Method and system for optical object detection

Abstract

A system for remote optical detection of objects in an environment comprises a laser system configured to transmit into the environment a laser beam diverged along two orthogonal directions, and an optical sensor configured to generate a signal responsive to backscattered optical radiation received from the objects in the environment. A processor detects in the environment presence of one or more objects having a subtended solid angle at the sensor that is less than a solid angle of the laser beam.

Description

[0001] METHOD AND SYSTEM FOR OPTICAL OBJECT DETECTION

[0002] RELATED APPLICATION

[0003] This application claims the benefit of priority of Israeli Patent Application No. 316778 filed on November 3, 2024, the contents of which are incorporated herein by reference in their entirety.

[0004] FIELD AND BACKGROUND OF THE INVENTION

[0005] The present invention, in some embodiments thereof, relates to remote detection and, more particularly, but not exclusively, to a method and system for remote optical object detection.

[0006] Light detection and ranging (LIDAR) is a remote sensing technology that measures distances to targets and creates detailed spatial representations of environments. A LIDAR system consists of a light source, typically a laser that emits light at specific wavelengths in the infrared, visible, or ultraviolet portions of the electromagnetic spectrum, and an optical receiver that detects the backscattered light from targets. The system operates by transmitting laser light toward objects, which scatter the light back to the receiver for analysis.

[0007] Examples where systems similar to LIDAR are used are referenced below.

[0008] An article titled "Laser Ranging at Few-photon Level by Photon-Number-Resolving Detection" by Bao et al., in Journal of Applied Optics Vol. 53 (2014) describes demonstrating laser ranging at a few-photon level using photon-number-resolving detectors.

[0009] An article titled "Low Intensity LiDAR using Compressed Sensing and a Photon Number Resolving Detector" by Sher et al., in Proceedings of the SPIE Vol. 10546 (2018) describes combining a high sensitivity photon number resolving diode with machine learning and a micromechanical digital mirror device to achieve 3D scanning.

[0010] An article titled "Enhancing LiDAR performance using threshold photon-number-resolving detection" by Wu et al., 2024, Optics Express, 32, 2:2574, discloses a detection scheme which combines noise suppression of threshold detection with signal amplification of photon-number- resolving detectors.

[0011] U.S. Published Application No. 2023228851 discloses an illumination system for scanned LIDAR, including a laser, an optic that receives the laser output and produces a fan-beam output, and a scanning system that scans the fan-beam output across a desired angular span.

[0012] SUMMARY OF THE INVENTION

[0013] According to some embodiments of the invention the present invention there is provided a system for remote optical detection of objects in an environment. The system comprises: a laser system configured to transmit into the environment a laser beam diverged along two orthogonal directions; an optical sensor configured to receive optical radiation backscattered from objects in the environment and generate a signal responsive to the received optical radiation; and a processor, configured to detect in the environment presence of at least one object having a subtended solid angle at the sensor that is less than a solid angle of the laser beam.

[0014] According to some embodiments of the invention the laser system comprises a laser source configured to produce a laser beam and a beam diverging optical element, configured to diverge the laser beam.

[0015] According to some embodiments of the invention the processor is configured to generate output pertaining to the presence of the object without mapping and / or imaging the environment.

[0016] According to some embodiments of the invention the processor is configured to register the presence of the at least one object while not determining a location of the at least one object.

[0017] According to some embodiments of the invention the system comprises a scanner configured to divert the laser beam into multiple sequential transmission optical paths to the environment.

[0018] According to some embodiments of the invention the scanner comprises a mirror configured to rotate independently about two orthogonal axes.

[0019] According to some embodiments of the invention the system comprises a further scanner configured to divert the backscattered radiation into respective multiple sequential reception optical paths to the sensor.

[0020] According to some embodiments of the invention the system comprises a controller configured to rotate the scanner and the further scanner in synchrony.

[0021] According to some embodiments of the invention the laser system is configured to generate laser pulses.

[0022] According to some embodiments of the invention the laser system is configured to transmit multiple laser beams, and the sensor is operable to receive multiple sets of backscattered optical radiation and to responsively generate respective multiple signals.

[0023] According to some embodiments of the invention the processor is configured to apply compressed sensing to the multiple signals to classify the at least one object.

[0024] According to some embodiments of the invention the system comprises a controller and optics configured to narrow the laser beam, and transmit multiple narrowed beams to the environment.

[0025] According to some embodiments of the invention the sensor is configured to receive multiple sets of radiation from the environment in response to the multiple narrowed diverged beams, and to output multiple signals, and the processor is configured to analyze the multiple signals to classify the object.

[0026] According to an aspect of some embodiments of the present invention there is provided a method of detecting presence of an object in an environment. The method comprises: transmitting into the environment a laser beam diverged along two orthogonal directions; receiving optical radiation backscattered from a solid angle subtended by the object, wherein the subtended solid angle is less than a solid angle of the laser beam; generating a signal responsive to the received optical radiation; and analyzing the signal to detect the presence of the object, and generating output pertaining to the detection.

[0027] According to some embodiments of the invention the method comprises producing a laser beam and diverging the laser beam.

[0028] According to some embodiments of the invention the output is devoid of mapping and / or imaging of the environment.

[0029] According to some embodiments of the invention the output is devoid of information pertaining to a location of the at least one object in the environment.

[0030] According to some embodiments of the invention the laser beam is characterized by a cross- sectional profile devoid of functional segmentation.

[0031] According to some embodiments of the invention the cross-sectional profile has a single irradiance peak along any direction within a cross-section of the diverged laser beam.

[0032] According to some embodiments of the invention the cross-sectional profile is devoid of any irradiance peak along any direction within a cross-section of the diverged laser beam.

[0033] According to some embodiments of the invention the at least one object is positioned within an off-center region of the diverged laser beam.

[0034] According to some embodiments of the invention the divergence of the laser beam is constant at all times, irrespectively of a distance to the object.

[0035] According to some embodiments of the invention a divergence of the laser beam is selected such that an attenuation of the backscattered radiation is proportional to an nth power of a range to the object, the n being greater than 3, e.g., about 4.

[0036] According to some embodiments of the invention a cross-sectional shape of the laser beam is characterized by an aspect ratio of from about 0.5 to about 1.5.

[0037] According to some embodiments of the invention the method comprises diverting the laser beam into multiple sequential transmission optical paths to the environment.

[0038] According to some embodiments of the invention the diverting is by a mirror configured to rotate independently about two orthogonal axes. According to some embodiments of the invention the orthogonal axes comprise an elevation axis and an azimuthal axis.

[0039] According to some embodiments of the invention the method comprises diverting the backscattered radiation into respective multiple sequential reception optical paths, wherein the receiving comprises receiving optical radiation propagating along each of the reception optical paths.

[0040] According to some embodiments of the invention the diverting of the backscattered radiation is synchronous with the diverting of the laser beam.

