Plastic objects in polarized light

Very exiting to experiment with plastic in front of polarized light sources. This is a simple foil from a cracker box put in front of a TFT(!) Monitor. Somehow not every foil or plastic object produces these colours. I tried a cup from the hospital I brought home, the top of a little box for keeping minerals and this foil with success. Best results can be reached by switching the monitor in a single white surface, then put the item in front, darken the room and use a pole filter with the camera. Turning the objects slightly produces different ranges of colour. Once I observed this effect even in the daylight on a plastic windshield of a motor-cycle with a pole filter on my camera.

Here still a further picture of Windshield of a motorcycle 90 degrees away from the sun, viewed through a polfilter on a Canon Reflex Camera.

More pictures: 1 – 2 – 3 – 4 – 5

Author: Rolf Kohl

Polarized Light in Nature

My book “Polarized Light in Nature” is now online available.

The pdf can be downloaded from my site, www.guntherkonnen.com. Go to English/Articles and scroll down to the year of publication (1985). The size of the download is 24 Mb.

The Dutch version (1980) can also been downloaded from the site (18 Mb).

Direct access is also possible:
http://s3.amazonaws.com/gunther-konnen/documents/249/1985_Pol_Light_in_Nature_book.pdf?1317929665 (English version)
or
http://s3.amazonaws.com/gunther-konnen/documents/246/1980_Gepolariseerd_Licht_boek.pdf?1317928523 (Dutch version),
but these addresses may change in case my site migrates to another server.

Author: Günther Können, Netherlands

Polarization Colours in Airplane Window

Patrice Touhar took this photograph through the window of an airplane using a polarization filter and so made these polarization colours appear.

The colours are generated by the combination of three circumstances:

1. There is polarized light behind the window
2. The window is made of a double refracting matter
3. A polarization filter is used in front of the window

Under these circumstances, the light gets split up into two coherences of polarized components which travel through the window at different speeds. This causes a phase difference the amount of which depends from the wavelength. This means that the polarization gets transformed once into a linear polarization of a different direction than the origin for a certain colour, and into a circular polarization for another colour (Lissagiu interference of two waves). As the polarization is now dependent from the colour, the colours appear when a polarization filter is used, no matter if this filter is placed in front of the eye or in front of a camera.

These colours can be seen and photographed under the following circumstances:

1. There is polarized on one side of the window coming from the blue sky (Rayleigh scattering) and reflection from water and the scattering caused by clouds
2. The window is made of plastic. In this material there are mechanical tensions which cause a double refraction.
3. There is a polarization filter in front of the camera.

The last condition is not necessary if you look at the window from an acute angle. Then the light becomes already polarized by the refraction. In this case there is no filter necessary to see the colours. However, the colours you can see under this circumstance are fainter than the colours seen through the polarization filter because refraction polarizes only a part of the light.

You can also find another observation of this kind in this former thread.

Colours in the airplane window

While flying from Izmir to Ankara in Turkey on monday the 2nd of April 2007 at 10.15am Selen Ediger wanted to take an aerial shot of the mountains below with my canon ef 10-22mm lens and Hoya multi coated polarizing filter. With naked eye the colors were not visible but when she looked through the camera she saw that the land and the sky was covered with rainbow colors. The contrast and the saturation are adjusted a bit.

What’s the origin of this colours?

Polarized fogbow in car headlights

I spent the past summer at Langmuir Laboratory on the Magdalena Mountains, in southwest-central New Mexico (USA) at an elevation of 3.2 km. The purpose of this was thunderstorm research. The monsoon here was unusually wet and on several days and nights the mountain laboratory was actually foggy. This is relatively rare considering the New Mexico climate. I took this opportunity to view polarized fogbows in my car”s headlights, and on September 2nd, I was particularly successful.

When I programmed a Mie simulation algorithm late last year and plotted a polarized fogbow on my screen, I was surprised that the polarized bow looked as it did, with the typical Brewster”s angle ”gap” in the main bow for parallel polarization. How excited I was to see that the actual fogbow indeed looked like the simulation! I had never seen it before in nature.

I am sure this has been done before by someone else, but I thought I would post the images anyway.

I covered up one of the car”s headlamps as to not have a double bow. I positioned myself about 50 meters in front of the truck, which I had parked on a slight inclination so the bow would be better visible against a featureless sky and be more complete. The fisheye lens was equipped with a polarizer at the place in the lens where the rays go parallel.

The simulation I made earlier, for a 10 micrometer radius droplet. It looks sharper because I assumed a point light source, assumed a monodisperse droplet distribution, and it was not divergent light. It is not a perfect match either considering the placement of the supernumeraries: probably the droplets in the actual display were a bit smaller. Because of the divergent light source, and because I don”t know the distance to the truck accurately, I doubt I will ever be able to accurately tell the actual droplet radii in the display.

The polarized glory was also obvious, but my shadow was blocking most of the part that was most polarized. I am including the unpolarized glory here.

The close-ups of the polarized and unpolarized fogbow were made with a 24mm/2.8 lens. The camera was a Canon 300d (modified version – i.e. with IR filter removed). I did not need to adjust the brightness and contrast much to get the results as displayed here. The fogbow had good contrast by itself.

About 10 days later I documented a natural fogbow in sunlight from the laboratory, through a polarizer. I photographed that with film; I have not processed those photos yet.

[Posted by Harald Edens]

Bright Fogbow with serveral supernumerary arcs

On October 3, 2005, on the Wendelstein mountain (1834 m) a very bright fogbow with several supernumerary arcs appeared during the partial solar eclipse. In the centre of the fogbow there also appeared the spectre of the Brocken in variable intensity and size, according to the distance to the clouds. The spectre was also surrounded by a bright glory. Using a polarization filter, Carolin Baumann made this impressive photograph.