Sterrekunde

Wat is die verskil tussen grisme en rooster?

Wat is die verskil tussen grisme en rooster?


We are searching data for your request:

Forums and discussions:
Manuals and reference books:
Data from registers:
Wait the end of the search in all databases.
Upon completion, a link will appear to access the found materials.

In spektroskopiese waarnemings ontmoet jy soms grisme, soms rooster.

Albei kan ligverspreiding veroorsaak, maar wat is die verskil?


Transmissieroosters op hul eie stel chromatiese afwyking in. Dit is omdat hulle die effektiewe brandpuntsafstand verander en dit as 'n funksie van golflengte doen. Die chromatiese aberrasie kan uitgeskakel word deur 'n prisma van die korrekte verspreiding in te voer. Die rooster / prisma-kombinasie, wat bekend staan ​​as 'n grism, bied 'n ongekende beeld in die 0de orde naas die spektrum, alhoewel die spektrum redelik lae resolusie het.


Prisma-spektroskope

'N Spleet-tipe prisma-spektroskoopontwerp kan geproduseer word vir die meeste van die diffraksieroosterinstrumente wat vroeër bespreek is deur die rooster deur die prisma te vervang. Die algemeenste sulke voorwerpe is die basiese spektroskoop (figuur 8.14) en die Littrow spektroskoop (figuur 8.15). Vir die Littrow-ontwerp sal 'n prisma van 30 ° gebruik word, met die agterste oppervlak aluminiseer. Die lig word dus weerkaats en gaan twee keer deur die prisma, wat dit gelykstaande is aan 'n enkele prisma van 60 °. Die gereflekteerde straal word byna in dieselfde rigting as die inkomende balk teruggestuur en gaan dus op 'n soortgelyke manier deur die stelsel

Figuur 8.23 ​​'n Objektiewe prisma-spektroskoop.

Figuur 8.23 ​​'n Objektiewe prisma-spektroskoop.

wat in figuur 8.15 getoon word. Daar is geen ekwivalent aan die geboë roosters nie, dus het die Rowland-sirkel- en Wadsworth-ontwerp geen prisma-gebaseerde ekwivalente nie.

'N Prisma kan 'n diffraksierooster op een van die oppervlaktes laat aanbring, en die kombinasie staan ​​dan bekend as 'n Grism. In een vorm bied dit 'n direkte visie-spektroskoop vir sonwerk, met die prisma se afwyking gelyk en teenoor dié van die vlamvolgorde van die transmissierooster op die oppervlak. Die lig het dan geen netto afwyking nie en is slegs versprei, wat die ontwerp van die hele instrument vereenvoudig deur komponente buite die as uit te skakel.

Die eenvoudigste spektroskoop van alles is die objektiewe prisma. In hierdie ontwerp dek 'n dun prisma die hele doel van die teleskoop, en word elke voorwerp in 'n beeld deur sy spektrum vervang. 'N Eenvoudige prisma kan gebruik word, in welke geval die teleskoop in 'n groot hoek na die gewenste rigting moet wys as gevolg van die afwyking wat die prisma veroorsaak. Alternatiewelik kan twee prisma's van verskillende brille in teenstelling gebruik word om geen afwyking te gee nie, terwyl die spreiding nog steeds behoue ​​bly (figuur 8.23). Dit is die presiese omgekeerde van die achromatiese lens, waar lense van twee verskillende brille gekombineer word om (naby) nulverspreiding te gee, terwyl die fokus steeds behou (dws afwyking). Die objektiewe prisma is 'n baie doeltreffende ontwerp omdat dit nie net die gleuf afgee nie en dus die deurset geweldig verbeter (sien vroeëre bespreking), maar baie spektra kan in een blootstelling verkry word. As 'n objektiewe prisma op 'n Schmidt-kamera toegepas word, kan daar meer as 105 spektra op 'n enkele plaat verkry word.

Ongelukkig hou die objektiewe prisma-spektroskoop ook ernstige nadele in. Die belangrikste is die moeilikheid om radiale snelhede uit die spektra te vind, omdat daar geen vergelykingspektrum is nie (hoofstuk 9). Verskeie pogings is aangewend om die probleem op te los, waarvan die suksesvolste is om twee blootstellings op dieselfde plaat te neem, met 'n effense verplasing van die teleskoop en met die prisma omgekeerd tussen die blootstellings. Elke voorwerp in die beeld het dan twee aangrensende spektra (figuur 8.24). Radiale bewegings van die voorwerpe sal aanleiding gee tot Doppler-verskuiwings, wat veroorsaak dat die skeiding van 'n bepaalde lyn in een spektrum van dieselfde lyn in die tweede spektrum verander. As sommige voorwerpe reeds bekende radiale snelhede het, kan die verandering in skeiding gekalibreer word om die snelhede van al die voorwerpe op die plaat te gee. Ander

Spektrum vanaf Spectrum vanaf die tweede die blootstelling aan die vuur met die prisma

Spectrum vanaf Spectrum vanaf die tweede die blootstelling aan die vuur met die prisma

Figuur 8.24 Dubbel blootgestelde objektiewe prisma-plaat wat die verandering in die skeiding van identiese lyne in pare spektra toon met die veranderende radiale snelhede van die voorwerpe.

Skeidings van dieselfde Pare spektrumlyne vir verskillende radiale snelhede vir elke voorwerp in die gesigsveld.

Figuur 8.24 Dubbel blootgestelde objektiewe prisma-plaat wat die verandering in die skeiding van identiese lyne in pare spektra toon met die veranderende radiale snelhede van die voorwerpe.

nadele sluit in die lae verspreiding van die spektra, en die gewig en koste van die prisma vir 'n groot teleskoop.

8.7 FOURIER TRANSFORM SPECTROSCOPE (MICHELSON INTERFEROMETER)

Die interferometer wat deur Michelson en Morley (figuur 8.25) in hul klassieke eksperiment van 1887 gebruik is om die beweging van die aarde deur die eter te probeer opspoor, kan die basis vorm van 'n tipe spektroskoop bekend as 'n Fourier Transform Spectroscope. Anders as die diffraksierooster of prisma, word die spektrum nie direk geproduseer nie. Die werkingsbeginsel kan egter uit 'n paar voorbeelde verstaan ​​word.

Lig uit 'n monochromatiese bron sal duidelik 'n eenvoudige interferensiepatroon vorm tydens die fokus van die instrument. As die detektor slegs 'n smal gedeelte van die patroon aanvaar, sal die uitset daarvan wissel namate die posisie van die bewegende spieël verander en die verskillende dele van die patroon daarop beweeg. As die beweeg

spieël glad geskandeer word, dan sal die detektoruitset 'n eenvoudige sinusgolf wees (figuur 8.26). Monochromatiese lig met 'n effens ander golflengte gee 'n soortgelyke uitset met 'n effens ander periode. 'N Enkele bron waarin beide golflengtes teenwoordig is, sal hierdie twee uitsette gekombineer deur reguit optel, om 'n uitset met 'n klopfrekwensie te gee (figuur 8.27).

In frekwensie is 'n monochromatiese bron 'n enkele delta-funksie, en die Fourier-transform (vergelyking (8.17)) is 'n sinusgolf. 'N Dubbele delta-funksie, wat ooreenstem met die bichromatiese bron, het 'n Fourier-transformasie met 'n klopfrekwensie. Ons kan dus sien dat die uitvoer van die instrument vir meer komplekse spektra verband hou met die Fourier-transformasie van die spektrum. Omgekeerd kan die spektrum gevind word vanaf die uitvoer na die inverse Fourier-transformasie (vergelyking (8.18)). Vandaar die naam wat aan die instrument gegee is. Die presiese verband tussen spektrum en uitvoer word verkry uit die werklike deel van die omgekeerde transformasie:

waar / (A.) die intensiteit in die spektrum by golflengte is, is A, AP die padverskil tussen die twee balke vir 'n bepaalde posisie van die bewegende spieël en I (AP) is die uitset (intensiteit) vanaf die instrument vir 'n spesifieke waarde van A P.

Aangesien daar geen spektrum direk geproduseer word nie, is daar geen ekwivalent aan die verspreiding van 'n diffraksierooster of prisma nie. Die spektrale resolusie van die Fourier-transformspektroskoop is teoreties oneindig. In die praktyk kan die padverskil egter nie uitgebrei word tot in die oneindigheid soos vereis deur vergelyking (8.34) nie, en dit, tesame met die metings wat diskreet moet plaasvind in plaas van deurlopend, plaas die beperking op die spektrale resolusie. Die spektrale resolusie word dus gegee deur


Waarom is 'n diffraksierooster beter as 'n prisma?