[0041] According to some embodiments of the invention a reception optical path and a corresponding transmission path have a common divergence.

[0042] According to some embodiments of the invention the laser beam is a pulsed laser beam.

[0043] According to some embodiments of the invention the pulsed laser beam is characterized by a pulse duration of from about 0.5 ns to about 5 ns.

[0044] According to some embodiments of the invention the method comprises transmitting multiple laser beams, receiving multiple sets of backscattered optical radiation, and responsively generating respective multiple signals.

[0045] According to some embodiments of the invention the method comprises applying compressed sensing to the multiple signals to classify the at least one object.

[0046] According to some embodiments of the invention the method comprises narrowing the laser beam, and transmitting multiple narrowed beams to the environment.

[0047] According to some embodiments of the invention the method comprises receiving multiple sets of radiation from the environment in response to the multiple narrowed diverged beams, generating multiple signals responsively to the multiple sets of radiation, and analyzing the multiple signals to classify the object.

[0048] According to some embodiments of the invention the object is in atmospheric air or vacuum, and the laser beam is transmitted through the atmospheric air or vacuum.

[0049] According to some embodiments of the invention object is in a liquid transparent to the laser beam, and the laser beam is transmitted through the liquid.

[0050] According to some embodiments of the invention the sensing is by a photon number resolving detector.

[0051] Unless otherwise defined, all technical and / or scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of embodiments of the invention, exemplary methods and / or materials are described below. In case of conflict, the patent specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and are not intended to be necessarily limiting.

[0052] Implementation of the method and / or system of embodiments of the invention can involve performing or completing selected tasks manually, automatically, or a combination thereof. Moreover, according to actual instrumentation and equipment of embodiments of the method and / or system of the invention, several selected tasks could be implemented by hardware, by software or by firmware or by a combination thereof using an operating system.

[0053] For example, hardware for performing selected tasks according to embodiments of the invention could be implemented as a chip or a circuit. As software, selected tasks according to embodiments of the invention could be implemented as a plurality of software instructions being executed by a computer using any suitable operating system. In an exemplary embodiment of the invention, one or more tasks according to exemplary embodiments of method and / or system as described herein are performed by a data processor, such as a computing platform for executing a plurality of instructions. Optionally, the data processor includes a volatile memory for storing instructions and / or data and / or a non-volatile storage, for example, a magnetic hard-disk and / or removable media, for storing instructions and / or data. Optionally, a network connection is provided as well. A display and / or a user input device such as a keyboard or mouse are optionally provided as well.

[0054] BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0055] Some embodiments of the invention are herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of embodiments of the invention. In this regard, the description taken with the drawings makes apparent to those skilled in the art how embodiments of the invention may be practiced.

[0056] In the drawings:

[0057] FIG. 1 is a schematic illustration of an object detection system, according to an embodiment of the present invention;

[0058] FIG. 2 is a flowchart of steps involved in operating the system, according to an embodiment of the present invention; and

[0059] FIG. 3 schematically illustrates an accumulative photon graph where an object signal is present, according to an embodiment of the present invention. DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

[0060] The present invention, in some embodiments thereof, relates to remote detection and, more particularly, but not exclusively, to method and system for remote optical object detection.

[0061] Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not necessarily limited in its application to the details of construction and the arrangement of the components and / or methods set forth in the following description and / or illustrated in the drawings and / or the Examples. The invention is capable of other embodiments or of being practiced or carried out in various ways.

[0062] Conventionally, LIDAR systems have been employed for imaging and / or mapping surfaces to generate precise, three-dimensional information about their shape, at a high resolution. LIDAR uses pulses of a narrow laser beam to reconstruct the shape of an object in a region of interest (ROI) towards which the beam is directed. As a numerical example, a pulse with a vertical and horizontal divergence of 0.1 mrad x 0.1 mrad covers an area of 10 cm x 10 cm at a distance of 1 km, and so, providing the pulse has sufficient energy, can reconstruct the shape of an object with a resolution of 10 cm, by reflecting back a portion of the transmitted pulse energy.

[0063] To cover a larger angular range of an ROI, for example 0.5 rad x 0.5 rad, the narrow beam pulse is scanned to cover the larger region. The number of pulses needed to cover the larger region is given by the ratio of the designated region divergence to the beam divergence, which in the example here is 2.5 x 10^. For a typical pulse repetition rate of 50 kHz, this requires approximately 500 s. This time may be reduced by increasing the pulse repetition rate; however, to reduce it to approximately 1 s requires a repetition rate of 25 MHz, and such a rate may only be available for systems delivering low energy pulses.

[0064] Thus, number of pulses / scans required to cover a given ROI is, other factors being equal, equal to the square of the ratio of the linear divergence of the ROI to the linear divergence of the pulsed laser beam.

[0065] The radiation returning from the ROI comprises noise (background) and signal photons. For an ROI that is in broad daylight, the signal to noise ratio (SNR) using a photo-diode detector may be -100 dB or less, and even though this ratio can be improved by spatial and spectral filtering, the improvement may not compensate sufficiently to provide a readable signal.

[0066] Embodiments of the present invention overcome the long scanning time and the poor SNR, by providing a system that diverges the pulses of the beam optionally and preferably along two orthogonal directions, so that the diverged beam may be scanned over the ROI in a short time period, e.g., about 5 s or less. Divergence of a beam herein is preferably two dimensional, namely in two directions orthogonal to the direction of light propagation. For example, the divergence can be along a vertical and a horizonal axes perpendicular to the axis of propagation. This is of the present embodiments achieved by applying a two-dimensional beam diverging optical element which receives a narrow laser beam and diverges it to output a diverged beam shaped as a cone. This is unlike a one-dimensional beam diverging optical element, which output a so-called "fan-beam" that has wide angular coverage in one direction (e.g., vertical) but remains narrow in the orthogonal direction (e.g., horizontal). The cross-section of the cone-beam can be of any shape, e.g., circular, elliptical, polygonal (such as triangular, rectangular, quadrangular, pentagonal, hexagonal, octagonal and the like, or irregular, non-convex, concave, or complex polygon), multi-faceted, amorphous, irregular, or freeform.

[0067] In some embodiments of the present invention laser applied to produce the beam is configured to output at least one optical pulse, and in some embodiments, the system operates with a single pulse. The pulse or pulses of the beam have relatively short duration, typically from about 0.5 ns to about 5 ns, e.g., approximately 1 ns. In some embodiments of the present invention a photon number resolving detector (PNRD) is employed as a sensor. This is advantageous for overcoming the poor SNR. Preferably, the PNRD is operated as with a response time equal to the pulse time. For example, for each transmitted set of transmitted pulses the respective signals from the PNRD can be placed in an accumulative photon graph, where the accumulation bin times are preferably sufficiently short for ensuring that the more frequent signals are statistically generated by thermal radiation sources, such as the Sun, and collected from the scanned section of the ROI, which have a probability of occurrence close to zero. Thus, when a signal does occur, the height of its bin, or of one of the bins of a set of contiguous bins herein termed a “signal bin set,” is substantially larger than the height of the bins that correspond to the background bins. A typical bin time suitable for these embodiments is from about 0.5 ns to about 5 ns, e.g., about 1 ns.

