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Echelle Grating
An echelle grating (from French ''échelle'', meaning "ladder") is a type of diffraction grating characterised by a relatively low groove density, but a groove shape which is optimized for use at high incidence angles and therefore in high diffraction orders. Higher diffraction orders allow for increased dispersion (spacing) of spectral features at the detector, enabling increased differentiation of these features. Echelle gratings are, like other types of diffraction gratings, used in spectrometers and similar instruments. They are most useful in cross-dispersed high resolution spectrographs, such as HARPS, PARAS, and numerous other astronomical instruments. History The concept of a coarsely-ruled grating used at grazing angles was discovered by Albert Michelson in 1898, where he referred to it as an "echelon". However, it was not until 1923 that echelle spectrometers began to take on their characteristic form, in which the high-resolution grating is used in tandem with a cro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diffraction Grating
In optics, a diffraction grating is an optical component with a periodic structure that diffracts light into several beams travelling in different directions (i.e., different diffraction angles). The emerging coloration is a form of structural coloration. The directions or diffraction angles of these beams depend on the wave (light) incident angle to the diffraction grating, the spacing or distance between adjacent diffracting elements (e.g., parallel slits for a transmission grating) on the grating, and the wavelength of the incident light. The grating acts as a dispersive element. Because of this, diffraction gratings are commonly used in monochromators and spectrometers, but other applications are also possible such as optical encoders for high precision motion control and wavefront measurement. For typical applications, a reflective grating has ridges or ''rulings'' on its surface while a transmissive grating has transmissive or hollow slits on its surface. Such a grating ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diffraction Order
In optics, a diffraction grating is an optical component with a periodic structure that diffracts light into several beams travelling in different directions (i.e., different diffraction angles). The emerging coloration is a form of structural coloration. The directions or diffraction angles of these beams depend on the wave (light) incident angle to the diffraction grating, the spacing or distance between adjacent diffracting elements (e.g., parallel slits for a transmission grating) on the grating, and the wavelength of the incident light. The grating acts as a dispersive element. Because of this, diffraction gratings are commonly used in monochromators and spectrometers, but other applications are also possible such as optical encoders for high precision motion control and wavefront measurement. For typical applications, a reflective grating has ridges or ''rulings'' on its surface while a transmissive grating has transmissive or hollow slits on its surface. Such a grating ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spectrometer
A spectrometer () is a scientific instrument used to separate and measure spectral components of a physical phenomenon. Spectrometer is a broad term often used to describe instruments that measure a continuous variable of a phenomenon where the spectral components are somehow mixed. In visible light a spectrometer can separate white light and measure individual narrow bands of color, called a spectrum. A mass spectrometer measures the spectrum of the masses of the atoms or molecules present in a gas. The first spectrometers were used to split light into an array of separate colors. Spectrometers were developed in early studies of physics, astronomy, and chemistry. The capability of spectroscopy to determine chemical composition drove its advancement and continues to be one of its primary uses. Spectrometers are used in astronomy to analyze the chemical composition of stars and planets, and spectrometers gather data on the origin of the universe. Examples of spectrometers are ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
High Accuracy Radial Velocity Planet Searcher
The High Accuracy Radial Velocity Planet Searcher (HARPS) is a high-precision echelle planet-finding spectrograph installed in 2002 on the ESO's 3.6m telescope at La Silla Observatory in Chile. The first light was achieved in February 2003. HARPS has discovered over 130 exoplanets to date, with the first one in 2004, making it the most successful planet finder behind the Kepler space observatory. It is a second-generation radial-velocity spectrograph, based on experience with the ELODIE and CORALIE instruments. Characteristics The HARPS can attain a precision of 0.97 m/s (3.5 km/h), making it one of only two instruments worldwide with such accuracy. This is due to a design in which the target star and a reference spectrum from a thorium lamp are observed simultaneously using two identical optic fibre feeds, and to careful attention to mechanical stability: the instrument sits in a vacuum vessel which is temperature-controlled to within 0.01 kelvins. The precision ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
PRL Advanced Radial-velocity All-sky Search
PRL Advanced Radial-velocity Abu-sky Search, abbreviated PARAS,Chakraborty, Abhijit & Mahadevan, Suvrath & Roy, Arpita & M. Pathan, Fazalahmed & Shah, Vishal & H. Richardson, Eric & Ubale, Girish & Shah, Rajesh. (2010)First light results from PARAS: The PRL Echelle spectrograph Proc SPIE. 7735. . is a ground-based extrasolar planet search device. Based at 1.2m telescope is located at Mt. Abu, India.The project is funded by Physical Research Laboratory, India. The spectrograph works at a resolution of 67000. With the help of simultaneous calibration technique, PARAS has achieved an RV accuracy of 1.3 m/s for the bright sun like quiet stars. Thorium-Argon lamp is used for calibration. New calibration techniques are also being explored by the project team. PARAS can detect planet in the habitable zone around M-type star In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Echelle Principle
