Abstract:
In a method and system to provide high intensity photic stimulation to disable target subjects, a high intensity light source is activated by trigger signals to produce light flashes in commanded patterns of duration and frequency. A user views a field illuminated through a shutter viewer such as shutter goggles. The goggles are gated to a light blocking state in response to trigger pulses. The light blocking state has a wider time width than the light flashes from the light source produced in response to the trigger pulses to avoid the need for close synchronization. The target subjects are exposed to the high intensity light flashes while the light flashes are blocked from the view of users. Due to a low duty cycle, the users&#39; view through the shutter goggles is unaffected by the intermittent opacity of the shutter goggles.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims priority to U.S. Provisional Patent Application Ser. No. 60/534,058 filed Jan. 5, 2004, the disclosure of which is incorporated herein by reference in its entirety. 

   FIELD OF THE INVENTION 
   The present subject matter relates to a method and system for high intensity photic stimulation. 
   BACKGROUND OF THE INVENTION 
   Photic stimulation comprises application of radiant energy to an organism at a frequency and intensity to which an organism will respond. Photic stimulation varies in its effect depending on wavelength, intensity and manner of application. Low intensity photic stimulation may be used for therapeutic purposes. However, high intensity photic stimulation may be used to apply non-lethal force having a disabling effect on humans or animals, who may be referred to as target subjects. High intensity light sources are incorporated in non-lethal weapons. “High intensity” in this context has an established meaning in the art both as to level of stimulation and as to light intensity. The stimulation is generally received by the eyes and interpreted through various mechanisms in the brain. 
   In civil unrest situations, peace officers may have an urgent need to quickly disable individuals or groups of people. Individuals or crowds can cause significant property damage and injury or death to others. However, the urgency of restoring order does not outweigh the undesirability of the use of deadly force on the civilian population. Therefore, use of high intensity light systems is highly desirable to produce disabling effects. High intensity light sources can cause “flash blindness,” which is temporary vision impairment. Recovery can take minutes to hours. Afterimages may remain for hours or days. Other effects triggered in response to high intensity photic stimulation include distraction, aversion, confusion, disorientation, fear and nausea. Strobe lights can also cause seizures to debilitate target subjects who are epileptogenic. 
   Users employing photic stimulation systems need to be protected from the system&#39;s effects. Using dark, neutral density goggles to reduce light reaching a user&#39;s eyes is undesirable as a measure to reduce the effect of the flashing light. The user&#39;s ability to see the when the light is not flashing may be severely limited, or if the user adapts to the dark filter, the resulting dilation of pupils in the eyes will render the user more susceptible to the light flashes because no time is provided for the eyes to adjust quickly to changing light levels. 
   Use of laser and non-laser light sources is reviewed in T. Donnelly,  Less Lethal Technologies —Initial Prioritisation and Evaluation Publication No.  12/01, (Police Scientific Development Branch, Home Office Policing And Crime Reduction Group, Hertfordshire, UK, 2001). It is pointed out that laser light may cause skin damage as well as permanent eye injury. A device that dazzles at a long range may cause permanent damage at short range. Prior art devices are described which use lasers providing 100–500 mW output power. Damage is more likely when the laser light is used at night, when a target subject&#39;s pupil may have a nominal diameter of 7 mm. In daytime, a target subject&#39;s nominal pupil diameter is 2 mm. Consequently, the pupil will admit approximately ten times as much light to the retina at night as in the daytime. 
   Another shortcoming of laser systems is that use of laser-based devices to cause blindness violates international law.  The Convention On Prohibitions Or Restrictions On The Use Of Certain Conventional Weapons Which May Be Deemed To Be Excessively Injurious Or To Have Indiscriminate Effects  (1980), particularly  Protocol IV, Protocol Relating to Blinding Laser Weapons  (1995), (International Committee of the Red Cross, Geneva, Switzerland), prohibits the use of laser weapons causing blindness to the naked eye or eye with corrective lenses. 
   A number of prior systems exist for purpose of disabling of target subjects with flashing light. U.S. Pat. No. 6,367,943 discloses a shield combined with light sources which produce light pulses. The light pulses are directed to disable a target subject whom the user of the shield wishes to capture or control. The light sources comprise lasers or light emitting diodes (LEDs). These sources have particular frequencies of light emission. The patent points out that if the target subjects are aware of the value of the frequency used in standard equipment, they can employ laser goggles to block the light pulses. In one form, light sources of two different frequencies are utilized, since two frequencies cannot easily be locked by wearing laser goggles. Providing for two different wavelengths of light increases cost and complexity of the system. Additionally, the laser embodiments of this system are subject to the drawbacks of laser systems as described above. 
