The quantitative difference between these systems is that correction of the deficiencies of the telescope itself (active optics) can be carried out relatively rarely - with an interval of several seconds to 1 minute; but it is necessary to correct interference introduced by the atmosphere (adaptive optics) much more often - from several tens to a thousand times per second. Therefore, the adaptive optics system cannot change the shape of the massive main mirror of the telescope and is forced to control the shape of a special additional “light and soft” mirror installed at the exit pupil of the telescope.
Implementationi adaptive optics
The possibility of correcting atmospheric image distortions using a deformable mirror was first pointed out in 1953 by the American astronomer Horace Babcock (Babcock H.W., b. 1912). To compensate for distortions, he proposed using the reflection of light from an oil film, the surface of which is deformed by electrostatic forces. Electrostatically controlled thin-film mirrors are being developed for similar purposes today, although piezoelectric elements with a mirror surface are the more popular actuator.
The flat front of a light wave, passing through the atmosphere, is distorted and near the telescope has a rather complex structure. To characterize distortion, the parameter r0 is usually used - the wavefront coherence radius, defined as the distance at which the root-mean-square phase difference reaches 0.4 wavelengths. In the visible range, at a wavelength of 500 nm, in the vast majority of cases r0 lies in the range from 2 to 20 cm; conditions when r0 = 10 cm are often considered typical. The angular resolution of a large ground-based telescope operating through a turbulent atmosphere with a long exposure is equal to that of an ideal telescope of diameter r0 operating outside the atmosphere. Since the value of r0 increases approximately in proportion to the wavelength of the radiation (r0 µ l6/5), atmospheric distortions in the infrared range are significantly less than in the visible.
For small ground-based telescopes, the diameter of which is comparable to r0, we can assume that within the lens the wavefront is flat and at each moment of time is inclined randomly by a certain angle. The slope of the front corresponds to a shift in the image in the focal plane or, as astronomers call it, jitter (in atmospheric physics the term “angle of arrival fluctuations” is accepted). To compensate for jitter in such telescopes, it is enough to introduce a flat controlled mirror tilting along two mutually perpendicular axes. Experience shows that such a simple actuator in the adaptive optics system of a small telescope significantly improves image quality during long exposures.
For large-diameter telescopes (D), the lens area contains about (D/r0)2 quasi-plane wavefront elements. This number determines the complexity of the compensating mirror design, i.e. the number of piezoelements, which, compressing and expanding under the influence of high-frequency control signals (up to hundreds of hertz), change the shape of the “soft” mirror. It is easy to estimate that on a large telescope (D = 8-10 m), complete correction of the wavefront shape in the optical range will require a correction mirror with (10 m / 10 cm)2 = 10,000 controlled elements. With the current development of adaptive optics systems, this is practically impossible. However, in the near infrared range, where the value of r0 = 1 m, the correction mirror should contain about 100 elements, which is quite achievable. For example, the adaptive optics system of the Very Large Telescope (VLT) interferometer at the European Southern Observatory in Chile has a correction mirror of 60 controllable elements.
Star images taken by the Keck 10th Telescope with turbulence correction turned on and off.
To generate signals that control the shape of the correction mirror, an instantaneous image of a bright single star is usually analyzed. A wavefront analyzer located at the exit pupil of the telescope is used as a receiver. Through a matrix of many small lenses, the light from the star hits a CCD matrix, the signals of which are digitized and analyzed by a computer. The control program, changing the shape of the correcting mirror, ensures that the image of the star has a perfectly “point-like” appearance.
Experiments with adaptive optics systems began in the late 1980s, and by the mid-1990s very encouraging results had already been obtained. Since 2000, almost all large telescopes have used such systems, allowing the angular resolution of the telescope to be brought to its physical (diffraction) limit. At the end of November 2001, the adaptive optics system began operating on the 8.2-meter Yepun telescope, part of the Very Large Telescope (VLT) of the European Southern Observatory in Chile. This has significantly improved the quality of the observed picture: now the angular diameter of the star images is 0.07І in the K band (2.2 μm) and 0.04І in the J band (1.2 μm).
