This PDF file contains the front matter associated with SPIE Proceedings Volume 8543, including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.
Protection of military aircraft from hostile threats is paramount to ensure the survivability of aircrews, platforms, and mission success. While the threat environment continues to become more complex, shrinking defense budgets places new challenges on the development of electronic warfare (EW) systems. This paper presents the trends in electro-optical EW system development including 1) features, 2) affordability, 3) open architecture, 4) multi-functionality, 5) integrated avionics survivability equipment, and 6) enabling technologies for sensors, and optical sources. While these system attributes are not new, they have grown in importance in the design of EW systems. And, if treated correctly can have a beneficial symbiotic relationship to each other and to the airframe they support.
Laser manufacturing in Edinburgh was initiated in 1963 by Ferranti (one of the previous names for SELEX Galileo).
Since 2003 a modernized range of military lasers has been established. Innovation, both technical and in other aspects of the business, has enabled the design and manufacture of world leading laser designators and countermeasure lasers. Specific examples will be given including: the application of Geometric Algebra to resonator design; novel alignment free optical parametric oscillators; techniques for designing thermally insensitive laser diode pump heads; and methods for contamination control in lasers.
After nearly two decades' development, the quantum cascade laser (QCL) has emerged from a cryogenically cooled
micro-watt emitter to room temperature continuous wave laser source with watt-level output powers. The recent
breakthroughs in the wall plug efficiency (WPE) of InP based mid-IR QCLs draws significant interest for IRCM
applications toward lower cost, weight, and overall power consumption of the system. Recent research highlight of high
power QCLs is presented, including power levels, beam quality, and reliability.
We describe a beam combiner based on a cascade of dichroic components implemented in a hollow waveguide
integrated optic format. The approach results in a compact, rugged, optically robust solution for providing simultaneous
multi-wavelength emission in the near and mid-IR atmospheric transmission windows. In the approach the individual
dichroic beam combiner components are held in precision alignment slots in the hollow waveguide circuit and the
different input wavelengths are guided between the components to a common output port. The hollow waveguide circuit
and the alignment slots for the components are formed in the surface of a Macor (machinable glass-ceramic) substrate
using precision CNC machining techniques. The hollow waveguides have fundamentally different propagation
characteristics to solid core waveguides leading to transmission characteristics close to those of the atmosphere while
still providing useful light guidance properties. Because of the hollow nature of the core, the transmission efficiency and
power handling of the hollow waveguide circuit can be designed to be very high across a broad waveband range. The
specifications for the dichroic beam combiners and the design of the hollow waveguide circuit are described in relation
to a beam combiner for combining three QCLs emitting at 3.95 μm, 4.05 μm and 4.6 μm and a Ho:YAG laser emitting at
2.1 μm. Details of the design, modeling and manufacturing work, and preliminary assessments of the associated
components, are described.
A simple scheme for efficient generation of two micron laser radiation is reported. Using a thulium fibre laser to pump a Q-switched Ho:YAG laser 31.7 W of average output power is achieved with an M2 of 1.5 (an optical-to-optical conversion efficiency of 67% in terms of absorbed pump power) at a wavelength of 2.1 μm. A single-pass pump geometry is used, eliminating the risk of feedback of unabsorbed light into the fibre laser.
In this paper we report on a high energy, low repetition rate 2-micron-laser, with high conversion efficiency in terms of
output energy per pump power. The laser consists of a Ho3+-doped LiYF4 (YLF) crystal cooled to cryogenic
temperatures in an unstable resonator, pumped by a thulium fiber laser. The cooling to 77 K makes Ho:YLF a quasi four
level laser system, which greatly enhances the extraction efficiency. We achieved 356 mJ in Q-switched operation at 1
Hz PRF when pumping the laser with 58 W for 36 ms. The high beam quality from the fiber laser and the use of an
unstable resonator with a graded reflectivity mirror (GRM) resulted in a high quality laser beam with a M2-value of 1.3.