   U.S. Pat. No. 6,767,108 discloses a flash grenade comprising a layer of flash lamps mounted in a cylindrical housing. Light flashes are intended to disable hostages or non-combatants as well as perpetrators. A trigger circuit for the flash lamps is included in the grenade. There is no opportunity to remotely control the ignition of the flash lamps. 
   U.S. Pat. No. 5,072,342 discloses a hand-held pulsed light focused by a reflector and mounted in a simulated gun. A user points the gun at an assailant&#39;s head for the purpose of causing temporary blindness. This apparatus has a limited field of illumination, and is not suited for a user facing a number of assailants. 
   The above-described prior art systems do not place any particular emphasis on protecting the user who is employing the system from the effects of high intensity flashing illumination. The user may be disabled as well as the target. Even when a high intensity light source is pointed in a direction away from a user, a user could be subjected to some degree of disability or immobilization from reflected light. Also, when one user is directing the high intensity light at target subjects, there may also be other users present in the field of illumination. Consequently friend as well as foe may be disabled. 
   An alternative to laser goggles is seen in U.S. Pat. No. 5,756,989, which discloses color night vision goggles using an image intensifier to amplify input radiant energy from a low-luminance field of view. A “bright source detector” is used to detect incoming radiation from a laser jamming system. Output pulses gate the image intensifier to disable the image intensifier in synchronism with laser jamming pulses. The system is independent of the jamming signal. It cannot be synchronized with the jamming signal, but must operate in response to receipt of the jamming signal. The system must account for lag time in responding to the beginning and end of incoming jamming pulses. 
   U.S. Pat. No. 5,081,542 discloses an eye protection device including a liquid crystal light valve which provides a user an image of a scene. The light valve comprises a mechanism for absorbing energy from a laser threat directed at the user. However, the light valve cannot simply turn substantially opaque to block incoming radiation. 
   SUMMARY OF THE INVENTION 
   Briefly stated, in accordance with embodiments of the present invention, there are provided a method and system for providing high intensity photic stimulation for immobilizing or otherwise impeding or disabling a target subject while protecting the user. The photic stimulation system comprises a trigger signal circuit providing a trigger signal. A high intensity light source including a lamp is connected to the lamp trigger circuit. The lamp flashes in response to the trigger signal. A shutter viewer is provided which is switchable between a transmissive state and an attenuating state. The shutter viewer is connected to a shutter viewer trigger circuit which changes the state of the shutter viewer in response to the trigger signal. A communication circuit transmits the trigger signal to the lamp trigger circuit and to the shutter viewer trigger circuit. 
   In a method of high intensity photic stimulation by a light source, a trigger signal is produced to initiate production of light flashes, which may be produced in bursts having commanded durations and a selected frequency of flashes within each burst. A shutter viewer being switchable between a transmissive state and an attenuating state is provided to view a field illuminated by the light source. The trigger signal is transmitted to trigger an intense flash from the light source circuit and to switch the shutter viewer to the attenuating state in response to the trigger signal. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects and advantages of the present subject matter will become apparent from the following description and the accompanying drawings wherein: 
       FIG. 1  is a block diagram of a system incorporating an embodiment of the invention; 
       FIG. 2 , consisting of  FIGS. 2   a– 2     e , is a waveform chart useful in understanding an embodiment of the present invention; 
       FIG. 3  is an illustration of an embodiment of the invention in operation; 
       FIG. 4  is an illustration of a further embodiment of the present invention; and 
       FIG. 5  is a view of a system comprising a plurality of control units. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  is a block diagram of a system  1  constructed in accordance with an embodiment of the present invention. The system  1  is operable to provide flashing light for disabling a target subject  4  while providing a user  6  freedom to operate unimpeded by the flashing light. The target subject  4  is exposed to the disabling effects of the flashing light. Means are provided to render the flashing light virtually invisible to the user  6 . “Target subject  4 ” or “user  6 ” may refer either to an individual or to a plurality of individuals. Individuals need not necessarily be human. 