Prisma's kan ligspektra in baie kleure versprei vir ontleding. Dit is dikwels goed genoeg. 'N Diffraksierooster doen baie dieselfde. 'N Diffraksierooster is egter minder sensitief vir die kleur van die lig en kan gemaak word om kleure oor 'n groter hoek as 'n prisma te versprei.

Die glas in 'n prisma is helder tot sigbaar, maar absorbeer en blokkeer die lig in die infrarooi en ultraviolet deel van die spektrum. Chemiese analise hang dikwels af van die identifisering van spesifieke kleure uit die spektrum van die monster wat buite die sigbare gebied is.

Die hoek van die eerste orde afbuiging (# theta #) kan beskryf word in terme van die afstand tussen lyne (# d #) en die golflengte (# lambda #).
#tan (theta) = (lambda) / d #
'N Diffraksierooster met 'n paar honderd lyne per duim kan lig in die middel van die sigbare spektrum met minstens 20 grade aflei. Die afbuighoek van 'n glasprisma is oor die algemeen baie kleiner as hierdie.


Diffraksierooster teen prisma

Die diffraksierooster is 'n presiese optiese komponent van spektroskope en verskillende meetmasjiene. Dit word gebruik soos 'n prisma, wat die lig in sy samestellende golflengtes skei, en kan bestaan ​​uit 'n oppervlak wat regeer word met duisende, noukeurige afstand, ewewydige splete; elke spleet is slegs ongeveer 'n enkele liggolflengte breed. Dit word transmissieroosters genoem. Sommige roosters bestaan ​​uit 'n reeks ewewydige weerkaatsende oppervlaktes (weerkaatsingsroosters). Roosters wat in die sigbare en ultravioletstreke gebruik word, het minstens 6 000 tot 18 000 lyne per sentimeter in die infrarooi streek, dit het minder as 500 tot 3 000 lyne per sentimeter. Roosters met soveel as 50 000 lyne per sentimeter is ontwikkel vir gebruik in instrumente met 'n hoë resolusie.

Die skeiding van lig in sy samestellende golflengtes met 'n rooster is die gevolg van konstruktiewe en vernietigende golfinterferensie nadat die lig afgebreek is deur die roosterreëls (sien afleiding). 'N Prisma daarenteen skei lig op grond van verskillende brekingsindekse. Wanneer 'n rooster in 'n regte hoek met 'n invallende ligstraal geplaas word, sal die ligstraal versprei word - dit wil sê, dit sal in die samestellende golflengtes verdeel word. Die resultaat is 'n spektrum van die inkomende lig.

In meetmasjiene word diffraksieroosters in pare gebruik, omdat die relatiewe beweging van twee roosters optiese patrone (moirépatrone) of rande skep. Hierdie patrone word deur fotocelle opgespoor en die uitsette daarvan word in 'n rekenaar gevoer om 'n digitale uitlees van beweging met 'n resolusie van ongeveer 0,00127 cm (0,0005 in) te bied.

In optika verwys prisma na enige deursigtige medium met twee of meer vlakke oppervlaktes. 'N Bekende voorbeeld is die driehoekige prisma, gewoonlik gemaak van glas, wat gebruik word om 'n straal wit lig in sy kleure te verdeel. Die vermoë van die prisma om dit te doen, spruit uit die feit dat die brekingsindeks van enige optiese medium afhang van die golflengte (kleur) van die lig, 'n eienskap wat dispersie genoem word. In alle gewone media - glas, water, ensovoorts - verhoog die brekingsindeks namate die golflengte korter word. Dus word die strale in die violette punt van die sigbare spektrum (wat ooreenstem met die korter golflengtes) skerper deur 'n prisma gebreek as die langer golflengtes in die rooi punt van die spektrum.

Nog 'n algemene tipe prisma is die regte hoek, totale reflekterende prisma. Hierdie prisma versprei nie die lig eerder in die kleure nie, dit weerkaats die lig deur die totale interne weerkaatsing (sien breking). Retroreflekterende prisma's word gebruik om 'n verkyker en ander optiese instrumente te maak.


Inhoud

'N Toestel wat monochromatiese lig kan produseer, het baie gebruik in die wetenskap en in die optika, omdat baie optiese eienskappe van 'n materiaal afhanklik is van die golflengte. Alhoewel daar 'n aantal nuttige maniere is om 'n smal band golflengtes te kies (wat in die sigbare gebied as 'n suiwer kleur beskou word), is daar nie soveel ander maniere om enige golflengteband maklik uit 'n wye reeks te kies nie. Kyk hieronder vir 'n bespreking van sommige van die gebruike van monochromatore.

In harde X-straal- en neutronoptika word kristalmonochromatore gebruik om golftoestande op die instrumente te definieer.

'N Monochromator kan die verskynsel van optiese verspreiding in 'n prisma, of die van diffraksie met behulp van 'n diffraksierooster, gebruik om die kleure van lig ruimtelik te skei. Dit het gewoonlik 'n meganisme om die geselekteerde kleur na 'n uitgangspleet te lei. Gewoonlik word die rooster of die prisma in 'n reflektiewe modus gebruik. 'N Reflektiewe prisma word gemaak deur 'n regte driehoek prisma te maak (gewoonlik die helfte van 'n gelyksydige prisma) met die een kant weerspieël. Die lig kom deur die skuinssy-gesig en reflekteer daardeur en word twee keer op dieselfde oppervlak gebreek. Die totale breking en die totale verspreiding is dieselfde as wanneer 'n gelyksydige prisma in die transmissiemodus gebruik word.

Collimasie wysig

Die verspreiding of diffraksie is slegs beheerbaar as die lig gekollimeer word, dit wil sê as al die ligstrale parallel of prakties so is. 'N Bron, soos die son, wat baie ver weg is, bied gekollimeerde lig. Newton het sonlig in sy beroemde eksperimente gebruik. In 'n praktiese monochromator is die ligbron egter naby, en 'n optiese stelsel in die monochromator skakel die uiteenlopende lig van die bron om in gekollimeerde lig. Alhoewel sommige monochromator-ontwerpe wel fokusroosters gebruik wat nie afsonderlike kollimators benodig nie, gebruik die meeste kollimerende spieëls. Reflektiewe optika word verkies, omdat dit nie verspreidingseffekte van hul eie het nie.

Czerny – Turner monochromator Edit

In die algemene Czerny – Turner-ontwerp, [1] is die breëbandbeligtingsbron (A) is gerig op 'n ingangsgleuf (B). Die hoeveelheid ligenergie wat beskikbaar is vir gebruik hang af van die intensiteit van die bron in die ruimte wat deur die gleuf (breedte × hoogte) en die aanvaardingshoek van die optiese stelsel gedefinieer word. Die gleuf word op die effektiewe fokus van 'n geboë spieël (die kollimator, C) sodat die lig van die spleet wat deur die spieël weerkaats word, gekollimineer word (gefokus op oneindig). Die gekollimeerde lig word van die rooster afgetrek (D) en word dan deur 'n ander spieël versamel (E), wat die lig, wat nou versprei is, weer op die uitgangspleet fokus (F). In 'n prisma-monochromator neem 'n weerkaatsende Littrow-prisma die plek in van die diffraksierooster, in welke geval die lig deur die prisma gebreek word.

By die uitgangspleet is die kleure van die lig uitgesprei (in die sigbare wys dit die kleure van die reënboog). Omdat elke kleur op 'n aparte punt in die uitgangsplitsvlak kom, is daar 'n reeks beelde van die ingangsopening wat op die vlak gefokus is. Omdat die ingangsgleuf eindig in breedte is, oorvleuel dele van die nabygeleë beelde. Die lig wat die uitgangspleet verlaat (G) bevat die hele prentjie van die ingangsgleuf van die gekose kleur plus dele van die ingangsgleufbeelde van nabygeleë kleure. 'N Rotasie van die verspreidingselement laat die kleureband relatief tot die uitgangspleet beweeg, sodat die gewenste ingangspleet op die uitgangspleet gesentreer word. Die verskeidenheid kleure wat die uitgangspleet verlaat, is 'n funksie van die breedte van die splete. Die ingangs- en uitgangspalwydtes word saamgestel.