In this paper we report the results of the research on a double side-pumped Er:Yb:glass slab laser. Due to the nonsymmetric power distribution inside the slab a displacement of the laser beam is observed thus leading to cavity
misalignment and consequently to extraction efficiency loss. At repetition rates of about 5Hz this allows just a burst
operation with an increased thermal load inside the slab. Numerical-theoretical studies about time-dependent temperature distribution in the laser material with appropriate boundary conditions concerning the considered asymmetric geometry lead to a model for mode axis thermal shift and allow to evaluate the amount of cavity misalignment in order to restore the maximal extraction efficiency. By turning or shifting the cavity mirrors is possible to improve the burst operation but the maximal overlap between the mode axis and the inverted region cannot be recovered. Then, an alternative optical configuration able to intrinsically account for the cavity misalignment has to be designed. The matrix formalism was effectively employed to calculate the specifics of one or more optical compensators to be inserted in the cavity to realign the laser resonator. Several configurations were analyzed and the beneficial effects on both thermal lensing and bending were predicted. Experimental measurements validated the model. In particular, an uninterrupted pulsed operation at the highest repetition rates was effectively recovered thus reducing the thermal load inside the laser slab and making such a laser system more effective in free-space laser applications.
We investigate the use of volume Bragg gratings (VBGs) to achieve single longitudinal mode operation in a simple 3
mirror, diode pumped Nd:YVO4 Laser cavity at both 1064nm and 1342nm. A double VBG configuration is constructed
and shown to achieve single longitudinal mode operation with output powers of 2.3W and 2W at 1342nm and 1064nm respectively, the spectral performance of the dual VBG setup is also analyzed. In another configuration, we investigate the use of VBGs as wavelength selective elements in a dual-wavelength laser. Using this method we were able to achieve a combined output power of 3.55W at 1342 and 1064nm emission simultaneously, with a conversion efficiency of 18%.
We report on the development and characteristics of infrared solid state laser as compact and robust light sources for
Directed Infrared Countermeasures (DIRCM). DIRCM against infrared missile seekers requires wavelength tunable laser sources. When adding an optical parametric oscillator (OPO) to a pump laser source, it is possible to cover the 2-5 μm wavelength transmission windows. After a risk reduction phase of five years, CILAS has designed a solid state laser source (SSLS) adapted for DIRCM jamming and has delivered a prototype to DGA-MI for testing and evaluation. The purpose of this paper is to recall the requirements of such a laser source, to present the main design trade-off and the testing experiments. This work is supported by the French MoD (DGA).
A tunable optically pumped HBr laser has been demonstrated for the first time. As pump source for the HBr oscillator,
we developed a single-frequency Ho:YLF laser- amplifier system which was locked to the 2064 nm absorption line of
HBr. Through the implementation of an intra-cavity diffraction grating, laser oscillation was demonstrated on nineteen
molecular transition lines including both the R-branch (3870 nm to 4015 nm) and the P-branch (4070 nm to 4453 nm).
The highest output energy for the given input energy was 2.4 mJ at 4133 nm.
