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Fourier-transform spectroscopy

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200:(hence the name, "Fourier-transform spectroscopy"). The raw data is sometimes called an "interferogram". Because of the existing computer equipment requirements, and the ability of light to analyze very small amounts of substance, it is often beneficial to automate many aspects of the sample preparation. The sample can be better preserved and the results are much easier to replicate. Both of these benefits are important, for instance, in testing situations that may later involve legal action, such as those involving drug specimens. 132: 265: 1804: 209: 1008:), a microwave pulse (EPR) or a radio frequency pulse (NMR) in a strong ambient magnetic field is used as the energizing event. This turns the magnetic particles at an angle to the ambient field, resulting in gyration. The gyrating spins then induce a periodic current in a detector coil. Each spin exhibits a characteristic frequency of gyration (relative to the field strength) which reveals information about the analyte. 1816: 1092:, thus precisely offset the Fellgett's advantage. For line emission sources the situation is even worse and there is a distinct `multiplex disadvantage' as the shot noise from a strong emission component will overwhelm the fainter components of the spectrum. Shot noise is the main reason Fourier-transform spectrometry was never popular for ultraviolet (UV) and visible spectra. 1057:
Some stationary forms retain the Fellgett multiplex advantage, and their use in the spectral region where detector noise limits apply is similar to the scanning forms of the FTS. In the photon-noise limited region, the application of stationary interferometers is dictated by specific consideration for the spectral region and the application.
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In general, the goal of absorption spectroscopy is to measure how well a sample absorbs or transmits light at each different wavelength. Although absorption spectroscopy and emission spectroscopy are different in principle, they are closely related in practice; any technique for emission spectroscopy
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In addition to the scanning forms of Fourier-transform spectrometers, there are a number of stationary or self-scanned forms. While the analysis of the interferometric output is similar to that of the typical scanning interferometer, significant differences apply, as shown in the published analyses.
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A pulsed Fourier-transform spectrometer does not employ transmittance techniques. In the most general description of pulsed FT spectrometry, a sample is exposed to an energizing event which causes a periodic response. The frequency of the periodic response, as governed by the field conditions in
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One of the most important advantages of Fourier-transform spectroscopy was shown by P. B. Fellgett, an early advocate of the method. The Fellgett advantage, also known as the multiplex principle, states that when obtaining a spectrum when measurement noise is dominated by detector noise (which is
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the light at a certain wavelength (the un-blocked wavelength is set by a knob on the monochromator). Then the intensity of this remaining (single-wavelength) light is measured. The measured intensity directly indicates how much light is emitted at that wavelength. By varying the monochromator's
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of the light to be measured at each different time delay setting, effectively converting the time domain into a spatial coordinate. By making measurements of the signal at many discrete positions of the movable mirror, the spectrum can be reconstructed using a Fourier transform of the temporal
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of the light. Michelson spectrographs are capable of very high spectral resolution observations of very bright sources. The Michelson or Fourier-transform spectrograph was popular for infra-red applications at a time when infra-red astronomy only had single-pixel detectors. Imaging Michelson
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Fourier-transform spectroscopy is a less intuitive way to get the same information. Rather than allowing only one wavelength at a time to pass through to the detector, this technique lets through a beam containing many different wavelengths of light at once, and measures the
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is measured (this is called the "sample spectrum"). The sample will absorb some of the light, causing the spectra to be different. The ratio of the "sample spectrum" to the "background spectrum" is directly related to the sample's absorption spectrum.
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As mentioned, computer processing is required to turn the raw data (light intensity for each mirror position) into the desired result (light intensity for each wavelength). The processing required turns out to be a common algorithm called the
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independent of the power of radiation incident on the detector), a multiplex spectrometer such as a Fourier-transform spectrometer will produce a relative improvement in signal-to-noise ratio, compared to an equivalent scanning
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The Fourier-transform spectrometer is just a Michelson interferometer, but one of the two fully reflecting mirrors is movable, allowing a variable delay (in the travel time of the light) to be included in one of the
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combination of wavelengths, giving a second data point. This process is repeated many times. Afterwards, a computer takes all this data and works backwards to infer how much light there is at each wavelength.