Verdwaalde lig Edit

Die ideale oordragfunksie van so 'n monochromator is 'n driehoekige vorm. Die piek van die driehoek is op die gekose nominale golflengte. Die intensiteit van die nabygeleë kleure neem dan weerskante van hierdie piek lineêr af totdat 'n mate van afsnypunt bereik word, waar die intensiteit ophou afneem. Dit word die genoem verdwaalde lig vlak. Die afsnypunt is gewoonlik ongeveer 'n duisendste van die piekwaarde, of 0,1%.

Spektrale bandwydte wysig

Spektrale bandwydte word gedefinieer as die breedte van die driehoek op die punte waar die lig die helfte van die maksimum waarde bereik het (volle breedte teen die helfte maksimum, afgekort as FWHM). 'N Tipiese spektrale bandwydte kan een nanometer wees, maar verskillende waardes kan gekies word om aan die behoefte aan analise te voldoen. 'N smaller bandwydte verbeter wel die resolusie, maar dit verminder ook die sein-ruis-verhouding. [2]

Verspreiding Wysig

Die verspreiding van 'n monochromator word gekenmerk as die breedte van die kleureband per spleeteenheid, byvoorbeeld 1 nm spektrum per mm spleetwydte. Hierdie faktor is konstant vir 'n rooster, maar wissel met die golflengte vir 'n prisma. As 'n skanderende prisma-monochromator in 'n konstante bandwydte-modus gebruik word, moet die spleetwydte verander namate die golflengte verander. Verspreiding hang af van die brandpuntsafstand, die roosterorde en die oplossing van die rooster.

Golflengtebereik Wysig

Die aanpassingsbereik van 'n monochromator kan die sigbare spektrum en 'n gedeelte van beide of die nabygeleë ultraviolet- (UV) en infrarooi (IR) spektra dek, alhoewel monochromatore gebou is vir 'n groot verskeidenheid optiese reekse en vir baie ontwerpe.

Dubbele monochromatore Redigeer

Dit is algemeen dat twee monochromatore in serie gekoppel word, met hul meganiese stelsels wat saam werk, sodat albei dieselfde kleur kies. Hierdie reëling is nie bedoel om die nouheid van die spektrum te verbeter nie, maar eerder om die afsnypeil te verlaag. 'N Dubbele monochromator kan 'n afsnyding van ongeveer een miljoenste van die piekwaarde hê, die produk van die twee afsnydings van die individuele afdelings. Die intensiteit van die lig van ander kleure in die uitgangsbundel word die verdwaalde ligvlak genoem en is die mees kritieke spesifikasie van 'n monochromator vir baie gebruike. Die bereiking van lae dwaallig is 'n groot deel van die kuns om 'n praktiese monochromator te maak.

Diffraksieroosters en vlamroosters Edit

Rooster-monochromatore versprei ultraviolet-, sigbare- en infrarooi-bestraling, gewoonlik deur gebruik te maak van replikas, wat vervaardig word uit 'n hoofrooster. 'N Meesterrooster bestaan ​​uit 'n harde, opties plat, oppervlak met 'n groot aantal parallelle en nou gegroefde groewe. Die konstruksie van 'n hoofrooster is 'n lang, duur proses omdat die groewe van dieselfde grootte moet wees, presies parallel en eweredig oor die lengte van die rooster (3–10 cm). 'N Rooster vir die ultraviolet en sigbare gebied het gewoonlik 300-2000 groewe / mm, maar 1200-1400 groewe / mm is die algemeenste. Vir die infrarooi streek het roosters 10-200 groewe / mm. [3] Wanneer 'n diffraksierooster gebruik word, moet die ontwerp van breëband-monochromatore versigtig wees, want die diffraksiepatroon het oorvleuelende orde. Soms word breëbandvoorkiesfilters in die optiese pad ingevoeg om die breedte van die afbreekordes te beperk sodat dit nie oorvleuel nie. Soms word dit gedoen deur 'n prisma te gebruik as een van die monochromatore van 'n dubbele monochromator-ontwerp.

Die oorspronklike afbreekroosters met hoë resolusie is beslis. Die konstruksie van hoëgehalte-enjins was 'n groot onderneming (en ook baie moeilik in die afgelope dekades), en goeie roosters was baie duur. Die helling van die driehoekige groef in 'n geroosterde rooster word gewoonlik aangepas om die helderheid van 'n bepaalde afbrekingsvolgorde te verbeter. Dit word 'n traliewerk genoem. Beheerde roosters het onvolmaakthede wat vaag 'spook'-afbrekingsordes oplewer wat die dwaalligvlak van 'n monochromator kan verhoog. 'N Latere fotolitografiese tegniek laat roosters toe uit 'n holografiese interferensiepatroon. Holografiese roosters het sinusvormige groewe en is dus nie so helder nie, maar het laer verspreide ligvlakke as vlamme. Byna al die roosters wat in monochromatore gebruik word, is noukeurig gemaakte replikas van gerolde of holografiese meesterroosters.

Prisma's wysig

Prisma's het 'n hoër verspreiding in die UV-streek. Prisma-monochromatore word verkies in sommige instrumente wat hoofsaaklik ontwerp is om in die verre UV-streek te werk. Die meeste monochromators gebruik roosters. Sommige monochromatore het verskillende roosters wat gekies kan word vir gebruik in verskillende spektrale streke. 'N Dubbele monochromator wat gemaak word deur 'n prisma en 'n rooster-monochromator in serie te plaas, het gewoonlik nie addisionele banddeurlaatfilters nodig om 'n enkele roostervolgorde te isoleer nie.

Brandpuntafstand

Die nouheid van die kleure wat 'n monochromator kan genereer, hou verband met die brandpuntsafstand van die monochromator-kollimators. Deur 'n optiese stelsel met 'n langer brandpunt te gebruik, verminder dit ongelukkig ook die hoeveelheid lig wat van die bron aanvaar kan word. Baie hoë resolusie monochromators het 'n brandpuntafstand van 2 meter. Die bou van sulke monochromatore verg uitsonderlike aandag aan meganiese en termiese stabiliteit. Vir baie toepassings word 'n monochromator van ongeveer 0,4 meter brandpuntsafstand as 'n uitstekende resolusie beskou. Baie monochromatore het 'n brandpuntlengte van minder as 0,1 meter.

Spleethoogte Wysig

Die mees algemene optiese stelsel gebruik sferiese kollimators en bevat dus optiese afwykings wat die veld krom waar die spletbeelde fokus, sodat splete soms gebuig word in plaas van eenvoudig reguit, om die kromming van die beeld te benader. Hierdeur kan groter splete gebruik word, wat meer lig versamel, terwyl 'n hoë spektrale resolusie steeds verkry word. Sommige ontwerpe volg 'n ander benadering en gebruik toroidale kollimerende spieëls om die kromming eerder reg te stel, wat hoër reguit gleuwe moontlik maak sonder om die resolusie prys te gee.

Golflengte teenoor energie

Monochromatore word dikwels gekalibreer in golflengte-eenhede. Eenvormige rotasie van 'n rooster veroorsaak 'n sinusvormige verandering in golflengte, wat ongeveer klein is vir klein roosterhoeke, dus is so 'n instrument maklik om te bou. Baie van die onderliggende fisiese verskynsels wat bestudeer word, is wel liniêr van energie, en aangesien golflengte en energie 'n wederkerige verhouding het, word spektrale patrone wat eenvoudig en voorspelbaar is as dit as 'n funksie van energie gestip word, verdraai as dit as 'n funksie van golflengte gestip word. Sommige monochromatore is gekalibreer in eenhede van wederkerige sentimeter of ander energie-eenhede, maar die skaal is dalk nie lineêr nie.

Dinamiese omvang Redigeer

'N Spektrofotometer gebou met 'n dubbele monochromator van hoë gehalte kan lig lewer van voldoende suiwerheid en intensiteit sodat die instrument 'n smal band optiese verswakking van ongeveer een miljoen keer kan meet (6 AE, Absorbansie-eenhede).

