Comments on: The polarization puzzle https://habitablezone.com/2023/08/26/the-polarization-puzzle/ Sun, 05 Apr 2026 21:05:37 -0700 hourly 1 http://wordpress.org/?v=3.3.1 By: RL https://habitablezone.com/2023/08/26/the-polarization-puzzle/#comment-52247 RL Thu, 31 Aug 2023 04:00:45 +0000 https://habitablezone.com/?p=100697#comment-52247 It was an early researcher of mineral optics that discovered Haidinger's brush.... It was an early researcher of mineral optics that discovered Haidinger’s brush….

]]> By: podrock https://habitablezone.com/2023/08/26/the-polarization-puzzle/#comment-52224 podrock Sun, 27 Aug 2023 15:52:26 +0000 https://habitablezone.com/?p=100697#comment-52224 The polarizing microscope is the essential tool for petrology. It works on exactly this principle. There are two polarizing filters, and a very thin slice of rock is placed on a rotating stage. (There are three axis stages too, but it gets weird.) The minerals each have their own polarizing properties. Much can be discerned from this: mineral type, mineral composition, mineral growth zonation... I spent a lot of time learning the optics and staring down a tube until my eyes crossed. Now, there are much better microscope cameras that help with the eye strain. Basically, that third middle lense is bending the light. https://www.youtube.com/watch?v=ZLk6IjBZteI The polarizing microscope is the essential tool for petrology.

It works on exactly this principle. There are two polarizing filters, and a very thin slice of rock is placed on a rotating stage. (There are three axis stages too, but it gets weird.) The minerals each have their own polarizing properties. Much can be discerned from this: mineral type, mineral composition, mineral growth zonation… I spent a lot of time learning the optics and staring down a tube until my eyes crossed. Now, there are much better microscope cameras that help with the eye strain.

Basically, that third middle lense is bending the light.

https://www.youtube.com/watch?v=ZLk6IjBZteI

]]> By: RL https://habitablezone.com/2023/08/26/the-polarization-puzzle/#comment-52222 RL Sun, 27 Aug 2023 02:21:21 +0000 https://habitablezone.com/?p=100697#comment-52222 Then if C is aligned with A or B the light will still be completely blocked. A and B have their axes at 90 degrees to each other... If A passes vertical polarization then that vertical vector has no component in the horizontal direction, so nothing is transmitted through horizontal polarizer B. But... if you add C between A and B and if C is at 45degree angle to A and B, then vertical polarization passes through A, this vertical polarization DOES have a component along the 45 degree axis- so C passes that component. But now, the light passed by C is now polarized at a 45 degree angle and so it now has a component in the horizontal direction and so some portion of the light DOES go through B. NOW, take just polarizers A and B, cross them so they block all light. Now put a piece of scotch tape between A and B- you will see a multicolored pattern of light passing through- scotch tape is birefringent, it rotates incident polarization of light, and the amount it rotates it by can be a function of wavelength.... so you see a pattern of colored light where the tape is. Finally Take one of the polarizers, get a white piece of paper and look at it through the polarizer in bright light for a moment and then slowly rotate the polarizer.... a certain percentage pf people will see a pattern rotate with the polarizer- it turns out that a fair number of people can detect polarization with their eye- the effect is called <a href="https://en.wikipedia.org/wiki/Haidinger%27s_brush" target="_blank" rel="nofollow">Haidinger's Brush</a> - is it a quirk of evolution, or was there a purpose for having that ability? In the Lunar Laser Communication Demonstration the space terminal transmitted circular polarization- lets say it was left hand circular polarization. The ground terminal had a quarter wave plate that turned left hand circular polarization into Horizontal polarization.... we then used a horizontal polarizer which transmitted all of the horizontally polarized signal, but blocked ~half of the (mostly) randomly polarized sky background- thus improving our signal to noise ratio. You can use polarizers to see stress in glass because stress can cause birefringence... <img src="https://3.bp.blogspot.com/-FYNFLn5OjeA/Up8A5AMrxwI/AAAAAAAAItw/WiEOnUTxK_Q/s1600/Photoelasticity--or-Birefringence-Photography.jpg" alt="" /> Then if C is aligned with A or B the light will still be completely blocked.
A and B have their axes at 90 degrees to each other… If A passes vertical polarization then that vertical vector has no component in the horizontal direction, so nothing is transmitted through horizontal polarizer B.
But… if you add C between A and B and if C is at 45degree angle to A and B, then vertical polarization passes through A, this vertical polarization DOES have a component along the 45 degree axis- so C passes that component. But now, the light passed by C is now polarized at a 45 degree angle and so it now has a component in the horizontal direction and so some portion of the light DOES go through B.

NOW, take just polarizers A and B, cross them so they block all light. Now put a piece of scotch tape between A and B- you will see a multicolored pattern of light passing through- scotch tape is birefringent, it rotates incident polarization of light, and the amount it rotates it by can be a function of wavelength…. so you see a pattern of colored light where the tape is.

Finally Take one of the polarizers, get a white piece of paper and look at it through the polarizer in bright light for a moment and then slowly rotate the polarizer…. a certain percentage pf people will see a pattern rotate with the polarizer- it turns out that a fair number of people can detect polarization with their eye- the effect is called Haidinger’s Brush – is it a quirk of evolution, or was there a purpose for having that ability?

In the Lunar Laser Communication Demonstration the space terminal transmitted circular polarization- lets say it was left hand circular polarization. The ground terminal had a quarter wave plate that turned left hand circular polarization into Horizontal polarization…. we then used a horizontal polarizer which transmitted all of the horizontally polarized signal, but blocked ~half of the (mostly) randomly polarized sky background- thus improving our signal to noise ratio.

You can use polarizers to see stress in glass because stress can cause birefringence…

]]>