Polarization switching lidar device and method

A method for remote detection and characterization of at least one airborne aggregation of particulates utilizing a polarization switching lidar device, the method comprising:

• generating a linearly polarized pulsed laser light beam having a predetermined direction of linear polarization;
• using at least a first actively controlled retarder, sequentially controllably switching a polarization state of the polarized pulsed laser light beam between a circularly polarized state polarized into a predetermined rotational sense, when the at least the first actively controlled retarder is controllably switched into a quarter-wave retardation state, and into a linearly polarized state linearly polarized in a direction substantially equivalent to the predefined direction of linear polarization when the at least the first actively controlled retarder is controllably switched into a zero retardation state such that a transmitted portion of polarized pulsed laser light beam exiting the at least the first actively controlled retarder is linearly polarized in the predetermined polarization direction when the at least the first actively controlled retarder is in the zero retardation state while the transmitted portion of polarized pulsed laser light beam exiting the at least the first actively controlled retarder is circularly polarized having the predetermined rotational sense when the at least the first actively controlled retarder is in the quarter-wave retardation state;
• scanning the transmitted portion of polarized pulsed laser light beam exiting the actively controlled retarder by at least a first telescoping assembly arranged to intersect the transmitted portion of polarized pulsed laser light beam exiting the actively controlled retarder and controllably redirect the intersected polarized pulsed laser light beam into a predetermined space angle toward at least one airborne aggregation of particulates;
• backscattering the scanned transmitted portion of the polarized pulsed laser light beam sequentially polarized into the circularly polarized state having the predetermined rotational sense and into the linearly polarized state having the predetermined polarization direction so that a fraction of photons scatters back from at least one airborne aggregation of particulates such that the photons in circularly polarized state having the predetermined rotational sense acquire an opposite rotational sense of circular polarization, while at least a fraction of photons polarized in the predetermined linearly polarized state, when scattered back, acquires a linear polarization state polarized in an orthogonal direction relative to the predetermined direction of linear polarization;
• collecting photons from the predetermined space angle and redirecting the collected photons onto the actively controlled retarder by at least a second telescoping assembly;
• sequentially converting by at least a second actively controlled retarder in the quarter-wave retardation state the collected backscattered photons having the circularly polarized state polarized in the opposite rotational sense relative to the rotational sense of the predetermined sense of circular polarization into the linearly polarized state having the polarization state polarized in an orthogonal direction relative to the predetermined direction of linear polarization, while transmitting the scattered back photons polarized in the linear polarization state having orthogonal direction of linear polarization relative to the predetermined direction of linear polarization when the actively controlled retarder in the zero retardation state, and redirecting the converted photons onto at least one polarizer;
• selectively separating the converted photons collected sequentially onto the at least one polarizer by transmitting only the linearly polarized photons having orthogonal direction of linear polarization relative to the predetermined direction of linear polarization;
• optically matching the transmitted linearly polarized photons having orthogonal direction of linear polarization relative to the predetermined direction of linear polarization using an optical matcher arranged to collect at least a fraction of the transmitted linearly polarized photons having orthogonal direction of linear polarization relative to the predetermined direction of linear polarization and focus the transmitted linearly polarized photons having orthogonal direction of linear polarization relative to the predetermined direction of linear polarization onto a photodetector arranged to generate at least two electronic signals proportional to the transmitted linearly polarized photons having orthogonal direction of linear polarization relative to the predetermined direction of linear polarization;
• separating at least one electrical signal of the at least two electrical signals, the separated at least one electrical signal being generated during the quarter-wave retardation state, from the at least another electrical signal, the at least another electrical signal being generated during the zero retardation state of the actively controlled retarder, and storing the separated signals into at least two dedicated memory sections.