NEW direction in the solar narrowband imaging.

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Valery
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NEW direction in the solar narrowband imaging.

Post by Valery » Sat Jun 23, 2018 6:08 am

TheSkyBurner wrote:
Thu Jun 21, 2018 5:08 pm
Valeryy, i just asked your question about the 854.2 filter , you are looking at a cost of $3500 to prototype it for two 27mm filters and the process to make them currently has a low yield with low success rate. So they are pretty rare to make exactly where you want them and have to be sorted out very carefully after something called annealing.

“The filters are always offband deeply blue winged, and they have to be baked at 200+ celcius for several weeks to raise the red wing. It must be analyzed very regularly during the annealing process and this is the hard part”
These $3500 are indeed a good price for two samples of such a filter. But...

1. What the bandwidth of these filters?
2. What the transmission curve profile? What the finesse?
3. What the transmission at the CWL?
4. What the uniformity (CWL and transmission) accross the filter aperture they can warrant ?
5. What the temperature stability of the CWL and bandwidth? If the stability is low, how can the temperature be maintained?

Without knowing these data it is quite risky to get a filter which will simply don't work.

Can you clarify what they can really offer? I believe that if the answers will be positive and such a filters can really work, especially in a Skybender tilt cell, many users can order such a working system.
854,21nm line shows real H-a like structures mixtured with a supergranulation of Ca-K - like. Overall is more impressive than H-a.


What do you, solar imagers think about such possible new direction in the solar narrowband imaging?
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Ca II IR vs H-a.jpg
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Re: NEW direction in the solar narrowband imaging.

Post by marktownley » Sat Jun 23, 2018 6:16 am

Would be good if it is feasible.
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Re: NEW direction in the solar narrowband imaging.

Post by Valery » Sat Jun 23, 2018 8:05 am

TheSkyBurner wrote:
Sat Jun 23, 2018 6:29 am

There is currently no industrial standardized process for these ultra narrow band wavelengths and it is the first time it has been attempted in 30 years of business.
This is not true at all. I have received two filters at 6568A with 0.8A FWHM and steep sides. They are not expensive.

I also can order 1.5A FWHM with transmission >55% any time I wish in any quantity. This is for 854, or 656 or 430nm - all according specs I give them.

The question is that to see filamentary structures, spiculaes, prominences etc the filter at 8542.1A must have not wider than 0,5A bandwidth and better if this will be a double stack of 0,7A ones.

Finally, I believe that if we can create a pool, we can order etalons for this wave length with about 0,6A. May be Lunt can do this with 35mm size Pressure Tuning etalons?


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Re: NEW direction in the solar narrowband imaging.

Post by marktownley » Sat Jun 23, 2018 8:51 am

Where are the comparison images from Valery?
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Re: NEW direction in the solar narrowband imaging.

Post by Valery » Sat Jun 23, 2018 9:05 am

marktownley wrote:
Sat Jun 23, 2018 8:51 am
Where are the comparison images from Valery?
I don't remember the exact article or website link. But this is from the IBIS imaging spectrograph.

Google Ca I 854nm IBIS and you will see a lot of pictures at 854nm/
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IBIS  scan in pikometers (0,01A) 2.gif
IBIS scan in pikometers (0,01A) 2.gif (1.28 MiB) Viewed 1681 times
_Ca-II-I-854nm-spicules_nso_big.jpg
_Ca-II-I-854nm-spicules_nso_big.jpg (493.49 KiB) Viewed 1681 times
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Re: NEW direction in the solar narrowband imaging.

Post by marktownley » Sat Jun 23, 2018 9:28 am

Thanks Valery
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Re: NEW direction in the solar narrowband imaging.

Post by Valery » Sat Jun 23, 2018 1:52 pm

TheSkyBurner wrote:
Sat Jun 23, 2018 9:36 am
Has anyone considered trying an h-alpha etalon without the red filter and replacing the spacers to change the reflectivity and blocking filter with a calcium filter? If we had a complete spectrum prof ile of a pst etalon it maybe way cheap to have the spacers remade for a different airspace to change the reflected interference and ouput.
The etalon plates theirselves are not that expensive. The problem is a proper coatings for this wave length. And the spacers.


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Re: NEW direction in the solar narrowband imaging.

Post by MalVeauX » Sat Jun 23, 2018 4:51 pm

If 854.2 were available and affordable, I would totally go for it. The longer wavelength has better seeing potential with our atmosphere, so it would be great for high resolution imaging. Showing all the features would be excellent. I'm curious why this doesn't already exist in a popular marketed form from one of the big distributors out there that specialize in solar imaging equipment.

Very best,

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Re: NEW direction in the solar narrowband imaging.

