Polarization

Basic physical explanation

Light can be described as a transverse electromagnetic wave that oscillates transversely to the direction of propagation. Usually only the direction of propagation and the electric field vector are described, since the magnetic field vector can be derived from them. Oscillations in all directions of the room are possible perpendicular to the direction of discharge.

If the direction of the transverse wave changes quickly and in a disorderly manner, it is unpolarized light.

Polarized light only oscillates in one plane and linearly polarized light only in a certain direction perpendicular to the direction of propagation.

Light generated by any light source (sun, fire, lamp, etc.) propagates as unpolarized light. Reflection or refraction on surfaces or small particles in the air also changes the light waves, so that a special polarizer is necessary if polarized light is required.


Applications of polarizers

Polarizers can be found in many places in our modern world. Sometimes they sit on the user's nose in 3-D glasses, are carried around by every smartphone owner, are buried in the ground with fiber optic cables, or fly through space in a space telescope.

Photographers use circular polarizing filters* to reduce reflections from reflecting surfaces as much as possible and to increase contrast. Reflections occur on almost all surfaces and even in the air due to tiny particles, so polarizing filters can make plants appear greener, the sky bluer, and underwater objects visible.  Colors become deeper and images more dramatically so. Of the adjacent images, A was taken without a polarizing filter and B with. The differences are clearly visible.

colorPol® polarizers are optimized for applications with special demands regarding contrast, transmission, accuracy of the polarization axis or for applications in the ultraviolet and infrared spectral range. Applications include:

  • Wavelength Selectable Switch -WSS
  • Medical technology (dental technology, endoscopy, etc.)
  • Laboratory use (e.g. spectroscopy, microscopy)
  • Optical communication (optical isolator, polarization control for PMD's)
  • Industrial measurement technology (polarimeters, ellipsometers, optical light barriers, light scanners, etc.)
  • and many more.

*A circular polarizing filter consists of a linear polarizing filter and a λ/4 plate.

 

Consists of two pictures, one taken without a polarizers and many reflection und another one taken with a polarizer without any glare.

How colorPol® polarizers work

Structure of the colorPol® polarizer

colorPol® polarizers are made of sodium silicate glass only 0.2 to 0.5 mm thick and silver nanoparticles. These particles are embedded in the glass near the two surfaces and are thus protected from environmental influences. Depending on the polarizer, the layer of silver particles is up to 10 µm thick.

 

Silver nanoparticles near the surface

The special production technology of CODIXX allows the size, density and orientation of the nanoparticles to be precisely determined. The zeppelin-like shape creates a long and short axis that are required for the polarization properties. Depending on the wavelength, they absorb all transverse waves of light and only allow those along the axes of symmetry to pass.

All nanoparticles are arranged absolutely parallel for perfectly linearly polarized light.

 

Single prolate nanoparticles with axes of symmetry

colorPol® polarizers always work in the ultraviolet, visible and infrared spectrum of light, but are optimized in terms of transmission and contrast for individual areas. It is important here that the short axis (blue) in the UV absorbs the short-wave light waves and only the waves along the long axis can pass. Between 420 nm and 450 nm, the absorption changes to the long axis and polarization is not possible. The area can be moved slightly but not avoided completely.

From 450 nm the long symmetry axis (red) takes over the absorption. This change is the reason for different polarization axes in the UV and VIS-IR range of colorPol® polarizers, especially noticeable with the colorPol® Laserline Nd: YAG BC4 for 355 nm, 532 nm and 1,064 nm.

 

A more detailed description of the operating principle of colorPol® polarizers and polarization can be found in our publication How colorPol® polarizers work.