Artificial star. To quickly analyze an image, an adaptive optics system uses a reference star, which must be very bright because its light is divided into hundreds of channels by the wavefront analyzer and recorded at a frequency of about 1 kHz in each of them. In addition, a bright reference star should be located in the sky near the object being studied. However, suitable stars are not always found in the field of view of a telescope: there are not many bright stars in the sky, so until recently adaptive optics systems were able to observe only 1% of the sky. To remove this limitation, it was proposed to use an “artificial beacon” that would be located near the object being studied and help probe the atmosphere. Experiments have shown that for the operation of active optics it is very convenient to use a special laser to create an “artificial star” (LGS = Laser Guide Star) in the upper layers of the atmosphere - a small bright spot that is constantly present in the field of view of the telescope. As a rule, a continuous-wave laser with an output power of several watts is used for this, tuned to the frequency of the sodium resonance line (for example, the D2 Na line). Its beam is focused in the atmosphere at an altitude of about 90 km, where there is a natural layer of air enriched with sodium, the glow of which is precisely excited by the laser beam. The physical size of the luminous area is about 1 m, which from a distance of 100 km is perceived as an object with an angular diameter of about 1I.
For example, in the ALFA (Adaptive optics with Laser For Astronomy) system, developed at the Institute of Extraterrestrial Physics and the Institute of Astronomy of the Society. Max Planck (Germany) and put into trial operation in 1998, a 25 W argon pump laser excites a dye laser with an output power of 4.25 W, which produces radiation in the sodium D2 line. This device creates an artificial star with a visual magnitude of 9-10. True, the appearance of an aerosol in the atmosphere or observation at large zenith distances significantly reduces the brightness and quality of an artificial star.
Since the beam of a powerful laser can blind an airplane pilot at night, astronomers are taking safety measures. A video camera with a field of view of 200 monitors through the same telescope the area of the sky around the artificial star and, when any object appears, issues a command to a shutter that blocks the laser beam.
Creation at the end of the 20th century. adaptive optics systems opened up new prospects for ground-based astronomy: the angular resolution of large ground-based telescopes in the visible range came very close to the capabilities of the Hubble Space Telescope, and in the near infrared range even noticeably exceeded them. Adaptive optics will make it possible in the very near future to put into operation large optical interferometers, capable, in particular, of studying planets around other stars.
At Mount Hopkins in Arizona, a beam of five laser beams is aimed at the sky to enhance the image of the 6.5-meter Multimirror Telescope (MMT).
A team of astronomers at the University of Arizona, led by Michael Hart, has developed a technique that allows the surface of a telescope to be calibrated with very high precision, resulting in very clear images of objects that would normally be quite blurry.
Laser adaptive optics is a relatively new technique for enhancing images on ground-based telescopes. It's great to be able to use space telescopes like Hubble and, in the not-too-distant future, James Webb, but they are certainly very expensive to launch and operate. And most importantly, there are a huge number of astronomers vying for a very limited time working on these telescopes. Telescopes such as the Very Large Telescope (ESO VLT) in Chile or the Keck Telescope in Hawaii already use laser adaptive optics to improve image quality.
Originally, adaptive optics focused on the brightest star close to the telescope's viewing area, and actuators at the back of the mirror were moved very quickly by a computer to compensate for atmospheric distortion. However, the capabilities of such a system are limited by the presence of areas of the sky near bright stars.
Laser adaptive optics is much more flexible - the technology uses a single laser to excite molecules in the atmosphere to produce a glow, which is used as a "guide star" to calibrate the mirror to compensate for distortions caused by atmospheric turbulence. The computer analyzes the light from the artificial "guiding star" and determines the behavior of the atmosphere, changing the shape of the mirror surface to compensate for distortions.
When using a single laser, adaptive optics can only compensate for turbulence over a very limited field of view. The new technology, which was first used at the MMT 6.5-m Multimirror Telescope in Arizona, uses not one, but five lasers to create five separate "guiding stars" across a wide two-arc-minute field of view. The angular resolution of a telescope is less than that of a single laser system, for example the Keck Telescope or ESO VLT can take images with an angular resolution of 30-60 milliarcseconds, but being able to have a sharper image over a larger field of view has a lot of advantages.
The ability to conduct spectral studies of old dim galaxies is one of the possible applications of this technology. With the help of spectral analysis, scientists are able to better understand the structure and structure of space objects. Using this technology, the study of the spectrum of galaxies ten billion years old, and they have a very high redshift, is possible even from the surface of the Earth.
Also, when using laser technology, it is much easier to structure supermassive star clusters, since telescope images spaced in time will allow astronomers to understand which stars are part of the cluster and which are gravitationally independent.
And I’ll remind you something about space now: remember and how it works. Now take a walk around The original article is on the website InfoGlaz.rf Link to the article from which this copy was made -
In a heterogeneous environment, using controlled optical elements. The main tasks of adaptive optics are increasing the resolution limit of observational instruments, concentrating optical radiation on the receiver or target, etc.
