Patent Description:
High-energy laser (HEL) systems are being developed for a number of commercial and defense-related applications. For example, high-energy lasers may be used to direct high-energy beams at incoming missiles, rockets, mortars, or other targets. Unfortunately, various factors can degrade a high-energy laser beam, which reduces the focused power of the beam on a desired target. This can increase the amount of time needed to achieve a desired result, such as damage or destruction of the target, or can prevent the desired result from being achieved.

<CIT> discloses a beam control system and method. The system includes, an arrangement for receiving a first beam of electromagnetic energy; measuring wavefront aberrations in the first beam with a wavefront sensor; and removing global tilt from the measured wavefront aberrations to provide higher order aberrations for beam control. In the illustrative embodiment, the invention uses a traditional (quad-cell) Shack-Hartmann wavefront sensor to measure wavefront aberrations. An adaptive optics processor electronically removes the global tilt (angular jitter) from this measurement leaving only the higher-order Zemike components. These higher-order aberrations are then applied to wavefront control elements, such as deformable mirrors or spatial light modulators that correct the tracker image and apply a conjugate distortion to the wavefront of the outgoing HEL beam. A track error (angular jitter) component is supplied by a separate fine track sensor. This jitter error is then applied by the adaptive optics processor to a fast steering mirror, which corrects jitter in the tracker image and applies a compensating distortion to the LOS of the HEL beam.

<CIT> discloses a method for local stabilization of a radiation spot on a remote target object, where the radiation spot is formed by a high energy laser beam that is aimed at the target object by a high energy radiation emitter, the method includes illuminating the target object by an illumination beam that is aimed at the target object by an illumination device. The method also includes receiving, by an image acquisition device, radiation reflected by the target object that is illuminated by the illumination beam, where the radiation reflected by the target object to the image acquisition device passes through the same optical path as the high energy laser beam. An image processing is performed by analyzing and comparing an image of the illuminated target object or part of the illuminated target object acquired by the image acquisition device to at least one image of the illuminated target object or part of the illuminated target object produced at a prior point in time or to an image stored in an object database. And a correction signal is determined, based on the comparison, with which an optical correction device arranged in the optical path passed through by both the high energy laser beam and the reflected radiation is actuated.

This disclosure relates to atmospheric jitter correction and target tracking using a single imaging sensor in high-energy laser systems.

In a first aspect, the present disclosure provides a system comprising: a target illumination laser 'TIL' configured to generate a TIL beam that illuminates a target; a beacon illumination laser 'BIL' configured to generate a modulated BIL beam that creates a spot on the target; an imaging sensor configured to (i) capture first images of the target at a first rate, the first images containing reflected TIL energy from the TIL beam without reflected BIL energy from the modulated BIL beam and (ii) capture second images of the target at a second rate different from the first rate, the second images containing reflected TIL energy from the TIL beam and reflected BIL energy from the modulated BIL beam; and at least one controller configured to perform target tracking using the first images and boresight error compensation using the second images.

In a second aspect, the present disclosure provides a least one non-transitory computer readable medium containing instructions that when executed cause at least one processor to: control a target illumination laser 'TIL to generate a TIL beam that illuminates a target; control a beacon illumination laser 'BIL' to generate a modulated BIL beam that creates a spot on the target; control an imaging sensor to (i) capture first images of the target at a first rate, the first images containing reflected TIL energy from the TIL beam without reflected BIL energy from the modulated BIL beam and (ii) capture second images of the target at a second rate different from the first rate, the second images containing reflected TIL energy from the TIL beam and reflected BIL energy from the modulated BIL beam; and perform target tracking using the first images and boresight error compensation using the second images.

In a third aspect, the present disclosure provides a method comprising: illuminating a target using a target illumination laser 'TIL' beam; creating a spot on the target using a modulated beacon illumination laser 'BIL' beam; using an imaging sensor, (i) capturing first images of the target at a first rate, the fitrst images containing reflected TIL energy from the TIL beam without reflected BIL energy from the modulated BIL beam and (ii) capturing second images of the target at a second rate, different from the first rate, the second images containing reflected TIL energy from the TIL beam and reflected BIL energy from the modulated BIL beam; and performing target tracking using the first images and boresight error compensation using the second images.

<FIG>, described below, and the various embodiments used to describe the principles of the present invention in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the invention. Those skilled in the art will understand that the principles of the present invention may be implemented in any type of suitably arranged device or system.

For simplicity and clarity, some features and components are not explicitly shown in every figure, including those illustrated in connection with other figures. It will be understood that any features illustrated in the figures may be employed in any of the embodiments described. Omission of a feature or component from a particular figure is for purposes of simplicity and clarity and is not meant to imply that the feature or component cannot be employed in the embodiments described in connection with that figure.

As noted above, high-energy laser (HEL) systems are being developed for a number of commercial and defense-related applications, such as to direct high-energy beams at incoming missiles, rockets, mortars, or other targets. Unfortunately, various factors can degrade a high-energy laser beam or interfere with its use. For example, optical turbulence in the atmosphere or other factors can degrade the effects of a high-energy laser beam by distorting the beam's wavefront profile. Target dynamics, such as changes in direction or velocity of the target, can introduce tracking errors when pointing the high-energy laser beam at the target. Jitter of the high-energy laser beam can alter the location where the beam strikes the target, and the jitter going up in the atmosphere is different than the jitter going down in the atmosphere and is therefore difficult to identify based on measurements generated by a tracking sensor on the ground. Wavefront errors introduced into a high-energy beam are typically composed of multiple-order errors, such as when the first two wavefront distortions are tip and tilt of beam jitter and the other wavefront errors are lumped into a category of higher-order errors. Overall, these issues can reduce the focused power of a high-energy beam on a desired target. This can increase the amount of time needed to achieve a desired result, such as damage or destruction of the target, or can prevent the desired result from being achieved.

Some approaches illuminate a target using a target illumination laser (TIL), which generates TIL laser energy that is offset in optical frequency from a high-energy beam. TIL energy reflects off the target and is imaged by a camera subsystem that is boresighted to the high-energy beam. The reflected TIL energy shifts based on downlink atmospheric jitter (jitter going down in the atmosphere), residual line of sight (LOS) stabilization errors in an LOS stabilization system, and target dynamics (such as target maneuvers). High-speed camera images of the reflected TIL energy can be used by a tracking system to estimate boresight error, and a fast steering mirror can be used in a closed-loop manner to compensate for the boresight error. However, the imaging of the reflected TIL energy does not fully identify uplink atmospheric jitter (jitter going up in the atmosphere), leaving the uplink jitter of the high-energy beam mostly uncorrected.

Other approaches use a beacon illumination laser (BIL) that is co-boresighted with the high-energy beam to generate a laser spot (also called a "see spot") on a target, which can be used to perform higher-order corrections. For example, a wavefront sensor can estimate a wavefront error based on reflected BIL laser energy, and a deformable mirror can be used to help compensate for the wavefront error. However, wavefront sensors are non-imaging and can only sense a wavefront, while the reflected BIL energy from the target may scintillate and contain many other signal sources creating errors in sensing. In addition, alignment errors between a BIL return sensor and a tracking camera create additional errors, which increase beam jitter and increase the overall size, weight, and power (SWaP) of the laser system or an overall system that includes the laser system.

In accordance with this disclosure, a single camera or other imaging sensor is used for both atmospheric jitter correction and target tracking in a high-energy laser system. As described in more detail below, a single imaging sensor, such as a short-wave infrared (SWIR) camera or other sensor, is co-boresighted to an optical path of a high-energy laser beam. In addition to the high-energy laser beam transmitted towards a target, a target illumination laser and a beacon illumination laser respectively transmit TIL laser energy and BIL laser energy towards the target. In some embodiments, the target illumination laser represents a continuous wave (CW) SWIR laser, and the beacon illumination laser represents an SWIR laser.

The single imaging sensor receives both reflected TIL energy and reflected BIL energy from the target, as well as other illumination that reflects from the target towards the imaging sensor. The imaging sensor is configured to capture images of the reflected TIL energy and of the reflected BIL energy. The image capture is interleaved or otherwise multiplexed such that the imaging sensor captures some images where reflected TIL energy (but not reflected BIL energy) is present and some images where both reflected TIL energy and reflected BIL energy are present. As a particular example, acousto-optic modulation or pulsing of the beacon illumination laser (such as by turning the beacon illumination laser on and off) allows (i) some images to be captured where reflected TIL energy is present without reflected BIL energy and (ii) other images to be captured where reflected TIL energy and reflected BIL energy are present. The different images that are captured in this manner can be used to perform different functions, such as when the TIL-related images are used for target tracking and the TIL/BIL-related images are used for boresight correction (including atmospheric jitter correction).