[0068] Unlike conventional LIDAR systems, the optical detection technique of the present embodiments is preferably not used for imaging and / or mapping. Instead, it is focused on the rapid scanning of large areas to detect the presence of objects at low resolution, optionally and preferably without determining the exact location of these objects, aside from the general direction covered by the width of the beam. For example, the present embodiments contemplate a system and method that issue an alert when the presence of an object is detected, but do not provide a map or image of the environment containing the object, and do not indicate its precise position within that environment. Thus, the present embodiments contemplate rapid scanning at the expense of resolution and imaging capability. A prerequisite for operational imaging of a surface is relatively low energy loss, where the attenuation of the backscattered radiation from the objects of interest is proportional to the square of the range to the respective object, a behavior known as "the 1 / r2power law." To achieve this prerequisite, traditional LIDAR systems use a narrow beam, or the aforementioned "fan-beam".

[0069] The optical detection technique of the present embodiments differs from traditional LIDAR systems in that it utilizes a divergent beam exhibiting a relatively wide angular spread in two orthogonal directions, where the degree of divergence is selected such that the attenuation of the backscattered radiation is proportional to the nth power of the range to the object, where n is greater than 3, for example, about 4. Thus, the present embodiments contemplate a configuration in which the attenuation of the backscattered radiation from the objects of interest is proportional to the fourth power of the range to the respective object, a behavior referred to herein as "the 1 / r4power law." These embodiments are useful because, although the attenuation is too great to allow imaging and mapping, the significant beam divergence provides rapid scanning. The 1 / r4power law is characteristic to radar systems, which operate at non-optical frequencies and similarly inhibit imaging and mapping. The inventors surprisingly found that introducing a radar-like characteristic to a LIDAR system provides the LIDAR system with enhanced acquisition speed.

[0070] While in some embodiments the presence of an object is detected without actually determining its position, some embodiments of the invention do contemplate extracting more information from the received radiation, both when a plurality of pulses are employed and when a single pulse is employed. For example, the presence of a signal bin set allows a processor operating the system to determine that an object exists within a section of the ROI that is irradiated by the scan having the signal bin set. In addition, the processor can register the time of transmission of each pulse, and the reception time of the signal bin set, as well as the pulse’s direction in elevation and azimuth. This allows the processor to determine a distance from the system to the object, and / or the elevation and azimuth of the section of the ROI containing the object. The processor can alternatively or additionally iterate the pulse generating the signal beam set, and apply compressed sensing to the signals generated by the PNRD. Using compressed sensing the processor can classify the object, and may optionally and preferably also find a position of the object within the section of the irradiated ROI. Also contemplated, are embodiments in which the processor provides an imaging device with a narrow field of view towards the section of the ROI, and / or actively scan that section, to classify and find the object’s position therein.

[0071] Referring now to the drawings, FIG. 1 is a schematic illustration of an object detection system 10, according to an embodiment of the present invention. System 10 is operated by a processor 12, which may also function as a controller. Alternatively, system 10 can comprise a separate controller (not shown). System 10 comprises a radiation illuminator 14, and a radiation receiver 16. In the following description of system 10, except where otherwise indicated, for clarity and simplicity illuminator 14 and receiver 16 are assumed to be mounted on a common chassis 18, so that the system as a whole may be directed, to a direction 22 towards a region of interest (ROI) 36 in the environment, by rotation of the chassis. Those having ordinary skill in the art will be able to adapt the description, mutatis mutandis, for the cases when illuminator 14 and receiver 16 are not so mounted, and all such arrangements are assumed to be comprised within the scope of the present invention.

[0072] Radiation illuminator 14 is preferably in the form of a laser system configured to transmit into the environment a laser beam 32 that diverges along two orthogonal directions. The two orthogonal directions define a plane perpendicular to the propagation direction of the center of the beam. In some embodiments of the present invention a constant divergence of laser beam 32 is maintained at all times, irrespectively of a distance to the objects which system 10 is designed to detect. The divergence of laser beam 32 is optionally and preferably selected such that the attenuation of radiation backscattered from objects in the environment is proportional to the nth power of the range to the respective object, as further detailed hereinabove. The cross-sectional shape of laser beam 32 is preferably characterised by an aspect ratio of from about 0.5 to about 1.5, or from about 0.6 to about 1.4, or from about 0.7 to about 1.3, or from about 0.8 to about 1.2, or from about 0.9 to about 1.1, or from about 0.95 to about 1.05. The aspect ratio is defined as the ratio between the largest and smallest widths of the beam's cross-section.

[0073] In some embodiments, the divergent angle of diverged beam 32 is smaller than an angle subtended by the ROI 36 at the system by at least a factor of two. Preferably, the divergent angle of the diverged beam 32 is smaller than an angle subtended by the ROI at the system by at least an order of magnitude

[0074] Preferably, laser beam 32 is characterized by a cross-sectional profile devoid of functional segmentation.

[0075] As used herein, "devoid of functional segmentation" means that the cross-sectional radiance distribution of the beam is described by a single continuous functional form over the beam’s domain, with no regions governed by different functions, or by a piecewise function.

[0076] The cross-sectional profile of beam 32 can, in some embodiments of the present invention, have a single irradiance peak along any direction within a cross-section of laser beam 32 without secondary maxima.

[0077] Laser source 20 may be of any kind, spanning ultraviolet (UV), visible, near-infrared (NIR), short-wave infrared (SWIR), mid-wave infrared (MWIR), and long-wave infrared (LWIR), and implemented using any architecture. Representative examples for implementations suitable for embodiments of the present invention include, without limitation, solid-state lasers implemented as rod, slab, thin-disk, or microchip lasers doped with Nd, Yb, Er, Tm, or Ho (e.g., Nd:YAG, Yb:YAG, Er:YAG), rare-earth-doped fiber lasers (e.g., Er-, Er / Yb-, Tm-, Ho-doped silica or fluoride fibers) or semiconductor lasers such as edge-emitting, DFB / DBR, external-cavity, VCSEL, and VECSEL devices based on InGaAs, GaAs / AlGaAs, or related III-V alloys. Output may be generated directly from the gain medium or produced via nonlinear conversion, including frequency doubling or higher harmonics, Optical Parametric Oscillations (OPO) or Optical Parametric Amplification (OPA), or Raman shifting.

