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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 381 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 352 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.