Detection of optical assemblies is important in revealing threats arising from snipers or other weapons guided by optical
means. Several approaches can be imagined using flood illumination or scanning laser techniques. One challenging
problem in optics detection applications in urban environments, particular if an autonomous approach is chosen, is to
reduce the false alarm rate. In this work a dual channel approach for optics detection using a narrow scanning rectangular
laser beam is described. One channel is used for locating targets in the vertical direction while a second channel
simultaneously determines the distance to the targets. An experimental system consisting of two channels operating at
0.8 micrometer wavelength was used to study the characteristics of different targets such as road signs, optical reflexes,
rifle sights, optical references and backgrounds at different ranges and in different environments. Schemes for refining
the target discrimination, reducing the false alarm rate and improving the performance are discussed using experimental
results. A dual channel approach is suggested to improve capabilities in optics detection using a scanning rectangular
Northrop Grumman presents analysis of near-field electrical field distributions of coherent sources and the resultant far-field energy distributions. This work comparatively analyzes the effect of coherent mode content, transverse phase modulation at the source, and apertures at the source. Gaussian, top-hat, and high order Hermite-Gaussian mode distributions are propagated to the far-field and the intensity distribution is compared. Both phase and aperture transformations are applied to the source distributions and the resultant far-field distributions are compared. Using the Fraunhofer approximation and Parseval’s theorem it is possible to provide an accurate intensity profile at ranges wherein the approximation is valid. Using this method various phase transformations at the aperture are analyzed with regard to their resultant far-field distribution. For an arbitrary given source energy with a Gaussian profile, the coherent source energy required to achieve a minimum intensity over a given area is determined for phase distributions at the source aperture. Assuming a desired intensity distribution in the far-field and Gaussian source, an adaptive-additive algorithm is employed to synthesize a phase transformation at the source to achieve the desired distribution. The far-field intensity distribution of this synthesized phase distribution applied to a Gaussian source is
compared to the far-field produced by a non-phase transformed Gaussian source.
Infrared guided missiles are a threat for modern naval forces. The vulnerability of ships can be reduced by applying
countermeasures such as infrared decoys and infrared signature reduction.
This paper presents recent improvements in a simulation toolset which can be used for assessing the effectiveness of
these measures. The toolset consists of a chain of models, which calculate the infrared signature of a ship (EOSM) and
decoys, and generate infrared image sequences of the ship in a realistic sea and sky background (EOSTAR). A complete
missile fly-out model (EWM) uses these images in closed loop simulations for the evaluation of countermeasure
effectiveness against simulated seekers. All model components will be discussed. Typical simulation results will be shown.
Electro-optical system design, data analysis and modeling involve a significant amount of calculation and processing. Many of these calculations are of a repetitive and general nature, suitable for including in a generic toolkit. The availability of such a toolkit facilitates and increases productivity during subsequent tool development: “develop once and use many times”. The concept of an extendible toolkit lends itself naturally to the open-source philosophy, where the toolkit user-base develops the capability cooperatively, for mutual benefit. This paper covers the underlying philosophy to the toolkit development, brief descriptions and examples of the various tools and an overview of the electro-optical toolkit.
The toolkit is an extendable, integrated collection of basic functions, code modules, documentation, example templates, tests and resources, that can be applied towards diverse calculations in the electro-optics domain. The toolkit covers (1) models of physical concepts (e.g. Planck’s Law), (2) mathematical operations (e.g. spectral integrals, spatial integrals, convolution, 3-D noise calculation), (3) data manipulation (e.g. file input/output, interpolation, normalisation), and (4) graphical visualisation (2-D and 3-D graphs).
Toolkits are often written in scriptable languages, such as Python and Matlab. This specific toolkit is implemented in Python and its associated modules Numpy, SciPy, Matlplotlib, Mayavi, and PyQt/PySide. In recent years these tools have stabilized and matured sufficiently to support mainstream tool development. Collectively, these tools provide a very powerful capability, even beyond the confines of this toolkit alone. Furthermore, these tools are freely available.
Rudimentary radiometric theory is given in the paper to support the examples given. Examples of the toolkit use, as described in the paper, include (1) spectral radiometric calculations of arbitrary source-medium-sensor configurations, (2) spectral convolution processing, (3) 3-D noise analysis, (4) loading of ASCII text files, binary files, Modtran tape7 and FLIR Inc *.ptw files, (5) data visualization in 2-D and 3-D graphs and plots, (6) detector modeling from detail design parameters (bulk material detectors), (7) color coordinate calculations, and (8) various utility functions.
The toolkit is developed as a cooperative effort between the CSIR, Denel SOC and DCTA. The project, available on Google Code at http://code.google.com/p/pyradi, is managed in accordance with general practice in the open source community.
