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Seeing Photons: Progress and Limits of Visible and Infrared Sensor Arrays 1 National Security Context of Detector Technologies BACKGROUND AND INTRODUCTION This is the ninth report issued by an ad hoc committee under the general purview of the National Research Council’s (NRC‘s) Standing Committee on Technology Insight—Gauge, Evaluate, and Review (TIGER). The statement of task for this study appears in Box 1-1 and is followed by a synopsis of the committee’s approach for conducting the study and a general discussion of uses of detector technologies for future military applications.1 Finally, a roadmap for the remaining report chapters explains the organization of this report. Since 2005, the TIGER Standing Committee has assisted the intelligence community2 (IC) in identifying appropriate areas of study to help that community better understand, assess, and forecast the national security implications of future scientific and technological advances. This particular study, initiated in 2009, focuses primarily on passive visible and infrared (IR) detectors. The Committee on Developments in Detector Technologies was formed to conduct the study. Biographical sketches of the committee members appear in Appendix A. During the course of the study the committee had several opportunities to in- 1 For this report, the committee defines a detector as representing a single pixel that receives photons. A focal plane array (FPA) is comprised of many detectors arranged in a two-dimensional grid and generates an image. A sensor system is comprised of FPAs plus other components, such as signal processing, data transmission, coolers, optics, and pointing and tracking mechanisms. 2 According to Intelligence.gov, the IC is composed of 17 federal agencies. Accessed March 24, 2010.
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Seeing Photons: Progress and Limits of Visible and Infrared Sensor Arrays BOX 1-1 Statement of Task The NRC will Consider the fundamental, physical limits to optical and infrared detector technologies with potential military utility, with priority on passive imaging systems. Elucidate trade-offs between sensitivity, spectral bandwidth and diversity, dynamic range, polarization sensitivity, operation temperature, etc. Compare these limits to the near-term state of the art, identifying the scaling laws and hurdles currently restricting progress. Identify key technologies that may help bridge the gaps within a 10-15 year time frame, the implications for future military applications, and any significant indicators of programs to develop such applications. Speculate on technologies and applications of relevance that are high-impact wild cards or have a low probability of feasible deployment within 15 years. Discuss trends in availability and format scalability and in available cooling technologies. Consider the pros and cons of implementing each existing or emerging technology, such as noise, dynamic range, processing or bandwidth bottlenecks, hardening, power consumption, weight, etc. Identify which entities currently lead worldwide funding, research, and development for the key technologies. Highlight the scale, scope, and particular strengths of these R&D efforts, as well as predicted trends, time scales, and commercial drivers. teract with members of the IC and gain a fuller understanding of the community’s needs relating to detectors. In summary, the key points were the following: Focus on the underlying science, physics, and fundamental limits. Identify where there is room for improvement across the spectrum of possibilities. Cover a breadth of topics rather than delve into great depth for a particular topic. In accordance with the statement of task, emphasize passive sensing; however, comment on developments in active sensing where appropriate. COMMITTEE APPROACH TO STUDY The committee met three times to receive briefings from government, industry, and university experts in the field of detectors. Mindful of its task, the committee
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Seeing Photons: Progress and Limits of Visible and Infrared Sensor Arrays cast a wide net for invited experts to help ensure broad coverage of the relevant aspects of detector science and technology. The committee met a fourth time to finalize its report. Appendix B lists specific meetings and participating organizations. Recognizing the relatively short period of time available for preparing its report, the committee concentrated on responding expeditiously, yet comprehensively, to the many elements of the statement of task. The committee also took extra steps to supplement the text of its report with numerous references aimed at bolstering the abilities of members of the IC, and other readers as well, to inquire more deeply into particular subjects as necessary. GENERAL DISCUSSION OF DETECTOR TECHNOLOGIES FOR FUTURE MILITARY APPLICATIONS Overview The first two paragraphs of the statement of task establish the military context of this study (i.e., the words “potential military utility” and “future military applications”). The statement of task covers a 10-15 year time frame and asks the committee to (1) identify technologies to help bridge gaps and (2) speculate on technologies and applications that are high-impact wild cards. Important as they are, detectors are only a part of usable military sensor systems, as shown in Figure 1-1, which include optics; coolers; pointing and tracking