Post by Valery » Tue Jun 26, 2018 2:16 am

MalVeauX wrote:
Sat Jun 23, 2018 4:51 pm
If 854.2 were available and affordable, I would totally go for it. The longer wavelength has better seeing potential with our atmosphere, so it would be great for high resolution imaging. Showing all the features would be excellent. I'm curious why this doesn't already exist in a popular marketed form from one of the big distributors out there that specialize in solar imaging equipment.

Very best,
Tell this to Jen Winter of DayStar. She readily introduced two almost useless Quarks (Sodium and Margenisum) instead of really intresting CaII I at 8542.1A !
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Re: NEW direction in the solar narrowband imaging.

Post by MalVeauX » Wed Jun 27, 2018 1:24 pm

Valery wrote:
Tue Jun 26, 2018 2:16 am


Tell this to Jen Winter of DayStar. She readily introduced two almost useless Quarks (Sodium and Margenisum) instead of really intresting CaII I at 8542.1A !
I do agree... I'm puzzled why anyone would want a Quark (for cost) for Sodium & Magnesium. :cry:

I'm curious why 854.2 isn't showing up with the big companies at all. Especially during a minimum when sales likely drop.

Very best,

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Re: NEW direction in the solar narrowband imaging.

Post by Valery » Wed Jun 27, 2018 2:33 pm

TheSkyBurner wrote:
Tue Jun 26, 2018 6:51 am
service@daystarfilters.com they will gladly make it for you. 5 angstroms at $5000
I can get 1,5A filter within 2K. But this makes no difference with 393nm. To see fibrils and other H-a like
features one need at least 0,5A - as double stacked of 0,7A etalons.
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Re: NEW direction in the solar narrowband imaging.

Post by christian viladrich » Wed Jun 27, 2018 7:09 pm

Skyburnner ... don't forget to read the paper you gave a link to :
https://www.aanda.org/articles/aa/full/ ... 82-06.html

The images you are showing are "numerically synthesized from a 3D solar magneto-convection simulation".

There are not actual images ;-)

An important point is missed in the discussion : the angular size of the fibrils. Just make the calculation ;-)
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Re: NEW direction in the solar narrowband imaging.

Post by christian viladrich » Wed Jun 27, 2018 7:54 pm

Please take 5 min to read the paper, these are simulations :

Image

Reading the caption just takes 30 s :-)

Figure 3 shows the computed synthetic intensity images ordered in wavelength from top to bottom.

Figure 3: Synthetic images for different spectral diagnostics identified per row at the right. The CN-band and G-band images are taken from Uitenbroek & Tritschler (2006). All images are grey-scaled to maximum display contrast. The rms intensity variation of the granulation (upper number) and the mean intensity excess of the bright points over the granulation (lower number) is indicated in each upper-left corner. Left: no spatial smearing. Middle: smeared with an Airy function corresponding to 1-m aperture. Right: image constructed by subtracting a scaled synthetic continuum image from the one in the center column.

BTW, the Ca 854.2, Ha and Hb synthetic images are on the wings of the lines in order to show photospheric details (the paper is on the detection on bright intergranular magnetic spots).
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Re: NEW direction in the solar narrowband imaging.

Post by Merlin66 » Thu Jun 28, 2018 12:21 am

A good SHG with large aperture and a good pixel/ chip sized camera would probably give you the results you're looking for.
The attached spreadsheet shows with a 900mm spectrograph and an 1200 grating an R>50000 could be achieved.
Theoretical bandwidth at 8542A around 0.09A; seeing at 2 arcsec would probably reduce this to 0.16A

Obviously increasing the grating l/mm to say 2400 l/mm would seem like a possible route to increased resolution, BUT the size of the grating (60 x 250mm!) and the required angle of incidence prevent this being used.
I think a 1800 l/mm (60 x 94mm if available?) could be made to work to give a R>100000 and a theoretical bandwidth of 0.05A

Bearing in mind as the bandwidth decreases, you need more and more aperture. Also you need a red sort filter when working above >7500A to suppress the 2nd order blue spectrum.
SimSpec SHG.xls
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Re: NEW direction in the solar narrowband imaging.

Post by Valery » Thu Jun 28, 2018 9:47 am

christian viladrich wrote:
Wed Jun 27, 2018 7:09 pm

An important point is missed in the discussion : the angular size of the fibrils. Just make the calculation ;-)
They are about the same as in H-a. See here http://www.arcetri.astro.it/science/solare/IBIS/

About a year ago I have communicated in length with Gianna Cauzzi (leading IBIS scientist) and she told me that fubrils in CaII I will be seen if we have 0,25A or better 0,2A bandwidth. With somewhat lower contrast they will be seen with 0,5A filter. But the best will be a double stacked 0,7 or 0,6A filters.

I see that Mark Wagner and Jen Winter are not willing to dive in this adventure with a new imaging filter.
May be there is a sense to ask Andy Lunt to make a small series of air-spaced and PT etalons for this wave length.
Should not be too expensive if we can create a pool of 10-12 customers.