[0078] Laser source 20 typically generate a laser beam 24 having a relatively narrow beam divergence, e.g., a beam divergence of less than 1 mrad or less than 0.5 mrad or 0.1 mrad along each of the two orthogonal directions. The solid angle covered by laser beam 24 is approximately the square of the linear divergence. For example, when the divergence is 0.1 mrad along one of the orthogonal directions, the solid angle is about 0.1 mrad x 0.1 mrad. When laser beam 24 has a narrow divergence, the laser system preferably comprises a beam diverging optical element 28, which diverges laser beam 24 to divergent beam 32. Beam diverging optical element 28 is optionally and preferably a two-dimensional beam diverging optical element that diverges laser beam 24 along two orthogonal directions as further detailed hereinabove. The beam divergence of beam 32 is substantially larger (e.g., at least two times larger or at least five times larger or at least ten times larger or at least twenty times larger or at least thirty times larger) than the beam divergence of beam 24. For example, beam 32 can have a beam divergence of at least 1 mrad or at least 2 mrad or at least 3 mrad or at least 6 mrad or at least 12 mrad or at least 24 mrad.

[0079] The laser system is optionally and preferably operated by the controller to emit pulses. In a disclosed embodiment the pulses have a time duration of from about 0.5 ns to about 5 ns, e.g., about 1 ns. Embodiments utilizing pulses with a duration shorter than 0.5 ns or longer than 5 ns are also contemplated. In embodiments of the laser source 20 of the laser system generates laser pulses having pulse energy of from about 50 nJ to about 80 pJ. Other embodiments may have a laser pulse energy outside this range. The description below provides more detail on the laser pulse energy that may be used.

[0080] ROI 36 of the environment is assumed to comprise an object of interest 38 which is substantially smaller, typically by several orders of magnitude, than ROI 36. Object 38 can be at any position within ROI 36 that is illuminated by photons of beam 32, either at a central region of beam 32 or at an off-center region thereof. Photons in beam 32 arrive at object 38 and are backscattered from object 38. The backscattered optical radiation is shown in FIG. 1 as one or more sets 60A, 60B. Receiver 16 of system 10 is designed to receive a portion of the backscattered radiation. In some embodiments, the receiver 16 is configured to detect radiation from the ROI any level of radiation, irrespective of intensity. In these embodiments, the operation protocol of system 10 does not employ any lower detection limit or a minimum threshold.

[0081] Receiver 16 comprises a sensor 48, operable to receive optical radiation and responsively generate an electrical signal 68, which, in some embodiments of the present invention is a digital signal, but can also be an analog signal. Due to the large divergence of beam 32, the subtended solid angle of object 38 at sensor 48 that is less than a solid angle of beam 32. It is appreciated that due to this relation between the solid angles, a great portion of the backscattered radiation from object 38 is lost, and only a small fraction, for example, less than 10’9, or less than IO10, or less than 1011, or less than 1012, of the backscattered photons actually arrive at sensor 48.

[0082] The sensitivity of sensor 48 is therefore selected to allow such a small fraction to be detected, and preferably to allow single photon detection. In some embodiments, signal 68 is a binary yes / no signal, indicative of whether or not a photon was detected. In some embodiments of the present invention sensor 48 comprises a PNRD. A PNRD is an improved single-photon detector in which, instead of generating a binary detection signal, it distinguishes how many photons arrive in a defined temporal or spatial mode by outputting an estimate of the photon count per event or per time bin. Examples of types of PNRD suitable for the present embodiments include: geiger- mode SPAD (Single-Photon Avalanche Diode) arrays, silicon photomultipliers (SiPM), MPPC (Multi-Cell Single Photon Multiplier), silicone avalanche photodiodes (Si-APD), InGaAs / InP avalanche photodiodes, and InGaAs / InP geiger-mode SPAD arrays. Preferably, the PNRD is reverse-biased so as to operate in a Geiger mode, wherein a single photon impinging on the PNRD causes an avalanche of photoelectrons. The effective detection time of the PNRD is preferably less than 10 ns or less than 9 ns or less than 8 ns or less than 7 ns or less than 6 ns or less than 5 ns or less than 4 ns or less than 3 ns or less than 2 ns, e.g., about 1 ns.

[0083] In some embodiments of the present invention beam 32 is transmitted to a scanner 42, which diverts a series of the diverged beams sequentially so as to cover a larger solid angle required for ROI 36. Since, as is explained further below, the results from each diverged beam 32 are immediately available, system 10 may detect the existence of the object of interest in the area covered by a given diverged beam before ROI 36 has been completely scanned. Scanner 42 can be of any type known in the art. Representative examples of scanning mechanisms suitable for the present embodiments include, wherein said one or more mirrors, acousto-optic deflectors, electrooptic beam steerers, liquid crystal beam steerers, rotating prisms, phased array optical beam steerers, diffractive optical elements, holographic optical elements, spatial light modulators, fiber optic switch arrays.

[0084] Optionally and preferably scanner 42 comprises a dual axis mirror 40 that has independent orthogonal axes of rotation, herein assumed to be elevation and azimuth axes of rotation, and the rotation about each axis is controlled by the controller, which optionally and preferably rotates the mirror separately in azimuth and in elevation.

[0085] By way of example, FIG. 1 illustrates two diverted beams 44A, 44B that are directed by scanner 40 and that are transmitted towards ROI 36. The diverted beams are collectively referred to as diverted beams 44. Preferably, each beam of diverted beams 44 has substantially the same divergence.

[0086] The number, N, of diverted beams 44 in the series of beams transmitted to cover ROI 36 is given by: where ARQI *Sthe solid angle subtended by ROI 36 at system 10, and Ap> is the solid angle of a diverted beam 44 transmitted from the system.

[0087] From equation (1), by way of example, for a diverted beam having a solid angle of 2 mrad x 2 mrad and an ROI having a solid angle of 0.5 rad x 0.5 rad, N is about 62,500. Thus, if laser source 20 is pulsed at, for example, 50 kHz, ROI 36 can be covered in approximately 1.25 s.

[0088] In embodiments in which scanner 42 is employed, receiver 16 optionally and preferably also comprises a scanner, shown at 50. Scanner 50 can employ any of the technologies listed above with respect to scanner 42. For example, scanner 50 can comprise a dual axis mirror 52 which can also be controlled by the controller. Preferably, the controller ensures that dual axis mirror 52 rotates synchronously with dual axis mirror 40, as is described further below. Dual axis mirror 52 is preferably configured to rotate independently about two orthogonal axes, herein assumed to comprise elevation and azimuth axes, and the direction of the mirror about each axis is set by the controller. Each reception optical path provided by scanner 50 preferably has a common divergence with a corresponding transmission path provided by scanner 42.

[0089] In some embodiments a digital micromirror device (DMD) 56, controlled by the controller, is interposed between mirror 52 and sensor 48. The DMD may be implemented to allow system 10 to apply compressed sensing to the signals from the sensor, as is described below.