systems; electronics, communication, processing, and information extraction subsystems; and displays (for detailed information on the fundamentals of detector technologies, see Chapter 2). Thus, it is essential to consider the combination of new detector technologies and the demand provided by military customers that drives the resulting sensor system developments. Many future military sensor system requirements are classified, and the more critical missions, which usually require the most advanced sensor system technology, are highly classified. For the above reasons, the committee used unclassified data and open literature references to (1) describe general categories of military applications and (2) hypothesize possible detector-related military developments 10-15 years in the future. This process is necessarily imperfect, but it captures many of the implications of future sensor systems employing detector technology advances. The following sections are general military applications that, in the committee’s estimation, will benefit from future advances in detector technologies. Wide-area, Continuous, Airborne Surveillance There is a strong interest in sensor systems for continuous, wide-area surveillance. One aspect of these types of sensors is the potential ability to hit “rewind” to
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Seeing Photons: Progress and Limits of Visible and Infrared Sensor Arrays FIGURE 1-1 Schematic representation of an imaging system showing important subsystems. determine exactly what happened in a particular situation, such as a terrorist attack. An example of how valuable a rewind capability can be comes from a bus bomb event in London, where there are cameras on most street corners. By monitoring many cameras and rewinding the recordings on them, the London police were able to trace the bus bomber back to the house that contained the bomb factory. Certainly in military situations this continuous, wide-area surveillance can have both real-time and postprocessing advantages. Inexpensive Airborne Sensors There is strong interest in having sensors on small drones to obtain close-up, multiple views of objects of interest. These cheap and small sensors can also be used for dangerous tasks, such as explosive removal. Visible- and uncooled IR sensor systems are strong candidates for this type of application. It is not worth spending much time defining exact sensor parameters. Each application will have specifics, but they will vary. Requirements for this application will bend to available technology. If one does not have the resolution, move the sensor system closer. Airborne Military Targeting A targeting sensor’s main function is to detect and identify an object as far away as possible. The main identification limitation for a targeting sensor will be
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Seeing Photons: Progress and Limits of Visible and Infrared Sensor Arrays the diffraction limit, which relates resolution to wavelength and aperture diameter (i.e., wavelength divided by diameter). Historic aircraft sensors have had about an 8-inch-diameter clear aperture. The First Gulf War modified earlier low-altitude operations, which avoided ground defenses by being low and fast, to higher-altitude operations because the United States and its allies could destroy most ground-based defenses. As a result air operations were conducted mostly above 15,000 feet, an altitude at which long-range target identification became an issue. Size and weight constraints reduced the clear aperture to about 5 or 6 inches in diameter, thus reducing identification ability at constant wavelength. Missile Warning Sensors One requirement for missile warning is field of view to see the approaching missile. Six well-placed sensors with 90 × 90 degree fields-of-regard can accomplish full (4π) situational awareness. For aircraft defense, the highest priority is to cover the rear. The second issue to consider is resolution. A missile has to be discriminated against a potentially cluttered background. The good news is that when missiles are fired they create a bright signature across many wavelengths. See-and-avoid Sensors These sensors can be very similar to the missile warning sensors mentioned above. One military application for this type of sensor is to allow drones to fly under visible flight rules. For visual flight rules an aircraft is supposed to be able to identify another aircraft and maneuver to avoid it. To meet Federal Aviation Administration guidelines, any see-and-avoid sensor must discriminate oncoming aircraft at least as well as a pilot, but this is actually an easy standard since a pilot does not see oncoming aircraft well. See-and-avoid sensors are needed for efficient drone flights in visual-flight-rule conditions, but they will also be used in the future as a supplement for general aviation. It is likely that initial systems will operate in the visible wavelengths. Infrared Search and Track Systems Another type of passive airborne sensor might be an infrared search and track system (IRST), a detection sensor for air-to-air targets. Field of regard is a major requirement. An IRST system should see other aircraft in the forward 2π of an aircraft (if one has 120 degrees in azimuth and 40 degrees in elevation, most potential threats will be detected). Resolution is important because of the need to detect aircraft at a distance, when they are points or near points; improved resolution helps discriminate against clutter.