Monochromators word in baie optiese meetinstrumente en in ander toepassings gebruik waar monochromatiese afstembaarheid verlang word. Soms word die monochromatiese lig op 'n monster gerig en word die weerkaatsde of oordraagbare lig gemeet. Soms word wit lig op 'n monster gerig en word die monochromator gebruik om die weerkaatsde of oordraagbare lig te ontleed. Twee monochromatore word in baie fluorometers gebruik, een monochromator word gebruik om die golflengte van die opwekking te kies en 'n tweede monochromator word gebruik om die uitgestraalde lig te analiseer.

'N Outomatiese skanderingsspektrometer bevat 'n meganisme om die golflengte wat deur die monochromator gekies is te verander en om die gevolglike veranderinge in die gemete hoeveelheid op te neem as 'n funksie van die golflengte.

As 'n beeldtoestel die uitgangsleuf vervang, is die resultaat die basiese konfigurasie van 'n spektrograaf. Hierdie konfigurasie maak dit moontlik om die intensiteit van 'n wye band kleure gelyktydig te ontleed. Fotofilms of 'n reeks fotodetektore kan gebruik word, byvoorbeeld om die lig te versamel. So 'n instrument kan 'n spektrale funksie opneem sonder meganiese skandering, hoewel daar kompromisse kan wees in terme van resolusie of sensitiwiteit.

'N Absorpsiespektrofotometer meet die absorpsie van lig deur 'n monster as 'n funksie van golflengte. Soms word die resultaat uitgedruk as persentasie oordrag en soms word dit uitgedruk as die omgekeerde logaritme van die oordrag. Die Beer-Lambert-wet hou verband met die absorpsie van lig met die konsentrasie van die ligabsorberende materiaal, die optiese baanlengte en 'n intrinsieke eienskap van die materiaal wat molêre absorptiwiteit genoem word. Volgens hierdie verband is die afname in intensiteit eksponensiaal in konsentrasie en padlengte. Die afname is lineêr in hierdie hoeveelhede wanneer die omgekeerde logaritme van die oordrag gebruik word. Die ou benaming vir hierdie waarde was optiese digtheid (OD), die huidige benaming is absorbansie-eenhede (AU). Een AU is 'n tienvoudige vermindering van die ligintensiteit. Ses AU is 'n miljoenvoudige vermindering.

Absorpsiespektrofotometers bevat dikwels 'n monochromator om lig aan die monster te gee. Sommige absorpsiespektrofotometers het outomatiese spektrale analise-vermoëns.

Absorpsiespektrofotometers het baie daaglikse gebruike in chemie, biochemie en biologie. Hulle word byvoorbeeld gebruik om die konsentrasie of verandering in konsentrasie van baie stowwe wat lig absorbeer, te meet. Kritieke eienskappe van baie biologiese materiale, byvoorbeeld baie ensieme, word gemeet deur 'n chemiese reaksie te begin wat 'n kleurverandering veroorsaak wat afhang van die teenwoordigheid of aktiwiteit van die materiaal wat bestudeer word. [4] Optiese termometers is geskep deur die verandering in absorbansie van 'n materiaal teen temperatuur te kalibreer. Daar is baie ander voorbeelde.

Spektrofotometers word gebruik om die spieëlweerkaatsing van spieëls en die diffuse weerkaatsing van gekleurde voorwerpe te meet. Dit word gebruik om die prestasie van sonbrille, laserbeskermende bril en ander optiese filters te kenmerk. Daar is baie ander voorbeelde.

In die UV, sigbare en naby IR, verlig die absorbansie- en refleksie-spektrofotometers die monster gewoonlik met monochromatiese lig. In die ooreenstemmende IR-instrumente word die monochromator gewoonlik gebruik om die lig wat uit die monster kom, te analiseer.

Monochromators word ook gebruik in optiese instrumente wat ander verskynsels meet, behalwe eenvoudige absorpsie of weerkaatsing, waar die kleur van die lig 'n beduidende veranderlike is. Sirkulêre dikroismespektrometers bevat byvoorbeeld 'n monochromator.

Lasers produseer lig wat baie meer monochromaties is as die optiese monochromatore wat hier bespreek word, maar slegs sommige lasers is maklik afstelbaar, en hierdie lasers is nie so eenvoudig om te gebruik nie.


Diffraksierooster

A. Die proses waardeur 'n ligstraal of ander golwestelsel versprei word as gevolg van 'n smal opening of oor 'n rand, gewoonlik gepaard met steuring tussen die golfvorms wat geproduseer word.

A. Dit is 'n opties plat glasplaat waarop 'n groot aantal ewewydige ewewydige lyne deur 'n fyn diamantpen geregeer word.

V. Wat is roosterelement?

A. Dit is die afstand tussen die middelpunte van twee opeenvolgende lyne of deursigtige strepe.

V. Wat is die verskil tussen prisma en roosterspektrum?

A. In roosterspektrum is violetkleur die minste afgewyk en rooi kleur is die meeste afgewyk, maar in prisma is die omgekeerde waar.

V.Wanneer sal die ewenaar orde-spektra verdwyn?

A. Hulle sal verdwyn as die grootte van ondeursigtige lyne en deursigtige strepe gelyk gemaak word.

Vraag: Waarom verskil rooi kleur in geval van rasper?

A. Dit is so, want in die geval van rasper sin θ = n λ / (e + d) di diffraksiehoek is eweredig aan die golflengte en die golflengte van rooi is maksimum.

Vraag: Wat gee 'n meer intense spektrum en 'n prisma of rooster?

A. 'n Prisma gee 'n meer intense spektrum, want in prisma word die hele lig in een spektrum gekonsentreer, terwyl in die geval van rooster lig versprei word in die roosterspektrum van verskillende ordes.


Verskille tussen 'n Alpy 600 en LHIRES III met verskillende rooster

Ek gebruik al 'n rukkie 'n LHIRES III met die 2400 lyne / mm-rooster, en ek wil 'n groter spektraal domein kry.

Wat sou die belangrikste verskille wees tussen 'n Alpy 600 en 'n LHIRES III met 'n laer resolusierooster, behalwe dat die LHIRES III meer onderhoud sou benodig (veral as die roosters uitgeskakel word), en die verskil in f-verhouding? Ek kry heel waarskynlik nog 'n LHIRES-rooster omdat dit goedkoper is, maar die LHIRES ly onder korter golflengtes, en die Alpy lyk beter reggestel.

Geredigeer deur oornag, 8 April 2019 - 19:29.

# 2 robin_astro

Ek dink jy het die verskille redelik goed opgesom. Ek het albei 'n ek dink die twee vul mekaar goed aan.

Die LHIRES sal met lae resolusie werk, maar dit is regtig spesifiek ontwerp vir hoë resolusie werk (steeds die hoogste resolusie wat kommersieel beskikbaar is) oor 'n smal golflengtebereik, dus die lens is 'n eenvoudige achromatiese dubbeltjie wat baie chromatiese afwyking en dus verlies aan resolusie toon. veral aan die blou einde daarbuite

4000A wanneer dit met 'n lae resolusie-rooster gebruik word, en selfs teen 'n medium resolusie met byvoorbeeld 'n 600l / mm-rooster wanneer u in hierdie streek werk. U kan 'n voorbeeld hiervan sien met my 150l / mm-rooster hier (Vega halfpad af)

en dit is die plot wat nodig is vir die aanpassing van die fokus, wat volg op wat u sou verwag vir 'n achromatiese dubbel

Dit is 'n voorbeeld van die prestasie met 'n 600l / mm-rooster in hierdie streek. Die spektrograaf was rondom die middel van die reeks gefokus en u kan agteruitgang van die Balmer-lyne sien, selfs oor hierdie betreklik beperkte reikwydte.

U kan die erns van hierdie effek met u LHIRES en 'n hoë resolusie-rooster verifieer deur op H beta in 'n warm reuse-ster met smal Balmer-lyne te fokus en dan geleidelik af te beweeg sonder om van fokus te verander.

Die ALPY daarenteen gebruik spesiale lense wat ontwerp is vir lae chromatisme en kan goed in die UV ingaan sonder om die resolusie te verloor.