[0090] While FIG. 1 illustrates the illuminator 14 and the receiver 16 as having separate dual axis mirrors 40 and 52, this need not necessarily be the illuminator 14 and the receiver case, since, for some applications, it may be desired to use a common dual mirror for the illuminator and the receiver. Those having ordinary skill in the art will be able to adapt the description, mutatis mutandis, for systems where the illuminator and the receiver have a common mirror, so that all such systems are assumed to be comprised within the scope of the present invention.

[0091] In embodiments of the invention, receiver 16 is configured to acquire returning radiation rays from regions of ROI 36 irradiated by diverted beams 44. When receiver 16 is at substantially the same position as illuminator 14, dual axis mirror 52 and DMD 56 are configured to acquire incoming rays from substantially the same solid angle, in direction and divergence relative to the receiver, as diverted beams 44.

[0092] Thus, receiver 16 receives a returning set 60A of rays in a cone 64A having substantially the same elevation, azimuth, and divergence as diverted beam 44A, and a returning set 60B of rays in a cone 64B having substantially the same elevation, azimuth, and divergence as diverted beam 44B. The returning sets and the cones are collectively referred to herein as returning sets 60 and cones 64.

[0093] In some embodiments of the present invention system 10 comprises a bandpass filter 66 positioned to filter the backscattered radiation before it arrives at the sensor 48. The advantage of this embodiment is that it contribute to noise reduction. The central wavelength of the bandpass of filter 66 is selected to be the wavelength of the laser generated by laser source 20. The bandwidth of the bandpass filter 66 is preferably less than 12 nm (e.g., from about 1 nm to about 12 nm) or less than 11 nm (e.g., from about 1 nm to about 11 nm) or less than 10 nm (e.g., from about 1 nm to about 10 nm), or less than 9 nm (e.g., from about 1 nm to about 9 nm), or less than 8 nm (e.g., from about 1 nm to about 8 nm), or less than 7 nm (e.g., from about 1 nm to about 7 nm), or less than 6 nm (e.g., from about 1 nm to about 6 nm), or less than 5 nm (e.g., from about 1 nm to about 5 nm), or less than 4 nm (e.g., from about 1 nm to about 4 nm), or less than 3 nm (e.g., from about 1 nm to about 3 nm), or less than 2 nm (e.g., from about 1 nm to about 2 nm), e.g., about 1 nm.

[0094] Processor 12 acquires signal 68 from sensor 48 and analyzes it to detect the presence of object 38. In some embodiments of the present invention, processor 12 generates output pertaining to the presence of object 38 without mapping and / or imaging the environment, and in some embodiments of the present invention processor 12 registers the presence of object 38 while not determining the location of object 38. The information generated by processor 12 can be presented to the user of system 10 in any form convenient to the user. By way of example, FIG. 1 illustrates a user interface 72 having a screen 76 and a pointing device 80 that a user may use to interact with elements of system 10, typically via processor 12. In some embodiments screen 76 may also operate as the pointing device. In the illustrated example, the results are presented visually on screen 76, but embodiments of the invention may use any other method known in the art for result presentation, such as another visual, an audio, and / or a haptic method, and all such methods are assumed to be comprised within the scope of the present invention.

[0095] The present disclosure also relates to a method for detecting the presence of objects in the environment by employing a diverged laser beam for object detection, optionally and preferably without performing detailed mapping or imaging of the environment. Objects within the environment may be positioned within off-center regions of the diverged laser beam while still being effectively detected. The method receives optical radiation backscattered from a solid angle subtended by the object, where this subtended solid angle is less than the solid angle of the transmitted laser beam.

[0096] A method of detecting presence of an object in the environment according to some embodiments of the present invention comprises transmitting into the environment a laser beam diverged along two orthogonal directions (e.g., beam 32), receiving, for example, by sensor 48, optical radiation backscattered (e.g., radiation 60). The method generates, e.g., by sensor 48, a signal (e.g., signal 68) responsive to the received optical radiation, and analyzes signal 68 to detect the presence of the object, as further detailed hereinabove. Output pertaining to the detection is then generated. The laser beam may be either continuous wave or pulsed. In pulsed embodiments, the pulse duration may range from about 0.5 ns to about 5 ns. The cross-sectional shape of the laser beam is characterized by an aspect ratio ranging from about 0.5 to about 1.5, as further detailed hereinabove.

[0097] The diverged laser beam is optionally and preferably characterized by a cross-sectional profile that lacks functional segmentation, as further detailed hereinabove. Preferably, the cross- sectional profile exhibits a single irradiance peak along any direction within the cross-section of the diverged laser beam. Alternatively, the cross-sectional profile of the diverged laser beam can be devoid of any irradiance peak, for example, the cross-sectional profile can be generally uniform along any direction within the cross-section of the diverged laser beam or has a plateau without a peak along two or more direction within the cross-section of the diverged laser beam. The divergence of the laser beam optionally and preferably remains constant at all times, regardless of the distance to the target object.

[0098] The method may include diverting the laser beam into multiple sequential transmission optical paths to the environment. This diversion can be accomplished using a mirror (e.g., mirror 40) configured to rotate independently about two orthogonal axes as further detailed hereinabove. Such a configuration allows systematic scanning of the environment while maintaining the benefits of the diverged beam approach. Correspondingly, the method may include diverting the backscattered radiation, e.g., by means of mirror 52, into respective multiple sequential reception optical paths. The diverting of backscattered radiation optionally and preferably operates synchronously with the diverting of the laser beam. Each reception optical path and its corresponding transmission path preferably maintain a common divergence characteristic.

[0099] Advanced embodiments of the method involve transmitting multiple laser beams and receiving multiple sets of backscattered optical radiation, responsively generating respective multiple signals. These multiple signals can be processed by means of compressed sensing techniques to classify detected objects. The method may also narrow the laser beam and transmit multiple narrowed beams to the environment. Multiple sets of radiation from the environment can be received in response to these multiple narrowed diverged beams, and multiple signals responsive to the multiple sets of radiation can be generated. These signals can then be analyzed to classify detected objects.

[0100] The method is adaptable to various environmental conditions. Objects may be located in atmospheric air or vacuum, with the laser beam transmitted through the respective medium. Alternatively, objects may be situated in liquids that are transparent to the laser beam wavelength, allowing underwater or other liquid-medium detection applications. Thus, the present embodiments are useful for identifying the presence or counting of objects of interests such as birds, flying objects, satellites, as well as subaqueous objects.

[0101] As used herein the term “about” refers to ± 10 %

[0102] The terms "comprises", "comprising", "includes", "including", “having” and their conjugates mean "including but not limited to".

[0103] The term “consisting of’ means “including and limited to”.

[0104] The term "consisting essentially of" means that the composition, method or structure may include additional ingredients, steps and / or parts, but only if the additional ingredients, steps and / or parts do not materially alter the basic and novel characteristics of the claimed composition, method or structure.

[0105] As used herein, the singular form "a", "an" and "the" include plural references unless the context clearly dictates otherwise. For example, the term "a compound" or "at least one compound" may include a plurality of compounds, including mixtures thereof.

