While playing with polarizing filters, I found a plastic ruler
that turns out to rotate the polarization angle of the light
passing through it by almost exactly 90 degrees. The ruler is
of a 1mm thick colourless plastic, rather flexible, clearly
not the usual polyethylene or polystyrene. It does not itself
polarize light, it just rotates it. The angle of rotation does
not seem to depend on wavelength. It's made in China.
What plastic could this be?
On 10/26/20 9:35 AM, Jeroen Belleman wrote:
While playing with polarizing filters, I found a plastic ruler that
turns out to rotate the polarization angle of the light passing
through it by almost exactly 90 degrees. The ruler is of a 1mm
thick colourless plastic, rather flexible, clearly not the usual
polyethylene or polystyrene. It does not itself polarize light, it
just rotates it. The angle of rotation does not seem to depend on
wavelength. It's made in China.
What plastic could this be?
There are quite a lot of optically-active plastics. Optical activity
is normally strongly dispersive--what wavelengths did you use?
Cheers
Phil Hobbs
On 2020-10-26 15:57, Phil Hobbs wrote:
On 10/26/20 9:35 AM, Jeroen Belleman wrote:
While playing with polarizing filters, I found a plastic ruler that
turns out to rotate the polarization angle of the light passing
through it by almost exactly 90 degrees. The ruler is of a 1mm
thick colourless plastic, rather flexible, clearly not the usual
polyethylene or polystyrene. It does not itself polarize light, it
just rotates it. The angle of rotation does not seem to depend on
wavelength. It's made in China.
What plastic could this be?
There are quite a lot of optically-active plastics. Optical activity
is normally strongly dispersive--what wavelengths did you use?
Cheers
Phil Hobbs
Just natural, white light. Some plastics show coloured fringes
when inserted between two polarizing sheets, which is sort-of
what I expected. This Chinese ruler is special: It rotates
the polarization. Inserted between two parallel polarizers, it
has four orientations spaced by 90 degrees where it blocks the
light. But it is not itself polarizing: I see no intensity
variations when looking through it with a single polarizer, nor
when superimposing multiple layers of the same plastic.
There are no colours.
On Mon, 26 Oct 2020 16:58:44 +0100, Jeroen Belleman
<jeroen@nospam.please> wrote:
On 2020-10-26 15:57, Phil Hobbs wrote:
On 10/26/20 9:35 AM, Jeroen Belleman wrote:
While playing with polarizing filters, I found a plastic ruler that
turns out to rotate the polarization angle of the light passing
through it by almost exactly 90 degrees. The ruler is of a 1mm
thick colourless plastic, rather flexible, clearly not the usual
polyethylene or polystyrene. It does not itself polarize light, it
just rotates it. The angle of rotation does not seem to depend on
wavelength. It's made in China.
What plastic could this be?
There are quite a lot of optically-active plastics. Optical activity
is normally strongly dispersive--what wavelengths did you use?
Cheers
Phil Hobbs
Just natural, white light. Some plastics show coloured fringes
when inserted between two polarizing sheets, which is sort-of
what I expected. This Chinese ruler is special: It rotates
the polarization. Inserted between two parallel polarizers, it
has four orientations spaced by 90 degrees where it blocks the
light. But it is not itself polarizing: I see no intensity
variations when looking through it with a single polarizer, nor
when superimposing multiple layers of the same plastic.
There are no colours.
It's very likely to be polystyrene.
Joe Gwinn
On Mon, 26 Oct 2020 16:58:44 +0100, Jeroen Belleman
<jeroen@nospam.please> wrote:
On 2020-10-26 15:57, Phil Hobbs wrote:
On 10/26/20 9:35 AM, Jeroen Belleman wrote:
While playing with polarizing filters, I found a plastic ruler that
turns out to rotate the polarization angle of the light passing
through it by almost exactly 90 degrees. The ruler is of a 1mm
thick colourless plastic, rather flexible, clearly not the usual
polyethylene or polystyrene. It does not itself polarize light, it
just rotates it. The angle of rotation does not seem to depend on
wavelength. It's made in China.