Die ALPY het ook baie vinniger optika (nominaal f5, maar kan afgaan na f3.5 sonder vignettering), wat meer sensitiwiteit beteken vir uitgebreide voorwerpe soos sterrestelsels, newels, ens. As dit saam met 'n bypassende vinnige teleskoop gebruik word. (Die toevoeging van 'n brandverminderaar kan egter probleme met chromatisme meebring. Nie 'n verlies aan resolusie nie, aangesien dit voor die spleet is, maar 'n selektiewe steekproef van die golflengte by die spleet wat die kontinuumvorm verwring as die fokus tussen die meet van die verwysingsster en die teiken)

Die ALPY is ook baie meer termies en meganies stabiel as die LHIRES, en dit moet selde eers aangepas word


Wat is die verskil tussen grisme en rooster? - Sterrekunde

Diffraksieroosters laat optiese spektroskopie toe. 'N Rooster is 'n stel ewewydige, nou, ewewydige bronne. 'N Rooster versprei lig van verskillende golflengtes om vir elke golflengte 'n smal rand te gee. Dit laat presiese spektroskopie toe. Hierdie bladsy ondersteun die multimedia tutoriaal Diffraksie.

Twee, drie, vier en baie splete

In Diffraksie het ons gesien dat die faseverskil onder hoek & phi & theta tussen strale vanaf twee bronne afstand a apart was & phi = 2 & pia sonde & theta/& lambda. Met twee splete, soos & phi wissel van 0 tot 2 & pi, draai die fasorsom sodat die amplitude daarvan van maksimum na nul tot maksimum gaan. Met drie splete met dieselfde spasiëring, dieselfde variasie in & theta en dus & phi neem ons van sentrale maksimum, na nul by & phi = 2 & pi / 3, tot 'n klein filiaal maksimum op & phi = 2 & pi / 2 = & pi, tot nul by & phi = 4 & pi / 3 en terug na 'n maksimum by & phi = 2 & pi. Vir vier splete, kom die eerste nul voor by & phi = & pi / 2 en daar is twee klein filiale maksima.

Beskou die breedte van die groot maksimum, d.w.s. die spasie tussen die nulle aan weerskante. Vir twee splete is die reeks & phi 2 & pi = 4 & pi / 2 vir drie splete is dit 4 & pi / 3, vir vier splete is dit 4 & pi / 4 en, vir N splete dit is 4 & pi /N. Let ook op dat die hoogte van die maksimum toeneem, omdat meer splete daartoe bydra. Onthou dat die intensiteit gaan as die kwadraat van die amplitude, dus sal die intensiteit van die helder rande wat in die diagramme hierbo voorgestel word, 2 2: 3 2: 4 2 = 4: 9: 16 = 1: 2,25: 4 wees.

Diffraksieroosters

In wit lig gesien, sien ons die verspreiding van verskillende golflengtes vir hierdie drie roosters.

Patrone met monochromatiese en breëbandbronne

Gratings with different line spacings illuminated with monochromatic light from a laser and then broad band light from an incandescent lamp.

The three gratings shown above are first illuminated successively with monochromatic (red) laser light. Note the successively greater dispersion: the first order fringe of the grating with 300 lines/mm occurs at the same angle as the third order fringe of the grating with 100 lines/mm. Then the same three gratings are illuminated with an incandescent lamp, which emits a continuous spectrum of wavelengths.

Note the central bright fringe: for all wavelengths, this occurs at &theta = 0, so this fringe is white. For the other fringes, sin &thetam = nm&lambda, waar m is the order of the fringe and n is the number of fringers per unit length.

Emission spectra

Now let's illuminate the grating with more complicated light sources. The central line is the undeflected beam of undispersed light at angle zero. The first order diffraction pattern appears on either side. A pure gas, when heated, emits light with specific wavelength (and thus specific energy per photon). Sodium and Mercury vapour lamps are viewed here through a grating. The incandescent lamp emits light from a hot metal filament with a continuous spectrum.

Absorption spectra

A pure gas absorbs light with specific wavelength (and thus specific energy per photon). When light with a continuous spectrum of wavelengths passes through a gas, black lines on the transmitted spectrum show the wavelengths that have been absorbed: an absorption spectrum. The pictures show the absorption spectra for hydrogen and helium. These gasses are the principal components of the sun and its atmosphere, Helium (named for the Greek word for the sun) is the only element that was not discovered on Earth: the presence of helium in the solar atmosphere was deduced from the theoretical prediction of the absorption lines for the element with two protons in the nucleus and the observation of those absorption lines in the spectrum of light from the sun.

Atomic energies and spectra

Why does a gas emit or absorb only discrete wavelengths, corresponding to photons with discrete energies? According to quantum mechanics, an electron in an atom can have only discrete values of energies, each energy corresponding to one particular orbital, described by a wave function. The diagram depicts the first several of these for hydrogen (the chance of interacting with an electron roughly corresponds to values of the square of the wavefunction, which is coded here as the brightness).


Beginner Question - Star Diagonals and Erecting Prisms

I'm relatively new to amateur astronomy but understand some things. I have a couple of refractors and a newtownian and I've been at it long enough that I'm upgrading some items, e.g. I should have an upgraded focuser for my 90eq in a couple of days. I use my 90eq mostly for lunar and planetary targets.

I'd also like to upgrade the diagonal on my Celestron 90eq but I'm a little baffled by the options and the googlez hasn't helped much so far. About the only thing I understand is that dielectric coatings are better than standard.

1. Can anyone direct me to a resource that I can study. Happy to do my own research and I'm usually pretty good with search engines but not this time.

2. Does a diagonal and an erecting prism do the same thing but one is a mirror and the other, well, a prism?

3. Are there different kind of diagonals, e.g. is a star diagonal something different than a regular diagonal?

4. What other questions should I be asking but I don't know enough to ask?

#2 LanceRFerguson

Oh! I just found this. Finally!

#3 Mitrovarr

#4 SteveG

Is your 90 EQ a long focus achromat? Then a prism diagonal will suite you well. For that scope, I would look at a standard Celestron prism:

For erect image, first decide if you want a 45 deg or 90 deg diagonal (both are available). The erect-image diagonals are not great for stars though, mainly designed for terrestrial use.

#5 Mitrovarr

Edited by Mitrovarr, 25 November 2019 - 03:00 PM.

#6 LanceRFerguson

Is your 90 EQ a long focus achromat? Then a prism diagonal will suite you well. For that scope, I would look at a standard Celestron prism:

https://agenaastro.c. r-diagonal.html

For erect image, first decide if you want a 45 deg or 90 deg diagonal (both are available). The erect-image diagonals are not great for stars though, mainly designed for terrestrial use.

1000mm achromat indeed. I'll check that out, thanks!

#7 LanceRFerguson

Also, don't think you have to spend a fortune to get a decent diagonal. That article you found describes top end gear for extremely experienced astronomers who already have high end gear aside from their diagonal. It really, really isn't aimed at beginners.

Oh yeah, I hear you. I really didn't look at the comparison too much. It was one of the few articles that I could find that explained anything. Did eventually find one on CN that was helpful. Starting to make some sense.

The stock diagonal is all plastic and hasn't had a tight fit since I bought it used. Barely holds an eyepiece steady and definitely not a smartphone. So I figured a diagonal upgrade wouldn't hurt anything.

#8 Mitrovarr

#9 j.gardavsky

you can spend quite a lot of money on the diagonal zenith mirrors and on the prisms.

As above, I would choose a quality zenith prism, and look around at the classified.

Regarding the dielectric mirrors, I have one which has not been cheap, but it has got some scratches from cleaning the dew during the observing sessions, so right now I am mostly using a prism. The expensive BBHS mirror is waiting for its first light in reserve.

Enjoy the hobby, and clear skies,

#10 wrvond

If you are using 2" oculars, your prism star diagonal choices are pretty limited (and expensive), but if you are using strictly 1.25" oculars there are a lot of choices out there. Dielectric mirrors are readily available in either size and can run the gamut for prices.

Here is a listing on the CN classifieds by a vendor selling one of each kind (star and erecting), additionally, the star diagonal is a prism, and the prices are very reasonable.

#11 LanceRFerguson

If you are using 2" oculars, your prism star diagonal choices are pretty limited (and expensive), but if you are using strictly 1.25" oculars there are a lot of choices out there. Dielectric mirrors are readily available in either size and can run the gamut for prices.

Here is a listing on the CN classifieds by a vendor selling one of each kind (star and erecting), additionally, the star diagonal is a prism, and the prices are very reasonable.

https://www.cloudyni. to-choose-from/

That's excellent, thanks! Have sent a message to seller as to availability. I looked briefly at CN classifieds but hadn't pursued very far as I'm still sorting out the difference. Though I have that pretty well in hand thanks to this thread.

