Calibration lamp for UVEX ?

Calibration lamp for UVEX ?

Postby Olivier GARDE » Sun Aug 18, 2019 4:52 pm

Today, I tested a spectral lamp from Lot Oriel, a Mercury/Argon lamp. (Light pen #6035 from Lot-Oriel) with an ALPY 600.

Image

This lamp need a high voltage power supply (I don't know the real voltage)

So here the spectrum (alpy 600 with 14µm slit : resolution around 1300). There are some visible lines around 4000 Å and one very useful for the UVEX at 3654,8 Å

Image

But my Alpy did not allow me to go lower than 3600 Å and Lot Oriel provided a data sheet with all the emission lines. So in green on my spectrum, 4 emissions lines that I could not see with the ALPY.

Image


This lamp cost around 230 € with an expected life around 5000 hours. it's a 5 cm long glass tube and 5mm in diameter. Be careful if you use this lamp, dont look directly the light and use UV protected glass.
LHIRES III #5, LISA, e-Shel, C14, RC400 Astrosib, AP1600
http://o.garde.free.fr/astro/Spectro1/Bienvenue.html
Olivier GARDE
 
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Location: Rhône Alpes FRANCE

Re: Calibration lamp for UVEX ?

Postby James Foster » Mon Aug 19, 2019 4:03 am

Nice work Olivier!
Im trying to use UV lights for reptile acquariums for UVEX calibration, but like yourself, cant test very below LhiresIII limit (about 3700A).
That light source cost as much as a good used SLR!

James
James Foster
Lhires III (2400/1800/600 ln/mm Grat) Spectroscope,
LISA IR/Visual Spectroscope (IR Configured Presently)
Alpy 600 with Guide/Calibration modules and Photometric slit
Star Analyzer 200
James Foster
 
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Re: Calibration lamp for UVEX ?

Postby Olivier GARDE » Mon Aug 19, 2019 6:11 am

Hi James,

A few months before, I had tested a UV lamp (to insolate the printed circuits) and the result showed some lines in emissions on a continuum in the form of hump ...

See the post here :

viewtopic.php?f=45&t=2253
LHIRES III #5, LISA, e-Shel, C14, RC400 Astrosib, AP1600
http://o.garde.free.fr/astro/Spectro1/Bienvenue.html
Olivier GARDE
 
Posts: 966
Joined: Thu Sep 29, 2011 6:35 am
Location: Rhône Alpes FRANCE

Re: Calibration lamp for UVEX ?

Postby Thibault N » Mon Aug 19, 2019 6:38 am

Very interesting work Olivier, thank you, looks like this solution would provide a good sampling for calibration ! Now waiting for the uvex version.

I don't know much about spectral calibration of spectroscopes in general, from what I understood from my beginner readings an afine model + eventually second order polynomial is usually enough to calibrate a spectroscope in wavelength with a good mse (However it is not clear to be what does the distribution of errors looks like).

Is there any reference paper/book about astronomical spectroscopy instrumentation / preprocessing that talks about this problem ?

Thank you in advance

Thibault

Edit: after a bit of wandering around, I found this source that looks like an interesting alternative:
https://oceanoptics.com/product/spectro ... ifications

I guess I am not the first one to mention this one, despite the price is there any other reason why it would not fit the usecase of uvex calibration ?
Thibault N
 
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Re: Calibration lamp for UVEX ?

Postby Benjamin Mauclaire » Mon Aug 26, 2019 4:30 pm

Bonjour Thibault,

Pour repondre a ta question il faut d'abord voir quelle est l'allure de la fonction reliant la position x sur le capteur et la longueur d'onde pour un reseau de diffraction. Car c'est elle que l'on va ajuster par un polynome dans nos logiciels.
Ta question, si j'ai bien comrpis, se ramene a savoir si un polynome ajuste correctement cette fonction.

Le calcul suivant, pour un montage simplifie (R, L et CCD paralleles) et f=200mm comme lentille de focalisation sur le CCD, donne cette fonction x=f(lambda), x=position en mm des longueurs d'onde sur le CCD :

Image

Ensuite tracons cette fonction :

- Pour le reseau 150 t/mm en incidence normale (i=0°) :

Image

- Pour le reseau 150 t/mm en incidence compatible avec la taille de nos CCD (i=10°) :

Image

- Pour le reseau 2400 t/mm en incidence compatible avec la taille de nos CCD (i=40°) :

Image

On constate que la fonction a une forme courbe simple.
Le choix d'un polynome est donc un bon moyen pour ajuster la dispersion de la lumière sur le CCD et obtenir une loi de calbiration.

L'erreur d'ajsutement peut s'obtenir en mesurant pour plusieures raies les differences Observe-Calcule (O-C) et une "moyenne" s'obtient par un calcul de RMS : RMS=1/N*somme(O-C)^2.
Le nuage de points formes par les residus O-C entoure la courbe formee par le polynome.

Benjamin
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