Polaimeters
Polarimeters, polarization measurement services, and custom polarimetry systems for all kinds of military and commercial applications are a specialty of Polaris Sensor Technologies, Inc. Feel free to call if you have a need in any of these areas.
What are polarimeters?
Devices that measure the optical characteristics of light beams and samples are known as polarimeters. There are two broad classifications of polarimeters;
a. Stokes vector polarimeters measure the polarization properties of a beam of light.
b. Mueller matrix polarimeters measure the polarization properties of a particular material.
Moreover, these categories may be divided into a number of sub classifications including:
complete vs. incomplete polarimeters
sequential vs. simultaneous polarimeters
monochromatic vs. polychromatic polarimeters
nonimaging vs. imaging polarimeters.
Finally, there exists a class of polarimeters devoted to the specific task of determining the refractive index and thickness of thin films deposited on substrates, typically called ellipsometers. Ellipsometers are usually incomplete, sequential, monochromatic, nonimaging systems, although systems exhibiting variations in one or many of these sub classifications are available.
Stokes vector polarimeters derive four characteristics of an incident light beam, the Stokes vector elements, by measuring the flux of the beam upon passing through four unique polarization filters. The components of the four element Stokes vector completely describe the polarization state of the incident light. This description includes the polarization magnitude and orientation.
The magnitude indicates the “purity” of the polarization state, and is conveniently described by another derived quantity called the Degree of Polarization (DoP). DoP is a normalized value that can range from zero for unpolarized (i.e., randomly oriented in space and time) light to one for completely polarized light. Intermediate values are indicative of elliptically polarized light.
Additionally, completely polarized light may belong to one of two families, linear polarization or circular polarization. The orientation derived from the Stokes vector only applies to linear and partially linear (i.e., elliptical) polarization states, indicating the angle at which the polarization state is canted with respect to a conveniently chosen coordinate system. While orientation is meaningless in the description of circularly polarized light, circular states can be further classified as right handed or left handed. Right or left handedness is defined with respect to the same coordinate system as for the linear states but also requires definition of the view direction, most commonly taken to be the view toward the source as seen from the polarimeter.
Mueller matrix polarimeters may be considered as a pair of Stokes vector polarimeters working in concert to determine the polarization properties of a particular material. Specifically, one Stokes vector polarimeter coupled to a light source and operating “in reverse”, is employed to now generate (as opposed to measure) known polarization states. These states are then made incident on a sample under test and the second Stokes vector polarimeter serves to analyze the light transmitted (or reflected or scattered) through the sample. The first polarimeter is called the polarization state generator while the second polarimeter is the polarization state analyzer.
Mueller polarimeters perform a series of at least 16 measurements using unique generator and analyzer states to deduce the 4 x 4 so-called Mueller matrix. As with the Stokes vector, the Mueller matrix describes completely the polarization properties of the sample. From this matrix, a number of optical properties of the sample may be deduced including diattenuation, retardance, and depolarization index. Diattenuation and retardance may further be resolved into linear and circular polarization.
The linear retardance of a sample is indicative of the phase shift imparted to an incident beam and is directly related to the material’s linear birefringence, while the circular retardance is indicative of its circular birefringence, often referred to as its optical activity. Noting that the sample’s light modifying behavior is representative of the (an)isotropy of the material’s structure, a great deal of information about both its short and long range organization may be determined from a polarimetrically resolved measurement. Indeed polarimeters have been used to determine the birefringence of all types of materials in all types of environments including target sensing, quality control, and even medical applications.
Applications of polarimeters
Now that we know what a polarimeter is and have a rough idea of how it is made, what is a polarimeter good for? Why would you build one in the first place?
Scientific research. Polarimeters can help us find out a great deal of information when doing research into materials that are being studied. Optically active compounds (compounds that cause light to become polarized) can be identified when studied with a polarimeter. Not only can they be identified, but the polarization state can yield information on the molecular structure of completely new compounds and knowledge of a materials molecular structure helps us know how that material can be used to improve our quality of life.