Adaptive optics is used in the design of ground-based astronomical telescopes, in optical communication systems, in industrial laser technology, in ophthalmology, etc., where it allows, respectively, to compensate for atmospheric distortions and aberrations of optical systems, including the optical elements of the human eye.
Encyclopedic YouTube
-
1 / 5
Structurally, an adaptive optical system usually consists of a sensor that measures distortion (wavefront sensor), a wavefront corrector, and a control system that communicates between the sensor and the corrector.
Wavefront sensors
There are a variety of methods that allow both qualitative assessment and quantitative measurement of the wavefront profile. The most popular sensors at present are the interference type and the Shack-Hartmann type.
The operation of interference sensors is based on the coherent addition of two light waves and the formation of an interference pattern with an intensity depending on the measured wavefront. In this case, a wave obtained from the radiation under study by spatial filtering can be used as a second (reference) light wave.
A Shack-Hartmann type sensor consists of an array of microlenses and a photodetector located in their focal plane. Each lens typically measures 1mm or less. The sensor lenses divide the wavefront under study into subapertures (the aperture of one microlens), forming a set of focal spots in the focal plane. The position of each spot depends on the local inclination of the wavefront of the beam arriving at the sensor input. By measuring the transverse displacements of the focal spots, it is possible to calculate the average wavefront inclination angles within each of the subapertures. From these values, the wavefront profile is calculated over the entire sensor aperture.
Wavefront correctors
Adaptive (deformable) mirror (English) is the most popular tool for wavefront control and optical aberration correction. The idea of wavefront correction with a composite mirror was proposed by V.P. Linnik in 1957. The possibility of creating such a system has appeared since the mid-1990s in connection with the development of technology and the possibility of precise computer control and monitoring.
In particular, unimorphic (semi-passive-bimorph) mirrors have become widespread. Such a mirror consists of a thin plate made of piezoelectric material, on which electrodes are arranged in a special way. The plate is attached to a substrate, on the front surface of which an optical surface is formed. When voltage is applied to the electrodes, the piezoelectric plate contracts (or expands), which causes the optical surface of the mirror to bend. The special spatial arrangement of the electrodes allows the formation of complex surface reliefs.
The speed of control of the shape of the adaptive mirror allows it to be used to compensate for dynamic aberrations in real time.
In astronomical applications, adaptive optics systems require a reference source that would serve as a brightness standard to correct distortions created by atmospheric turbulence, and it should be located at a sufficiently close angular distance from the sky region being studied. Some systems use an "artificial star" as such a source, created by exciting sodium atoms at an altitude of 90 km above the Earth's surface with a ground-based laser.
ADAPTIVE OPTICS
ADAPTIVE OPTICS
The branch of optics that deals with the development of optical devices. systems with dynamic control of the wavefront shape to compensate for random disturbances and increase the efficiency. resolution limit observed devices, the degree of radiation concentration at the receiver or target, etc. A. o. began to develop intensively in the 1950s. in connection with the task of compensating for front distortions caused by atm. turbulence and superimposing bases. limitation on resolution ground-based telescopes. Later, to this were added the problems of creating orbital telescopes and powerful laser emitters that are susceptible to other types of interference. Adaptive optical systems are classified according to the order of wave aberrations (see Aberrations of optical systems), which they are able to compensate (that is, according to the degree of the polynomial, in the form of which the phase correction over the beam cross section is represented).
The simplest systems - 1st and 2nd orders - change the overall inclination of the wave front and its curvature by simply moving the parts. optical elements of a fixed shape. For higher-order systems, mirrors, divided into an appropriate number of independently movable segments, were most often used as corrective elements at first. They are gradually being replaced by flexible (“membrane”) mirrors, the shape of the surface of which is controlled either by the creation of bending moments inside the mirror itself, or by the action of forces from the supporting structure. Small deformable piezoelectric mirrors are often used. drives installed in optical areas. systems with moderate cross-sectional dimensions of the light beam (not far from the focal plane of the telescope lens, etc.).
Information about the required impact on is obtained by the method of test disturbances or directly. measuring the shape of the front. Both of these methods are used to create both receiving and emitting systems.
Test perturbation method (or aperture probing). It involves measuring the response to small, intentional inputs. The controlled parameter in this case is usually the focused spot or the intensity of light scattered by the target. The effects for which different types of phase distortions are responsible are divided either by frequency (the so-called multivibrator method) or by time (the so-called multi-stage or sequential method). In the first case, small harmonics are excited. diff. sections of the mirror (or the oscillating mirror as a whole) with different frequencies; the resulting signal allows you to establish the magnitude and direction of changes in the front shape necessary to optimize the system. In the second case of oscillations, dep. sections or modes of the mirror are carried out sequentially in time.
