SolarChat!

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?

Would be good if it is feasible.

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?


Valery

Where are the comparison images from Valery?

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/

Thanks Valery

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.


Valery

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,

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 !

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.

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,

TheSkyBurner wrote: ↑Tue Jun 26, 2018 6:51 am [email protected] 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.

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 ;-)

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



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).

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.

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.


Valery

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.

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.

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.

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

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.


Valery

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

Alexandra

Montana wrote: ↑Fri Jun 29, 2018 7:08 am he seems very keen about any new ideas

More elaboration required!

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.

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?


Valery

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

I've seen the etalon bands all the way down to the UV, but never paid attention to the NIR, I expect to see them all the way.
How close is one band to the required CWL I think will be the issue.
(OK, found an old spectrum of a PST etalon - low resolution and not focused for the NIR but the wavelength coverage is out to the >9000A.
This was taken with a Canon 1000D Fully modded. You can clearly see the etalon "comb" band passes. The broad absorption is the Telluric band(s) the prominent one at 7620A. You can see some absorption bands in the NIR but I need to do some calibration to define them.
Hopefully this at least shows the etalon does cove the NIR region.)

Looking more closely at the Liege solar atlas, it appears we have the double CaII lines in the NIR - 8542A and 8662A.
I've done a rough calibration on the PST spectrum to show these lines.......

Merlin66 wrote: ↑Sun Jul 01, 2018 12:51 am Looking more closely at the Liege solar atlas, it appears we have the double CaII lines in the NIR - 8542A and 8662A.
I've done a rough calibration on the PST spectrum to show these lines.......

Ken,

Can you, please, tell us does the PST etalon has enough transmission at 8542,1A ?
Or it is worthless to consider it as a ready etalon for this line?


Valery

Valery,
I’ll see what I can do.
An exposure of the NIR same camera, same exposure, with and without the etalon will be influenced by the etalon comb......let me think about it.

Well i've just tried stacking my pst etalon on the Na Quark and made no improvement to anything with a dimmer image.

Guys,
Unless you can analyse the etalon comb/ CWL's in the "new" target wavelength - it's just a guess.....

I'm going to set up the spectrograph (R=10000) which should give at least 0.1A resolution and record the PST "comb" at the NIR CaII lines...if all goes well then I can try other lines......
If successful it still leaves the issue of finding a suitable blocking/ sort filter.......

Thanks Ken for your support. Looking for the results of your PST etalon measurements!

Blocking filters are not a principal problem. Just a question of some money.


Valery

Quick update - the weather has been absolutely terrible - clouds, clouds and wind, rain...repeat....
I did manage to set up the Spectra-L200 with a 1200 l/mm grating, resolution around 0.7A and get the CaK II lines focused in the NIR. Needed a red sort filter to suppress the 2nd order spectrum. Just used the bright (!!???) sky as a target. A good first step.

Then set up the SM60/ED80 without the blocking filter with the Spectra-L200 attached.....not very good....I had "issues" getting the spectrograph to sit nicely in the ED80 ( I ABSOLUTELY hate those 2" to T thread adaptors with the ""safety recess" feature - should be called un-safe feature...a royal PITA!) the SM60 resonance lines were visible around the CaKII lines (8542/8662A) but need an improved set-up to get the clarity needed for analysis. Now the set-up is ready (!) next opportunity should deliver some results.
Stay tuned.

No sun, but bright cloud (!!)
The illustration below shows the SM60 etalon bands and the CaK II absorption lines.

Not good news...
The FWHM of the bands is 7A in this region...finesse 18.7A and the tilt adjustment gives 1.2A towards the blue.

Any comment/ feedback?

That is what I though it would look like. I guested 24Ang peak separation.
Attached is a coating design for Ha. The narrower peaks will be where the transmission is the highest. As the transmission drops the HW will broaden and the bottom of the curve will not be near zero.

The graph is for a simple 1/4 wave design. The high end etalons for solar will use a broad band mirror. So they are usually from K-line to Ha or Ha to the Ca lines in the IR.
The broad band mirrors will have more layers which means a higher cost.
Mark W.