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Re: NEW direction in the solar narrowband imaging.

Posted: Sat Jun 30, 2018 6:48 am
by Merlin66
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.)
PST etalon_NIR.JPG
PST etalon_NIR.JPG (186.5 KiB) Viewed 1342 times

Re: NEW direction in the solar narrowband imaging.

Posted: Sun Jul 01, 2018 12:51 am
by Merlin66
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.......
Liege_PST etalon_NIR_Ca II.JPG
Liege_PST etalon_NIR_Ca II.JPG (188.97 KiB) Viewed 1277 times

Re: NEW direction in the solar narrowband imaging.

Posted: Sun Jul 01, 2018 3:57 am
by Valery
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

Re: NEW direction in the solar narrowband imaging.

Posted: Sun Jul 01, 2018 4:27 am
by Merlin66
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.

Re: NEW direction in the solar narrowband imaging.

Posted: Sun Jul 01, 2018 10:15 am
by marktownley
Well i've just tried stacking my pst etalon on the Na Quark and made no improvement to anything with a dimmer image.

Re: NEW direction in the solar narrowband imaging.

Posted: Tue Jul 03, 2018 1:49 am
by Merlin66
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.......

Re: NEW direction in the solar narrowband imaging.

Posted: Tue Jul 03, 2018 3:49 pm
by Valery
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

Re: NEW direction in the solar narrowband imaging.

Posted: Tue Jul 10, 2018 5:39 am
by Merlin66
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.

Re: NEW direction in the solar narrowband imaging.

Posted: Fri Jul 13, 2018 3:14 am
by Merlin66
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?
SM60ED80_CaK II.JPG
SM60ED80_CaK II.JPG (109.41 KiB) Viewed 608 times

Re: NEW direction in the solar narrowband imaging.

Posted: Sat Jul 14, 2018 1:08 am
by mdwmark
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.
etalon mirror Ha.gif
etalon mirror Ha.gif (9.62 KiB) Viewed 579 times

Re: NEW direction in the solar narrowband imaging.

Posted: Sun Jul 15, 2018 5:57 am
by mdwmark
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.