[0106] Throughout this application, various embodiments of this invention may be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.

[0107] Whenever a numerical range is indicated herein, it is meant to include any cited numeral (fractional or integral) within the indicated range. The phrases “ranging / ranges between” a first indicate number and a second indicate number and “ranging / ranges from” a first indicate number “to” a second indicate number are used herein interchangeably and are meant to include the first and second indicated numbers and all the fractional and integral numerals therebetween.

[0108] It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination or as suitable in any other described embodiment of the invention. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments, unless the embodiment is inoperative without those elements.

[0109] Various embodiments and aspects of the present invention as delineated hereinabove and as claimed in the claims section below find experimental support in the following examples.

[0110] EXAMPLES

[0111] Reference is now made to the following examples, which together with the above descriptions illustrate some embodiments of the invention in a non limiting fashion.

[0112] Example Parameter Values

[0113] An equation, similar to the radar equation, for the energy Erreceived from object of interest 38 in ROI 36, assuming that the size of the object of interest is less than the size of the section of the ROI being illuminated by a diverted beam 44, can be written in the form: where E is the energy of the diverted beam 44 irradiating the object, a is the albedo of object 38, s is the linear size of object 38, A is the linear optical aperture of receiver 16, D is the distance of system 10 to object 38, and ©beam is the linear divergence of the diverted beam 44.

[0114] Equation (2) may be rearranged to give an equation (3) for E, and as described below the equation may be used to estimate the pulse energy for laser 20. As is described herein, system 10 uses PNRD 48 to detect single photons from object 38 in ROI 36. Each photon has an approximate energy of 4- 10" 9 J, so that when, for example, PNRD 48 is to detect 10 photons, the value of Erin equation (3) is J. This value may be used to calculate the value of E, the energy of a pulse from laser 20, which can be used by system 10 to detect 10 photons.

[0115] The example herein assumes that the distance D from system 10 to ROI 36 is about 1 km, and the optical aperture A of receiver 16 is about 10 cm. The linear divergence ©beamsctby beam diverging optical element 28 is assumed to be about 2 mrad, so that a diverted beam 44 has a solid angle of about 2 mrad x 2 mrad. Object 38 in ROI 36 is assumed to have an albedo a of about 0.5, and the size s of object 38 is assumed to be about 10 cm.

[0116] Using the example values provided above in equation (3), E, the pulse energy of laser 20, is approximately 2 pj.

[0117] Referring back to equation (1), when ROI 36 subtends a solid angle of about 0.5 rad x 0.5 rad at system 10, and diverted beams 44 have solid angles of about 2 mrad x 2 mrad, the controller may pulse laser source 20 at about 50 kHz in order for system 10 to scan the complete ROI 36 in about 1.25 s. As another example, when ROI 36 subtends a solid angle of about 2 rad x 0.5 rad at system 10, the complete ROI 36 may be scanned in about 5 s.

[0118] It will be appreciated that the numerical values given above of the parameters used in system 10 are purely by way of example, to aid in understanding the invention. Those having ordinary skill in the art will be able to formulate different values of the parameters, such as different values for distance D, and / or the solid angle subtended by ROI 36 and / or the solid angle of diverted beams 44, and use these values to derive values associated with system 10, such as the energy of laser source 20 and the rate at which it is pulsed, and all such values are assumed to be comprised within the scope of the present invention.

[0119] It will also be appreciated that to detect a 10 cm object in an ROI at 1 km, using a conventional LIDAR system, requires a significantly smaller diverted beam than the examples given above. Such smaller diverted beam consequently requires a longer time, by many orders of magnitude, to cover the ROI. For example, for an ROI with a solid angle of 2 rad x 0.5 rad, scanned at 50 kHz with a resolution selected to detect a 10 cm object, a conventional LIDAR system requires approximately 2000 s to scan the complete ROI. Thus, the system of the present embodiments is advantageous over traditional LIDAR system, at least in terms of the scanning time. Example Operation Method

[0120] FIG. 2 is a flowchart 100 of example operations which may be executed in order to operate system 10, according to an embodiment of the present invention.

[0121] At 104, values of parameters of illuminator 14 are calculated, and are implemented for the illuminator and also, as necessary, for the receiver 16. An example of the values that may be used has been given above, and these values are also used in describing further operations of the flowchart. It is appreciated that this is not to be considered as limiting and that other suitable values of the parameters may be used.

[0122] Processor 12 is configured to operate mirror 40 and mirror 52 in synchrony, so that the solid angle of a given deviated beam 44 from mirror 52 is substantially the same, in azimuth, elevation, and divergence, as the solid angle for the corresponding receiving set 60 of rays at mirror 52. Processor 12 also sets common bounds for the rotation, in elevation and azimuth, for mirror 40 and for mirror 52, so that ROI 36 is completely scanned. In a disclosed embodiment the bounds may be set according to equations (4): where 9azboundand ^elboundarc^e rotation azimuth and elevation bounds for mirrors 40 and 52, 0a / and 0C| are the azimuth and elevation of ROI 36 with respect system 10, corresponding to direction 22 (see FIG. 1), and OazdivROIand ^eldivROIarc^e azimuth and elevation divergence of ROI 36.

[0123] As is described further below, processor 12 analyzes signals generated by PNRD 48. The analysis uses a signal threshold level to identify if object 38 is present in ROI 36, and the threshold level is set at 104, or may be set dynamically, using background radiation signals generated by PNRD 48. Properties of the background radiation are referred to below.

[0124] At 108, the controller pulses laser source 20 at the frequency set at 104, so that after the divergence by beam diverging optical element 28 an initial diverted beam 44 is transmitted towards ROI 36 from mirror 40. Using the example provided above, the pulse length is assumed to be approximately 1 ns, and the laser is pulsed at 50 kHz. The controller may set the direction of the initial diverted beam to have any convenient values of elevation and azimuth within the bounds set at 104.

[0125] At 112, PNRD 48 is activated and processor 12 begins sampling and acquiring the signals generated by the PNRD. PNRD 48 is activated, by the controller or processor 12 at the same time as laser source 20 is pulsed, and the signals are sampled for a period approximately equal to the laser pulse length, e.g., about 1 ns. The actual duration of sampling may be determined by the bandwidth of receiver 16, which is a function of the optical and electrical characteristics of the receiver. In some embodiments, processor 12 inputs the signals into signal bins of an accumulative photon graph, each bin having a length equal to that of the sampling duration, herein assumed to be 1 ns. FIG. 3 described further below, schematically illustrates such an accumulative photon graph.