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Seeing Photons: Progress and Limits of Visible and Infrared Sensor Arrays Inexpensive Terrestrial-based Sensors There is strong interest in having sensors on small, unmanned ground robots and in stationary locations on structures to obtain close-up and multiple, views. These cheap, small sensors can also be used for dangerous tasks, such as explosive removal. Visible and uncooled IR sensor systems are strong candidates for this application. Each application will have specific parameters, and they will vary. Also, requirements for this application will bend to available technology. Ground-based Targeting Sensors Tanks, for example, require targeting sensors. Atmospheric turbulence can be an issue along the ground. A range of a few kilometers is desirable. Satellite Platforms This discussion is intended to characterize the important considerations for satellite sensor system designs, as opposed to an extensive discussion of specific applications and specific designs; specific sensor systems are mentioned only to illustrate the satellite platform considerations. Mission requirements usually start the sensor design process, and the usual “top-down” and “bottom-up” system engineering discipline develops the sensor system. Through the course of this process, the particular platform selected for the mission strongly influences the design choices. Detector materials and ancillary components are selected to optimize the design for a given satellite platform subject to the particular sensing requirements. In turn, expected performance improvements in materials or components influence the overall sensor performance relative to the design. Several U.S. organizations launch satellite sensors for diverse purposes. By far the largest users of satellite sensors are U.S. government intelligence and military agencies whose missions, payloads, and orbits are usually classified.3 Most of the early satellite sensors were deployed for strategic intelligence collection but have gradually become an indispensable tool for tactical military missions. On the nonmilitary side, collectors of geophysical data and various mapping and weather observation organizations—for example, the National Aeronautics and Space Administration (NASA) and National Oceanic and Atmospheric Administration—also employ optical, IR, and radio-frequency sensor systems. Most satellite platforms are intended to gather data on the Earth; hence atmospheric parameters dominate the collection channel. Naturally occurring molecules 3 A.D. Wheelon. 1997. Corona: The first reconnaissance satellite. Physics Today 50(2):24-30. This series of satellite imagery sensors began with the first successful Corona launch in August 1960.
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Seeing Photons: Progress and Limits of Visible and Infrared Sensor Arrays dominate the absorption spectrum (e.g., CO2 and H2O) and limit the clear spectral windows available for satellite imaging. Surface weather producing cloud cover, dust storms, et cetera, further obstructs the collection channel. Other satellites gather data using the “deep-space” collection channel. NASA observatories in orbit, including the Hubble, are examples. Another example is the Missile Defense Agency’s mission of detecting mid-course ballistic-missile payloads with cold space as a background. The nature of the mission is also important and constrains both the choice of orbit for the platform and the sensor design. Obviously, viewing the Earth’s surface is best done in the clear windows listed above. On the other hand, picking out a “target of interest,” such as a hot missile or aircraft exhaust, against the thermal Earth background would employ a sensor tailored to that particular emission spectrum.4 NASA might employ a very narrow spectrum sensor matched to an excited ionic or atomic species in the upper atmosphere to monitor the atmospheric physics. These comments set the stage for the discussion below of orbital platform choices. Orbits and Applications The selection of the specific orbit is mission dependent. Orbits commonly used are LEO (low Earth orbit, up to approximately 500 km altitude); MEO (middle Earth orbit, up to approximately 8,000 km altitude); GEO (geosynchronous orbit, up to approximately 36,000 km altitude); and HEO (high Earth orbit, with looping, elliptical pattern having apogee at LEO and perigee at GEO over one of the poles). LEO satellites orbit Earth in approximately 1.5 hours; sun-synchronous orbits are roughly 580 km high; and GEO satellites are stationary overhead, with an orbital time of 24 hours, or one day. Obvious direct consequences of the orbit choice are optical resolution fixed by altitude, wavelength, and aperture and time to view events fixed by the transit time relative to a fixed point on Earth. Another obvious impact is the sun’s position relative to the sensor viewing geometry, which influences the choice of wavelength. One indirect consequence is the constraint of the communication channel used to relay collected data to Earth, which affects the on-board data processing and storage requirements; either ground-data nodes must be in view globally or a cross-link to a data relay satellite has to be provided. Yet another indirect consequence is the payload weight, size, and power dependence on the available booster size and overall mission cost. More subtle consequences include the natural radiation environment that requires shielding of sensors and electronics; particularly sensitive is the MEO 4 The Defense Support Program has provided early warning of intercontinental ballistic missile launches for several decades.