Better Medicines. Different fluids, compounds, and materials reflect polarized light in different ways. Using a polarimeter, we can exploit this fact by measuring the polarization transmitting (or reflecting) properties of any material, making sure that all kinds of manufacturing processes are being done correctly. For example, polarimeters help in keeping us healthy. In pharmaceutical applications, many of the chemicals used in making our medicines must be pure. Many of these pure chemicals have very definite and well known polarizing characteristics. If a polarimeter is used to monitor the light transmitted (or reflected) from these chemicals and the result is not right for that chemical, then we know that there is a contaminant in the chemical and the mixing process can be stopped before an inferior (possibly useless or even harmful) medicine is created.
Better Food. An application similar to the pharmaceutical industry is the food industry. Polarimeters are used in many food processing situations to monitor the quality of the food and to detect contaminants or to ensure that mixtures are composed of the correct concentrations of the individual ingredients. Sugars (glucose, fructose, sucrose, etc.) in particular have very distinctive polarization signatures so polarimeters are very important in identifying the purity or concentrations of these sweeteners to make sure that our foods taste just right.
Safety. When light reflects off of some surfaces, there is very little polarization. Off of other surfaces, there is a great deal of polarization. When ice is on a road surface or an airplane wing, the ice has different polarization characteristics than the airplane wing or the surface of the road. By using polarimeters to monitor these reflections, one can detect the presence of ice and know if the road is safe to drive on. Likewise, in the aviation industry, ice on an airplane's wing can have catastrophic results so polarimeters can be employed to help detect the presence of ice.
Military and Surveillance. Polarization is a property that opens up the possibility of detecting things that might go undetected by other means. For example, when a land mine is buried the dirt that is used to cover up the mine has a different polarization signature from the surrounding soil. So, in a hostile environment, if a polarimeter is flown above a dirt road that a convoy will be using it can detect areas of the road that have been disturbed. This section of the road can then be investigated before a vehicle drives over it and potentially is damaged and people are injured or even killed. Polarimeters are also very good at detecting man made objects. There are times when neither visible nor infrared light can do a good job of detecting an object that will stand out like a sore thumb when examined by a polarimeter.
As you can see, polarimeters add a great deal to our quality of life. If you have an application where a polarimeter might be useful, feel free to call. For more information on polarimeters, you may also refer to our pages on polarization and polarimetry.
Polarimeters, polarization measurement services, and custom polarimetry systems for all kinds of military and commercial applications are a specialty of Polaris Sensor Technologies, Inc. Feel free to call if you have a need in any of these areas.
What are polarimeters?
Devices that measure the optical characteristics of light beams and samples are known as polarimeters. There are two broad classifications of polarimeters;
a. Stokes vector polarimeters measure the polarization properties of a beam of light.
b. Mueller matrix polarimeters measure the polarization properties of a particular material.
Moreover, these categories may be divided into a number of sub classifications including:
complete vs. incomplete polarimeters
sequential vs. simultaneous polarimeters
monochromatic vs. polychromatic polarimeters
nonimaging vs. imaging polarimeters.
Finally, there exists a class of polarimeters devoted to the specific task of determining the refractive index and thickness of thin films deposited on substrates, typically called ellipsometers. Ellipsometers are usually incomplete, sequential, monochromatic, nonimaging systems, although systems exhibiting variations in one or many of these sub classifications are available.
Stokes vector polarimeters derive four characteristics of an incident light beam, the Stokes vector elements, by measuring the flux of the beam upon passing through four unique polarization filters. The components of the four element Stokes vector completely describe the polarization state of the incident light. This description includes the polarization magnitude and orientation.
The magnitude indicates the “purity” of the polarization state, and is conveniently described by another derived quantity called the Degree of Polarization (DoP). DoP is a normalized value that can range from zero for unpolarized (i.e., randomly oriented in space and time) light to one for completely polarized light. Intermediate values are indicative of elliptically polarized light.
Additionally, completely polarized light may belong to one of two families, linear polarization or circular polarization. The orientation derived from the Stokes vector only applies to linear and partially linear (i.e., elliptical) polarization states, indicating the angle at which the polarization state is canted with respect to a conveniently chosen coordinate system. While orientation is meaningless in the description of circularly polarized light, circular states can be further classified as right handed or left handed. Right or left handedness is defined with respect to the same coordinate system as for the linear states but also requires definition of the view direction, most commonly taken to be the view toward the source as seen from the polarimeter.