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Last edited by Valery on Thu Jun 28, 2018 6:35 pm, edited 1 time in total.
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Re: NEW direction in the solar narrowband imaging.

Post by Spectral Joe » Thu Jun 28, 2018 3:54 pm

As has been pointed out, the 8542 line is similar in width to H alpha, unlike the UV CaII lines. Thus, bandpass requirements for an imaging system at this wavelength are similar to that at H alpha. The reflectivity of the coatings on the etalon plates is a major factor in determining the finesse of the etalon, the reflectivity needs to be high, higher than 90% and typically around 95%. For this, specialized multilayer coatings are used. It would be a fantastic coincidence if the coatings on a PST etalon had reflectivity that high at a wavelength far removed from the design wavelength. A purpose built etalon is needed if a non dispersive approach is the plan.
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Re: NEW direction in the solar narrowband imaging.

Post by Valery » Thu Jun 28, 2018 6:34 pm

Spectral Joe wrote:
Thu Jun 28, 2018 3:54 pm
As has been pointed out, the 8542 line is similar in width to H alpha, unlike the UV CaII lines. Thus, bandpass requirements for an imaging system at this wavelength are similar to that at H alpha. The reflectivity of the coatings on the etalon plates is a major factor in determining the finesse of the etalon, the reflectivity needs to be high, higher than 90% and typically around 95%. For this, specialized multilayer coatings are used. It would be a fantastic coincidence if the coatings on a PST etalon had reflectivity that high at a wavelength far removed from the design wavelength. A purpose built etalon is needed if a non dispersive approach is the plan.
This is a first prohibiting factor. The second one is that if we can use the spacers from, say, LUNT LS35 or LS50 etalon, make new plates (not a problem at all) with special coating for 854nm (not a problem too) - it will be needed a very high or very low pressure (depends of spacers actual thickness) in the etalon vacuum chamber to come to the 8542,1A core.
Last edited by Valery on Fri Jun 29, 2018 5:25 am, edited 1 time in total.
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Re: NEW direction in the solar narrowband imaging.

Post by christian viladrich » Thu Jun 28, 2018 6:57 pm

Does anybody with a spectrograph can have a look at the transmission spikes of a Coronado etalon around 854 nm ?
It would be a marvellous coincidence if a transmision peak was right at 854.2 nm.
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Re: NEW direction in the solar narrowband imaging.

Post by Merlin66 » Fri Jun 29, 2018 12:40 am

Christian,
I have access to a SM60 external etalon and a PST etalon and a hi-res Littrow spectrograph (R=10000).
I have previously looked at the transmission peaks but not in detail or at the nominated wavelength.
Let me see what I can do.
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Re: NEW direction in the solar narrowband imaging.

Post by Valery » Fri Jun 29, 2018 5:29 am

Merlin66 wrote:
Fri Jun 29, 2018 12:40 am
Christian,
I have access to a SM60 external etalon and a PST etalon and a hi-res Littrow spectrograph (R=10000).
I have previously looked at the transmission peaks but not in detail or at the nominated wavelength.
Let me see what I can do.
Ken
Hi Ken,

Looking for good news! Keep fingers crossed.


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Re: NEW direction in the solar narrowband imaging.

Post by Montana » Fri Jun 29, 2018 7:08 am

Might be worth asking the new owner of Solarscope about the etalons, he seems very keen about any new ideas :)

Alexandra

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Re: NEW direction in the solar narrowband imaging.

Post by marktownley » Fri Jun 29, 2018 7:43 pm

Montana wrote:
Fri Jun 29, 2018 7:08 am
he seems very keen about any new ideas :)
More elaboration required!
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Re: NEW direction in the solar narrowband imaging.

Post by Merlin66 » Sat Jun 30, 2018 1:24 am

Looking at the solar spectrum map....
There seems to be an interesting CaII line at 8498.1A as well as the large shallow CaII 8542.2A.
If I ever see the Sun again I'll see how the etalons perform out in the NIR.
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Re: NEW direction in the solar narrowband imaging.

Post by Valery » Sat Jun 30, 2018 2:41 am

Merlin66 wrote:
Sat Jun 30, 2018 1:24 am
Looking at the solar spectrum map....
There seems to be an interesting CaII line at 8498.1A as well as the large shallow CaII 8542.2A.
If I ever see the Sun again I'll see how the etalons perform out in the NIR.
Thanks, Ken, for the info. Can you, please, tell us how much less or more strong (wide, intensity) this line vs 8542,1A one?


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Re: NEW direction in the solar narrowband imaging.

Post by Merlin66 » Sat Jun 30, 2018 2:57 am

Valery,
The attached screen from BASS2000 shows both lines.....
CaII_NIR.JPG
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