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Seeing Photons: Progress and Limits of Visible and Infrared Sensor Arrays orbit that transits the Van Allen belts. Design life, fixed by mission and cost for the sensor platform, overarches the above considerations; continuous boost for a LEO satellite to keep it in orbit to achieve the design life has to be traded against the lower available payload weight for a GEO satellite whose life is limited by component failures. The above criteria for choosing an orbit for a specific mission are the conventional guidelines that are adjusted by advances in launch capability and other satellite technology. Specialized government missions entail the admission of other criteria based on advances in foreign capability. A particularly direct influence relates to foreign threats to U.S. satellites. In 2007 a Chinese antisatellite (ASAT) capability was established,5 which may impact future orbit choices for satellite imagery. Planned future applications stretch the boundaries of sensor performance. For example, the James Webb Space Telescope (JWST),6 in development, is an IR observatory with a planned launch date of 2013. The primary mirror size of 6.5 m stretches the boundaries of precision space construction for sensor systems given the launch weight limitations. A low-cost and short-development-time satellite sensor example is provided by Advanced Responsive Tactically Effective Military Imaging Spectrometer (ARTEMIS), a multispectral sensor configured from existing components launched recently on TacSat 3.7 Finally, some totally new sensing concepts are being explored by the Defense Advanced Research Projects Agency (DARPA).8 Fractionated Space Systems Fractionated (or networked) space systems offer a novel concept for replacing the large, monolithic systems currently fielded. Such systems divide the functions of a large satellite between many small satellites, which are networked together as a large spacecraft. For example, a networked system could have separate spacecraft for each subsystem, such as power, payload, and navigation, or these subsystems could 5 Kaufman Marc and Dafna Linzer. 2007. China criticized for anti-satellite missile test. Washington Post, p. A01, January 19. Available at http://www.washingtonpost.com/wp-dyn/content/article/2007/01/18/AR2007011801029.html. Last accessed March 24, 2010. 6 For additional information on the JWST, see http://www.jwst.nasa.gov/index.html. Last accessed March 24, 2010. 7 See Raytheon press release, June 2009, available at http://raytheon.mediaroom.com/index.php?s=43&item=1289&pagetemplate=release. Accessed March 24, 2010. 8 Jason C. Eisenreich , Major, United States Air Force. 2009. The All Seeing Eye: Space-Based Persistent Surveillance in 2030. Alabama: Maxwell Air Force Base. Available at https://www.afresearch.org/skins/rims/q_mod_be0e99f3-fc56-4ccb-8dfe-670c0822a153/q_act_downloadpaper/q_obj_351d0f8b-02da-4fae-90fc-0daec34a01d9/display.aspx?rs=enginespage. Accessed March 24, 2010.
