Polarimetry and Polarization

What is polarization?

Polarization is a description of the orientation of a light waves propagations.
Polarization is the characteristic of a light wave that describes the orientations of its oscillations as it propagates through space. Light waves can be randomly polarized, linearly polarized, circularly polarized, and elliptically polarized. Light directly from the sun is unpolarized, or in other words randomly polarized, but when sunlight interacts with the atmosphere or reflects off of physical objects, it usually becomes polarized. Some birds, insects and marine animals exploit this effect to navigate or to improve vision contrast. Human eyes are incapable of distinguishing unpolarized light from polarized light such as glare. But glare, which is simply light reflecting off of shiny objects, is always polarized and is significantly reduced by the linear polarizing filters used in our sunglasses.

What is Polarimetry?

The way in which the polarization of light waves change when they interact with objects reveals details about those objects. Polarimetry is the field of science that utilizes these polarization changes to reveal or measure specific properties of an object.

Often with polarimetry, an object is illuminated with light that has been polarized in a very specific/known way, often linear. While many lasers are inherently linearly polarized, it is relatively straight-forward to generate linearly polarized light from unpolarized light sources such as incandescent bulbs or LEDs. Unpolarized light consists of many different random oscillations of light. When you pass unpolarized light through a linear polarizer (like your polarized sunglasses), all the vibrations except one are filtered out (or rejected) and it becomes linear polarized. The figure below illustrates this concept. The light exiting the linear polarizer oscillates in one plane (in the case of figure 1, along the vertical axis).

To achieve non-linearly polarized light, such as circular or elliptical, you need to retard the light in an asymmetric way. This can be done with birefringent materials, which are often crystalline and have different indices of refraction depending on the orientation of the material. This asymmetric refractive index retards the light such that polarization change occurs. For example, a birefringent retarder plate with a quarter wave of retardation will change a linearly polarized beam to circular. Circular polarized light can be used to measure the birefringence of an unknown material by measuring how the circularly polarized light is changed after passing through the material.

Polarimetry

Polarimetry

PolarCam cameras, with PolarView software, provide real-time display and calculation of key polarization parameters, including Degree of Linear Polarization (DoLP), Angle of Linear Polarization (AoLP), linear Stokes parameters (S0, S1 and S2) and more. Use the many included tools to process and analyze the data, then save images and movies of each parameter for comprehensive analysis.

Birefringence Measurement

4D snapshot micropolarizer cameras measure birefringence in glass and plastic, in real time, even on moving and rotating targets. These innovative cameras provide repeatable measurement of birefringence, letting manufacturers spot stress in bottles, flat panel substrates and optics.

Measuring birefringence with a polarimeter camera

3D Shape

3D reconstruction

PolarCam cameras and PolarView software calculate the linear Stokes polarization parameters to map the Angle of Linear Polarization of a 3D scene. The differing polarization angles of light from a surface can be used to determine the surface normals and reconstruct 3D scenes with a high degree of accuracy.

Remote Sensing

remote sensing

By capturing key polarization parameters including the linear Stokes parameters, 4D PolarCam cameras highlight information in remote sensing data for applications ranging from oceanography to astronomy.

Defect Detection

Defect Detection

Snapshot micropolarizer array technology enables PolarCam cameras to detect and measure defects in production environments. High speed imaging allows PolarCams to spot defects on moving and rotating objects, capturing problems that other cameras simply miss.

The 4D InSpec Surface Gauge is the first instrument for handheld, high resolution measurement of surface defects on precision surfaces.

Learn about the new 4D InSpec Surface Gauge for high resolution surface measurement, right on the shop floor.

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Machine Vision

Machine Vision

4D PolarCam snapshot micropolarizer cameras detect and quantify differences in polarization to spot defects in materials, identify missing or excess material, reduce glare from highly specular parts, or to aid in pick and place operations.

Autonomous Vehicle Vision

Autonomous Vehicle Vision

4D PolarCam snapshot micropolarizer cameras detect and quantify differences in polarization, enabling glare reduction to provide discrimination between false reflected images and real images that other technologies cannot provide.

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