What plastic could this be?
There are quite a lot of optically-active plastics. Optical activity
is normally strongly dispersive--what wavelengths did you use?
Cheers
Phil Hobbs
Just natural, white light. Some plastics show coloured fringes
when inserted between two polarizing sheets, which is sort-of
what I expected. This Chinese ruler is special: It rotates
the polarization. Inserted between two parallel polarizers, it
has four orientations spaced by 90 degrees where it blocks the
light. But it is not itself polarizing: I see no intensity
variations when looking through it with a single polarizer, nor
when superimposing multiple layers of the same plastic.
There are no colours.
It's very likely to be polystyrene.
On 2020-10-26 18:33, Joe Gwinn wrote:
On Mon, 26 Oct 2020 16:58:44 +0100, Jeroen Belleman
<jeroen@nospam.please> wrote:
On 2020-10-26 15:57, Phil Hobbs wrote:
On 10/26/20 9:35 AM, Jeroen Belleman wrote:
While playing with polarizing filters, I found a plastic ruler that
turns out to rotate the polarization angle of the light passing
through it by almost exactly 90 degrees. The ruler is of a 1mm
thick colourless plastic, rather flexible, clearly not the usual
polyethylene or polystyrene. It does not itself polarize light, it
just rotates it. The angle of rotation does not seem to depend on
wavelength. It's made in China.
What plastic could this be?
There are quite a lot of optically-active plastics. Optical activity
is normally strongly dispersive--what wavelengths did you use?
Cheers
Phil Hobbs
Just natural, white light. Some plastics show coloured fringes
when inserted between two polarizing sheets, which is sort-of
what I expected. This Chinese ruler is special: It rotates
the polarization. Inserted between two parallel polarizers, it
has four orientations spaced by 90 degrees where it blocks the
light. But it is not itself polarizing: I see no intensity
variations when looking through it with a single polarizer, nor
when superimposing multiple layers of the same plastic.
There are no colours.
It's very likely to be polystyrene.
Joe Gwinn
Polystyrene typically shows coloured fringes, stresses frozen in
the material, does it not? The transparent plastic CD box I have
here, presumably polystyrene, certainly does.
The Chinese ruler
is different. There are no visible stress fringes. It just rotates
the polarization by basically the same angle for all colours
everywhere. It doesn't 'feel' like polystyrene either. Too flexible
and rather tough, not brittle.
I'd like to find a clean sheet of the stuff, so that I can make
some more serious measurements. My wife objects to me cutting up
her rulers.
On Mon, 26 Oct 2020 20:07:16 +0100, Jeroen Belleman
<jeroen@nospam.please> wrote:
On 2020-10-26 18:33, Joe Gwinn wrote:
On Mon, 26 Oct 2020 16:58:44 +0100, Jeroen Belleman
<jeroen@nospam.please> wrote:
On 2020-10-26 15:57, Phil Hobbs wrote:It's very likely to be polystyrene.
On 10/26/20 9:35 AM, Jeroen Belleman wrote:Just natural, white light. Some plastics show coloured fringes
While playing with polarizing filters, I found a plastic ruler that >>>>>> turns out to rotate the polarization angle of the light passingThere are quite a lot of optically-active plastics. Optical activity >>>>> is normally strongly dispersive--what wavelengths did you use?
through it by almost exactly 90 degrees. The ruler is of a 1mm
thick colourless plastic, rather flexible, clearly not the usual
polyethylene or polystyrene. It does not itself polarize light, it >>>>>> just rotates it. The angle of rotation does not seem to depend on
wavelength. It's made in China.
What plastic could this be?