All oculars are 1.25" at this point (with the exception of some .965 stuff on my starter scope).

#12 clearwaterdave

William Optics makes a nice correct image prism diagonal if you want CI for nighttime use.,At least to me I saw no lack in the view.,It does restrict the widest fov eps at lowest power.,but not bad imho.,good luck with your choice.,

#13 SloMoe

Morning Lance, here's what I've learned for myself,

Mirror vs. prism, google it, and you'll find the article linked, don't breeze through it, read it.

I have a lot of diagonals and I do both terrestrial & celestial viewing.

I have and used both the 45° prisms the one you see Scopehead selling and the WO 45°, both are good up to about 125X then the aberration mentioned starts to set in in a refractor, in a Mak/SCT you can kick it to 200X and still have a sharp image,

The view starts to dim at about 175X .

Now that's with the correct image 45° diagonals, both types I've mentioned and own have the same fov, personally I couldn't tell any difference between the two, save your money and get the type Scopehead sells.

When you point your scope up the 90° becomes more comfortable to use, the dielectric's I've used are outstanding compared to the less expensive stock prism's, the view is brighter, if they dew or fog up, it's time to switch to another, don't clean them at night in the field, just like with eyepieces, they will scratch very easily, don't worry the stars will be out again the next night.

Prisms would be nice for some very deep sky stuff and when you're using line filters,

I have a Zeiss-Baader 34mm that I use on a 70mm finder, mainly because of it's helical focus eyepiece holder, now that's a sharp image, and a high price tag.

The infamous Celestron "94", Celestron give away price is a key to their success, with those it's hit or miss as far as the good ones go, a few more miss than hit, if they were a quality product Celestron wouldn't give them away so cheap, also there's a guy here that claims to be able to collimate them and fix them, and those he can't he dumps back into CN classifieds,

So if you want an inexpensive prism check our sites sponsor's selection or Agena, but buy them new, not from the Classifieds, too many dud's floating around there.

All of the more common brighter DSO's and planets the mirror just does a better job of the detail in the view.

I have had a couple of Orion Dielectrics, good mirrors, GSO and a few others just as good, depends on what drops into your lap when you go hunting for the bargain.

The correct image diagonals need a lot of light to work well for a crisp image and that's their downfall, at night there's not a lot of light so they don't preform, when you start bending light in every know direction it starts to loose clarity.

Layman's terms and to go into why is not what we need, the quick answer is they don't work well at high mag in low light conditions.

I found a while back a diagonal that has a 1.6X Barlow lens incorporated into it, it turned out to be a nice view, crisp with relatively no aberration up to about 185X, don't use it much but seems to be fairly rare, got a pile of Barlow's anyway, just something different.

I have both the W'O correct image diagonal's 45° & 90°, can't figure why they wouldn't put their helical focus eyepiece holder on the 45° so I did, it's the one I use for terrestrial high mag viewing.

If you're interested in the diagonal with the Barlow in it pm me.

EDIT: Scope's a good guy to deal with, if you have a problem with a product he'll work with you.

EDIT: #2. it's either this way or I start a second post.

So here's another thing, it's your eye that determines the view, sometimes we get lost in the numbers of what is what when it comes to light % transmission, 5% or even 10% difference you're going to have a hard time knowing which is which when you're staring through it.

Edited by SloMoe, 26 November 2019 - 08:16 AM.

#14 LanceRFerguson

Morning Lance, here's what I've learned for myself,

Mirror vs. prism, google it, and you'll find the article linked, don't breeze through it, read it.

I have a lot of diagonals and I do both terrestrial & celestial viewing.

I have and used both the 45° prisms the one you see Scopehead selling and the WO 45°, both are good up to about 125X then the aberration mentioned starts to set in in a refractor, in a Mak/SCT you can kick it to 200X and still have a sharp image,

The view starts to dim at about 175X .

Now that's with the correct image 45° diagonals, both types I've mentioned and own have the same fov, personally I couldn't tell any difference between the two, save your money and get the type Scopehead sells.

When you point your scope up the 90° becomes more comfortable to use, the dielectric's I've used are outstanding compared to the less expensive stock prism's, the view is brighter, if they dew or fog up, it's time to switch to another, don't clean them at night in the field, just like with eyepieces, they will scratch very easily, don't worry the stars will be out again the next night.

Prisms would be nice for some very deep sky stuff and when you're using line filters,

I have a Zeiss-Baader 34mm that I use on a 70mm finder, mainly because of it's helical focus eyepiece holder, now that's a sharp image, and a high price tag.

The infamous Celestron "94", Celestron give away price is a key to their success, with those it's hit or miss as far as the good ones go, a few more miss than hit, if they were a quality product Celestron wouldn't give them away so cheap, also there's a guy here that claims to be able to collimate them and fix them, and those he can't he dumps back into CN classifieds,

So if you want an inexpensive prism check our sites sponsor's selection or Agena, but buy them new, not from the Classifieds, too many dud's floating around there.

All of the more common brighter DSO's and planets the mirror just does a better job of the detail in the view.

I have had a couple of Orion Dielectrics, good mirrors, GSO and a few others just as good, depends on what drops into your lap when you go hunting for the bargain.

The correct image diagonals need a lot of light to work well for a crisp image and that's their downfall, at night there's not a lot of light so they don't preform, when you start bending light in every know direction it starts to loose clarity.

Layman's terms and to go into why is not what we need, the quick answer is they don't work well at high mag in low light conditions.

I found a while back a diagonal that has a 1.6X Barlow lens incorporated into it, it turned out to be a nice view, crisp with relatively no aberration up to about 185X, don't use it much but seems to be fairly rare, got a pile of Barlow's anyway, just something different.

I have both the W'O correct image diagonal's 45° & 90°, can't figure why they wouldn't put their helical focus eyepiece holder on the 45° so I did, it's the one I use for terrestrial high mag viewing.

The 90° I don't use at all,

If you're interested in the diagonal with the Barlow in it pm me.

Guess that covers $.02

EDIT: Scope's a good guy to deal with, if you have a problem with a product he'll work with you.

EDIT: #2. it's either this way or I start a second post.

So here's another thing, it's your eye that determines the view, sometimes we get lost in the numbers of what is what when it comes to light % transmission, 5% or even 10% difference you're going to have a hard time knowing which is which when you're staring through it.

This is extremely helpful, thanks for taking the time to write it up. I'll have to go through it a couple of times to catch everything but it answers a number of questions. It helps gives me a basis for judging what I'm looking at. I wanted another diagonal because the cheap, plastic stock one isn't very mechanically sound anymore. It's a Celestron 90eq so getting something pricey doesn't make sense. I like the scope but I'm realistic about it, too. I figure for $20 I'll roll the dice and see what the difference is between the existing mirror and a prism. I'll either have a nicer diagonal and/or I'll learn something. In this hobby learning something for $20 is pretty cheap!

Good to know on Scopehed as yesterday I ordered the 90 degree from him!

Thank you again for the details!

EDIT: Not to mention having the right search terms can make all the difference! This morning I'm reading some info that prisms are good in slow scope and they like long focal lengths. My 90eq is both so even better.


Should you buy or avoid BK-7 prism binoculars?

From the said above it becomes clear than BK-7 can’t beat quality of BAK-4 prism.

If you choose binoculars with magnification up to 8x then BK-7 still can be acceptable. Because magnification up to 8x has a wide field of view.

When magnification increases field of view becomes narrower. This means in how power binoculars with BK-7 prism image quality may not be acceptable at all.

This means if you are on a tight budget and plan to buy BK-7 binocular choose one with a small magnification, preferably up to 8x and exit pupil should be at least 4mm.

Generally speaking I recommend to buy BK-7 prism binoculars only if you are on a tight budget.


Prism Spectrometer and Diffraction Grating: 787550

Dispersion of a beam of white light into its component colours by a glass prism is due to the variation in refractive index of the glass with the frequency (colour) of the light. This is a result of the variation in the speed of the light in the medium. Thus blue light (higher frequency) will be refracted more than red light (lower frequency) as it passes through the prism. The angle between the undeviated path of an incident ray and the final path of the ray as it exits the prism is called the deviation angle. When the ray passes symmetrically through the prism, (so that its path in the prism is parallel to the base), minimum deviation occurs.

Referring to the diagram, either increasing or decreasing θ will result in an increase in the deviation angle.