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Seeing Photons: Progress and Limits of Visible and Infrared Sensor Arrays be hosted on more than one spacecraft. Currently, DARPA is executing Project F6 to investigate the feasibility and value of fractionated space systems. This example emphasizes the need to continually and creatively explore new satellite imaging sensor designs to maximize mission results. Implications for Sensor Systems Arguably, satellite platforms present the most exacting requirements for intelligence, surveillance, and reconnaissance (ISR) sensors. Satellite payloads are more expensive, typically around $100,000 per pound versus an order of magnitude less for avionic-based platforms, and the lifetime requirements are much more severe since they cannot be easily repaired. Many mission requirements are exacting, special, and innovative to the extent that precision in ranking needed improvements in sensor design is difficult. The general statements below are only intended to provide a context for this class of platform-based applications. Resolution and field of view (FOV). Most if not all applications in all orbits profit from increased optical resolution, which means larger apertures for a fixed wavelength. Two colors. Most target detection and tracking systems utilize two or more colors to discriminate targets against a static background and clutter. Filter wheels and related technologies have provided the mechanisms in the past. Dual- and multi-wavelength detectors enable a more robust, nonmechanical means to accomplish this. Data readout and processing. For most advanced designs, the information handling is crucial to successful mission performance and tied to the data channel to Earth. Coolers. Radiation cooling of detector arrays is a tried and true method for satellite-based sensors. This method requires solar thermal shielding using appropriate sunshades, which strongly depend on the orbit choice, and a means for ensuring the radiator always looks to deep space. Phase-change heat pipes are occasionally employed to physically configure the position of radiators on the satellite, and thermal blankets are routine. Auxiliary coolers ease the mechanical design constraints and are essential for achieving particularly low temperatures, approximately 25 K, for cold-object detection. Advanced means for cooling would enhance satellite-based sensors. Radiation shielding. Space is a harsh environment, and radiation can severely impact the operation of low-noise electronics, a source of lifetime limitations for many components. In addition to normal environmental radiation, defense missions often have additional nuclear-burst requirements. Shielding is routinely provided by appropriate baffles and electronic
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Seeing Photons: Progress and Limits of Visible and Infrared Sensor Arrays redundancy, and circuitry to sense and handle single-event upsets is necessary. Finally, designers for satellite sensors select electronic chips and other components that are specifically designed for radiation tolerance or have been screened for sustained functionality in the radiation environment. Designing to thwart threats. All optical sensors are susceptible to saturation or destruction by in-band, high-power optical radiation.9 Tactical system designs have included this type of requirement for several years, beginning with eye protection goggles. As laser technology has improved and larger-diameter mirrors have been launched in satellites to collect and focus optical radiation, the need to harden space sensors has increased. Inclusion of spectral rejection filters, baffles, or limiters creates a major new “optical path” design consideration that impacts resolution and detectivity. Elements for hardening usually require cooling, which imposes new physical constraints. Finally, this threat mitigation requirement may well impact the choice of orbit to conduct the mission since LEOs are the lowest altitude and, hence, the most susceptible to intentional disruption. POSSIBLE FUTURE DETECTOR-RELATED MILITARY DEVELOPMENTS In considering the 10-15 year time frame, the statements below reflect content, in the form of presentations or documentation, provided to the committee during its data-gathering stage: Second-generation focal plane array (FPA) and forward-looking infrared (FLIR) technology is being globally distributed;10 China is establishing world-class FPA fabrication facilities;11 Single-photon detectors for short-wavelength infrared (SWIR) are under aggressive development;12 9 Jeff Hecht. 2009. Half a century of laser weapons. Optics and Photonics News 20(2):14-21. 10 Zvi Kopolovich. 2009. Status and Trends at Semiconductor Devices—Cooled and Uncooled Detectors. Presentation to the committee on January 21. John Miller. 2009. Future of Imaging. Presentation to the committee on January 21. FPAs and FLIR are discussed in Chapter 2. 11 John Miller. 2009. Future of Imaging. Presentation to the committee on January 21. Paul Norton. 2009. Georgia Tech trip to China and Korea. Information provided to the committee in June 2009. 12 Mark Itzler. 2010. Ultimate Sensitivity at Shortwave Infrared Wavelengths Using Single Photon Detection. Presentation to the committee on February 16. Hooman Mohseni. 2010. Novel Nano-injector Detectors: Towards High-resolution Single-photon Imagers at Short-wave Infrared (SWIR). Presentation to the committee on February 16. Bill Farr. 2010. Detectors for Photon-starved Optical Communications: Present and Future Directions. Presentation to the committee on February 17. SWIR has wavelengths of 0.7 to 2.5 microns (see Chapter 2).