   Subsystems in the system  1  comprise a control unit  10 , a lighting subsystem  14  and a viewer subsystem  18 . One or more control units  10  may be utilized at one time. The control unit  10  may be remote from the lighting subsystem  14  and the viewer subsystem  18 . The control unit  10  could comprise a freestanding unit used on-site with the lighting subsystem  14 . Alternatively or additionally, the control unit  10  may take the form of one or more handheld remote activators  16 , each carried by a user  6 . As a further alternative, the control unit  10  could comprise a base station installation or be on a command vehicle. Control between various locations may also be shared. The lighting subsystem  14  may comprise one or a plurality of light sources further described below. Light sources may be hand-held, included in stationary structures or mounted on vehicles. The viewer subsystem  18  may comprise a personal, wearable viewing device, further described below, for each member of a group of users  6 . Alternatively or additionally, the viewer subsystem  18  may comprise a display screen which may be at a remote location. 
   The control unit  10  is illustrated in block diagrammatic form as a number of discrete components. This is done for clarity in description. Many ways of embodying the functions performed by these components will suggest themselves to those skilled in the art other than the specific arrangement shown. The control unit  10  may be embodied in whole or in part by a single integrated circuit, a circuit card with discrete components, a combination of an integrated circuit and software or other means. A start circuit  20  initiates the production of light flashes. The start circuit  20  may be activated either manually or by a condition-responsive sensor as further described below. The control unit  10  includes a pattern selection circuit  21  at which a flashing pattern may be commanded. The flashing pattern is the arrangement of light pulses that will be produced. One preferred flashing pattern could comprise a periodic train of light pulses at a first frequency, of with the periodic pulse train being gated on and off at lower frequency than the first frequency. In this manner, repetitive bursts may be commanded having selected durations and a selected frequency of flashes within each burst. Alternative flashing patterns could comprise a stored aperiodic pattern, a sequence controlled by a random number generator or a combination of sequences or patterns. The pattern selection circuit  21  may include a user interface to select a pattern or may comprise a circuit establishing a preselected pattern. 
   The pattern selection circuit  21  may address a processor  22  to provide outputs to a pulse forming circuit  24 . The pulse forming circuit  24  produces trigger pulses. Trigger pulses may be produced in any of a number of well-known ways. Different patterns may be stored in a lookup table in a memory. In this embodiment, the pattern selection circuit  21  comprises means generating an address for the lookup table. In traditional analog discrete component embodiments, the pattern selection circuit  21  may comprises means for varying values of resistance or capacitance in time constant circuits. The trigger pulses are encoded in a signal train that is transmitted by a communications circuit  26 . The communications circuit  26  transmits the trigger pulses via a link  27 . In one embodiment, the communications circuit is a radio frequency transmitter and the link  27  is a radio frequency antenna. Optical links could be used. An advantage of a radio frequency link is that it is not constrained by line-of-sight limitations. 
   The lighting subsystem  14  comprises one or more light fixtures  30 . A plurality of light fixtures  30  is in a lighting subsystem  14  need not be identical. Each light fixture  30  may comprise a reflector  32  and a flashlamp  34 . The flashlamp  34  may conveniently comprise a xenon gas discharge lamp which produces a flash when pulsed with a trigger voltage. Use of the reflector  32  is optional and affords the ability to direct light flashes in a particular direction. If it is desired to concentrate and direct light flashes in a particular direction, the light fixture  30  may further comprise a lens  35 . A preferred form of lens is a Fresnel lens. The inherent flatness of a Fresnel lens facilitates ease in construction of the light fixture  30 . At the present time, edge-emitting semiconductor sources do not provide sufficient intensity, but such devices may become available in the future. Such components would not need a reflector to provide light which is directed toward a field of illumination. 
   The trigger voltage to cause the flashlamp  34  to flash is supplied by a gating circuit  36 . The gating circuit is operated in response to a lamp trigger circuit  38 . The lamp trigger circuit  38  produces lamp triggering signals in response to the trigger signal detected or otherwise derived from a receiver  40 . The receiver  40  is linked to the control unit  10  by a communications link  42 . The receiver  40  may be a radio frequency receiver, and the link  42  may be a radio frequency antenna. Each light fixture  30  may be powered by a battery  44  for portable operation. 
   Each remote activator  16  comprises a housing  46 . Many different forms of remote activators  16  may be provided. In the illustration of  FIG. 1 , the activator  16  comprises a start button  47  which may be operated by a user  6  to activate the start circuit  20 . A pulse pattern selector  48  may be provided to select one of a plurality of flash patterns or to command particular sequences. A display  49  may be included to inform the user  6  of current settings. 