[0126] The method optionally continues to 124 at which processor 12 analyzes the signal acquired at 112. The photons received by PNRD 48 comprise two types of photons: (1) those from object 38 due to the irradiation of the object by radiation from laser source 20, for example, radiation generated at the ROI in response to the diverted diverged beam, and (2) thermal background photons reflected from ROI 36. In system 10, wherein PNRD 48 is operated at an acquisition and detection time of 1 ns, the actual numbers of photons for each time period registered by the PNRD are low, and for the background photons, where the probabilities of occurrence follow a Poisson distribution, the numbers are very low and are similar to those corresponding to the exponential tail of the Poisson distribution. Measurements of the background radiation can be executed at 104 and be used to set the threshold level. Thus, processor 12 compares the signal generated by PNRD 48 to the threshold level set at 104. When the threshold level is exceeded, processor 12 assumes that the signal is generated from radiation from object 38. Alternatively, radiation from the ROI can be detected without a lower detection limit or a minimum threshold. In these embodiments, no minimum threshold is employed at 124. For example, 124 can be skipped and not be executed.

[0127] At decision 128, processor 12 checks if an object, assumed herein to be object 38, has been detected at 124. If the decision returns positive, namely object 38 has been detected, the method continues to 150 at which the processor uses a time t, between the time from when the laser was pulsed at 108 (or at 120 described below) to the time of 112, to find the distance from system 10 to object 38. The distance d from system 10 to object 38 can be calculated according to equation (5): where c is the speed of light within the medium between system 10 and object 38.

[0128] In addition to calculating the distance, processor 12 can also record the elevation and azimuth of the diverted beam 44 and returning set 60 that produce the signals sampled at 112.

[0129] The processor may present the distance, elevation, and azimuth to the user of system 10 by any convenient method, such as on screen 76.

[0130] From 150, or, in case in which the decision 128 returns negative, from decision 128, the method continues to decision 116 at which the processor 12 checks if the sampling and acquisition of the PNRD signals has been performed for one complete period of the frequency at which laser source 20 is pulsed (a period of 2- 10’5 s, in the present example). If decision 116 returns negative, namely one complete period has not been sampled, the method returns to 112 along line Pl, and processor 12 continues sampling and acquiring the signals from the PNRD. If the decision 116 returns positive, namely one complete period has been sampled, the method continues along line P2 to 120 at which processor 12 increments the elevation or the azimuth, pulses the laser, and transmits a diverged beam 44 of the new pulse in the incremented direction. The processor then proceeds to 112.

[0131] If 116 returns negative, namely a complete period since the last laser pulse has not passed, the method returns to 112, so that the processor continues sampling and acquiring signals from PNRD 48.

[0132] The flowchart illustrates that processor 12 performs two iterations. In one iteration the processor follows a path including line Pl in the flowchart and PNRD 48 is sampled for the duration of the period at which laser source 20 is pulsed. In a second iteration, the processor follows a path including line P2 in the flowchart and the direction of deviated beam 44 and received set 64 is incremented. It will be understood that during the iterations including line Pl, decision 128 may return positive more than one time. Each such time corresponds to another object other than object 38 being present in the section of ROI being irradiated by the one diverted beam 44. As for object 38 the processor may formulate results characteristic of the other object or objects, and present the results to the user.

[0133] FIG. 3 schematically illustrates an accumulative photon graph 130 where an object signal 134 is present, according to an embodiment of the present invention. The accumulative photon graph may be produced by processor 12, and illustrates typical signal values, from an object such as object 38 and from the background of a ROI such as ROI 36 where the object is present. By way of example, accumulative photon graph 130 uses 1 ns bins, the size of the bins corresponding to the acquisition time of PNRD 48, and each bin is filled by the signal acquired at the respective bin time. The number of bins corresponds to the duration of one period for the frequency at which laser 20 is pulsed (2- 10’5 s in this example) when the laser is pulsed at 50 kHz. In accumulative photon graph 130 object signal 134, that is larger than a threshold value 148, is present in an accumulative photon graph bin 138. In some embodiments object signal 134 may be one of a multiplicity 136 of non-zero object signals in contiguous bins of the accumulative photon graph.

[0134] Background signals 142 are also illustrated in accumulative photon graph 130, and as shown, a number of bins of the accumulative photon graph are empty of background signals, since no photons are acquired by PNRD 48 for those bin times. It will be understood that object signal 134 is derived from photons received from object of interest 38, and that the object signal overlays the background signals that are also present.

[0135] FIG. 3 illustrates that the time t of object signal 134 is the time from the origin of the accumulative photon graph, and it will be appreciated that the time of origin of the accumulative photon graph corresponds to the time when laser source 20 is pulsed. The distance d from image system 10 to object 38 is given by equation (5) above.

[0136] Object Classification

[0137] In an alternative embodiment of the present invention, once processor 12 has identified the presence an object such as object of interest 38 in ROI 36, the controller may repeat the transmission of the diverted beam 44 used to identify the presence of the object. The controller implements the repetition by pulsing laser source 20 while pausing mirrors 40 and 52 in the orientations used to initially identify the presence of the object. The processor then acquires from PNRD 48 further signals of the object, and may use compressed sensing, implemented using DMD 56 (FIG. 1), on the acquired signals to generate a high resolution image of the object. The processor may use the high resolution image to classify the object, and present a classification of the object to a user of system 10, for example on screen 76.

[0138] Processor 12 may also use the acquired signals to derive values of a path and a speed for the object, and present the values to the user.

[0139] In some embodiments of the invention, beam diverging optical element 28 provides a narrower beam than the one used to identify the presence of object 38 in ROI 36. The narrower beam may be used passively to direct further beam pulses towards object 38, and the signals generated in response to the further pulses may be used to classify the object. Alternatively, the narrower beam may be actively scanned, by rotating mirrors 40 and 52, and the signals generated can be used to classify the object.

[0140] Implementation Examples

[0141] The inventors have implemented many systems based on the principles of the present invention described herein, for example: detecting the presence of an object of interest (e.g., a bird) at 2km with a 50nJ source; detecting the presence of an object of interest (e.g., an aeroplane) at 23km with an 80pJ source; detecting low Earth orbit (LEO) satellites in 800- 1700km orbits; in bathymetry, detecting the presence of an object at a 25m depth with an 80pJ source; and detecting a balloon at 5km with a 20pJ source.

[0142] Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.

[0143] It is the intent of the applicant(s) that all publications, patents and patent applications referred to in this specification are to be incorporated in their entirety by reference into the specification, as if each individual publication, patent or patent application was specifically and individually noted when referenced that it is to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present invention. To the extent that section headings are used, they should not be construed as necessarily limiting. In addition, any priority document(s) of this application is / are hereby incorporated herein by reference in its / their entirety.

Claims

WHAT IS CLAIMED IS:

1. A system for remote optical detection of objects in an environment, the system comprising: a laser system configured to transmit into the environment a laser beam diverged along two orthogonal directions; an optical sensor configured to receive optical radiation backscattered from objects in the environment and generate a signal responsive to said received optical radiation; and a processor, configured to detect in the environment presence of at least one object having a subtended solid angle at said sensor that is less than a solid angle of said laser beam.