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Seeing Photons: Progress and Limits of Visible and Infrared Sensor Arrays Persistent ISR doctrine will provide real-time information to warfighters;13 Computational imaging work is accelerating;14 and Trends are toward more extensive on-FPA signal processing.15 These major statements are embellished in the other chapters of this report. To this list the committee adds factual open knowledge: U.S. rules of engagement in battle strive for zero collateral damage and zero unintended casualties;16 Urban warfare scenarios stress sensor system designs that meet ISR needs (namely, detecting improvised explosive devices [IEDs] and suicide bombers); Lasers are reaching maturity suitable for battlefield deployment;17 China's new focus on satellite capability challenges U.S. supremacy;18 and Tests of a U.S. airborne laser (ABL) have demonstrated success in shooting down missiles with a high-power laser.19 Deductions, Extrapolations, and Speculations From the preceding discussions the future status of evolutionary sensor systems can be inferred (see Chapters 2, 3, and 4 for details of the detector technologies highlighted below): 13 John Pellegrino. 2009. Emerging Sensor Technologies for Army Applications. Presentation to the committee on December 8. Lyn Brown. 2010. Air Force Research in Detector Technologies. Presentation to the committee on January 20. 14 John Miller. 2009. Future of Imaging. Presentation to the committee on January 21. John Pellegrino. 2009. Emerging Sensor Technologies for Army Applications. Presentation to the committee on December 8. Nbir Dhar. 2010. Discussion with the committee on February 18. 15 John Miller. 2009. Future of Imaging. Presentation to the committee on January 21. Vyshnavi Suntharalingam. 2010. Advanced Imager Technology Development at MIT Lincoln Laboratory. Presentation to the committee on January 21. Nbir Dhar. 2010. Discussion with the committee on February 18. 16 Department of Defense. 2007. U.S. Army Counterinsurgency Handbook. New York: Skyhorse Publishing, Inc. 17 10 kw Fiber Laser; available at www.ipqphotonics.com. Accessed March 24, 2010; numerous Laser Focus World issues. 18 John Miller. 2009. Future of Imaging.” Presentation to the committee on January 21. Lyn Brown. 2010. Air Force Research in Detector Technologies. Presentation to the committee on January 20. 19 U.S. Missile Defense Agency press release; available at http://www.mda.mil/news/10news0002.html. Accessed March 24, 2010.