   Both the lighting subsystem  14  and the viewer subsystem  18  operate in response to the trigger signal provided from the control unit  10 . It is desirable that the viewer system  18  is switched to a radiation blocking state before the light fixture  30  flashes. Therefore, the viewing system must have the opportunity to respond, as further described below, to the trigger signal before the lighting subsystem  14  responds to the trigger signal to flash the flashlamp  34 . Various factors will affect the difference in response time to the trigger signal between viewer system  18  and the lighting subsystem  14 . If, for example, the viewer system  18  is one half mile farther from the control unit  10  than the lighting subsystem  14 , it will take approximately 2.7 μsec longer for the triggering signal to reach the viewer system  18  that the lighting subsystem  14 . There may be differences in propagation times of the trigger signal through the viewer system  18  and the lighting subsystem  14 . Additionally, a “rise-time” must be allowed for in order for the physical occurrence of the phenomenon which causes the viewer system  18  to assume its radiation blocking state after having a gating pulse applied thereto. Therefore, it is desirable to provide with the trigger circuit  38  a delay in response to the trigger signal. A delay on the order of milliseconds will allow for difference in transmission time and for the darkening of the viewer subsystem  18 . 
   Commercially available xenon flashlamps are a suitable choice for the flashlamp  34 . The xenon flashlamp provides intense, white light. The light is also incoherent. Consequently, a higher maximum illumination level may be applied to target subjects  4  without causing permanent damage that may be applied using laser light. Nominal commercially available xenon flashlamps may provide output light pulses each having a duration of 10 or 20 μsec. These flashlamps may be gated at a rate of 30 or 60 Hz. The xenon flashlamp produces a light pulse of fixed duration each time it is triggered. Halogen lamps are generally utilized at lower triggering frequencies. 
   The viewer subsystem  18  comprises one or more shutter viewers  50 . A shutter viewer is a viewer that is transmissive in an ambient state and which is gated to increase in opacity, and which may be substantially opaque, in response to a trigger signal. Liquid crystal lenses are utilized in well-known forms of shutter viewers. One form of a shutter viewer comprises shutter goggles  52  worn by a user  6 . In the prior art, a common use of shutter goggles is to alternately darken right and left lenses to produce a stereoscopic effect. In accordance with embodiments of the present invention, the shutter viewer  50  is rendered substantially opaque when light flashes from the light fixture  30  are provided. Since the light flashes are brief in duration, the shutter viewer  50  may be darkened for less than a millisecond at a time. This operation completely blocks light flashes from the light fixture  30  while leaving the vision of the user  6  substantially unaffected. The shutter viewer  50  could also or alternatively comprise a single gated lens  54  in front of an image sensor such as a video camera as further described with respect to  FIG. 4  below. The video camera may provide images to a remote terminal. The shutter viewer  50  may further alternatively comprise a system in which the image sensor is gated to an “off” state in addition to or instead of gating the lens. Control of the shutter viewer  50  is active rather than passive in that the shutter viewer  50  is gated in response to a programmed trigger signal. The shutter viewer  50  is not gated in response to incoming optical signals. 
   In the present illustration, the shutter viewer  50  comprises a set of shutter goggles  52 . The shutter goggles  52  comprise a right lens  54  and a left lens  56 . Each of the lenses  54  and  56  comprises a liquid crystal light shutter. The lenses  54  and  56  are coupled to a shutter viewer trigger circuit  60 . The shutter trigger circuit  60  receives input pulses from a receiver  62  coupled to a communications link  64 . The receiver  62  and the communications link  64  may respectively comprise a radio frequency receiver and radio frequency antenna. The receiver  62  may be tuned to receive signals from the communications circuit  26 . The lenses  54  and  56  may be connected to receive common gating signals. It is desired to render both lenses  54  and  56  substantially opaque for at least the duration of a light pulse emanating from the light fixture  30 . Operation of the shutter viewer  50  needs to be synchronized with operation of the light fixture  30 . 
     FIG. 2 , consisting of  FIGS. 2   a– 2     e , is a waveform chart useful in understanding operation of the present embodiment. In  FIG. 2 , a common abscissa represents time. The widths of the illustrated waveforms are not drawn to scale. The ordinate is amplitude in arbitrary units.  FIG. 2   a  represents the trigger signal, here a train of trigger pulses, produced by the pulse forming circuit  24 . The pulses are transmitted, as, for example, on a carrier, and received by the communications circuit  40 . The trigger circuit  38  derives intelligence from the communications circuit  40 . Lamp triggering pulses are produced in response to the trigger signal. The shape of the illustrated lamp triggering pulses is arbitrary. Many forms of triggering pulses are well-known. The particular sort of triggering pulse depends on the circuit design selected. For purposes of the present illustration, the triggering pulses are illustrated as square waves in  FIG. 2   b . A delay t is built in to the generation of the triggering pulses. The value of t is selected to permit the shutter viewer  50  to be set to its blocking state before light pulses are produced. In many embodiments, t could have a value of 1 msec. The triggering pulses are provided to the gate circuit  36  to trigger the light fixture  30 . The light pulses are illustrated in  FIG. 2   c  as spikes since they are of very short duration compared to the trigger signal or lamp triggering pulses. 