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Pulsed FT spectrometry gives the advantage of requiring a single, time-dependent measurement which can easily deconvolute a set of similar but distinct signals. The resulting composite signal, is called a
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can also be used for absorption spectroscopy. First, the emission spectrum of a broadband lamp is measured (this is called the "background spectrum"). Second, the emission spectrum of the same lamp
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dominated, the noise will be proportional to the square root of the power, thus for a broad boxcar spectrum (continuous broadband source), the noise is proportional to the square root of
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To be more specific, between the light source and the detector, there is a certain configuration of mirrors that allows some wavelengths to pass through but blocks others (due to
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because typically the signal will decay due to inhomogeneities in sample frequency, or simply unrecoverable loss of signal due to entropic loss of the property being measured.
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Accordingly, the technique of "Fourier-transform spectroscopy" can be used both for measuring emission spectra (for example, the emission spectrum of a star),
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of a light source: how much light is emitted at each different wavelength. The most straightforward way to measure a spectrum is to pass the light through a
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into an actual spectrum. The peak at the center is the ZPD position ("zero path difference"): Here, all the light passes through the
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Hegenbarth, R; Steinmann, A; Mastel, S; Amarie, S; Huber, A J; Hillenbrand, R; Sarkisov, S Y; Giessen, H (2014).
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The intensity as a function of the path length difference (also denoted as retardation) in the interferometer
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place the sample after the interferometer in the optical path. The total intensity at the detector is
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of light, and the vertical axis represents how much light is emitted by the torch at that wavelength.
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wavelength setting, the full spectrum can be measured. This simple scheme in fact describes how
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An "interferogram" from a Fourier-transform spectrometer. This is the "raw data" which can be
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Pulsed sources allow for the utilization of Fourier-transform spectroscopy principles in
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is the number of sample points comprising the spectrum. However, if the detector is
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There are several methods for measuring the temporal coherence of the light (see:
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spectrometers are a possibility, but in general have been supplanted by imaging
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the spectrometer, is indicative of the measured properties of the analyte.
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to be modulated by the sample before the interferometer. In fact, most
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absorption spectra (for example, the absorption spectrum of a liquid).
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http://www.opticsinfobase.org/viewmedia.cfm?uri=as-57-9-1078&seq=0
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is the spectrum to be determined. Note that it is not necessary for