For test excitations and final adjustment of the phase distribution, different mirrors are usually used - one provides small phase changes with high temporal frequencies, the second has a much larger range of shape changes and may be more inertial. The associated complication of the basic optical path in definition degree is compensated by the use of only one non-coherent radiation receiver.
Direct wave front shape. A wide variety of and sometimes very original methods have been developed for it (mainly interferometric methods), usually used in combination with the wavefront compensation method (for receiving systems) and the phase conjugation method (for emitters). The compensation method consists in restoring the wave front of the radiation coming from a point object to an ideal spherical shape. shape (lost due to the influence of atmospheric turbulence and aberrations of the telescope lens).
Scheme of the phase conjugation method. The thick line is the wave front of the original; thin - wavefront of reference radiation; The arrows indicate the direction of propagation of wave fronts.
In the phase conjugation method, the wavefront of radiation emitted by a powerful source is given a shape conjugate in phase with the front of the reference radiation scattered by the target and arriving at the source (Fig.; for preliminary illumination of the target in order to obtain reference radiation, both the main and auxiliary radiation can be used . source). Thus, such distortions are superimposed on the emitted wave in advance that subsequent distortions along the path of its propagation are compensated; this achieves max. radiation behind targets.
Often to A. o. also includes the field of laser technology associated with the use of phase-conjugate waves for auto-compensation of wavefront distortions in high-power laser amplifiers. In some cases it is possible directly. converting a reference wave into a conjugate wave using nonlinear optics and holography methods (see. Wavefront reversal).
Lit.. Hardy J. W., Active new technique for controlling the light beam, [trans. from English], "TIIER", 1978, 66, No. 6, p. 31; Adaptive optics, "J. Opt. Soc. Amer.", 1977, v . 67,№ 3. Yu. A. Ananyev.
Physical encyclopedia. In 5 volumes. - M.: Soviet Encyclopedia. Editor-in-chief A. M. Prokhorov. 1988 .
See what "ADAPTIVE OPTICS" is in other dictionaries:
Adaptive optics is a branch of physical optics that studies methods for eliminating irregular distortions that arise when light propagates in an inhomogeneous medium using controlled optical elements. The main tasks of adaptive optics ... ... Wikipedia
Optical system with automatic wavefront correction. Back in 1953, the American astronomer Horace Babcock proposed using the same method that is used in active... ... to combat the harmful effects of atmospheric turbulence. Astronomical Dictionary
The section of optics, in which optical technologies are being developed. systems with dynamic controlling the shape of the wave front to compensate for random disturbances and distortions acquired by the wave when passing through an inhomogeneous medium (atmosphere, optical system) ... Natural science. encyclopedic Dictionary
- (Greek optike the science of visual perceptions, from optos visible, visible), a branch of physics in which optical radiation (light), the processes of its propagation and phenomena observed during the influence of light and in va are studied. Optical radiation represents... ... Physical encyclopedia
Table “Optics” from the 1728 encyclopedia About ... Wikipedia
- (from other Greek ἀστήρ “star, luminary” and φυσικά “nature”) science at the intersection of astronomy and physics, studying physical processes in astronomical objects, such as stars, galaxies, etc. The physical properties of matter on ... ... Wikipedia
Optical optical a part (made of glass, metal, glass-ceramic or plastic), one of the surfaces has a regular shape, is covered with a reflective layer and has a roughness not greater than hundredths of a light wavelength. Depending on the… … Physical encyclopedia
The term aberration has other meanings, see aberration. Aberrations of optical systems errors, or image errors in an optical system, caused by the deviation of the beam from the direction in which it should go in ... ... Wikipedia
For the term Aberration, see other meanings. Aberration of an optical system is an error or image error in an optical system caused by the deviation of the beam from the direction in which it should go in an ideal optical ... ... Wikipedia
This term has other meanings, see Reflector. BTA, SAO, Russia Reflector is an optical telescope using mirrors as light-collecting elements. The reflector was first built by Isaac Newton around 1670. This is... ... Wikipedia
Books
- Adaptive optical systems for tilt correction. Resonant adaptive optics, O. I. Shanin, The book outlines the physical, computational, theoretical and technical issues of designing the simplest, at first glance, adaptive optical systems - tilt correction systems.… Category: Radio electronics Publisher: Tekhnosphere, Manufacturer:
Loading...