Cheers
Phil Hobbs
when inserted between two polarizing sheets, which is sort-of
what I expected. This Chinese ruler is special: It rotates
the polarization. Inserted between two parallel polarizers, it
has four orientations spaced by 90 degrees where it blocks the
light. But it is not itself polarizing: I see no intensity
variations when looking through it with a single polarizer, nor
when superimposing multiple layers of the same plastic.
There are no colours.
Joe Gwinn
Polystyrene typically shows coloured fringes, stresses frozen in
the material, does it not? The transparent plastic CD box I have
here, presumably polystyrene, certainly does.
Clear CD boxes are usually polystyrene. and yes that is how that
behaves. So, I agree that polystyrene is ruled out.
The Chinese ruler
is different. There are no visible stress fringes. It just rotates
the polarization by basically the same angle for all colours
everywhere. It doesn't 'feel' like polystyrene either. Too flexible
and rather tough, not brittle.
If you dissolve it in acetone, do you get a powder residue?
In other words, is the rotation due to the plastic, or to a mineral
filler (if any)?
I'd like to find a clean sheet of the stuff, so that I can make
some more serious measurements. My wife objects to me cutting up
her rulers.
Liquid crystal polymers (LCPs) are typically very tough. But I'm not
sure any are transparent. Or that one would make cheap rulers from
LCPs.
Wonder if it's polycarbonate, which is transparent like polystyrene.
But I don't recall that it rotates polarization.
Where did this mystery ruler come form?
Joe Gwinn
Joe Gwinn wrote:
On Mon, 26 Oct 2020 20:07:16 +0100, Jeroen Belleman
<jeroen@nospam.please> wrote:
On 2020-10-26 18:33, Joe Gwinn wrote:
On Mon, 26 Oct 2020 16:58:44 +0100, Jeroen Belleman
<jeroen@nospam.please> wrote:
On 2020-10-26 15:57, Phil Hobbs wrote:It's very likely to be polystyrene.
On 10/26/20 9:35 AM, Jeroen Belleman wrote:Just natural, white light. Some plastics show coloured fringes
While playing with polarizing filters, I found a plastic ruler that >>>>>>> turns out to rotate the polarization angle of the light passingThere are quite a lot of optically-active plastics. Optical activity >>>>>> is normally strongly dispersive--what wavelengths did you use?
through it by almost exactly 90 degrees. The ruler is of a 1mm
thick colourless plastic, rather flexible, clearly not the usual >>>>>>> polyethylene or polystyrene. It does not itself polarize light, it >>>>>>> just rotates it. The angle of rotation does not seem to depend on >>>>>>> wavelength. It's made in China.
What plastic could this be?
Cheers
Phil Hobbs
when inserted between two polarizing sheets, which is sort-of
what I expected. This Chinese ruler is special: It rotates
the polarization. Inserted between two parallel polarizers, it
has four orientations spaced by 90 degrees where it blocks the
light. But it is not itself polarizing: I see no intensity
variations when looking through it with a single polarizer, nor
when superimposing multiple layers of the same plastic.
There are no colours.
Joe Gwinn
Polystyrene typically shows coloured fringes, stresses frozen in
the material, does it not? The transparent plastic CD box I have
here, presumably polystyrene, certainly does.
Clear CD boxes are usually polystyrene. and yes that is how that
behaves. So, I agree that polystyrene is ruled out.
The Chinese ruler
is different. There are no visible stress fringes. It just rotates
the polarization by basically the same angle for all colours
everywhere. It doesn't 'feel' like polystyrene either. Too flexible
and rather tough, not brittle.
If you dissolve it in acetone, do you get a powder residue?
In other words, is the rotation due to the plastic, or to a mineral
filler (if any)?
I'd like to find a clean sheet of the stuff, so that I can make
some more serious measurements. My wife objects to me cutting up
her rulers.
Liquid crystal polymers (LCPs) are typically very tough. But I'm not
sure any are transparent. Or that one would make cheap rulers from
LCPs.