The use of a single boresighted imaging sensor to capture reflected TIL energy and reflected BIL energy helps to reduce or eliminate optical alignment jitter or other optical static or dynamic alignment errors that can occur when using multiple cameras or other imaging subsystems. Moreover, the ability to multiplex image capture of the reflected TIL energy and the reflected BIL energy allows a single imaging sensor, boresighted to the high-energy beam, to capture these reflections in order to balance and reduce/minimize atmospheric uplink jitter, higher-order atmospheric distortions, and dynamic target tracking errors for high-energy beam pointing. For example, a modulation (on-off) frequency of the beacon illumination laser can be optimized for uplink tip-tilt suppression, higher-order wavefront error suppression, and dynamic target tracking precision performance, and the modulation can be synchronized with the frame time of the imaging sensor. As a particular example, in the case of a tactical laser used when looking up over the horizon, imaging of the reflected BIL energy can be multiplexed with imaging of the reflected TIL energy to obtain <NUM> TIL imagery and <NUM>,<NUM> BIL imagery. This functionality may help to achieve a tracking accuracy of one micro-radian (µrad) or less, as well as an uplink atmospheric jitter estimation and correction accuracy of one µrad or less (such as <NUM> µrad or less). In addition, the same multiplexed imaging sensor configuration can be used to help correct for higher-order wavefront errors, such as by using power-in-the-bucket techniques like stochastic parallel gradient descent.

In this way, systems can be used to more accurately identify atmospheric effects and other effects impacting a high-energy laser beam and its use and to compensate for those effects. This can be achieved by correcting for uplink jitter of the high-energy beam going up to a target due to atmospheric optical turbulence while still tracking target dynamics. This enables precision high-energy beam pointing with a compact optical system that substantially reduces tip and tilt in the uplink beam transmission. Overall, this can significantly increase the ability of a high-energy laser beam to reach an intended target consistently and with greater effect.

<FIG> illustrates an example system <NUM> supporting atmospheric jitter correction and target tracking using a single imaging sensor for a high-energy laser according to this disclosure. As shown in <FIG>, the system <NUM> includes a high-energy laser system <NUM> that is being used to engage a target <NUM>. The target <NUM> in this example represents a rocket or missile. However, the high-energy laser system <NUM> may be used with any other suitable targets, such as one or more targets on the ground, in the air, or in space.

The laser system <NUM> in this example generates an HEL beam <NUM>, a TIL beam <NUM>, and a BIL beam <NUM>. The HEL beam <NUM> represents a beam of laser energy that typically has a high power or energy level, such as at least about <NUM> kilo-Watts (kW) of power. Often times, the HEL beam <NUM> is ideally focused to as small an area as possible on the target <NUM>, which is done in order to achieve the maximum possible effect on the target <NUM>. However, because of this, the HEL beam <NUM> is particularly susceptible to jitter or other non-consistent placement of the HEL beam <NUM> on the target <NUM>.

The TIL beam <NUM> represents a beam of laser energy that spreads out to illuminate most or all of the target <NUM>. By spreading the TIL beam <NUM> and making it wider than the target <NUM> (or at least wider than a relevant portion of the target <NUM>), there may be less or no concern about atmospheric jitter affecting the TIL beam <NUM> reaching the target <NUM>. The TIL beam <NUM> typically has a much lower power or energy level compared to the HEL beam <NUM>. Reflections of the TIL beam <NUM> off the target <NUM> can be received at the laser system <NUM> and used to measure, for instance, the distance and angle of the target <NUM> relative to the laser system <NUM> or relative to a high-energy laser in the laser system <NUM>. In some embodiments, the TIL beam <NUM> may represent a continuous wave <NUM> nanometer (nm) laser beam, although other suitable longer or shorter wavelengths may be used for the TIL beam <NUM>.

The BIL beam <NUM> represents a beam of laser energy that is used to generate a more focused illumination spot or "see spot" on the target <NUM>. In some cases, a particular intended location on the target <NUM> to be illuminated by the BIL beam <NUM> may be selected. For example, it may be predetermined to illuminate a particular feature on the nose of the target <NUM>. The BIL beam <NUM> can be subject to optical turbulence in the atmosphere or other effects that create uplink jitter or other boresight error for the BIL beam <NUM>. Thus, the actual location of the see spot on the target <NUM> may vary from the intended or expected location of the see spot, and the difference between the actual and intended/expected locations of the see spot can be used to determine the uplink jitter or other boresight error. In some embodiments, the BIL beam <NUM> may represent a <NUM> laser beam, although other suitable longer or shorter wavelengths may be used for the BIL beam <NUM>. The wavelength of the BIL beam <NUM> can be close to the wavelength of the HEL beam <NUM>.

The BIL beam <NUM> is offset (such as in angle) relative to the HEL beam <NUM> so that the BIL beam <NUM> and the HEL beam <NUM> strike the target <NUM> at different locations. However, both beams <NUM> and <NUM> travel from the laser system <NUM> to the target <NUM> in very close proximity to one another, and the actual distance between the strike points for the two beams <NUM> and <NUM> can be very small. Because of this, compensating for the uplink jitter or other boresight error associated with the BIL beam <NUM> will (ideally) also correct for the same uplink jitter or other boresight error associated with the HEL beam <NUM>. If the wavelength of the BIL beam <NUM> is close to the wavelength of the HEL beam <NUM>, the two beams <NUM> and <NUM> can experience approximately the same uplink jitter.

As described in more detail below, the laser system <NUM> uses a single camera or other imaging sensor to capture images of the target <NUM> as illuminated using the TIL beam <NUM> and images of the target <NUM> as illuminated using the TIL beam <NUM> and the BIL beam <NUM>. Among other things, this helps to avoid alignment errors typically associated with the use of multiple cameras. This may be highly desirable since alignment errors, even small ones, may introduce jitter of a high-energy beam on the target <NUM>, thereby reducing overall system performance. Moreover, this enables the laser system <NUM> to more effectively compensate for atmospheric uplink jitter, higher-order atmospheric distortions, and dynamic target tracking errors. As a result, the laser system <NUM> can engage in more effective or accurate beam pointing for the HEL beam <NUM>.

In this particular example, the laser system <NUM> includes or is used with a multi-axis gimbal <NUM>, which mounts the laser system <NUM> on a vehicle <NUM>. The multi-axis gimbal <NUM> includes any suitable structure configured to point the laser system <NUM> in a desired direction. In some embodiments, the multi-axis gimbal <NUM> can rotate the laser system <NUM> about a vertical axis for azimuth control and about a horizontal axis for elevation control. However, any other suitable mechanisms for pointing the laser system <NUM> (such as about a single axis or multiple axes) may be used here. Also, in this particular example, the vehicle <NUM> on which the laser system <NUM> is mounted represents an armored land vehicle. However, the laser system <NUM> may be used with any other suitable type of vehicle (such as any other suitable land, air, or space vehicle), or the laser system <NUM> may be mounted to a fixed structure (such as a building).

Among other things, the functionality implemented within the laser system <NUM> as described below helps to reduce or minimize beam jitter or other movement of the HEL beam <NUM> on the target <NUM>. The ability to maintain the HEL beam <NUM> at substantially the same position on the target <NUM>, even during maneuvering of the target <NUM>, can help increase the effectiveness of the laser system <NUM>. For example, this can help to increase the effectiveness of the laser system <NUM> in causing damage to or destruction of the target <NUM>, or this can help to increase the effectiveness of the laser system <NUM> in interfering with the normal operation of the target <NUM>.

Although <FIG> illustrates one example of a system <NUM> supporting atmospheric jitter correction and target tracking using a single imaging sensor for a high-energy laser, various changes may be made to <FIG>. For example, the laser system <NUM> may be used in any other suitable environment and for any other suitable purpose. Also, while shown here as being used to damage or destroy a moving hostile target <NUM>, the laser system <NUM> can be used in any number of other ways depending on the application.

As noted above, there are various commercial and other non-defense-related applications for high-energy laser systems that may benefit from the approaches described in this patent document. For instance, in commercial mining applications like drilling, mining, or coring operations, a high-energy laser can be used to soften or weaken an earth bed prior to drilling, which may allow for fewer drill bit changes and extended lifetimes and reliabilities of drill bits. In remote laser welding, cutting, drilling, or heat treating operations like industrial or other automation settings, a high-energy laser can be used to allow for the processing of thicker materials at larger working distances from the laser system while minimizing the heat-affected zone and maintaining vertical or other cut lines. This helps to support welding or cutting operations where proximity to the weld or cut site is difficult or hazardous and helps to protect the laser system and possibly any human operators from smoke, debris, or other harmful materials. In construction and demolition operations like metal resurfacing or deslagging, paint removal, and industrial demolition operations, a high-energy laser can be used to ablate material much faster and safer compared to conventional operations. As a particular example of this functionality, a high-energy laser can be used to support demolition of nuclear reactors or other hazardous structures, such as by cutting through contaminated structures like contaminated concrete or nuclear containment vessels or reactors from long distances. This avoids the use of water jet cutting or other techniques (which creates contaminated water or other hazardous waste) and provides improved safety (since human operators can remain farther away from contaminated structures being demolished). A number of additional applications are possible, such as with a high-energy laser in power beaming applications (where a beam is targeted to photovoltaic cells of remote devices to be recharged) or hazardous material applications (where a beam is used to heat and decompose hazardous materials into less harmful or non-harmful materials).