2. The system according to claim 1, wherein said laser system comprises a laser source configured to produce a laser beam and a beam diverging optical element, configured to diverge said laser beam.

3. The system according to any of claims 1 and 2, wherein said processor is configured to generate output pertaining to said presence of said object without mapping and / or imaging the environment.

4. The system according to any of claims 1-3, wherein said processor is configured to register said presence of said at least one object while not determining a location of said at least one object.

5. The system according to any of claims 1-4, wherein said laser beam is characterized by a cross-sectional profile devoid of functional segmentation.

6. The system according to claim 5, wherein said cross-sectional profile has a single irradiance peak along any direction within a cross-section of said diverged laser beam.

7. The system according to claim 5, wherein said cross-sectional profile is devoid of any irradiance peak along any direction within a cross-section of said diverged laser beam.

8. The system according to any of claims 1-6, wherein said at least one object is positioned within an off-center region of said diverged laser beam.

9. The system according to any of claims 1-8, wherein said laser system is configured to maintain a constant divergence of said laser beam at all times, irrespectively of a distance to said object.

10. The system according to any of claims 1-9, wherein a divergence of said laser beam is selected such that an attenuation of said backscattered radiation is proportional to an nth power of a range to said object, said n being greater than 3.

11. The system according to claim 10, wherein a cross-sectional shape of said laser beam is characterized by an aspect ratio of from about 0.5 to about 1.5.

12. The system according to any of claims 1-11, comprising a scanner configured to divert said laser beam into multiple sequential transmission optical paths to the environment.

13. The system according to claim 12, wherein said scanner comprises a mirror configured to rotate independently about two orthogonal axes.

14. The system according to claim 13, wherein said orthogonal axes comprise an elevation axis and an azimuthal axis.

15. The system according to any of claims 12-14, comprising a further scanner configured to divert said backscattered radiation into respective multiple sequential reception optical paths to said sensor.

16. The system according to claim 15, comprising a controller configured to rotate said scanner and said further scanner in synchrony.

17. The system according to claim 16, wherein a reception optical path and a corresponding transmission path have a common divergence.

18. The system according to any of claims 1-17, wherein said laser system is configured to generate laser pulses.

19. The system according to any claim 18, wherein said laser pulses have a duration of from about 0.5 ns to about 5 ns.

20. The system according to any of claims 1-19, wherein said laser system is configured to transmit multiple laser beams, and said sensor is operable to receive multiple sets of backscattered optical radiation and to responsively generate respective multiple signals.

21. The system according to claim 20, wherein said processor is configured to apply compressed sensing to said multiple signals to classify said at least one object.

22. The system according to any of claims 1-21, comprising a controller and optics configured to narrow said laser beam, and transmit multiple narrowed beams to the environment.

23. The system according to claim 22, wherein said sensor is configured to receive multiple sets of radiation from the environment in response to said multiple narrowed diverged beams, and to output multiple signals, and said processor is configured to analyze said multiple signals to classify the object.

24. The system according to any of claims 1-22, wherein a medium between the system and the objects comprises atmospheric air or a vacuum.

25. The system according to any of claims 1-24, wherein a medium between the system and the objects comprises a liquid transparent to the laser beam.

26. The system according to any of claims 1-25, wherein said sensor comprises a photon number resolving detector.

27. A method of detecting presence of an object in an environment, the method comprising: transmitting into the environment a laser beam diverged along two orthogonal directions; receiving optical radiation backscattered from a solid angle subtended by the object, wherein said subtended solid angle is less than a solid angle of said laser beam; generating a signal responsive to said received optical radiation; andanalyzing said signal to detect the presence of the object, and generating output pertaining to said detection.

28. The method according to claim 27, comprising producing a laser beam and diverging said laser beam.

29. The method according to any of claims 27 and 28, wherein said output is devoid of mapping and / or imaging of the environment.

30. The method according to any of claims 27-29, wherein said output is devoid of information pertaining to a location of said at least one object in the environment.

31. The method according to any of claims 27-30, wherein said laser beam is characterized by a cross-sectional profile devoid of functional segmentation.

32. The method according to claim 31, wherein said cross-sectional profile has a single irradiance peak along any direction within a cross-section of said diverged laser beam.

33. The method according to claim 31, wherein said cross-sectional profile is devoid of any irradiance peak along any direction within a cross-section of said diverged laser beam.

34. The method according to any of claims 27-32, wherein said at least one object is positioned within an off-center region of said diverged laser beam.

35. The method according to any of claims 27-34, wherein said divergence of said laser beam is constant at all times, irrespectively of a distance to said object.

36. The method according to any of claims 27-35, wherein a divergence of said laser beam is selected such that an attenuation of said backscattered radiation is proportional to an nth power of a range to said object, said n being greater than 3.

37. The method according to claim 36, wherein a cross-sectional shape of said laser beam is characterized by a aspect ratio of from about 0.5 to about 1.5.

38. The method according to any of claims 27-37, comprising diverting said laser beam into multiple sequential transmission optical paths to the environment.

39. The method according to claim 38, wherein said diverting is by a mirror configured to rotate independently about two orthogonal axes.

40. The method according to claim 39, wherein said orthogonal axes comprise an elevation axis and an azimuthal axis.

41. The method according to any of claims 38-40, comprising diverting said backscattered radiation into respective multiple sequential reception optical paths, wherein said receiving comprises receiving optical radiation propagating along each of said reception optical paths.

42. The method according to claim 41, wherein said diverting of said backscattered radiation is synchronous with said diverting of said laser beam.

43. The method according to claim 42, wherein a reception optical path and a corresponding transmission path have a common divergence.

44. The method according to any of claims 27-43, wherein said laser beam is a pulsed laser beam.

45. The method according to claim 44, wherein said pulsed laser beam is characterized by a pulse duration of from about 0.5 ns to about 5 ns.

46. The method according to any of claims 27-45, comprising transmitting multiple laser beams, receiving multiple sets of backscattered optical radiation, and responsively generating respective multiple signals.

47. The method according to claim 46, comprising applying compressed sensing to said multiple signals to classify said at least one object.

48. The method according to any of claims 27-47, comprising narrowing said laser beam, and transmitting multiple narrowed beams to the environment.

49. The method according to claim 48, comprising receiving multiple sets of radiation from the environment in response to said multiple narrowed diverged beams, generating multiple signals responsively to said multiple sets of radiation, and analyzing said multiple signals to classify the object.

50. The method according to any of claims 27-48, wherein the object is in atmospheric air or vacuum, and said laser beam is transmitted through said atmospheric air or vacuum.

51. The Method according to any of claims 27-50, wherein object is in a liquid transparent to the laser beam, and said laser beam is transmitted through said liquid.

52. The method according to any of claims 27-51, wherein said sensing is by a photon number resolving detector.

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