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aacc66
member


Reged: 03/28/13

Using Fourier Transform IR (FTIR) spectormeters
      #6118989 - 10/05/13 12:41 PM

I am looking for some one that had used a Fourier Transform IR (FTIR) with a telescope. I am trying to figure how would you do it given that there is not a good source for the background measurement. Usually with experiments with an FTIR down in earth you use a black body source with a similar temperatures to your target for the background measurement, but with a star I am not sure what would be a good source for this part of the measurement.

Any suggestions will be appreciated.

Alvaro


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llanitedave
Humble Megalomaniac
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Reged: 09/26/05

Loc: Amargosa Valley, NV, USA
Re: Using Fourier Transform IR (FTIR) spectormeters new [Re: aacc66]
      #6119223 - 10/05/13 03:49 PM

Aren't there standard calibration stars such as Vega?

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dickbill
scholastic sledgehammer


Reged: 09/30/08

Re: Using Fourier Transform IR (FTIR) spectormeters new [Re: llanitedave]
      #6120300 - 10/06/13 10:01 AM

You may ask on this spectro forum

http://www.spectro-aras.com/forum/index.php?sid=2880d7d29885acd6ea9098875a7cc4b9


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kw6562
Authoritative Ignoramus
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Reged: 06/25/08

Loc: MA
Re: Using Fourier Transform IR (FTIR) spectormeters new [Re: aacc66]
      #6120901 - 10/06/13 04:26 PM

Hi Alvaro - I haven't used FTIR with a telescope, but I have used it at work for determining film composition and silicon thickness. Usually the frequency range is 400 to 4000 cm-1, which corresponds to a wavelength range of 25 to 2.5um. I don't know if standard optics would transmit well at those wavelengths, and moisture in the atmosphere would be a big problem also. I probably don't understand your setup so maybe those issues are irrelevant; I'm just curious about what you are trying to do. Clear skies --Keith

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aacc66
member


Reged: 03/28/13

Re: Using Fourier Transform IR (FTIR) spectormeters new [Re: llanitedave]
      #6126183 - 10/09/13 12:24 AM

Well, after my posting I went and did some reading and I realized, that the background for a star will be a black body with the same temperature as the one of the star. Vega or any other star would not be ok, as each one will have their own spectra that will make them act as a non black body. Any way after reading, for these cases, or any case where you cannot get a black body source, you have to simulate it as close as possible as you can get it and then do your background subtraction yourself. The FTIR is most cases, does the work for you, but not for extreme cases like these ones.

However, the idea of using the FTIR have some failures, grave ones. Glass becomes opaque at 3.39 microns, so FTIR is of not use with my SCT. Maybe with a Newtonian.

regards,

Alvaro


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aacc66
member


Reged: 03/28/13

Re: Using Fourier Transform IR (FTIR) spectormeters new [Re: dickbill]
      #6126193 - 10/09/13 12:30 AM

yes, thank you for the link.

Alvaro


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aacc66
member


Reged: 03/28/13

Re: Using Fourier Transform IR (FTIR) spectormeters new [Re: kw6562]
      #6126202 - 10/09/13 12:37 AM

You are correct about the optics not transmitting in the IR. Usually fused silica (glass) will not transmit beyond 3.39 micrometers, and my telescope is an SCT, which I assume has fused silica, or maybe BK7 (it does not help there either) as the corrector glass. I don't know what I was thinking when I posted the problem.

Now, I do know there are some spectrometers in the visible and they are quite compact, from ocean optics that connect through a fiber, so that leaves the question: is there some kind of concocted eyepiece that couples to a fiber, instead of having lenses? Just musing right now.

Alvaro


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dsnope
Carpal Tunnel


Reged: 04/28/06

Loc: OC California
Re: Using Fourier Transform IR (FTIR) spectormeters new [Re: aacc66]
      #6132416 - 10/12/13 02:46 AM

I've used 2D FFT convolutions for matched filters to find dark asteroids against a dark background. For both IR and Vis CCD sensors. Assuming the background is gaussian noise, spacially and temporally, it will not pass much energy through a smooth background filter template.

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