<FIG> illustrates an example high-energy laser system <NUM> supporting atmospheric jitter correction and target tracking using a single imaging sensor according to this disclosure. For ease of explanation, the high-energy laser system <NUM> shown in <FIG> may be described as being used in the system <NUM> of <FIG> to engage a hostile target <NUM>. However, the high-energy laser system <NUM> of <FIG> may be used in any other suitable environment and for any other suitable purpose.

As shown in <FIG>, the high-energy laser system <NUM> includes a high-energy laser <NUM>, a target illumination laser <NUM>, and a beacon illumination laser <NUM>. As described above, the high-energy laser <NUM> is used to generate the HEL beam <NUM>, the target illumination laser <NUM> is used to generate the TIL beam <NUM>, and the beacon illumination laser <NUM> is used to generate the BIL beam <NUM>. Each laser <NUM>, <NUM>, and <NUM> represents any suitable structure configured to generate the appropriate laser energy. In some embodiments, the high-energy laser <NUM> includes a planar waveguide (PWG) amplifier or other optical amplifier, which amplifies a seed laser beam using pump power provided to the optical amplifier by one or more pump sources (such as one or more laser diode arrays) to produce the HEL beam <NUM>. However, any other suitable laser may be used here as the high-energy laser <NUM>. Also, the target illumination laser <NUM> may represent a continuous wave <NUM> laser, and the beacon illumination laser <NUM> may represent a <NUM> laser. However, any other suitable lasers may be used here as the target illumination laser <NUM> and the beacon illumination laser <NUM>.

In this example, the HEL beam <NUM> is transmitted towards a fold mirror <NUM>, which redirects the HEL beam <NUM> towards a deformable mirror <NUM>. The fold mirror <NUM> includes any suitable reflective structure configured to reflect one or more laser beams in a desired direction. The deformable mirror <NUM> includes at least one deformable reflective surface that can be used to alter a wavefront of the HEL beam <NUM> and optionally a wavefront of the BIL beam <NUM>. This allows for pre-distortion of the wavefront of at least the HEL beam <NUM> prior to transmission towards the target <NUM>, which helps to compensate for atmospheric wavefront errors. The actual pre-distortion provided by the deformable mirror <NUM> can be controlled based on wavefront errors sensed by an optional wavefront sensor, which is not shown in <FIG> for convenience. The deformable mirror <NUM> includes any suitable deformable reflective structure configured to reflect laser beams in a desired direction. In some embodiments, the deformable mirror <NUM> may represent a digital micro-mirror device (DMD), which may include numerous very small mirrors that can be repositioned or reoriented to provide the desired wavefront correction.

Two fast steering mirrors <NUM> and <NUM> and an additional fold mirror <NUM> are used to provide the BIL beam <NUM> from the beacon illumination laser <NUM> to the deformable mirror <NUM>. Each of the fast steering mirrors <NUM> and <NUM> is configured to be repositioned, reoriented, or reshaped in order to generally align the BIL beam <NUM> with the HEL beam <NUM> as desired. The BIL beam <NUM> here can be dynamically offset but otherwise aligned with the HEL beam <NUM> using the fast steering mirrors <NUM> and <NUM>. This enables the BIL beam <NUM> to be offset (such as in angle) relative to the HEL beam <NUM> but to still travel in substantially the same direction towards the target <NUM>. The fold mirror <NUM> redirects the BIL beam <NUM> towards the deformable mirror <NUM>. Each fast steering mirror <NUM> and <NUM> includes any suitable reflective structure configured to reflect one or more laser beams in a controllable direction, and each fast steering mirror <NUM> and <NUM> typically includes at least one servo for controlling how the one or more laser beams are directed. The fold mirror <NUM> includes any suitable reflective structure configured to reflect one or more laser beams in a desired direction.

Two additional fast steering mirrors <NUM> and <NUM> are used to redirect the HEL beam <NUM> and the BIL beam <NUM> through the optical assembly. Since these fast steering mirrors <NUM> and <NUM> are being used to transport the beams <NUM> and <NUM> generally along the polar axis of the laser system <NUM>, the fast steering mirrors <NUM> and <NUM> may be referred to as Coudé Path fast steering mirrors. Each fast steering mirror <NUM> and <NUM> includes any suitable reflective structure configured to reflect laser beams in a controllable direction, and each fast steering mirror <NUM> and <NUM> typically includes at least one servo for controlling how the laser beams are directed.

An aperture sharing element <NUM> reflects the HEL beam <NUM> and the BIL beam <NUM> towards a high-speed mirror <NUM>, which can be reoriented to provide tip and tilt compensation for the HEL beam <NUM> and the BIL beam <NUM>. For example, the high-speed mirror <NUM> can be controlled using a fine tracking control loop that allows very small changes to be made very quickly to the orientation of the high-speed mirror <NUM>. This can help to keep the HEL beam <NUM> and the BIL beam <NUM> at desired positions on the target <NUM> and reduce jitter caused by optical turbulence in the atmosphere or other boresight error. The high-speed mirror <NUM> includes any suitable reflective structure configured to reflect laser beams in a controllable direction, and the high-speed mirror <NUM> typically includes at least one servo for controlling how the laser beams are directed.

The high-speed mirror <NUM> also receives reflected laser energy <NUM> from the target <NUM> and redirects the reflected laser energy <NUM> towards the aperture sharing element <NUM>, which passes the reflected laser energy <NUM> to an imaging sensor <NUM>. The aperture sharing element <NUM> here can reflect or otherwise redirect the outgoing beams <NUM> and <NUM> towards the high-speed mirror <NUM> and transmit or otherwise allow passage of the reflected laser energy <NUM> from the high-speed mirror <NUM>. This supports simultaneous transmission of the beams <NUM> and <NUM> towards the target <NUM> and reception of the reflected laser energy <NUM> from the target <NUM>. The aperture sharing element <NUM> includes any suitable structure configured to redirect some laser energy and to allow passage of other laser energy, such as a dichroic mirror. Note that the reflected laser energy <NUM> here may not be redirected by the fast steering mirrors <NUM>, <NUM>, <NUM>, and <NUM>, which means the fast steering mirrors can be used to control the HEL beam <NUM> and the BIL beam <NUM> separate from any control used to provide the reflected laser energy <NUM> to the imaging sensor <NUM>.

The imaging sensor <NUM> is co-boresighted with the HEL beam <NUM>, and the imaging sensor <NUM> is configured to capture images of the target <NUM> and the reflected laser energy <NUM>. The reflected laser energy <NUM> here can include reflected TIL energy and possibly reflected BIL energy (depending on the modulation state of the beacon illumination laser <NUM>). The reflected laser energy <NUM> can also include any other illumination reflected from the target <NUM> towards the laser system <NUM>, such as a reflected portion of the HEL beam <NUM>. The imaging sensor <NUM> represents a camera or other suitable imager configured to capture images of a scene. In some embodiments, the imaging sensor <NUM> represents a high-speed SWIR camera. The images captured by the imaging sensor <NUM> include (i) images that contain reflected TIL energy without reflected BIL energy and (ii) images that contain both reflected TIL energy and reflected BIL energy.

The images captured by the imaging sensor <NUM> are provided to a controller <NUM>, which controls the overall operation of the laser system <NUM> and possibly a larger system into which the laser system <NUM> is integrated. For example, the controller <NUM> can control the operation of the lasers <NUM>, <NUM>, and <NUM> and the operation of the imaging sensor <NUM>. The controller <NUM> can also process the TIL-related images from the imaging sensor <NUM> to perform target tracking, and the controller <NUM> can process the TIL/BIL-related images from the imaging sensor <NUM> to perform atmospheric jitter correction and other boresight error correction. As particular examples, the controller <NUM> may process the images from the imaging sensor <NUM> to identify locations of the HEL beam <NUM> and the BIL beam <NUM> on the target <NUM> and adjust one or more of the fast steering mirrors <NUM>, <NUM>, <NUM>, <NUM> or the high-speed mirror <NUM> to change how one or both of the HEL beam <NUM> and the BIL beam <NUM> are directed towards the target <NUM>. This allows the controller <NUM> to maintain separation of the HEL beam <NUM> and the BIL beam <NUM> actually on the target <NUM>. The controller <NUM> may further process the images from the imaging sensor <NUM> to identify atmospheric jitter or other boresight error and control the high-speed mirror <NUM> to help compensate for the jitter. In addition, the controller <NUM> may interact with an acoustic-optical modulator <NUM> or other mechanism used to modulate or pulse the operation of the beacon illumination laser <NUM> so that, at times, images containing reflected TIL energy without reflected BIL energy can be obtained by the imaging sensor <NUM> and processed by the controller <NUM>. Of course, other mechanisms for modulating the BIL beam <NUM> (such as physically blocking or redirecting the BIL beam <NUM> away from the target <NUM>) may be used.

As can be seen in this example, the fast steering mirrors <NUM> and <NUM> are disposed outside the common optical path traveled by the HEL beam <NUM> and the BIL beam <NUM>, which extends between the deformable mirror <NUM> and the target <NUM>. The fast steering mirrors <NUM> and <NUM> can therefore help to bias the BIL beam <NUM> from the HEL beam <NUM> so that the beams <NUM> and <NUM> strike the target <NUM> at different locations. Moreover, the fast steering mirrors <NUM> and <NUM> allow the path of the BIL beam <NUM> to be controlled independent of the adjustments made to both beams <NUM> and <NUM> by the fast steering mirrors <NUM> and <NUM>.

