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Fiber optic use for spectroscopy.

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#1 Jack160219

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Posted 30 May 2020 - 11:35 AM

I’m building a spectroscope with lens and 1200 l/mm grating ,using the transpec excel layout but want to use a fiber link to my scope. I have an continuously adjustable slit. It is an f6 setup. Does anyone have any suggestions about the best fiber optic to use and best connections? Thanks john



#2 lee14

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Posted 30 May 2020 - 12:55 PM

There's a description of fiber optic types for spectroscopy here that you may find useful:

 

https://arxiv.org/pdf/1704.01274.pdf

 

Lee


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#3 robin_astro

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Posted 31 May 2020 - 07:08 PM

A  grating with 1200 l/mm will give a very high dispersion angle and transmission gratings this fine are not very efficient. What design are you proposing that only uses one lens ? (normally 2 are needed collimator and objective)

 

Here is a suitable fibre

https://www.shelyak....r-50µm/?lang=en

 

I don't want to put you off using a fibre but building a fibre feed is tough compared with a telescope mounted slit spectrograph. Both types need a guider module of some sort, (something many home builders forget). Typically a guider with a mirror slit is used with telescope mounted spectrographs and mirror slits are now available for home builders but fibre feed guiders are difficult to home build and are expensive to buy eg

https://www.shelyak....n-unit/?lang=en

 

 

Cheers

Robin


Edited by robin_astro, 31 May 2020 - 07:13 PM.


#4 robin_astro

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Posted 31 May 2020 - 07:19 PM

If you do decide to go ahead with a fibre feed though, this work by the Pro Am CAOS group has useful information on fibres for home builders

https://spectroscopy...ess.com/fibres/

 

Cheers

Robin



#5 gregj888

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Posted 04 June 2020 - 05:30 PM

Jack,  I'll second the link to the CAOS group, they have a lot of good information and some good designs.  Their reflective guide head is pretty much the go to setup.

 

This is a paper from 2002 that pretty well lays it out with a lot of discussion about FRD which is the killer for most in this application.  The other is fiber selection, also discussed.  Fiber selection , mounting and handling are a big  deal!

 

https://www.jstor.or...fo_tab_contents

 

There are new fibers all the time so worth checking the vendors sites.  This one is a few years old but more current than the Harvard paper-

https://www.molex.co...py_Jun_2008.pdf

 

Watch the fiber size vs the seeing disk.  IMHO fiber is a better fit for larger scopes say 14 or 16" and larger.  50um is generally the smallest used with some throughput concerns if smaller.  I have 100 um for my 20" but it's still under construction so no data.  I printed and LowSpec for my 8" SCT to so I can get in the game and learn the SW side.



#6 KLWalsh

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Posted 16 June 2020 - 09:48 PM

In my day job as an optics engineer for a small electronics company, I had to build a spectroradiometer for testing LEDs, filters, etc.
I bought optical fibers and spectroscopes from OceanOptics (now OceanView) in Largo, FL. I made it work using an old Orion flip mirror, a Meade eyepiece, an old Minolta SLR lens, and some other lab equipment I bought.
You might contact OceanView and see if they have any samples/seconds/returned fibers they would sell you cheap.

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Edited by KLWalsh, 16 June 2020 - 09:49 PM.

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#7 gregj888

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Posted 17 June 2020 - 03:43 PM

KL, your LEDs don't move much. 

 

On the telescope use a plate beam splitter in place of the mirror  so you can see the guide star.   If you swap the fiber and eyepiece so the fiber is on the through path a microscope slide cover can work as a beam splitter if not going too faint.

 

I think the CAOS group mentions this too, not my original idea.


Edited by gregj888, 17 June 2020 - 07:42 PM.


#8 KLWalsh

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Posted 17 June 2020 - 04:52 PM

KL, you LEDs don't move much.

On the telescope use a plate beam splitter in place of the mirror so you can see the guide star. If you swap the fiber and eyepiece so the fiber is on the through path a microscope slide cover can work as a beam splitter if not going too faint.

I think the CAOS group mentions this too, not my original idea.


No, that’s true. The LEDs don’t move much. The little buggers are soldered onto a pwb and then screwed into an aluminum housing. They only move when I TELL them to move!
😀
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