Mueller matrix polarimeters may be considered as a pair of Stokes vector polarimeters working in concert to determine the polarization properties of a particular material. Specifically, one Stokes vector polarimeter coupled to a light source and operating “in reverse”, is employed to now generate (as opposed to measure) known polarization states. These states are then made incident on a sample under test and the second Stokes vector polarimeter serves to analyze the light transmitted (or reflected or scattered) through the sample. The first polarimeter is called the polarization state generator while the second polarimeter is the polarization state analyzer.
Mueller polarimeters perform a series of at least 16 measurements using unique generator and analyzer states to deduce the 4 x 4 so-called Mueller matrix. As with the Stokes vector, the Mueller matrix describes completely the polarization properties of the sample. From this matrix, a number of optical properties of the sample may be deduced including diattenuation, retardance, and depolarization index. Diattenuation and retardance may further be resolved into linear and circular polarization.
The linear retardance of a sample is indicative of the phase shift imparted to an incident beam and is directly related to the material’s linear birefringence, while the circular retardance is indicative of its circular birefringence, often referred to as its optical activity. Noting that the sample’s light modifying behavior is representative of the (an)isotropy of the material’s structure, a great deal of information about both its short and long range organization may be determined from a polarimetrically resolved measurement. Indeed polarimeters have been used to determine the birefringence of all types of materials in all types of environments including target sensing, quality control, and even medical applications.
Applications of polarimeters
Now that we know what a polarimeter is and have a rough idea of how it is made, what is a polarimeter good for? Why would you build one in the first place?
Scientific research. Polarimeters can help us find out a great deal of information when doing research into materials that are being studied. Optically active compounds (compounds that cause light to become polarized) can be identified when studied with a polarimeter. Not only can they be identified, but the polarization state can yield information on the molecular structure of completely new compounds and knowledge of a materials molecular structure helps us know how that material can be used to improve our quality of life.
Better Medicines. Different fluids, compounds, and materials reflect polarized light in different ways. Using a polarimeter, we can exploit this fact by measuring the polarization transmitting (or reflecting) properties of any material, making sure that all kinds of manufacturing processes are being done correctly. For example, polarimeters help in keeping us healthy. In pharmaceutical applications, many of the chemicals used in making our medicines must be pure. Many of these pure chemicals have very definite and well known polarizing characteristics. If a polarimeter is used to monitor the light transmitted (or reflected) from these chemicals and the result is not right for that chemical, then we know that there is a contaminant in the chemical and the mixing process can be stopped before an inferior (possibly useless or even harmful) medicine is created.
Better Food. An application similar to the pharmaceutical industry is the food industry. Polarimeters are used in many food processing situations to monitor the quality of the food and to detect contaminants or to ensure that mixtures are composed of the correct concentrations of the individual ingredients. Sugars (glucose, fructose, sucrose, etc.) in particular have very distinctive polarization signatures so polarimeters are very important in identifying the purity or concentrations of these sweeteners to make sure that our foods taste just right.
Safety. When light reflects off of some surfaces, there is very little polarization. Off of other surfaces, there is a great deal of polarization. When ice is on a road surface or an airplane wing, the ice has different polarization characteristics than the airplane wing or the surface of the road. By using polarimeters to monitor these reflections, one can detect the presence of ice and know if the road is safe to drive on. Likewise, in the aviation industry, ice on an airplane's wing can have catastrophic results so polarimeters can be employed to help detect the presence of ice.
Military and Surveillance. Polarization is a property that opens up the possibility of detecting things that might go undetected by other means. For example, when a land mine is buried the dirt that is used to cover up the mine has a different polarization signature from the surrounding soil. So, in a hostile environment, if a polarimeter is flown above a dirt road that a convoy will be using it can detect areas of the road that have been disturbed. This section of the road can then be investigated before a vehicle drives over it and potentially is damaged and people are injured or even killed. Polarimeters are also very good at detecting man made objects. There are times when neither visible nor infrared light can do a good job of detecting an object that will stand out like a sore thumb when examined by a polarimeter.
As you can see, polarimeters add a great deal to our quality of life. If you have an application where a polarimeter might be useful, feel free to call. For more information on polarimeters, you may also refer to our pages on polarization and polarimetry.