As noted above, the operation of the beacon illumination laser <NUM> can be modulated or pulsed so that the imaging sensor <NUM> is able to generate both (i) images containing reflected TIL energy without reflected BIL energy and (ii) images containing reflected TIL energy and reflected BIL energy. To generate the first type of images, the TIL beam <NUM> can be sent towards the target <NUM>, while the beacon illumination laser <NUM> is deactivated or is otherwise not sent towards the target <NUM>. To generate the second type of images, the TIL beam <NUM> and the BIL beam <NUM> can be sent simultaneously towards the target <NUM>.

A TIL-based tracking function of the controller <NUM> can process images of the target <NUM> containing reflected TIL energy but not reflected BIL energy. As a result, the tracking function can be used to help stabilize the HEL beam <NUM> and the laser system's line-of-sight on the target <NUM> using images captured by the imaging sensor <NUM> based on reflected TIL energy. The fast steering mirrors <NUM> and <NUM> can be used for target tracking and HEL beam pointing, which ensures that the BIL beam <NUM> (once generated or otherwise transmitted towards the target <NUM>) will also be on the target <NUM>. The actual location where the HEL beam <NUM> arrives at the target <NUM> is based on boresight error, which includes any atmospheric uplink tip-tilt or jitter.

When the beacon illumination laser <NUM> is activated or the BIL beam <NUM> is otherwise sent towards the target <NUM>, images captured by the imaging sensor <NUM> include reflected TIL energy and reflected BIL energy. The reflected BIL energy identifies a see spot on the target <NUM> where the BIL beam <NUM> actually strikes the target <NUM>. Any difference between the actual location of the BIL beam <NUM> on the target <NUM> and the intended/expected location of the BIL beam <NUM> on the target <NUM> can be treated by the controller <NUM> as the boresight error, which affects both the BIL beam <NUM> and the HEL beam <NUM>. The see spot generated by the BIL beam <NUM>, including its sidelobes, can be quite broad spatially at the target <NUM> at tactical ranges and can cover the target <NUM> and/or target-like features with high enough amplitude to generate one or more images that can be interpreted by the controller <NUM>. The high-speed mirror <NUM> can then be used for things like atmospheric jitter correction, which helps to ensure that the HEL beam <NUM> remains at substantially the same location on the target <NUM>.

In some embodiments, the controller <NUM> executes or performs an imaging tracking algorithm to estimate uplink motion of the see spot generated by the BIL beam <NUM> relative to one or more features on the target <NUM> (such as the nose of the target <NUM>), which can be identified with morphological image processing of the captured images. Estimates of the motion of the see spot from frame to frame can be obtained, such as by correlating the expected area of the see spot location in one image with a reference image. The reference image may be a recursively-integrated, shift-corrected see spot image from prior frames. The controller <NUM> can also execute or perform a predictive estimation algorithm that uses spot motion estimates to predict uplink beam jitter on the target <NUM> when the HEL beam <NUM> arrives at the target <NUM>. The prediction can be forward in time and can consider the round trip speed-of-light delay of the BIL beam <NUM> reaching the target <NUM> and returning, as well as any fast steering mirror servo delays, high-speed mirror servo delays, and processing delays. The controller <NUM> may then control one or both fast steering mirrors <NUM>, <NUM> and/or the high-speed mirror <NUM> to compensate for predicted jitter, such as by causing the HEL beam <NUM> to move in the opposite direction as the predicted jitter. Ideally, this minimizes or eliminates atmospheric uplink jitter by the time the HEL beam <NUM> reaches the target <NUM>.

The controller <NUM> includes any suitable structure configured to process images and control one or more operations of a laser system. For example, the controller <NUM> may include any suitable hardware or combination of hardware and software/ firmware instructions for processing images and controlling one or more operations of a laser system, and the controller <NUM> may be programmable or dedicated.

In some embodiments, the controller <NUM> includes at least one processor <NUM>, at least one memory <NUM>, and at least one communication interface <NUM>. The at least one processor <NUM> may be configured to execute instructions stored in and obtained from at least one memory <NUM>. The at least one processor <NUM> may include any suitable number(s) and type(s) of processing devices or other computing or control devices in any suitable arrangement. As specific examples, the at least one processor <NUM> may include one or more microprocessors, microcontrollers, digital signal processors (DSPs), field programmable gate arrays (FPGAs), application specific integrated circuits (ASICS), or discrete circuitry. The at least one memory <NUM> may include any suitable number(s) and type(s) of data storage and retrieval devices, such as random access memory, read only memory, Flash memory, a hard drive, an optical drive, or other memory. The at least one communication interface <NUM> may include any suitable number(s) and type(s) of interfaces allowing communication with other components of the laser system <NUM> or a larger system, such as one or more wired or wireless interfaces. Note that while shown and described as having a single controller <NUM>, the laser system <NUM> may include multiple controllers that are used to control different aspects of the laser system <NUM>.

Note that in this example, the TIL beam <NUM> is directed towards the target <NUM> separate from the HEL beam <NUM> and the BIL beam <NUM>, and the TIL beam <NUM> does not pass through the aperture sharing element <NUM> and is not reflected by the high-speed mirror <NUM>. In fact, in this example, the TIL beam <NUM> does not share any part of its optical path with the HEL beam <NUM> and the BIL beam <NUM> inside the laser system <NUM>. However, that need not be the case, and the TIL beam <NUM> may follow a common optical path through part of the laser system <NUM> as the HEL beam <NUM> and the BIL beam <NUM>. Also, while not shown here for convenience, one or more mirrors (such as one or more fast steering mirrors) and other optical devices may be used to direct the TIL beam <NUM> towards the target <NUM>.

<FIG> illustrates another example high-energy laser system <NUM> supporting atmospheric jitter correction and target tracking using a single imaging sensor according to this disclosure. In particular, <FIG> illustrates a more detailed example implementation of the laser system <NUM> compared to <FIG>. However, the laser system <NUM> shown in <FIG> operates in the same or similar manner as the laser system <NUM> shown in <FIG>. For ease of explanation, the high-energy laser system <NUM> shown in <FIG> may be described as being used in the system <NUM> of <FIG> to engage a hostile target <NUM>. However, the high-energy laser system <NUM> of <FIG> may be used in any other suitable environment and for any other suitable purpose.

As shown in <FIG>, the laser system <NUM> includes a high-energy laser generator <NUM>, which generates the HEL beam <NUM> and an auto-alignment (AA) beam <NUM>. In some embodiments, the high-energy laser generator <NUM> includes one or more lasers that generate beams at different wavelengths and a spectral beam combining unit that combines the beams to produce a single overlapping beam, which here includes the HEL beam <NUM> and the AA beam <NUM>. The AA beam <NUM> can be used internally within the laser system <NUM> for alignment purposes.

The laser system <NUM> also includes a laser alignment module (LAM) <NUM>, which generally operates to produce additional laser beams and to align those additional beams with the HEL beam <NUM>. In this example, a target illumination laser <NUM> (such as a <NUM> laser) produces the TIL beam <NUM>, and a beacon illumination laser <NUM> (such as a <NUM> laser) produces the BIL beam <NUM>. Variable divergence optics <NUM> can be used to alter the divergence of the TIL beam <NUM> in order to obtain a variable beam footprint for the TIL beam <NUM>, which can help to ensure that the TIL beam <NUM> spreads over the entire target <NUM> or a desired portion of the target <NUM>. A polarizer <NUM> can be used to set or alter the polarization of the BIL beam <NUM>, and one or more beam expanders <NUM> can be used to increase the cross-sectional size of the BIL beam <NUM>.

An additional laser <NUM> (such as a <NUM> laser) is provided in the laser system <NUM> for laser range-finding. The range-finding laser <NUM> generates a range-finding beam <NUM>, which is provided to a beam splitter <NUM>. The beam splitter <NUM> divides the range-finding beam <NUM> into a first portion that is directed towards the target <NUM> and a second portion that is directed towards a range-finding receiver <NUM>. The range-finding receiver <NUM> also senses part of the range-finding beam <NUM> that reflects off the target <NUM>. Time-of-flight calculations, such as based on a time difference between reception of the second portion of the range-finding beam <NUM> from the beam splitter <NUM> and reception of the reflection at the receiver <NUM>, or other calculations can be performed to estimate the distance to the target <NUM>. Note, however, that the use of a laser range-finder is not required in the laser system <NUM>.

