Fibre feed question

As an antidote to the long, normally cloudy, Scottish winter nights I built
a Czerny Turner Spectroscope loosely based on Dale Mais' design in
'Practical Amateur Spectroscopy.



Using an 1800 lpmm grating , resolution is less than an Angstrom in the
orange. Everything went fine until I came to the fibre optic delivery system
when, using the design guidance in PAS, I simply placed the fibre (Ocean
Optics, na about 0.2, 400um fibre with a Y for calibration) next to the
slit.



I was prepared for the inefficiency of this arrangement but not the
horrendous distortion which appeared - the slit was simply not focusable.
Opening the slit allowed me to refocus on the fibre itself but that really
reduces the resolution.



With the help of some modelling software (OpticsLab) I suspect that this
may be related to poor matching of the fibre - slit - collimator mirror
arrangement and I eventually solved the problem with an Ocean Optics fibre
collimator lens



However, while this removed the distortion it is even less efficient (the
collimated beam is about 3mm in diameter) and it merges the image of my two
fibres (one for measurement the other for calibration).



Looking on the web I see a wide variety of possibilities, some quite complex
(and presumably lossy) while others look like the original design in PAS.



I wondered if anyone in the group has any experience building and using
conditioning and delivery optics for a fibre feed spectroscope?



Many Thanks



Iain

"Iain Mackay" no_one@here wrote in message
...


As an antidote to the long, normally cloudy, Scottish winter nights I
built
a Czerny Turner Spectroscope loosely based on Dale Mais' design in
'Practical Amateur Spectroscopy.

SNIP

Hi Ian,

Dale Mais can sometimes be found on the amateur spectroscopy group
http://groups.yahoo.com/group/amateur_spectroscopy/

Robin
----------------------------------------------------------------------------
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Robin Leadbeater
54.75N 3.24W
http://www.leadbeaterhome.fsnet.co.uk/astro.htm
----------------------------------------------------------------------------
-

Originally Posted by Iain Mackay

As an antidote to the long, normally cloudy, Scottish winter nights I built
a Czerny Turner Spectroscope loosely based on Dale Mais' design in
'Practical Amateur Spectroscopy.
Iain

Sounds an interesting project Iain - do you have photo and an application ?

Nytecam

Maurice

I have in mind some planetary spectroscopy (hence the resolution), possibly
Titan If I can coax my old C14 back into life.
As a start, just to see how the device performs, I'll probably do the old
rotational velocity experiment using the D lines on the E-W solar limbs.
Further down the line I may have a look at the Mid IR (my day job involves
working in that region of the spectrum, so a sensor may be available). Have
to look at new gratings though.

I'll post a photo / link once I've sorted out these last bugs with the feed.

Incidentally, did you ever pursue commercializing your own compact hi res
spectroscope - you mentioned the possibility a few years ago when we last
spoke?

All the best

Iain

Robin
Thanks for that. I'll resurect my Yahoo account and repost there.

Hi Iain,

i dont know if you have looked at this site or not, but i had it buried
in my bookmarks:
http://www.physics.usyd.edu.au/~kelz/steffi/steffi.html

Fibre feed spectrograph for C14. Some quite detailed design documents
too.

Cheers, Callum

Callum
Thanks for that. I had seen this and it seems to be one of the designs that
simply use the fibre as the slit. For my instrument that means giving away
too much resolution (because of the thickness of the fibre).
Thanks

Iain

Originally Posted by

Maurice

I have in mind some planetary spectroscopy (hence the resolution), possibly
Titan If I can coax my old C14 back into life.
As a start, just to see how the device performs, I'll probably do the old
rotational velocity experiment using the D lines on the E-W solar limbs.
Further down the line I may have a look at the Mid IR (my day job involves
working in that region of the spectrum, so a sensor may be available). Have
to look at new gratings though.

I'll post a photo / link once I've sorted out these last bugs with the feed.
***************************
That sound good Iain - the beauty slit/ fibreoptic feed spectroscopy aligned in RA, small scope miss tracks still record data.
***************************
Incidentally, did you ever pursue commercializing your own compact hi res
spectroscope - you mentioned the possibility a few years ago when we last
spoke?
*******************************
Maybe three years back Starlight Xpress were talking of say 100 units which I said was wholly unrealistic for the amateur market. Terry Platt raised it again with me as London Astrofest. His image-shift system [rocking glass plate] has a pickoff prism for the autoguider essentially identical to my WPO Littrow spectrograph and he will reinvestigate the possibilities and maybe make a mockup. Essentially he has all the components to hand except off-the-shelf grating and imaging [camera] lens.
*******************************

All the best Iain

Been rethinking your defocus problem. If I recall the SBIG SGS CzT is an Ebert arrangement http://home.freeuk.com/m.gavin/ebert.htm with two extra flats to align the input-output beams to a common axis. The slit is imaged full size onto the detector [just like the Littrow]. Are you confident these two beams are of equal length? If not light projected onto the grating will not be parallel and the image scale at slit and detector will be of dissimilar scale.