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The Michelson spectrograph is similar to the instrument used in the
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Fourier Transform Spectroscopy Topical Meeting and Tabletop Exhibit
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with a movable mirror. The beams interfere, allowing the temporal
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The method of Fourier-transform spectroscopy can also be used for
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Internet Journal of Vibrational Spectroscopy – How FTIR works
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Digital Array Scanned Interferometer, issued Dec. 11, 1990
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Description of how a Fourier transform spectrometer works
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beam intensity. Next, the beam is modified to contain a
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Semiautomated depositor for infrared microspectrometry
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or not. It can be applied to a variety of types of
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Stationary forms of Fourier-transform spectrometers
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Oxford University Press: Oxford, UK. 1302: 163:, an instrument that blocks all of the light 1374:Vibrational spectroscopy of linear molecules 1166:, Cambridge University Press: Cambridge, UK. 295:instruments, which are easier to construct. 37:are collected based on measurements of the 1369:Nuclear resonance vibrational spectroscopy 1309: 1295: 1032:Nanoscale spectroscopy with pulsed sources 362:{\displaystyle {\tilde {\nu }}=1/\lambda } 298: 121: 1742:Inelastic electron tunneling spectroscopy 1422:Resonance-enhanced multiphoton ionization 1123:Time stretch dispersive Fourier transform 963: 756: 1510:Extended X-ray absorption fine structure 1164:Principles of Nuclear Magnetic Resonance 1133:Infrared spectroscopy of metal carbonyls 263: 207: 130: 1018: 220:because its two arms have equal length. 14: 1835: 1038:scanning near-field optical microscopy 1290: 1076:, of the order of the square root of 1060: 987:Pulsed Fourier-transform spectrometer 1815: 1187:Peter Atkins, Julio De Paula. 2006. 232:", a common technique in chemistry. 49:or space-domain measurements of the 1013:Fourier-transform mass spectrometry 33:is a measurement technique whereby 24: 872: 685: 618: 564:{\displaystyle I({\tilde {\nu }})} 526:{\displaystyle I({\tilde {\nu }})} 25: 1864: 1727:Deep-level transient spectroscopy 1479:Saturated absorption spectroscopy 1260: 1814: 1803: 1802: 1732:Dual-polarization interferometry 1316: 204:Measuring an absorption spectrum 1747:Scanning tunneling spectroscopy 1722:Circular dichroism spectroscopy 1717:Acoustic resonance spectroscopy 151:One of the most basic tasks in 1676:Fourier-transform spectroscopy 1364:Vibrational circular dichroism 1241: 1194: 1181: 1169: 1156: 1048:(often < 1%) of the probe. 960: 951: 936: 922: 910: 891: 885: 853: 847: 838: 812: 806: 766: 753: 750: 741: 726: 711: 708: 702: 693: 659: 647: 641: 626: 598: 592: 558: 552: 543: 520: 514: 505: 476: 462: 430: 427: 421: 412: 403: 397: 382: 339: 127:Measuring an emission spectrum 100:Fourier-transform spectrograph 96:Fourier-transform spectrometer 31:Fourier-transform spectroscopy 18:Fourier transform spectrometer 13: 1: 1474:Cavity ring-down spectroscopy 1379:Thermal infrared spectroscopy 1227:10.1088/2040-8978/16/9/094003 1149: 143:. The horizontal axis is the 1608:Inelastic neutron scattering 1113:Forensic polymer engineering 1040:techniques. Particularly in 7: 1669:Data collection, processing 1545:Photoelectron/photoemission 1095: 275:Michelson–Morley experiment 10: 1869: 1754:Photoacoustic spectroscopy 1696:Time-resolved spectroscopy 1118:Nuclear magnetic resonance 1064: 1000:In magnetic spectroscopy ( 238:shining through the sample 228:. 