A first dichroic mirror or other beam splitter/combiner <NUM> reflects the BIL beam <NUM> and transmits the first portion of the range-finding beam <NUM> towards a first fast steering mirror <NUM>. The first fast steering mirror <NUM> and a second fast steering mirror <NUM> redirect the BIL beam <NUM> and the first portion of the range-finding beam <NUM>. This can be done to help ensure that the BIL beam <NUM> is offset from the HEL beam <NUM> at the target <NUM>. A second dichroic mirror or other beam splitter/combiner <NUM> reflects the HEL beam <NUM> and the AA beam <NUM> and transmits the TIL beam <NUM>. A third dichroic mirror or other beam splitter/combiner <NUM> reflects the HEL beam <NUM>, the AA beam <NUM>, and the TIL beam <NUM> and transmits the BIL beam <NUM> and the range-finding beam <NUM>. At this point, the various beams <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> are generally aligned and follow a common optical path through part of the laser system <NUM>. The third dichroic mirror or other beam splitter/combiner <NUM> also reflects a small portion of the BIL beam <NUM> and transmits a small portion of the AA beam <NUM> to a BIL/AA alignment sensor <NUM>, which can sense the locations of the BIL beam <NUM> and the AA beam <NUM>. This information can be used (such as by the controller <NUM>, which is not shown in <FIG>) to adjust one or both fast steering mirrors <NUM> and <NUM> in order to obtain a desired alignment and offset of the BIL beam <NUM> relative to the AA beam <NUM> (and therefore relative to the HEL beam <NUM>).

Additional mirrors <NUM>, <NUM>, and <NUM> redirect the aligned beams <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> as needed. In some embodiments, the mirrors <NUM>, <NUM>, and <NUM> may represent fold mirrors. In other embodiments, the mirrors <NUM> and <NUM> may represent fold mirrors, and the mirror <NUM> may represent an adaptive optic, such as a deformable mirror, used to correct for higher-order wavefront errors in at least the HEL beam <NUM> (and possibly in one or more of the other beams <NUM>, <NUM>, <NUM>, and <NUM>).

The laser system <NUM> further includes a beam director <NUM>, which generally operates to direct the various beams <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> towards the target <NUM>. In this example, the beam director <NUM> includes an azimuth gimbal <NUM> and an elevation gimbal <NUM>. The azimuth gimbal <NUM> may rotate various components (including the elevation gimbal <NUM>) about a vertical axis for azimuth control, and the elevation gimbal <NUM> may rotate various components about a horizontal axis for elevation control.

The azimuth gimbal <NUM> in this example includes a fast steering mirror <NUM> and two fold mirrors <NUM> and <NUM>, and the elevation gimbal <NUM> in this example includes a fast steering mirror <NUM>. The fast steering mirrors <NUM> and <NUM> may represent Coudé Path fast steering mirrors, and the fold mirrors <NUM> and <NUM> may represent Coudé Path fold mirrors (since they are being used to transport the beams generally along the polar axis of the laser system <NUM>). A first dichroic mirror or other beam splitter/combiner <NUM> is used to separate the TIL beam <NUM> from the other beams <NUM>, <NUM>, <NUM>, and <NUM>. The TIL beam <NUM> is redirected by a mirror <NUM> to a fast steering mirror <NUM>, which can be adjusted (such as by the controller <NUM>) in order to control how the TIL beam <NUM> is directed towards the target <NUM>.

The other beams <NUM>, <NUM>, <NUM>, and <NUM> are redirected using mirrors <NUM>, <NUM>, and <NUM> to a second dichroic mirror or other beam splitter/combiner <NUM>. The second beam splitter/combiner <NUM> reflects the HEL beam <NUM>, the BIL beam <NUM>, and the range-finding beam <NUM> towards a fast steering mirror <NUM>. The beam second splitter/combiner <NUM> also transmits incoming energy <NUM> (such as SWIR energy), where the incoming energy <NUM> may include reflections of the TIL beam <NUM> and the BIL beam <NUM>. Further, the second beam splitter/combiner <NUM> may provide at least part of the AA beam <NUM> to an LOS/AA alignment sensor <NUM>, which can sense the location of the AA beam <NUM>. This information can be used (such as by the controller <NUM>) to adjust one or more fast steering mirrors <NUM>, <NUM>, <NUM>, and <NUM> to obtain a desired line-of-sight to the target <NUM>. In addition, the second beam splitter/combiner <NUM> may provide a portion of the AA beam <NUM> and a portion of the BIL beam <NUM> to an imaging subsystem <NUM>, which also receives the incoming energy <NUM>.

The imaging subsystem <NUM> in this example includes optics <NUM>, such as polarizers, lenses, or other components used to pre-process the portion of the AA beam <NUM>, the portion of the BIL beam <NUM>, and the incoming energy <NUM>. A beam splitter <NUM> reflects the portion of the AA beam <NUM> to a position sensitivity detector <NUM> (such as a SWIR camera), which can detect the location of the AA beam <NUM>. The beam splitter <NUM> also transmits the portion of the BIL beam <NUM> and the incoming energy <NUM> to an imaging sensor <NUM> (such as a Fourier transform spectrometer). Among other things, the imaging sensor <NUM> can capture images of the target <NUM>, and the images can include reflected TIL energy and possibly reflected BIL energy (depending on the modulation of the beacon illumination laser <NUM> at the time of image capture).

The beams <NUM>, <NUM>, and <NUM> as reflected by the fast steering mirror <NUM> are reflected by a mirror <NUM> to a telescope <NUM>. The mirror <NUM> may represent a fold mirror or an adaptive optic, such as a deformable mirror used for focus control. The mirror <NUM> also reflects the incoming energy <NUM>, which is received by the telescope <NUM>, towards the fast steering mirror <NUM>. The telescope <NUM> directs the beams <NUM>, <NUM>, and <NUM> towards the target <NUM> and receives the incoming energy <NUM>, which can include TIL, BIL, and other optical energy reflected from the target <NUM>. In this example, the telescope <NUM> represents an afocal telescope having a large primary mirror and two smaller adjustable mirrors, although other types of telescopes may be used.

Various additional components may be used in the laser system <NUM> shown in <FIG>. For example, a digital camera <NUM> may be used to capture visible images of a scene. A telescope <NUM> (such as an afocal telescope having a large primary mirror and a smaller adjustable mirror), a fast steering mirror <NUM>, optics <NUM>, and an infrared camera <NUM> (such as a mid-wave infrared or "MWIR" camera) may be used to capture infrared images of a scene. A dichroic mirror or other beam splitter/combiner <NUM> may be used to pass the second portion of the range-finding beam <NUM> to the range-finding receiver <NUM> while reflecting a portion of the BIL beam <NUM> (which is provided via the dichroic mirror or other beam splitter/combiner <NUM> and the beam splitter <NUM>) to a wavefront sensor <NUM>. One or more humidity sensors 396a-396b may be used to sense moisture within the laser system <NUM>, which may be considered by the controller <NUM> when performing certain functions (such as determining how to adjust one or more fast steering mirrors). At least one safety scraper <NUM> can be used to absorb stray laser energy or redirect the stray laser energy to a beam dump or other location(s) for termination. At least one safety sensor <NUM> can be used to detect if stray laser energy presents a safety concern or other issue, which may allow the controller <NUM> to shut down the laser system <NUM>, adjust one or more fast steering mirrors, or take other corrective action. Note, however, that one, some, or all of these features may be omitted.

As with the example shown in <FIG>, the laser system <NUM> in <FIG> uses a single imaging sensor (the imaging sensor <NUM>) to capture images that contain reflected TIL energy and images that contact reflected TIL energy and reflected BIL energy. Among other things, this allows the controller <NUM> to perform target tracking using the TIL-related images and to perform boresight correction (including jitter correction) using the TIL/BIL-related images. Also, the operation of the beacon illumination laser <NUM> can be modulated or pulsed as described above in order to facilitate the capture of these various images. As a result, the images can be used by the controller <NUM> to reduce or minimize atmospheric jitter, higher-order atmospheric distortions, and dynamic target tracking errors for very accurate high-energy beam pointing.

Although <FIG> and <FIG> illustrate examples of high-energy laser systems <NUM> supporting atmospheric jitter correction and target tracking using a single imaging sensor, various changes may be made to <FIG> and <FIG>. For example, the makeup and arrangement of the laser systems <NUM> shown in <FIG> and <FIG> are for illustration only, and components can be added, omitted, combined, further subdivided, replicated, or placed in any other suitable configuration according to particular needs. As a particular example, the arrangements of mirrors and other optical devices in <FIG> and <FIG> to route different optical beams may be based on specific implementation needs, and other arrangements of mirrors and other optical devices may be used to direct optical beams in the desired manner. Also, the number(s) and type(s) of mirrors and other optical devices can vary based on the specific needs in a laser system. In general, this disclosure is not limited to any specific arrangement of mirrors and other optical devices. Further, note that any single feature or any combination of features shown in <FIG> but not in <FIG> may be added to the laser system <NUM> of <FIG> as needed or desired. In addition, note that any single feature or any combination of features shown in <FIG> but not in <FIG> may be omitted from the laser system <NUM> of <FIG> as needed or desired.

<FIG> illustrate an example control system <NUM> supporting atmospheric jitter correction and target tracking using a single imaging sensor for a high-energy laser according to this disclosure. For ease of explanation, the control system <NUM> shown in <FIG> may be described as being used with the high-energy laser system <NUM> of <FIG> or <FIG> in the system <NUM> of <FIG> to engage a hostile target <NUM>. However, the control system may be used with any other suitable high-energy laser system in any other suitable environment and for any other suitable purpose.