The refractive index of the prism is given by

Where A = prism angle D = angle of minimum deviation

The value of n is different for different wavelengths, and a relationship between n and l was given by Cauchy:

(2)where a and b are constants and λ is the free space wavelength.

Figure 2 Determination of Minimum Deviation Angle

  1. Turn on the sodium lamp and allow to warm up for at least 10 minutes.
  1. Position the prism on the prism table with the unpolished side flush with the prism holder and lock into place. (Nota: Do not over tighten).
  1. Rotate the telescope to the straight through position.
  1. Open the slit adjust to give a wide yellow line through the telescope. Note: You will have to physically move the spectrophotometer and the telescope to be able to see the line.
  1. Close the slit adjust to give a sharp narrow yellow line. Nota: You will probably have to adjust the focus on (a) the collimator and (b) the telescope. While you are at it adjust the focus for the cross hairs, which is at the eyepiece end of the telescope.

Nota: All focus controls pull in and out.

  1. Ensure that the prism table lock is released (anticlockwise) and rotate the prism table until it is in the position in the diagram. Lock the table in this position.
  1. Ensure the telescope lock is released (anticlockwise) and rotate the telescope until spectral lines are observed. Nota: You may have to adjust both the prism table and the telescope to achieve this.

– 8 -The position of minimum deviation may be obtained by rotating the prism table in one direction – the spectral lines will appear to move across the field of view, stop and reverse their motion. Nota: You will need to adjust both the prism table and the telescope to achieve this.

The point where a particular spectral line changes direction corresponds to the minimum deviation for that particular wavelength in the prism.

  1. Line the cross hairs of the telescope up on the red spectral line, release the prism table lock and rotate the prism table until that spectral line changes direction. Lock the prism table where this occurs. Nota: Do not adjust the prism table until all the measurements have been obtained. (This is not technically correct but for this instrument it is far more accurate than attempting to find the minimum deviation angle for each spectral line).
  1. Position the telescope near the spectral line, lock it, and use the telescope fine adjust to line up the cross hairs on that line.
  2. When this is done, note the reading on the scale. This is angle A for that spectral line. (Nota: It is a vernier scale and should be read to at least 0.1 o )
  3. Repeat parts 10-11 of the procedure for the other five (5) strong lines.
  1. Note the colour, and the wavelength of each of the lines you have measured.
  1. Repeat steps 9-13 and find the average value.

NOTE: To do the next section you will have to move the prism to Position B and the telescope to the ‘B’ angle position as per Figure 2

  1. Repeat Parts 3-14 of the procedure.
  1. Tabulate all results.
  1. Determine the angle of minimum deviation, D, for each line by subtracting the mean of the smaller angle from the mean of the larger angle and halving the result.
  1. Construct a calibration curve of minimum deviation angle versus wavelength.
  1. Use the prism spectrometer to examine the spectra of the other light sources available in the laboratory.

Vir one other light source, determine the angular positions of at least three spectral lines at minimum deviation and using your graph of D vs λ obtained for the sodium lamp, calculate the wavelengths of these lines.

Compare the results with tabulated values.

Diffraction Grating

Diffraction of monochromatic light in a Young’s double slit experiment produces an intensity pattern which consists of a double slit “interference” pattern which is modulated by a single slit diffraction pattern.

The position of the maxima in the double slit interference pattern is given by

where d is the separation of the slits, θ is the angular position of a given maximum with respect to the x-axis, n is the order of a given maximum and λ is the wavelength of the light.

A diffraction grating consists of a system of many slits (in fact, grooves ruled on a transparent material) and equation (3) may be used to describe the position of the principal maxima produced by a diffraction grating. If non-monochromatic light is incident on the grating, the different wavelengths of light will be dispersed (ie occur at different values of θ) within each order of diffraction.

  1. Replace the prism with the transmission diffraction grating supplied. Fix the grating to the surface of the prism table using the clamp provided. You will have to remove the prism clamp and replace it with the diffraction grating clamp.
  1. With the grating aligned approximately perpendicular to the collimator, find (by eye) the sodium spectra produced on either side of the straight-through position.
  1. Rotate the telescope to the position of the first-order spectrum on one side and align the cross hairs with a spectral line. Note the angular setting of the telescope.
  • Comment on any differences between the sodium spectrum you observe with the diffraction grating and that observed with the prism.
  1. Repeat the procedure for as many lines as possible, for the first-order spectra.
  1. If the angle is increased past the first order spectral lines another set of spectra lines, known as the second order, will be observed. Nota: You may need to increase the intensity of the light by opening the slit adjust. Note the angular setting of the telescope for as many lines as possible.

NOTE: To do the next section you will have to position the telescope in the ’B’ angle position.

  1. Repeat Parts 3-5 of the procedure.
  1. Draw up a table showing the angular settings for each line (wavelength) on the right and left of the straight through position. Determine θ for both first-order and second-order lines by subtracting the smaller angle from the larger angle and dividing by two.
  • Explain how, and why, the angular separation between the spectral lines varies between the first-order and second order spectra.
  1. Plot λ vs sin θ for both first-order and second-order spectra, and determine the slope of each line. Hence obtain an average value for the spacing, d, of the lines on the diffraction grating. Give an estimate of the error involved in the value you obtain.
  • Compare your values of d with the value printed on the diffraction grating.
  • 5 –
  • Simulation software

If time permits, use the simulation software provided to compare your value of the slit separation with that predicted by the program.

  1. Choose Applications of Interference and Diffraction from the menu.
  1. Choose Gratings from the menu at the top of the screen.
  1. Choose the Transmission Grating – Spectrum option from the pull-down menu.
  1. Enter the wavelengths of two of the lines you have measured, a slit width of 0.0001 mm and the slit separation you determined.
  1. Compare the predicted angular positions of the lines with the values you measured. Comment on the result.
  1. Investigate the effect of changing the slit width, slit separation or wavelength of the radiation.

Sodium Line Spectra Neon Line Spectra
λ (nm) Kleur λ (nm) Kleur
614.8 red 701 red
589.5 yellow 1 691 red
588.9 yellow 2 671 red
568.6 green 666 red
515.0 light blue green 658 red
498.0 blue green 652 red
466.6 light indigo 649 red
454.3 indigo 639 red
442.1 light purple 637 red
Helium Line Spectra 632 red
629 red
λ (nm) Kleur 626 red
667.8 red 621 red
587.5 yellow 615 red
501.5 blue green 614 orange
492.2 blue green 609 orange
471.3 blue 607 orange
447.3 purple 602 orange
438.9 purple (faint) 597 yellow
594 yellow
Cadmium Line Spectra 588 yellow
λ (nm) Kleur 585 yellow
644 red 576 green (faint)
510 blue green 540 green
481 blue 534 blue green
468 blue
442 purple (faint)
Mercurius Line Spectra
λ (nm) Kleur
579.1 yellow
577.0 yellow
546.2 green
491.7 blue
436.0 purple
407.9 purple
404.8 purple

Experimental Aim

This experiment aims at estimating the refractive index of a prism for different wavelengths of the Sodium Spectrum and then plotting calibration and dispersion curves through the use of Prism Spectrometer.

Inleiding

A spectrometer is an instrument used in the analyses of the spectra of radiations. The glass-prism spectrometer is ideal in taking measurements of ray deviations as well as refractive indices. At times, diffraction grating may be used instead of the prims in the study of optical spectra. A prism is capable of refracting light into one spectrum while diffraction grating spreads the available light in numerous spectra (Duarte 2015). Due to this, slit images that are formed using a prism are mostly brighter as compared to the ones formed through grating. The only challenge in this is that the enhanced brightness of the spectral lines is often offset through a decreased resolution as the prism cannot effectively separate the various lines as the case of grating. However, these brighter lines permit a slit width that is narrow in shape to be used which is partially able to compensate for the lowered resolution (Guanter et al., 2015).

There is no direct proportionality between the angle of refraction and the wavelength of light in a prism. For this reason, the measurement of the wavelengths using a prism is achieved through the construction a calibration graph of the deviation angle against the wavelength and using the source of light with a known spectrum. The wavelength of the unknown spectral lines can thus be interpolated from the obtained graph (Hadni 2016). Future determinations of wavelengths is validated upon the creation of a calibration graph for th prism and this is only possible if they are made from prism that is aligned precisely just the same it was at the time of production of the graph. To achieve the reproduction of such an alignment, all the measurements must be made when the prism is aligned to enable refracting the light at the angle of the lowest possible deviation.