I have a Sivo fibreoptic feed spectrograph http://www.astroman.fsnet.co.uk/sivo.htm and frankly the throughput and resolution was initially very poor where the 30[?] stacked fibres form a virtual slit and where the collimator and image [camera] lens were of similar focal length the result was gross oversampling. I suggested incorporating a barlow between virtual slit and collimator [eg doubling its focal length] so slit image onto detector half size and so much sharper - see footnote to about 'review'. Reimaging may be the route with fibreoptics to improve resolution but does little to help throughput with those horrendous numeric[?] apertures.

best regards

Nytecam

Maurice
Thanks for that.
However, I think the observation that I can image a nice sharp slit (when
illuminated with a collimated fibre) *or* a reasonable 'spot' when using a
raw fibre possibly exonerates any path lengths issues. Incidently, my
earlier comments about Optics Lab confirming the problem were probably a red
herring (poor definition of source in the model) .

I'll repost this question to the Yahoo spectroscopy group that Robin L
mentioned and possibly the optics ng and see if any one there has come up
against the issue.

Since my posting I've been also looking at a few more devices on the web
and the vast majority seem to use a raw fibre (no slit) but this really
canes the resolution. The one exception that I've seen is the commercial
Ocean Optics USB device - I have a couple of them here - which uses both
slit and a fibre feed so it clearly *can* be done, but doesn't for some
reason seem very popular (maybe I'm finding out why...).

Iain


"nytecam" wrote in message
...

Wrote:
Maurice

I have in mind some planetary spectroscopy (hence the resolution),
possibly
Titan If I can coax my old C14 back into life.
As a start, just to see how the device performs, I'll probably do the
old
rotational velocity experiment using the D lines on the E-W solar
limbs.
Further down the line I may have a look at the Mid IR (my day job
involves
working in that region of the spectrum, so a sensor may be available).
Have
to look at new gratings though.

I'll post a photo / link once I've sorted out these last bugs with the
feed.
***************************
That sound good Iain - the beauty slit/ fibreoptic feed spectroscopy
aligned in RA, small scope miss tracks still record data.
***************************
Incidentally, did you ever pursue commercializing your own compact hi
res
spectroscope - you mentioned the possibility a few years ago when we
last
spoke?
*******************************
Maybe three years back Starlight Xpress were talking of say 100 units
which I said was wholly unrealistic for the amateur market. Terry
Platt raised it again with me as London Astrofest. His image-shift
system [rocking glass plate] has a pickoff prism for the autoguider
essentially identical to my WPO Littrow spectrograph and he will
reinvestigate the possibilities and maybe make a mockup. Essentially
he has all the components to hand except off-the-shelf grating and
imaging [camera] lens.
*******************************

All the best Iain

Been rethinking your defocus problem. If I recall the SBIG SGS CzT is
an Ebert arrangement http://home.freeuk.com/m.gavin/ebert.htm with two
extra flats to align the input-output beams to a common axis. The slit
is imaged full size onto the detector [just like the Littrow]. Are you
confident these two beams are of equal length? If not light projected
onto the grating will not be parallel and the image scale at slit and
detector will be of dissimilar scale.

I have a Sivo fibreoptic feed spectrograph
http://www.astroman.fsnet.co.uk/sivo.htm and frankly the throughput and
resolution was initially very poor where the 30[?] stacked fibres form a
virtual slit and where the collimator and image [camera] lens were of
similar focal length the result was gross oversampling. I suggested
incorporating a barlow between virtual slit and collimator [eg doubling
its focal length] so slit image onto detector half size and so much
sharper - see footnote to about 'review'. Reimaging may be the route
with fibreoptics to improve resolution but does little to help
throughput with those horrendous numeric[?] apertures.

best regards

Nytecam


--
nytecam

[quote=Iain Mackay]

Maurice
I have a couple of them here - which uses both slit and a fibre feed so it clearly *can* be done, but doesn't for some reason seem very popular (maybe I'm finding out why...).

Iain

Good luck in your quest and keep us posted. I'm sure it can be done efficiently. Appreciating the Sivo fibreoptic spectrograph on my 30cm SCT was an early model - the 20 min exposure to record a blurred emission spectrum of beta Lyr spoke volumes about throughput.

Nytecam