As shown in <FIG>, the control system <NUM> includes a target tracker executive function <NUM>, which generally operates to control the other functions of the control system <NUM>. For example, the target tracker executive function <NUM> can control the tracking states, control modes, timing, and functions that are performed in the control system <NUM>.

An acquisition and tracking controller (ATC) function <NUM> generally operates to identify and output coarse target tracks for one or more targets <NUM>. In this example, the ATC function <NUM> includes a single target tracker function <NUM> and a multi-target tracker function <NUM>. The single target tracker function <NUM> generally operates to identify small individual targets <NUM> in a field of view and output target positions, such as in pixel coordinates. In some embodiments, the single target tracker function <NUM> can identify the centroid of each target <NUM>, correlate the movements of each target <NUM>, and generate target state estimates and tracking errors for gimbal pointing. The single target tracker function <NUM> can also acquire targets <NUM> and reject false detections, such as by using kinematics-matching filters. In this example, the single target tracker function <NUM> receives input from an MWIR camera (such as the infrared camera <NUM>), although other or additional input may be used here.

The multi-target tracker function <NUM> generally operates to identify multiple targets <NUM> in a field of view and output target positions, such as in pixel coordinates. In some embodiments, the multi-target tracker function <NUM> can identify the centroid of each target <NUM>, correlate the movements of each target <NUM>, and generate target state estimates and tracking errors for gimbal pointing. The multi-target tracker function <NUM> can also acquire targets <NUM> and reject false detections, such as by using kinematics-matching filters, and facilitate break-lock reacquisition. In this example, the multi-target tracker function <NUM> receives input from an MWIR camera (such as the infrared camera <NUM>), although other or additional input may be used here.

A target state estimator (TSE) function <NUM> processes various information to determine current and predicted states of one or more identified targets <NUM>. For example, the TSE function <NUM> can receive target locations from the ATC function <NUM> and can exchange additional target locations or other information with a fine target tracker (FTT) function <NUM>. The TSE function <NUM> can also receive additional inputs, such as cues from other sensors and inputs from an inertial navigation system (INS). The TSE function <NUM> processes this or other information and generates inertial target state estimates for the identified targets <NUM>, such as by using extended Kalman filter (EKF) tracking. The TSE function <NUM> can also engage in break-lock reacquisition. One or more filters can be used with the identified target locations to help filter out disturbances in the estimated locations. The TSE function <NUM> can further convert the determined target state estimates or other information into line-of-sight information, gimbal coordinates, and/or estimated ranges.

A gimbal pointing function <NUM> controls the direction in which a gimbal (such as the multi-axis gimbal <NUM> or the gimbals <NUM>-<NUM>) is pointing a laser system <NUM>. The gimbal pointing function <NUM> can use the target state estimates and tracking errors from the ATC function <NUM> and the gimbal coordinates from the TSE function <NUM> to determine where to point the laser system <NUM>. In some embodiments, a solar avoidance function <NUM> can initially process the gimbal coordinates from the TSE function <NUM> in order to exclude potentially pointing the laser system <NUM> into or near the sun or other source of bright irradiance. A focus control function <NUM> controls the focus of the laser system <NUM> based on the estimated range to at least one target <NUM>.

The FTT function <NUM> generally operates to provide line-of-sight stabilization for the laser system <NUM>. For example, the FTT function <NUM> can track one or more centroids of one or more targets <NUM> (which can be used for HEL pointing), update target state estimates and tracking errors to the TSE function <NUM>, and perform line-of-sight stabilization. The FTT function <NUM> also provides information identifying desired aimpoints of one or more laser beams (such as the HEL beam <NUM>, TIL beam <NUM>, and BIL beam <NUM>) and a desired pointing location for the BIL beam <NUM>. Adjustments to the locations of the HEL beam <NUM> and the BIL beam <NUM> on a specific target <NUM> can be controlled based on this information, such as by adjusting one or more of the fast steering mirrors <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>. In this example, the FTT function <NUM> receives input in the form of images containing reflected TIL energy without reflected BIL energy from an SWIR camera (such as the imaging sensor <NUM> or <NUM>), although other suitable imaging sensors may be used here.

An adaptive optics (AO) function <NUM> generally operates to provide uplink tip-tilt correction and other boresight error correction. For example, the AO function <NUM> can identify a see spot location gradient (a difference in actual and expected/desired locations of a see spot generated by the BIL beam <NUM> on a target <NUM>), identify the position of the HEL beam <NUM> (such as in in pixel coordinates) on the target <NUM>, correlate the centroid position of the target <NUM>, and generate tip-tilt corrections. The AO function <NUM> can also identify how the BIL beam <NUM> should be offset from the HEL beam <NUM> on a target <NUM>. The corrections and offset can be controlled based on this information, such as by adjusting one or more of the fast steering mirrors <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and/or the high-speed mirror <NUM>. Ideally, this stabilizes the BIL beam <NUM> on the target <NUM> and therefore stabilizes the HEL beam <NUM> at a desired aimpoint on the target <NUM>. In this example, the AO function <NUM> receives input in the form of images containing reflected TIL energy and reflected BIL energy from an SWIR camera (such as the imaging sensor <NUM> or <NUM>), although other suitable imaging sensors may be used here.

An FTT LOS fast steering mirror (FSM) pointing function <NUM> and an AO FSM pointing function <NUM> generally operate to adjust the optical devices in the laser system <NUM> to provide the desired adjustments to the HEL beam <NUM>, the TIL beam <NUM>, and the BIL beam <NUM>. For example, the pointing functions <NUM> and <NUM> may cause adjustments to be made to any of the fast steering mirrors <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and/or the high-speed mirror <NUM>. The pointing function <NUM> helps to achieve fine tracking changes in the line-of-sight for a target <NUM> by keeping the laser system <NUM> directed at the selected aimpoint on the target <NUM>. The pointing function <NUM> helps to achieve fine HEL corrections in the position of the HEL beam <NUM> on the target <NUM>.

Each of the functions <NUM>-<NUM> shown in <FIG> may be implemented in any suitable manner. For example, one, some, or all of the functions <NUM>-<NUM> may be implemented using dedicated hardware, such as at least one DSP, FPGA, or ASIC. As another example, one, some, or all of the functions <NUM>-<NUM> may be implemented using hardware with software/firmware instructions, such as at least one processor that executes software/firmware instructions. A combination of dedicated hardware and hardware with software/firmware can also be used. In general, the control system <NUM> is not limited to any specific configuration and can be implemented in any number of ways.

<FIG> illustrates an example TIL processing algorithm <NUM> that can be performed as part of the FTT function <NUM>. As shown in <FIG>, the TIL processing algorithm <NUM> receives input images <NUM> that contain reflected TIL energy but not reflected BIL energy. In this example, the images <NUM> are received at a specific rate (namely <NUM>), although the images <NUM> can be received at any other suitable rate. Although not shown here, the images <NUM> may be pre-processed in any suitable manner, such as by performing initial clutter processing to enable easier target acquisition.

The images <NUM> are processed using an upsample function <NUM>, which increases the amount of image data contained in the images <NUM>. Any suitable technique can be used here to upsample the image data. Various techniques for upsampling data are known in the art, and other techniques are sure to be developed in the future. The upsampled images are processed using a subpixel correlation function <NUM>, which aligns the upsampled images at the sub-pixel level. Any suitable technique can be used here to correlate the upsampled image data, such as map-based correlation. Various techniques for correlating image data are known in the art, and other techniques are sure to be developed in the future. The result is a set of aligned upsampled images.

A super resolution mapping function <NUM> processes the aligned upsampled images to generate one or more images having super-resolution, meaning a resolution higher than the original images <NUM>. Various techniques for combining image data to produce super-resolution images are known in the art, and other techniques are sure to be developed in the future. The super-resolution images are processed using an edge segmentation function <NUM>, which identifies edges or other features of at least one target <NUM> contained in the images. Various techniques for edge detection are known in the art, and other techniques are sure to be developed in the future. An aimpoint recognition function <NUM> uses this information to identify one or more selected aimpoints for one or more lasers on the at least one target <NUM>. The aimpoint recognition function <NUM> can enable automatic selection of an aimpoint on a target <NUM>, which may be based on various factors (such as the visible profile of the target <NUM> relative to the laser system <NUM>). In some embodiments, the aimpoint recognition function <NUM> can select the aimpoint as the centroid of the target <NUM>, where the centroid is based on the edges detected in one or more super-resolution images.

<FIG> illustrates an example BIL processing algorithm <NUM> that can be performed as part of the adaptive optics function <NUM>. As shown in <FIG>, the BIL processing algorithm <NUM> receives input images <NUM> that contain reflected TIL energy and reflected BIL energy, and these images <NUM> are multiplexed with the input images <NUM> (which are processed using the TIL processing algorithm <NUM>). The multiplexing allows operations to be performed based on reflected BIL energy while still allowing the laser system <NUM> to maintain line-of-sight on a target <NUM> using target tracking based on the images <NUM>. In this example, the images <NUM> are received at a specific rate (namely <NUM>,<NUM>), although the images <NUM> can be received at any other suitable rate (which may or may not equal the rate of the images <NUM>). Although not shown here, the images <NUM> may be pre-processed in any suitable manner.