   The trigger signal will be received at substantially the same time at the receiver  62  in the shutter viewer  50  as at the communications circuit  40  in the lighting subsystem  14 .  FIG. 2   d  represents a series of shutter viewer triggering pulses produced in response to the trigger signal.  FIG. 2   e  illustrates application of gating voltage to the lenses  54  and  56  to render them temporarily opaque. A nominal duration for the gating signal applied to the lenses  54  and  56  is 10 msec. This period is selected to provide a window during which the flashlamp  34  will flash. The duty cycle of the blocking state of the shutter viewer  50  is greater than the duty cycle of the flashlamp  34 . By having an opacity period which is long in comparison to the length of a flash, the need for precise synchronization of the opacity of the lenses  54  and  56  with the occurrence of the light flash from the flashlamp  34  is avoided. A window of 10 msec will allow for differences in time of the trigger signal reaching viewer system  18  and the lighting subsystem  14 , whether the trigger signal gets to the viewer system  18  or the lighting subsystem  14  first. The time window for activation of the viewer system  18  to the blocking state must allow time for the lenses  54  and  56  to turn opaque. This period of opacity will not adversely affect vision of user  6 . The period of persistence of vision is at least 30 msec. Therefore, the user  6  will view the field of illumination substantially normally, and the flashes from the flashlamp  34  will be blocked from view. In effect, the flashes are rendered “invisible” to the user  6 . 
     FIG. 3  is an illustration of an embodiment of the present invention in use. In the embodiment of  FIG. 3 , the present system is used for perimeter protection. A plurality of lighting subsystems  14  are built into an enclosure  100 . A sensor  102  in a housing  104  senses intruders who may comprise target subjects  4 . When target subjects  4  are detected intruding, the sensor  102  enables the control unit  10  to produce a trigger signal. The control unit  10  may be combined in the housing  104  with the sensor  102 . Alternatively, the control unit  10  may be remote from the sensor  102  and coupled by wire or wirelessly. Users  6  may comprise security personnel. 
   In the embodiment of  FIG. 4 , a user  6  is located at a location remote from a field of illumination. The user  6  views the field through a monitor  110 . The remote monitor displays an image from a camera  114  at the remote site. The camera  114  is included in a shutter viewer  50 . The gated shutter device in this embodiment is a single liquid crystal lens  54 . The camera  114  comprises an image sensor, which could be, for example, an image intensifier  120 . Image intensifiers are used to provide images under very low light conditions. The gated lens  54  is placed in front of the image intensifier  120  in order to protect the image intensifier  120  during the occurrence of light flashes. The shutter viewer  50  could also or alternatively comprise a single gated lens  54  in front of an image sensor such as a video camera as further described with respect to  FIG. 4  below. The video camera may provide images to a remote terminal. The shutter viewer  50  may further alternatively comprise a system in which the image intensifier  120  is gated to an “off” state in addition to or instead of gating the lens  54 . 
   In the embodiment of  FIG. 5 , a plurality of lighting subsystems  14  are provided and a plurality of control units  10  are also provided. Each control unit  10  provides a trigger signal on a separate frequency to trigger one or a selected plurality of lighting subsystems  14 . Three control units  10   a ,  10   b  and  10   c  may have transmission frequencies of f 1 , f 2  and f 3  respectively. Each of the lighting subsystems  14  is tuned to respond to one carrier frequency f 1 , f 2  or f 3 . Each shutter viewer  50  may be tuned to respond to each carrier frequency f 1 , f 2  and f 3 . The shutter viewer  50  could comprise shutter goggles as illustrated in  FIG. 5 , or could take other forms. Consequently, separate applications of non-lethal force may be made from separate lighting subsystems  14 . Users  6  who may be in the vicinity of any or all of the lighting subsystems  14  will have their vision protected. 
   Embodiments of the present invention provide for reliable protection of users while providing for the application of non-lethal force to target subjects. Time synchronization is simplified in that a time window for blocking light flashes in a viewer may be much wider than the width of the light pulses and still leave the vision of a user unimpeded. The present subject matter being thus described, it will be apparent that the same may be modified or varied in many ways. Such modifications and variations are not to be regarded as a departure from the spirit and scope of the present subject matter, and all such modifications are intended to be included within the scope of the following claims.