An echelle grating (from French ''échelle'', meaning "ladder") is a type of diffraction grating characterised by a relatively low groove density, but a groove shape which is optimized for use at high incidence angles and therefore in high diffraction orders. Higher diffraction orders allow for increased dispersion (spacing) of spectral features at the detector, enabling increased differentiation of these features. Echelle gratings are, like other types of diffraction gratings, used in spectrometers and similar instruments. They are most useful in cross-dispersed high resolution spectrographs, such as HARPS, PARAS, and numerous other astronomical instruments. History The concept of a coarsely-ruled grating used at grazing angles was discovered by Albert Michelson in 1898, where he referred to it as an "echelon". However, it was not until 1923 that echelle spectrometers began to take on their characteristic form, in which the high-resolution grating is used in tandem with a cro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Albert Abraham Michelson
Albert Abraham Michelson FFRS HFRSE (surname pronunciation anglicized as "Michael-son", December 19, 1852 – May 9, 1931) was a German-born American physicist of Polish/Jewish origin, known for his work on measuring the speed of light and especially for the Michelson–Morley experiment. In 1907 he received the Nobel Prize in Physics, becoming the first American to win the Nobel Prize in a science. He was the founder and the first head of the physics departments of Case School of Applied Science (now Case Western Reserve University) and the University of Chicago. Life Michelson was born in Strelno, Posen, Kingdom of Prussia (modern-day Strzelno, Poland), to Jewish parents, the son of Samuel Michelson and his wife, Rozalia Przyłubska. He moved to the US with his parents in 1855, at the age of two. He grew up in the mining towns of Murphy's Camp, California, and Virginia City, Nevada, where his father was a merchant. His family was non-religious, and Michelson himself was a l ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Blazed Grating
A blazed grating – also called echelette grating (from French ''échelle'' = ladder) – is a special type of diffraction grating. It is optimized to achieve maximum grating efficiency in a given diffraction order. For this purpose, maximum optical power is concentrated in the desired diffraction order while the residual power in the other orders (particularly the zeroth) is minimized. Since this condition can only exactly be achieved for one wavelength, it is specified for which ''blaze wavelength'' the grating is optimized (or ''blazed''). The direction in which maximum efficiency is achieved is called the ''blaze angle'' and is the third crucial characteristic of a blazed grating directly depending on blaze wavelength and diffraction order. Blaze angle Like every optical grating, a blazed grating has a constant line spacing d, determining the magnitude of the wavelength splitting caused by the grating. The grating lines possess a triangular, sawtooth-shaped cross sec ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Grating
A grating is any regularly spaced collection of essentially identical, parallel, elongated elements. Gratings usually consist of a single set of elongated elements, but can consist of two sets, in which case the second set is usually perpendicular to the first (as illustrated). When the two sets are perpendicular, this is also known as a wikt:grid (as in grid paper) or a mesh. As filters A grating covering a drain (as illustrated) can be a collection of iron bars (the identical, elongated elements) held together (to ensure the bars are parallel and regularly spaced) by a lighter iron frame. Gratings over drains and air vents are used as filters, to block movement of large solids (e.g. people) and to allow movement of liquids. A register is a type of grating used in heating, ventilation, and air conditioning, which transmits air, while stopping solid objects. File:Vindobona Hoher Markt-71.JPG, Grating - drain cover, ancient Roman architecture at Vindobona, Austria. File:Montr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dispersive Prism
In optics, a dispersive prism is an optical prism that is used to disperse light, that is, to separate light into its spectral components (the colors of the rainbow). Different wavelengths (colors) of light will be deflected by the prism at different angles. This is a result of the prism material's index of refraction varying with wavelength (dispersion). Generally, longer wavelengths (red) undergo a smaller deviation than shorter wavelengths (blue). The dispersion of white light into colors by a prism led Sir Isaac Newton to conclude that white light consisted of a mixture of different colors. Triangular prisms are the most common type of dispersive prism. Other types of dispersive prism exist that have more than two optical interfaces; some of them combine refraction with total internal reflection. How dispersive prisms work Light changes speed as it moves from one medium to another (for example, from air into the glass of the prism). This speed change causes the light ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Defocus
In optics, defocus is the aberration in which an image is simply out of focus. This aberration is familiar to anyone who has used a camera, videocamera, microscope, telescope, or binoculars. Optically, defocus refers to a translation of the focus along the optical axis away from the detection surface. In general, defocus reduces the sharpness and contrast of the image. What should be sharp, high-contrast edges in a scene become gradual transitions. Fine detail in the scene is blurred or even becomes invisible. Nearly all image-forming optical devices incorporate some form of focus adjustment to minimize defocus and maximize image quality. In optics and photography The degree of image blurring for a given amount of focus shift depends inversely on the lens f-number. Low f-numbers, such as to 2.8, are very sensitive to defocus and have very shallow depths of focus. High f-numbers, in the 16 to 32 range, are highly tolerant of defocus, and consequently have large depth ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aberration In Optical Systems
In optics, aberration is a property of optical systems, such as lenses, that causes light to be spread out over some region of space rather than focused to a point. Aberrations cause the image formed by a lens to be blurred or distorted, with the nature of the distortion depending on the type of aberration. Aberration can be defined as a departure of the performance of an optical system from the predictions of paraxial optics. In an imaging system, it occurs when light from one point of an object does not converge into (or does not diverge from) a single point after transmission through the system. Aberrations occur because the simple paraxial theory is not a completely accurate model of the effect of an optical system on light, rather than due to flaws in the optical elements. An image-forming optical system with aberration will produce an image which is not sharp. Makers of optical instruments need to correct optical systems to compensate for aberration. Aberration can be anal ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