The images <NUM> are provided to a target feature estimation function <NUM>, which processes the images <NUM> to identify features of a target <NUM> and the BIL beam <NUM> on the target <NUM>. For example, the target feature estimation function <NUM> can identify the top, bottom, and side edges of the target <NUM> and the location of the BIL beam <NUM> on the target <NUM>. The top, bottom, and side edges of the target <NUM> can be determined in any suitable manner, such as based on movement of the target <NUM> over time. As described above, the location of the BIL beam <NUM> on the target <NUM> can vary based on a number of factors, including atmospheric uplink jitter and other boresight error. Various techniques for identifying target features are known in the art, and other techniques are sure to be developed in the future. The target feature estimation function <NUM> can also identify a desired offset of the BIL beam <NUM> from the HEL beam <NUM> on the target <NUM>. The desired offset can be used to control the laser system <NUM>, such as by adjusting one or more of the fast steering mirrors <NUM>, <NUM>, <NUM>, <NUM>.

A spot correlation window function <NUM> defines a window around the see spot formed by the BIL beam <NUM> on the target <NUM> in each image <NUM>, and a correlation processing function <NUM> processes at least the windows of the images <NUM> to identify shifts of the see spot formed by the BIL beam <NUM> on the target <NUM>. For example, the correlation processing function <NUM> can align the image data in the windows of the images <NUM> and then identify movements of the see spot on the target <NUM> in both x and y directions, which can be arbitrarily defined but which are typically orthogonal (although other coordinate systems may be used). A super resolution mapping function <NUM> processes at least the windows of the images <NUM> to generate one or more images or image portions having super-resolution, meaning a resolution higher than the original images <NUM>. Various techniques for combining image data to produce super-resolution images are known in the art, and other techniques are sure to be developed in the future. The super-resolution images or image portions are processed by an automatic aimpoint function <NUM>, which uses this information to detect the intended aimpoint for the BIL beam <NUM> on the target <NUM>.

A prediction function <NUM> processes various information in order to predict the likely future jitter and other boresight error that will affect the BIL beam <NUM> over time. For example, the prediction function <NUM> can use the measured jitter and other boresight error of the BIL beam <NUM> during prior time periods to project forward what the boresight error will be in the future (for at least one or several future time periods, however large or small). The prediction function <NUM> can consider various factors in making the predictions, such as the round trip speed-of-light delay of the BIL beam <NUM> reaching the target <NUM> and returning, fast steering mirror servo delays, high-speed mirror servo delays, and processing delays. The predicted jitter and other predicted boresight error can be used to adjust one or more mirrors (such as one or more fast steering mirrors or a high-speed mirror) that direct the BIL beam <NUM> and the HEL beam <NUM> towards the target <NUM>. Ideally, the adjustments alter at least one mirror to move the BIL beam <NUM> and the HEL beam <NUM> in the opposite direction as the predicted jitter or other boresight error, thereby helping to reduce or minimize movement of the BIL beam <NUM> and the HEL beam <NUM> on the target <NUM>.

Each of the functions <NUM>-<NUM> and <NUM>-<NUM> shown in <FIG> may be implemented in any suitable manner. For example, one, some, or all of the functions <NUM>-<NUM> and <NUM>-<NUM> may be implemented using dedicated hardware, such as at least one DSP, FPGA, or ASIC. As another example, one, some, or all of the functions <NUM>-<NUM> and <NUM>-<NUM> may be implemented using hardware with software/ firmware, such as at least one processor that executes software/ firmware instructions. A combination of dedicated hardware and hardware with software/firmware can also be used. In general, the processes <NUM> and <NUM> are not limited to any specific configuration and can be implemented in any number of ways.

<FIG> illustrates an example process <NUM> that can be performed as part of the prediction function <NUM>. As shown in <FIG>, the process <NUM> includes a BIL spot centroid measurement function <NUM>, which identifies the centroid of the see spot formed by the BIL beam <NUM> on the target <NUM> in the images <NUM> (or at least the windows of the images <NUM>). In some embodiments, the centroids are calculated based on the top, bottom, and side edges of the target <NUM> detected earlier in the process <NUM>.

An auto-regressive system model sliding window function <NUM> is used to estimate an autoregressive input-output model that characterizes uplink jitter and other boresight error. The model here is estimated based on motion of the see spot, which is based on changes in the centroid of the see spot over time. The model is estimated since there are typically no dynamical models of optical turbulence in the atmosphere, and an autoregressive input-output model can be used to suitably represent temporally-correlated atmospheric conditions. The autoregressive input-output model may be multi-pole, and the model's coefficients can be estimated on-line (such as by the controller <NUM>). In some embodiments, the autoregressive input-output model can be estimated using least squares correlation estimation in a sliding window, and the model can be updated every time step or image. Note, however, that other types of models may be used to estimate atmospheric disturbances.

The model is used by an N-step prediction function <NUM> to predict the motion of the see spot generated by the BIL beam <NUM> on the target <NUM> for N future time periods (where N is an integer greater than or equal to one). For example, the N-step prediction function <NUM> can use the model and the prior measurements of the see spot's motion to make one or more predictions about how the see spot will move in the near future. Note that the accuracy of the predictions can be dependent on a number of factors, such as the number of future time periods and the sample rates of various data (including the see spot's motion).

Since atmospheric uplink jitter is typically band-limited to certain frequencies (typically below <NUM>) and can have a f-<NUM>/<NUM> temporal frequency roll-off, sampling the motion of the atmosphere at high speed enables accurate prediction out to many time steps (or images) in the future. When a single imaging sensor <NUM> or <NUM> is used for capturing both return TIL energy and return BIL energy, the TIL tracking and the BIL processing can be optimized to minimize total uplink jitter and to keep the BIL beam <NUM> pointed on the target <NUM>. In some embodiments, the speed of the imaging sensor <NUM> or <NUM> for tactical ground-to-air scenarios may be approximately <NUM>, while the target illumination laser <NUM> or <NUM> may operate at <NUM> or less to maintain initial pointing accuracy. The high speed of the imaging sensor <NUM> or <NUM> can help to keep prediction errors small.

<FIG> illustrates an example control loop <NUM> that incorporates the TIL and BIL processing algorithms <NUM> and <NUM> and other functions discussed above. In some embodiments, the control loop <NUM> involves the use of the controller <NUM>, which can perform control actions and execute the TIL and BIL processing algorithms <NUM> and <NUM> and other functions. However, as noted above, the use of a single controller <NUM> is not required, and the various operations of the control loop <NUM> can be performed using multiple controllers <NUM> and/or other components of the laser system <NUM>.

As shown in <FIG>, the control loop <NUM> includes three lower-level loops, including an opto-mechanical stabilization loop <NUM>, a target LOS stabilization loop <NUM>, and a tip-tilt correction loop <NUM>. The function of the opto-mechanical stabilization loop <NUM> is to stabilize the pointing of a high-energy laser relative to the line-of-sight from movement caused by mechanical vibration of the overall system, such as platform vibration. This mechanical vibration (also referred to as mechanical jitter) is represented in <FIG> as θJ. In the opto-mechanical stabilization loop <NUM>, the controller <NUM> receives the mechanical vibration θJ and the line-of-sight of the imaging sensor <NUM> or <NUM>, which is represented by θLOS. The controller <NUM> operates to determine the compensation needed for correction of the mechanical vibration. Based on the determined compensation, the controller <NUM> controls at least one mirror <NUM> (such as at least one fast steering mirror <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and/or the high-speed mirror <NUM>) to adjust the line-of-sight. An inertial measurement unit (IMU) <NUM>, such as a fiber optic gyroscope, can be used here to measure forces acting on the laser system <NUM>.

The target LOS stabilization loop <NUM> stabilizes the return off the target <NUM> from the target illumination laser <NUM>, <NUM>. A steering angle command to be applied to the target illumination laser <NUM>, <NUM> is denoted θTIL in <FIG>. The reflected TIL energy is affected by atmospheric downlink jitter <NUM>, and the target LOS stabilization loop <NUM> senses the atmospheric downlink jitter <NUM> and compensates for the downlink jitter <NUM>. A downlink time delay <NUM> is considered in the target LOS stabilization loop <NUM>, where the downlink time delay <NUM> is a measure of the inherent speed-of-light time delay in the downlink for the TIL energy to reflect off the target <NUM> and be received at the imaging sensor <NUM> or <NUM>. In the target LOS stabilization loop <NUM>, the TIL processing algorithm <NUM> can be used to indicate where the TIL illumination from the target illumination laser <NUM> or <NUM> is aimed towards the target <NUM>. The TSE function <NUM> can be updated based on the output of the TIL processing algorithm <NUM>.