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Seeing Photons: Progress and Limits of Visible and Infrared Sensor Arrays Third-generation IR two-color FPAs will achieve maturity; Single-photon detectors (SPDs) for the SWIR will be ready for sensor system insertion; Quantum-well and quantum-dot IR photo detectors (QWIP and QDIP) and type II strain-layer superlattice (SLS) technologies will achieve a sufficient performance level for specialized system needs; Establishment of on-FPA analog-to-digital converters and increased on-board digital data processing will occur; Improved filters, coolers, lightweight optics, et cetera, will mature; and More capable strategic satellite sensors will be deployable having higher resolution, multispectral capability, and data fusion signal processing. To the above sensor system status statements can be added potential revolutionary or wild-card achievements during the next 10-15 years: Single-photon detectors using mid-wavelength infrared (MWIR, at 2.5 to 7.0 μm) and long-wavelength infrared (LWIR, at 7.0 to 12 μm) sensor systems via wavelength translation into the visible; a 10-times signal-to-noise ratio is possible for reduced cooling; All digital processing capability directly on-FPA will emerge to provide improved data compression, feature extraction, and lowered overall data system complexity; and Computational imaging application to “conformal imaging,” “speckle imaging,” and “hyperspectral” for new airborne platforms; these techniques feature system configuration advantages to compensate for atmospheric turbulence, airfoil boundary-layer effects, and optical train optimization. These specific detector advancements could then be used to establish new or extended sensor system performance for whichever entity were to develop them. The committee notes that an evolutionary or wild-card detector technology for system insertion cannot just be an academic demonstration; the technology has to be practical and producible at a reasonable cost. The committee believes the above listing conforms to these criteria. (A counterexample would be single-photon superconductor sensors operating at 4 K, which are deemed impractical because of the cooling requirement; preliminary experiments suggest that materials having higher critical temperatures will not be suitable for this application.) All of the above developments provide the design tools for the sensor system architect to respond to operational system requirements of the next decade:
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Seeing Photons: Progress and Limits of Visible and Infrared Sensor Arrays Active imaging to extract three-dimensional information for greater target or adversary location capability in the battlefield (using SPDs and laser radar); Passive or active imaging sensor systems merging all available data via new digital data processing, sensor fusion, and global positioning system coordinates to provide a total ISR solution for the battlefield (uses the technology listed above plus two- and multicolor FPA, active-pixel complementary metal oxide semiconductors, decision-making algorithms, and other evolutionary improvements); Addition of laser jamming to deny the enemy the use of second-generation FLIRs and maintain total night vision superiority—selected searchlight laser illumination may be employed to provide greater target discrimination at longer ranges (via latest fiber laser, diode-pumped solid-state lasers, and other anti-surface-to-air-missile technology); and All of the above items in a airborne platform with sensing and laser jamming power sufficient to deny LEO satellite ISR over U.S. territory. If a space conflict were to develop in the next decade the first phase may well involve sensor jamming or destruction in an ever-escalating series of steps (via conformal imaging, segmented mirrors, speckle imaging, etc., and high-power laser technology). Areas Not Considered or Considered Superficially Again, in accord with the statement of task and due to the relatively short time line of the study, some important areas for sensor systems and sensor mission applications were not considered in detail sufficient to include in this report, including (1) short-range sensor systems and applications possible with cell phone cameras, medical imagers, perimeter-intrusion detection, netted arrays of short-range sensors, and pollution sensors; (2) coherent receivers to receive or eavesdrop on all laser communication links that relate to entangled photon-encryption channels; (3) image feature extraction for terrain, automatic target recognition, change detection, and facial recognition; (4) specific military missions, such as warning detection, missile seekers, missile fusing, and star trackers; and (5) satellite sensor system trades for classified missions. Sensor system designs involve intricate trades impacting the choice of imaging sensor and a host of ancillary components affecting size, weight, and power. For example, satellite mission requirements critically determine booster throw-weight, choice of orbit, data transmission method, mission life, and cost. In turn, all sensor parameters, such as collector aperture, cooling method, needed power, and radiation shielding, have to be chosen to conform. This is an intricate process, and
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Seeing Photons: Progress and Limits of Visible and Infrared Sensor Arrays improvements in mundane engineering materials or processes can have a major impact on overall sensor system performance. REPORT ORGANIZATION The report is structured as follows to correspond to the four main paragraphs of the statement of task. Chapter 2, “Fundamentals of Ultraviolet, Visible, and Infrared Detectors,” covers the first paragraph. The report addresses the second and third paragraphs in the statement of task according to whether the important technologies are considered evolutionary or emerging. Thus, Chapter 3, “Key Current Technologies and Evolutionary Developments,” addresses the elements of both the second and the third paragraphs for existing technologies expected to undergo significant evolution in the next 10-15 years. Chapter 4, “Emerging Technologies with Potentially Significant Impacts,” does the same for potentially “game-changing” technologies that might emerge and have a major impact during the same time frame. With respect to the fourth paragraph in the statement of task, Chapter 5, “The Global Landscape of Detector Technologies,” discusses the international scope of work in the detector, FPA, and sensory system fields.