Advanced Optical Technologies Research and Development in Physical Optics

Active/Laser Polarimetry FAQ

What is Laser Polarimetry?

Laser polarimetry consists of illuminating material objects with a polarized probe laser beam and recording the reflected or transmitted laser light, which defines unique polarization signatures that can be utilized for rapid identification and/or assessment of physical state. The polarization signature provides the data needed to determine the material’s relationship to a reference material or to discriminate the object from background and/or clutter.

How does Laser Polarimetry Differ from Ellipsometry?

Ellipsometry applies models of polarized light interaction with materials to measure parameters such as thickness and refractive index. For many materials accurate models do not exist, so ellipsometry is limited to relatively simple material systems. By utilizing machine-learning algorithms to discover patterns in polarization-signature data, laser polarimetry can be applied to more general material systems than ellipsometry. AOT’s polarization-components techniques (PCT) are the application of machine-learning algorithms to polarization signatures.

What’s the Difference between Active Polarimetry and Passive Polarimetry?

Active polarimetry utilizes a laser beam to stimulate a material response. The set of responses to a complete basis-set of polarization states is termed the polarization signature and is represented mathematically by the Mueller matrix, which describes the complete linear response to an electromagnetic wave. Passive polarimetry relies on ambient light sources, most commonly the Sun or thermal infrared emission. Unlike a laser beam, the polarization state of ambient light cannot be controlled, and passive polarimetry cannot provide the complete polarization signature. Passive polarimeter data is actually a subset of the active signature. While passive polarimetry can be realized with simpler equipment, it has much less discriminatory power than active polarimetry.

What are Applications of Laser Polarimetry?

Laser polarimetry is a solution for applications that benefit from rapid, non-destructive identification and assessment of materials. It can be deployed at long ranges and in harsh environments such as process control, space, and tactical scenarios, and can be integrated into existing sensor systems to provide full-spectrum sensing capability. Some examples include identification of man-made objects in cluttered environments, inspection and health assessment of structural composite materials, and quality control of manufactured products.

Can Laser Polarimetry Improve Production?

Laser polarimetry can provide rapid, online discrimination of product material state in comparison to desired product quality. If you have a need to determine material quality during manufacturing, this capability can be used to improve your product process control.

How is Laser Polarimetry Applied?

Polarimeter operation can be as simple as “point, acquire, and read,” or can entail more sophisticated statistical data collection and interpretation for advanced process control. Monitoring systems can be automated to run without an operator and transmit product statistics to a facility network. AOT can implement a solution for your unique application and make it usable by your staff. AOT will perform an assessment to determine the feasibility of laser polarimetry for your application. This may include preliminary material characterization in our polarimeter laboratory. Once we have determined that PCT has a high probability of success for your application, we will use your material samples to develop a more complete signature database and customized PCT algorithms to operate on the data. We will customize hardware designs for your application and integrate the new algorithms and hardware into a complete system for installation at your site. The following diagram illustrates the typical development roadmap for a custom application:

Custom Application Technical Roadmap

AOT develops stand-alone polarimeters as well as components for integration with larger systems. Existing electrical utility infrastructure is usually sufficient to power a laser-polarimetry system, and size and weight are generally small enough for an individual to install, operate, and maintain the system.

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