The tip-tilt correction loop <NUM> corrects for the effects of atmospheric uplink jitter on the BIL beam <NUM> and the HEL beam <NUM>. A steering angle command to be applied to the beacon illumination laser <NUM>, <NUM> is denoted θBIL in <FIG>. In the tip-tilt correction loop <NUM>, the controller <NUM> generates an input for an autoregressive model, and the input to the autoregressive model establishes where to point the BIL beam <NUM> to generate a see spot. Since the BIL beam <NUM> travels to the target <NUM>, the BIL beam <NUM> is subject to atmospheric uplink jitter <NUM>. The atmospheric uplink jitter <NUM> is reflected in movement of the see spot generated by the BIL beam <NUM> from an expected location to an actual location on the target <NUM>. An uplink and downlink time delay <NUM> is considered in the tip-tilt correction loop <NUM>, where the time delay <NUM> represents a measure of the inherent speed-of-light time delay in the uplink for the BIL beam <NUM> to reach the target <NUM> and return back to the imaging sensor <NUM> or <NUM>. The BIL processing algorithm <NUM> receives the images <NUM> of the see spot from the imaging sensor <NUM> or <NUM> and predicts the uplink jitter of the BIL beam <NUM> (and therefore of the HEL beam <NUM>) at a future point in time when the beams <NUM>, <NUM> reach the target <NUM>. The prediction results are used for jitter compensation, which includes movement of at least one mirror <NUM> (such as at least one fast steering mirror <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and/or the high-speed mirror <NUM>). Note that the mirror(s) <NUM> used for LOS correction may or may not be the same mirror(s) <NUM> used for jitter correction.

Overall, the control loop <NUM> (including the target LOS stabilization loop <NUM> and the tip-tilt correction loop <NUM>) can be used to mitigate all or substantially all disturbances and focus the HEL beam <NUM> on the desired target <NUM>. This can significantly increase the effectiveness of the high-energy laser system <NUM> on the target <NUM>. Consistent with what is described above, the target LOS stabilization loop <NUM> can operate at a slower rate than the tip-tilt correction loop <NUM>. In the example shown in <FIG>, the target LOS stabilization loop <NUM> operates at a frequency of <NUM>, and the tip-tilt correction loop <NUM> operates at a frequency of <NUM>,<NUM>. However, each loop <NUM>, <NUM>, and <NUM> may operate at any other suitable frequency.

Although <FIG> illustrate one example of a control system <NUM> supporting atmospheric jitter correction and target tracking using a single imaging sensor for a high-energy laser, various changes may be made to <FIG>. For example, the approaches for using a single imaging sensor to support atmospheric jitter correction or other boresight error correction and target tracking as described in this patent document are not limited to use with the particular control system <NUM> shown in <FIG>.

<FIG> illustrates an example method <NUM> for atmospheric jitter correction and target tracking using a single imaging sensor in a high-energy laser system according to this disclosure. For ease of explanation, the method <NUM> shown in <FIG> may be described as involving the use of the high-energy laser system <NUM> of <FIG> or <FIG> in the system <NUM> of <FIG> to engage a hostile target <NUM>. However, the method <NUM> may be used with any other suitable high-energy laser system in any other suitable environment and for any other suitable purpose.

As shown in <FIG>, a target to be illuminated is identified at step <NUM>. This may include, for example, the laser system <NUM> performing the ATC function <NUM> to identify a target <NUM> and a coarse track of the target <NUM>. An HEL beam and a TIL beam are generated and transmitted towards the target at step <NUM>. This may include, for example, the high-energy laser <NUM> or the high-energy laser generator <NUM> generating the HEL beam <NUM> and the target illumination laser <NUM> or <NUM> generating the TIL beam <NUM>. This may also include the controller <NUM> controlling one or more fast steering mirrors <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and/or the high-speed mirror <NUM> to direct the beams <NUM> and <NUM> towards the target <NUM>.

First images of the target containing reflected TIL energy are generated using an imaging sensor at step <NUM>. This may include, for example, the imaging sensor <NUM> or <NUM> generating images <NUM> of the target <NUM> containing reflected TIL energy. The first images can be generated at a specific rate, such as <NUM> or other rate. In some embodiments, the imaging sensor <NUM> or <NUM> is a high-speed SWIR camera or other imaging sensor that is co-boresighted with the HEL beam <NUM>.

Target tracking is performed using the first images at step <NUM>. This may include, for example, the laser system <NUM> performing the TIL processing algorithm <NUM> to process the images <NUM> and identify or update an aimpoint on the target <NUM> over time. This may also include the controller <NUM> controlling one or more fast steering mirrors <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and/or the high-speed mirror <NUM> to maintain the beams <NUM> and <NUM> on the target <NUM>.

A BIL beam is generated and transmitted towards the target to generate a see spot on the target at an expected location at step <NUM>. This may include, for example, the beacon illumination laser <NUM> or <NUM> generating the BIL beam <NUM>. This may also include the controller <NUM> controlling one or more fast steering mirrors <NUM>, <NUM>, <NUM>, <NUM> so that the BIL beam <NUM> has a desired offset from the HEL beam <NUM> on the target <NUM>. This may further include the controller <NUM> controlling one or more fast steering mirrors <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and/or the high-speed mirror <NUM> to direct the BIL beam <NUM> (along with the beams <NUM> and <NUM>) towards the target <NUM>.

Second images of the target containing reflected TIL and BIL energy are generated using the same imaging sensor at step <NUM>. This may include, for example, the imaging sensor <NUM> or <NUM> generating images <NUM> of the target <NUM> containing reflected TIL energy and reflected BIL energy. The second images can be generated at a specific rate, such as <NUM>,<NUM> or other rate. Depending on the implementation, the HEL beam <NUM>, TIL beam <NUM>, and BIL beam <NUM> are at different wavelengths but are close enough in wavelength that they can be imaging using the same imaging sensor <NUM> or <NUM>. The imaging sensor <NUM> or <NUM> generates the images <NUM> and <NUM> in an interleaved or other multiplexed manner.

Actual locations of the see spot on the target are identified at step <NUM> and used to identify motion of the see spot on the target at step <NUM>. This may include, for example, the laser system <NUM> performing the BIL processing algorithm <NUM> to process the images <NUM>, identify where the BIL beam <NUM> actually generates the see spot on the target <NUM>, and identify changes in the position of the see spot on the target <NUM> over time. In some embodiments, the motion of the see spot can be estimated relative to one or more identified features on the target <NUM>.

Future jitter or other boresight error of the HEL beam on the target is estimated based on the see spot motion at step <NUM>. This may include, for example, the controller <NUM> predicting uplink jitter of the HEL beam <NUM> based on the see spot motion. In some embodiments, the uplink jitter is predicted by generating an autoregressive input-output model or other model of atmospheric turbulence and using the model to predict future jitter or other boresight error based on the identified prior motion of the see spot. The predictions can consider the round trip speed-of-light delay of the BIL beam <NUM> reaching the target <NUM> and returning, fast steering mirror servo delays, high-speed mirror servo delays, and processing delays. One or more mirrors are controlled to substantially cancel the predicted jitter or other boresight error at step <NUM>. This may include, for example, the controller <NUM> controlling movement of one or more fast steering mirrors <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and/or the high-speed mirror <NUM> to move the HEL beam <NUM> and the BIL beam <NUM> in the opposite direction as the predicted jitter or other boresight error.

Although <FIG> illustrates one example of a method <NUM> for atmospheric jitter correction and target tracking using a single imaging sensor in a high-energy laser system, various changes may be made to <FIG>. For example, while shown as a series of steps, various steps in <FIG> can overlap, occur in parallel, occur in a different order, or occur any number of times. As a particular example, the generation and use of the first images for target tracking can occur repeatedly, the generation and use of the second images for jitter or other boresight correction can occur repeatedly, and the generation and use of the first and second images can be multiplexed. Also, various steps can be combined or removed and additional steps can be added according to particular needs.

In some embodiments, various functions described in this patent document are implemented or supported by a computer program that is formed from computer readable program code and that is embodied in a computer readable medium. A non-transitory computer readable medium includes media where data can be permanently stored and media where data can be stored and later overwritten, such as a rewritable optical disc or an erasable storage device.

It may be advantageous to set forth definitions of certain words and phrases used throughout this patent document. The terms "application" and "program" refer to one or more computer programs, software components, sets of instructions, procedures, functions, objects, classes, instances, related data, or a portion thereof adapted for implementation in a suitable computer code (including source code, object code, or executable code). The term "communicate," as well as derivatives thereof, encompasses both direct and indirect communication. The phrase "associated with," as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, have a relationship to or with, or the like.

Claim 1:
A system (<NUM>) comprising:
a target illumination laser, TIL, (<NUM>) configured to generate (<NUM>) a TIL beam (<NUM>) that illuminates a target (<NUM>);
a beacon illumination laser, BIL, (<NUM>) configured to generate (<NUM>) a modulated BIL beam (<NUM>) that creates a spot on the target;
an imaging sensor (<NUM>) configured to (i) capture (<NUM>) first images (<NUM>) of the target at a first rate, the first images containing reflected TIL energy from the TIL beam without reflected BIL energy from the modulated BIL beam and (ii) capture (<NUM>) second images (<NUM>) of the target at a second rate different from the first rate, the second images containing reflected TIL energy from the TIL beam and reflected BIL energy from the modulated BIL beam; and
at least one controller (<NUM>) configured to perform target tracking using the first images and boresight error compensation using the second images.