POLARIMETER DEVICE PROJECT

[Joan Guarro Flo]

Hello,

In this picture, you can see a comparison of a polarimeter design and The-Maid polarimeter, also some prices of their optical components.

Regards, J. Guarro.

[Martin Dubs]

Hi Joan,

I have followed your polarimeter project with great interest. Looking at your newest Project, Maid, I noticed that you position the HWR after the slit. I do not think that this a good idea. According to vector theory of diffraction, a slit produces some amount of polarization (similar to the polarization effect of a linear grating or a wire grid polarizer). I could not estimate the size of the effect, my books on diffraction theory only give results for one polarization, so I do not know if this is a serious problem. However I strongly recommend to place the slit aftrer the halfwave plate, in order to eliminate possible effects of the slit polarization.

Clear skies,

Martin

[Joan Guarro Flo]

Hallo Martin,

Many thanks for your advice! I have just modified the drawing after reading your feedback.

The-Maid aim is try to get a range from 3700 to 8500 Angstroms, instead of the 4200 to 7550 The-Giver ones, and Thorlabs' AHWP10M-580 is an adequate Half-wave retarder, really the only one that I know.

A question for you, The-Giver has the Half-wave polymer retarder before the Alan Gee II Telekompresor, following the suggestions that Gary Cole gave
me during its design. Now, due to in fact an issue size, I put the Alan Gee II first in The-Maid drawing. What consequences do you think it would have?

Many thanks again, Joan.

[Joan Guarro Flo]

Hello,

Spectropolarimetry can show different particularities of every star throughout this wavelength range.
You can notice in Gam Cas the replicated H spectrum lines, also H Gamma, that don't appear in this
spectrum. Gam Cas polarization is rising from IR to UV.

This phenomenon is more evident in star Shelyak.

On the other hand, Pi Aqr doesn't have its H Alpha replicated.

It seems that all works well in The-Giver spectropolarimeter, as one can see in the standard non-polarized star Bet Cas.
Making tests from time to time is necessary.

Regards, J. Guarro.

[Joan Guarro Flo]

Hello,
Gerardo Ávila studied The-Maid design and found that the aspheric achromatic lens is not useful as a lens camera objective,as you can see in this image.  He proposes a photographic  100mm focal objective, but it requires changing the 600 l/mm  grating for another 300 one.

This has modified not only The-Maid's design if not that it has an incidence in its budget.

The-Giver L-R Spectropolarimeter is using a Nikon Noct 58mm f/1.2, the same as you can see in the SPOL
scheme. The alternative of a Nikon 105mm f/2.8 with a 300 l/mm grating could be a really good solution.

Regards, J.Guarro.

[Joan Guarro Flo]

Hello at all,

These are some of the last The-Giver L-R Spectropolarimeter.

These kind of observations give surprises sometimes similar as you can see in Saturn graphics.

The current and main difficulty is find some analyst that wants to work with them, give time to time...

Best regars, J. Guarro.

[Joan Guarro Flo]

Hello,

One more affordable solution is transforming one DADOS spectrograph into a spectropolarimeter.

Gerardo Ávila, a Caos, (Chaos) Group member who designed the DADOS, ( DICE ) spectrograph,
and also a former optical ESO engineer, recommended that I keep the original collimator lens, as you
can see in the last image.

The new mechanical parts don't have an insurmountable obstacle. Of course, it would be to solve some small
details, and the same as other options, it lacks a little electronic card, its software, and the reduction software
for the observations.

I'm sure that these last issues could be solved by Toni Jove supplying the same that I use with The-Giver.

Cheers, Joan.

[Joan Guarro Flo]

Hello,

As a complementary explanation, I want to express these points that can help you understand a bit better some
spectropolarimeter aspects.

In The-Giver, the unique optical element that turns is the Half-wave Achromatic Retarder, see my message from October 11.
It turns from 0º position and stops every 22.5º, where you can take a series of images, when it arrives at the 4th position,
that is, 67.5º, and after you take the series 4th, the observation is finished.

Of course, one can continue observing 90º, 112.5º, 135º, 157.5º, and more, but all of them will overlap. So, 0º= 90º, 22.5º=112.5º,
45º= 135º and 67.5º= 157.5º. In fact, currently I observe my targets until the 157.5º, with the sense of collecting more signal levels.

Q and U come from the Ordinary and Extraordinary Beams, and the software uses them to find the Polarization % and
the Theta Angle. They are separated by the Wollaston Prism.

To know if a spectrometer works well, there are lists of Standard Polarized and Non-polarized Stars, one of them is
the star Phi Cas that you can see in the first and second graphics.

Then come graphics with surprising and amazing results, that is the advantage of a spectropolarimeter over
a polarimeter.

A spectropolarimeter shows every point result, instead of a polarimeter that only shows the average of a long filter
region, hiding a lot of information and details.

Regards, J. Guarro.