Wonder if it's polycarbonate, which is transparent like polystyrene.
But I don't recall that it rotates polarization.
Where did this mystery ruler come form?
It's Chinese, I can't read the brand name. It's a 'comma shaped
French curve ruler'. There are lots of brands that look alike.
On 10/27/20 5:00 AM, Jeroen Belleman wrote:
Joe Gwinn wrote:
On Mon, 26 Oct 2020 20:07:16 +0100, Jeroen Belleman
<jeroen@nospam.please> wrote:
On 2020-10-26 18:33, Joe Gwinn wrote:
On Mon, 26 Oct 2020 16:58:44 +0100, Jeroen Belleman
<jeroen@nospam.please> wrote:
On 2020-10-26 15:57, Phil Hobbs wrote:It's very likely to be polystyrene.
On 10/26/20 9:35 AM, Jeroen Belleman wrote:Just natural, white light. Some plastics show coloured fringes
While playing with polarizing filters, I found a plastic ruler that >>>>>>>> turns out to rotate the polarization angle of the light passing >>>>>>>> through it by almost exactly 90 degrees. The ruler is of a 1mm >>>>>>>> thick colourless plastic, rather flexible, clearly not the usual >>>>>>>> polyethylene or polystyrene. It does not itself polarize light, it >>>>>>>> just rotates it. The angle of rotation does not seem to depend on >>>>>>>> wavelength. It's made in China.There are quite a lot of optically-active plastics. Optical
What plastic could this be?
activity
is normally strongly dispersive--what wavelengths did you use?
Cheers
Phil Hobbs
when inserted between two polarizing sheets, which is sort-of
what I expected. This Chinese ruler is special: It rotates
the polarization. Inserted between two parallel polarizers, it
has four orientations spaced by 90 degrees where it blocks the
light. But it is not itself polarizing: I see no intensity
variations when looking through it with a single polarizer, nor
when superimposing multiple layers of the same plastic.
There are no colours.
Joe Gwinn
Polystyrene typically shows coloured fringes, stresses frozen in
the material, does it not? The transparent plastic CD box I have
here, presumably polystyrene, certainly does.
Clear CD boxes are usually polystyrene. and yes that is how that
behaves. So, I agree that polystyrene is ruled out.
The Chinese ruler
is different. There are no visible stress fringes. It just rotates
the polarization by basically the same angle for all colours
everywhere. It doesn't 'feel' like polystyrene either. Too flexible
and rather tough, not brittle.
If you dissolve it in acetone, do you get a powder residue?
In other words, is the rotation due to the plastic, or to a mineral
filler (if any)?
I'd like to find a clean sheet of the stuff, so that I can make
some more serious measurements. My wife objects to me cutting up
her rulers.
Liquid crystal polymers (LCPs) are typically very tough. But I'm not
sure any are transparent. Or that one would make cheap rulers from
LCPs.
Wonder if it's polycarbonate, which is transparent like polystyrene.
But I don't recall that it rotates polarization.
Polystyrene generally has a lot of stress birefringence, which is what
gives the coloured fringes when it's placed between crossed polarizers.
Where did this mystery ruler come form?
It's Chinese, I can't read the brand name. It's a 'comma shaped
French curve ruler'. There are lots of brands that look alike.
To get optical activity, the polymer has to be chiral, like biological molecules. (A strong sugar solution is optically active as well.)
Cheers
Phil Hobbs
While playing with polarizing filters, I found a plastic ruler
that turns out to rotate the polarization angle of the light
passing through it by almost exactly 90 degrees. The ruler is
of a 1mm thick colourless plastic, rather flexible, clearly
not the usual polyethylene or polystyrene. It does not itself
polarize light, it just rotates it. The angle of rotation does
not seem to depend on wavelength. It's made in China.
What plastic could this be?