The light that is studied is rendered parallel using a collimator that is composed of a tube that has a slit of adjustable width at an end and a convex lens at the other end. The collimator must be maintained in a highly focused through the adjustment of the position of the slit to the point at which it is at the focal point of the lens (Hartmann et al., 2014). The parallel beams that originate from the collimator are made to pass through a glass prism that is on a prism table which is rotatable, levelized, lowered or even raised. The prism then deviates the components colours of the released light through various amounts and spectrum so generated is examined through the use of a telescope that is mounted on a rotating arm and oscillates over the divided angular scale.

The theory of the prism spectrometer illustrates that a spectrum that has maximum definition is achieved when the light ray angular deviation of the light ray that goes through the prism is least. Under such conditions it can be demonstrated that they ray goes through the prism is a symmetrical manner. For a specific wavelength of light that is traversing a certain prism, that exists a characteristic incidence angle for which the deviation angle is least. This angle is dependent in the refractive index of the prism and the angle that is formed between the two sides of the prism that have been traversed by light (Hossain et al., 2015). The equation below is used in illustrating the relationship between the two variables

in which n is the refractive index of the prism, the angle formed between the two sides of the prism that has been traversed by light and A the angle of minimum deviation.

Figure 2: Determination of Minimum Deviation Angle

  1. The sodium lamp was turned on and allowed to warm up for more than 10 minutes
  2. The prism was positioned on the prism table having the unpolished side flush with the holder of the prism and then locked into place (Leedle et al., 2015)
  3. The telescopes was rotated to the straight through position
  4. The slit adjust was open to provide a wide yellow line through the telescope
  5. The slit adjust was then closed to provide a sharp narrow yellow line
  6. The prism table lock was ascertained to be released in an anticlockwise manner and then the prism table rotated until it was in the position as illustrated in the diagram.
  7. The telescope lock was ascertained to be released in an anticlockwise directed and then the telescope rotated until the spectral lines were noticed.
  8. The position of the minimum deviation was obtainable through the rotation of the prism table in one direction only where the spectral lines would seem to move across the field of view, stop and the move in a reverse direction (Mouroulis et al., 2014)
  9. The cross hairs of the telescope were lined up on the red spectral line and the prism table lock released and the prism table rotated until there was a change in position of the spectral line. The prism table was then locked when it occurred
  10. The telescope was position close to the spectral line and the telescope fine adjust was then used in lining up the cross hairs on the line
  11. The reading on the scale was noted which was the angle A of the spectral line
  12. The parts 10-11 of the procedure were repeated for the other five string lines
  13. The wavelength and the colour were noted for each of the lines measured
  14. Steps 9-13 were repeated to estimate the average value

Nota: The prism has to be moved to position B and the telescope moved to the B angle position as illustrated in figure 2 in order to perform the next section

  1. Parts 3-14 of the method were repeated
  2. The results were tabulated
  3. The minimum angle of deviation, D, was then determined for every line through subtracting the mean of the smaller angle from the mean of the greater angle and then halving the result
  4. A calibration curve was constructed of the minimum deviation angle against the wavelength (Piascik et al., 2014)
  5. The prism spectrometer was used in the examination of the spectra of the other sources of light that were available in the laboratory. Comparison was made with the tabulated values

Diffraction Grating Procedure

  1. The prims were substituted with the transmission diffraction grating that was supplied in which the grating was fixed to the prism table surface with the clamp given.
  2. The sodium spectra generated on either side of the straight-through position was determined using the eye while the grating was aligned about perpendicular to the collimator
  3. The telescope was rotated to the position of the first order spectrum on one of the side and then the cross hairs aligned with the spectral line. The angular setting of the telescope was taken care of.
  4. The procedure was repeated for as numerous lines as possible for the first order spectra
  5. Another set of spectral lines known as second order would be observed upon an increase in the angle beyond the first order spectra lines

Nota: Performing the next section of this experiment required moving the telescope to B angle position

  1. The Parts 3-5 of the method were repeated
  2. A table illustrating the angular setting for every line on the right as well as left of the straight line through position was then drawn. The Ɵ was determined for both the first order and second order lines through finding the difference between the smaller angle and the larger angle and the final answer divided by two (Squires, Constable & Lewis (2015)
  3. Graphs of λ versus sin Ɵ were plotted for both the first order and second order spectra and then the slope of each of the lines determined. The averaged value of the spacing, d, of each of the lines on the diffraction grating was then determined and an estimate of the error incurred determined.

Prism Spectrometer Experiment

colour Deviation angle (degree) Lemda (nm)
Red 133.9 614.8
orange 133.5 589.5
green 133 568.6
Dark green 132 498
light blue 131.5 466.6
violet 130.4 442.1

Table 1: Sodium calibration results

Figure 3: Sodium calibration plot

Diffraction grating
colour deviation angle (sintheta) lemda (nm)
violet 0.282 442.1
light blue 0.3 466.6
Dark green 0.312 498
lime green 0.344 515
orange 0.357 588.9
red 0.371 614.8

Table 2: Diffraction Grating results

Figure 3: Diffraction Grating plot

Discussion and Conclusion

The prism spectrum that was obtained for the sodium lamp that could be seen with the resolution of the prism was provided as shown in the table from top to bottom. The measured angles i.e. 2A= and thus the angle of the prismA= (Vaughan 2017). The behavior of the dispersion curve was observed that there is no rapid fall over the range of the wavelengths thus it can be concluded that there is no heavy sloping line meaning that the dispersion of the different spectral lines do not vary so much from each other which is illustrated by the closeness of the refractive index of the provided wavelength range.

For the calibration curve, it is almost a straight line illustrating that the impact of the wavelength of the Angle of Minimum Deviation tends to being linear (Vaughan 2017). This curve can be used in establishing the wavelength of the spectral line that has an unknown wavelength but the Angle of Minimum Deviation is determined using the very apparatus. The aims and objectives of this experiment were thus met with the results illustrating high correlation with the theoretical values as recorded in literature.

Duarte, F. J. (2015). Tunable laser optics. CRC Press

Guanter, L., Kaufmann, H., Segl, K., Foerster, S., Rogass, C., Chabrillat, S., … & Straif, C. (2015). The EnMAP spaceborne imaging spectroscopy mission for earth observation. Remote Sensing, 7(7), 8830-8857

Hadni, A. (2016). Essentials of Modern Physics Applied to the Study of the Infrared: International Series of Monographs in Infrared Science and Technology (Vol. 2). Elsevier

Hartmann, N., Helml, W., Galler, A., Bionta, M. R., Grünert, J., Molodtsov, S. L., … & Bostedt, C. (2014). Sub-femtosecond precision measurement of relative X-ray arrival time for free-electron lasers. Nature photonics, 8(9), 706

Hossain, M. A., Canning, J., Ast, S., Cook, K., Rutledge, P. J., & Jamalipour, A. (2015). Combined “dual” absorption and fluorescence smartphone spectrometers. Optics letters, 40(8), 1737-1740

Leedle, K. J., Pease, R. F., Byer, R. L., & Harris, J. S. (2015). Laser acceleration and deflection of 96.3 keV electrons with a silicon dielectric structure. Optica, 2(2), 158-161

Mouroulis, P., Van Gorp, B., Green, R. O., Dierssen, H., Wilson, D. W., Eastwood, M., … & Loya, F. (2014). Portable Remote Imaging Spectrometer coastal ocean sensor: design, characteristics, and first flight results. Applied optics, 53(7), 1363-1380

Piascik, A. S., Steele, I. A., Bates, S. D., Mottram, C. J., Smith, R. J., Barnsley, R. M., & Bolton, B. (2014, July). SPRAT: spectrograph for the rapid acquisition of transients. In Ground-based and Airborne Instrumentation for Astronomy V(Vol. 9147, p. 91478H). International Society for Optics and Photonics

Squires, A. D., Constable, E., & Lewis, R. A. (2015). 3D printed terahertz diffraction gratings and lenses. Journal of Infrared, Millimeter, and Terahertz Waves, 36(1), 72-80

Vaughan, M. (2017). The Fabry-Perot interferometer: history, theory, practice and applications. Routledge


Kyk die video: Combinatoriek - routes in een rooster - WiskundeAcademie (November 2022).