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Smith 1207:Journal of Optics 954: 905: 850: 769: 744: 705: 662: 644: 555: 517: 465: 424: 400: 342: 316:{\displaystyle p} 258:Fourier-transform 230:FTIR Spectroscopy 198:Fourier transform 190:wave interference 104:Fourier transform 81:mass spectrometry 16:(Redirected from 1860: 1848:Fourier analysis 1818: 1817: 1806: 1805: 1666: 1665: 1577:phenomenological 1326:Vibrational (IR) 1311: 1304: 1297: 1288: 1287: 1254: 1252: 1245: 1239: 1238: 1198: 1192: 1185: 1179: 1173: 1167: 1160: 982: 980: 979: 974: 956: 955: 947: 929: 925: 906: 898: 875: 870: 852: 851: 843: 824: 822: 821: 816: 788: 786: 785: 780: 778: 771: 770: 762: 746: 745: 737: 707: 706: 698: 688: 683: 668: 664: 663: 655: 646: 645: 637: 621: 616: 570: 568: 567: 562: 557: 556: 548: 532: 530: 529: 524: 519: 518: 510: 491: 489: 488: 483: 475: 471: 467: 466: 458: 426: 425: 417: 402: 401: 393: 368: 366: 365: 360: 355: 344: 343: 335: 322: 320: 319: 314: 252:Continuous-wave 135:An example of a 21: 1868: 1867: 1863: 1862: 1861: 1859: 1858: 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179: 173: 171: 166: 162: 161:monochromator 158: 154: 146: 142: 138: 133: 119: 117: 113: 109: 105: 101: 97: 93: 88: 86: 82: 78: 74: 70: 66: 62: 61: 56: 52: 48: 44: 40: 36: 32: 19: 1843:Spectroscopy 1819: 1807: 1787:(a misnomer) 1773:Applications 1691:Time-stretch 1675: 1582:paramagnetic 1400:Fluorescence 1318:Spectroscopy 1243: 1210: 1206: 1196: 1188: 1183: 1171: 1163: 1158: 1089: 1081: 1077: 1070: 1055: 1035: 1025: 1022: 1010: 999: 990: 791: 494: 302: 272: 260:spectrograph 257: 253: 245: 243: 237: 234: 223: 194: 187: 181: 177: 174: 169: 164: 153:spectroscopy 150: 141:butane torch 99: 95: 89: 75:, FT-NIRS), 60:spectroscopy 58: 30: 29: 1359:Vibrational 293:Fabry–PĂ©rot 47:time-domain 1837:Categories 1565:Two-photon 1467:absorption 1349:Rotational 1150:References 1086:shot-noise 325:wavenumber 145:wavelength 63:including 1643:Terahertz 1624:Radiowave 1522:Mössbauer 1138:nano-FTIR 1042:nano-FTIR 952:~ 949:ν 943:π 934:⁡ 895:− 873:∞ 864:∫ 848:~ 845:ν 767:~ 764:ν 742:~ 739:ν 733:π 724:⁡ 703:~ 700:ν 686:∞ 677:∫ 660:~ 657:ν 642:~ 639:ν 619:∞ 610:∫ 553:~ 550:ν 515:~ 512:ν 463:~ 460:ν 454:π 443:⁡ 422:~ 419:ν 398:~ 395:ν 357:λ 340:~ 337:ν 288:coherence 283:coherence 254:Michelson 182:different 51:radiation 43:radiative 39:coherence 1809:Category 1538:Electron 1505:Emission 1455:emission 1412:Vibronic 1235:49192831 1096:See also 1080:, where 157:spectrum 137:spectrum 108:spectrum 1821:Commons 1648:ESR/EPR 1596:Nucleon 1424:(REMPI) 1215:Bibcode 35:spectra 1662:Others 1450:Atomic 1233:  495:where 269:beams. 165:except 1603:Alpha 1572:Auger 1550:X-ray 1517:Gamma 1495:X-ray 1428:Raman 1339:Raman 1334:FT-IR 1231:S2CID 178:total 41:of a 369:is 323:and 170:some 83:and 73:FTIR 1631:NMR 1223:doi 1011:In 1006:NMR 1002:EPR 931:cos 721:cos 440:cos 256:or 246:and 98:or 1839:: 1636:2D 1555:UV 1229:. 1221:. 1211:16 1209:. 1205:. 1004:, 825:: 118:. 67:, 53:, 1310:e 1303:t 1296:v 1237:. 1225:: 1217:: 1090:m 1082:m 1078:m 971:. 968:p 965:d 961:) 958:p 940:2 937:( 927:] 923:) 920:0 917:= 914:p 911:( 908:I 903:2 900:1 892:) 889:p 886:( 883:I 879:[ 868:0 860:4 857:= 854:) 839:( 836:I 813:) 810:p 807:( 804:I 773:. 758:d 754:] 751:) 748:p 730:2 727:( 718:+ 715:1 712:[ 709:) 694:( 691:I 681:0 673:= 651:d 648:) 633:, 630:p 627:( 624:I 614:0 606:= 599:) 596:p 593:( 590:I 559:) 544:( 541:I 521:) 506:( 503:I 480:, 477:] 473:) 469:p 451:2 447:( 437:+ 434:1 431:[ 428:) 413:( 410:I 407:= 404:) 389:, 386:p 383:( 380:I 353:/ 349:1 346:= 311:p 71:( 20:)

Index

Fourier transform spectrometer
spectra
coherence
radiative
time-domain
radiation
electromagnetic
spectroscopy
optical spectroscopy
infrared spectroscopy
FTIR
nuclear magnetic resonance
mass spectrometry
electron spin resonance
field-autocorrelation
Fourier transform
spectrum
interferometers
Wiener–Khinchin theorem

spectrum
butane torch
wavelength
spectroscopy
spectrum
monochromator
wave interference
Fourier transform

Fourier-transformed

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