On Monday, October 26, 2020 at 7:35:22 AM UTC-6, Jeroen Belleman wrote:
While playing with polarizing filters, I found a plastic ruler
that turns out to rotate the polarization angle of the light
passing through it by almost exactly 90 degrees. The ruler is
of a 1mm thick colourless plastic, rather flexible, clearly
not the usual polyethylene or polystyrene. It does not itself
polarize light, it just rotates it. The angle of rotation does
not seem to depend on wavelength. It's made in China.
What plastic could this be?
As has been noted, optical activity is quite common in plastics.
If you put a mildly crumpled cellophane wrapper from a pack of cigarettes between two polarizing filters, you will see beautiful colors.
John Savard
On 2020-10-26 15:57, Phil Hobbs wrote:
On 10/26/20 9:35 AM, Jeroen Belleman wrote:
While playing with polarizing filters, I found a plastic ruler that
turns out to rotate the polarization angle of the light ...
There are quite a lot of optically-active plastics.
Just natural, white light. Some plastics show coloured fringes
when inserted between two polarizing sheets, which is sort-of
what I expected. This Chinese ruler is special: It rotates
the polarization. Inserted between two parallel polarizers, it
has four orientations spaced by 90 degrees where it blocks the
light.
On Monday, October 26, 2020 at 8:58:48 AM UTC-7, Jeroen Belleman wrote:
On 2020-10-26 15:57, Phil Hobbs wrote:
On 10/26/20 9:35 AM, Jeroen Belleman wrote:
While playing with polarizing filters, I found a plastic ruler that
turns out to rotate the polarization angle of the light ...
There are quite a lot of optically-active plastics.
Just natural, white light. Some plastics show coloured fringes
when inserted between two polarizing sheets, which is sort-of
what I expected. This Chinese ruler is special: It rotates
the polarization. Inserted between two parallel polarizers, it
has four orientations spaced by 90 degrees where it blocks the
light.
I think that means it's birefringent, i.e. has an orientation (probably because the polymer was stretched in one direction as the sheet
was rolled out).
When linear polarized light has E-field parallel to the orientation,
the film is N wavelengths thick. When it is perpendicular, the film
is N+1/2 wavelengths thick. There are four inbetween orientations
that correspond to quarter-wave mismatched in two components, that make the linear polarized light into circular polarized. Circular polarized isn't blocked
by the second linear polarizer.
Inexpensive acetate is the most likely material for a transparent ruler. Two layers
of acetate laminated around a printed film with the markings, perhaps?
whit3rd wrote:
On Monday, October 26, 2020 at 8:58:48 AM UTC-7, Jeroen Belleman wrote:
On 2020-10-26 15:57, Phil Hobbs wrote:
On 10/26/20 9:35 AM, Jeroen Belleman wrote:
While playing with polarizing filters, I found a plastic ruler that
turns out to rotate the polarization angle of the light ...
There are quite a lot of optically-active plastics.
Just natural, white light. Some plastics show coloured fringes when
inserted between two polarizing sheets, which is sort-of what I
expected. This Chinese ruler is special: It rotates the polarization.
Inserted between two parallel polarizers, it has four orientations
spaced by 90 degrees where it blocks the light.
I think that means it's birefringent, i.e. has an orientation (probably
because the polymer was stretched in one direction as the sheet
was rolled out).
When linear polarized light has E-field parallel to the orientation,
the film is N wavelengths thick. When it is perpendicular, the film
is N+1/2 wavelengths thick. There are four inbetween orientations
that correspond to quarter-wave mismatched in two components, that
make the linear polarized light into circular polarized. Circular
polarized isn't blocked
by the second linear polarizer.
Inexpensive acetate is the most likely material for a transparent
ruler. Two layers
of acetate laminated around a printed film with the markings, perhaps?
Thanks for your comments. I'll do some more experimenting.
The linearly polarized light is still linearly polarized
after passing through the ruler, because there are still
two orientations where the second polarizer blocks all
light. They're just different orientations.
Jeroen Belleman
On 2020-11-10 18:52, Phil Hobbs wrote:
On 11/10/20 8:25 AM, Jeroen Belleman wrote:
whit3rd wrote:
On Monday, October 26, 2020 at 8:58:48 AM UTC-7, Jeroen Belleman wrote: >>>>> On 2020-10-26 15:57, Phil Hobbs wrote:
On 10/26/20 9:35 AM, Jeroen Belleman wrote:
While playing with polarizing filters, I found a plastic ruler
that turns out to rotate the polarization angle of the light ...
There are quite a lot of optically-active plastics.
Just natural, white light. Some plastics show coloured fringes when
inserted between two polarizing sheets, which is sort-of what I
expected. This Chinese ruler is special: It rotates the
polarization. Inserted between two parallel polarizers, it has four
orientations spaced by 90 degrees where it blocks the light.
I think that means it's birefringent, i.e. has an orientation (probably >>>> because the polymer was stretched in one direction as the sheet
was rolled out).
When linear polarized light has E-field parallel to the orientation,
the film is N wavelengths thick. When it is perpendicular, the film >>>> is N+1/2 wavelengths thick. There are four inbetween orientations
that correspond to quarter-wave mismatched in two components, that
make the linear polarized light into circular polarized. Circular
polarized isn't blocked
by the second linear polarizer.
Inexpensive acetate is the most likely material for a transparent
ruler. Two layers
of acetate laminated around a printed film with the markings, perhaps?
Thanks for your comments. I'll do some more experimenting.
The linearly polarized light is still linearly polarized
after passing through the ruler, because there are still
two orientations where the second polarizer blocks all
light. They're just different orientations.
Jeroen Belleman
Try tipping the ruler and see if that changes.
Cheers
Phil Hobbs
Oriented at its darkest, the extinction ratio gets worse
and the residual light passing through takes a deep blue
or brownish hue. There is no perceptible colouration of
the light passing through when angles are adjusted for
maximum transmission
Whit3d is correct that the thing is laminated. Is industrially
produced acetate chiral with one enantiomer dominating?
Probably, I found sources stating it's made from wood pulp.
Thanks,
Jeroen Belleman
On 11/10/20 8:25 AM, Jeroen Belleman wrote:has four orientations spaced by 90 degrees where it blocks the light.
whit3rd wrote:
On Monday, October 26, 2020 at 8:58:48 AM UTC-7, Jeroen Belleman wrote: >>>> On 2020-10-26 15:57, Phil Hobbs wrote:
On 10/26/20 9:35 AM, Jeroen Belleman wrote:
While playing with polarizing filters, I found a plastic ruler that turns out to rotate the polarization angle of the light ...
There are quite a lot of optically-active plastics.
Just natural, white light. Some plastics show coloured fringes when inserted between two polarizing sheets, which is sort-of what I expected. This Chinese ruler is special: It rotates the polarization. Inserted between two parallel polarizers, it
I think that means it's birefringent, i.e. has an orientation (probably
because the polymer was stretched in one direction as the sheet
was rolled out).
When linear polarized light has E-field parallel to the orientation,
the film is N wavelengths thick. When it is perpendicular, the film
is N+1/2 wavelengths thick. There are four inbetween orientations
that correspond to quarter-wave mismatched in two components, that make the linear polarized light into circular polarized. Circular polarized isn't blocked
by the second linear polarizer.
Inexpensive acetate is the most likely material for a transparent ruler. Two layers
of acetate laminated around a printed film with the markings, perhaps?
Thanks for your comments. I'll do some more experimenting.
The linearly polarized light is still linearly polarized
after passing through the ruler, because there are still
two orientations where the second polarizer blocks all
light. They're just different orientations.
Jeroen Belleman
Try tipping the ruler and see if that changes.
Cheers
Phil Hobbs
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