Efficient laser emission in the medium wave infrared (MWIR) is a long established requirement for directed infrared countermeasures (DIRCM). However, until the last decade, there has not been a viable technology for the direct generation of wavelengths in the 3-5μm region and instead indirect methods using optical parametric conversion have been the subject of intense development. Several indirect methods have been developed using different pump wavelengths which represent mature laser technology. For example, 1.54μm from Er:YAG or non-linear conversion from Nd:YAG (1.064μm); 2.1μm from Ho derived from Tm at 1.97μm, or co-doped Ho:Tm in a fibre. These approaches produce the required pump wavelength for efficient 3-5μm generation using either ZGP or OPGaAs , however, they are less efficient than direct generation by quantum cascade lasers (QCL). The direct conversion from electrical to optical energy in a QCL is very efficient; wall-plug efficiencies of <10%, depending on wavelength and operating temperature, are typical. High efficiency, together with the high average powers that are now commercially available suggests that the QCL is an attractive laser for DIRCM.
However, as protection measures and signal processing techniques advance, one can anticipate that the requirement for sophisticated laser emission in the MWIR becomes more refined. In particular, broadband emission covering a wider, continuous, spectral region will prove harder to counter than that from a few discrete wavelengths. A supercontinuum has been suggested as a possible mechanism for broadband emission. In most investigations into supercontinuum generation, the emphasis has been on producing a wide, flat spectrum covering several hundred nanometres in the visible, near and short wave infrared for stand-off spectroscopic sensing of chemical agents, atmospheric sensing or hyperspectral sensing. These supercontinua are characterised by a spectral bandwidth to pump wavelength ratio of, δλ/λp<1 for a pump wavelength λp in the visible or near infrared. In most applications, the simultaneous generation of a wide spectrum is not required; instead a tuned output suffices. This has the added benefit of improving the efficiency of the laser sensor system since wavelengths which are not required, are not generated. The problem is to understand how a limited continuum might be generated. In the context of DIRCM, the spectral requirement is to produce a controlled spectral emission which matches the 3-5μm atmospheric transmission window.
In this paper, a theoretical calculation is presented which shows that a continuous spectrum spanning a few hundred nanometres in the mid infrared (δλ/λp~0.2) can be generated in a simple pump geometry from a mode-locked, ultra-short pulse train using self phase modulation (SPM). Spectral broadening centered on the CO2 absorption band at 4.26μm can be excited to produce all wavelengths for emission in band IV DIRCM. The parameters which affect the spectral output such as pulse power, interaction length, pulse duration and pulse shape are considered for the case where the pump geometry is a collimated beam propagating through a mid infrared glass characterised by a non-linear refractive index n2. The prospects for developing a suitable pump laser are also discussed, in particular, the possibility of using a modelocked QCL.
This paper describes the development of a target tracking algorithm for an anti-ship imaging infrared seeker. The
tracking algorithm uses feature extraction and machine learning to discriminate between a desired target ship and decoys within the seeker’s field of view. The algorithm is developed within a high fidelity simulation architecture, used to simulate engagements of infrared missiles against ships, aircraft and land vehicles. The proposed seeker tracking
algorithm will be evaluated in a naval engagement scenario, against a ship deploying countermeasures. The tracking
algorithm performs the tasks of object detection, feature extraction and target selection. Object detection is achieved via thresholding the image of the seeker’s field of view, and thereafter, shape and intensity based features are calculated for each resulting object. These features are then used as inputs to a neural network, which performs the task of target selection, to determine the seeker’s aim-point. Object features such as peak and average intensity, intensity moments, eccentricity, roundness, minimum, maximum and average radial perimeter distances are considered, to determine their discriminatory power. A training set of images of different ships and decoys, generated by the front end of a seeker model within the simulation architecture, is used to obtain a comprehensive collection of these features. An analysis is performed to determine which of the features are the most discriminatory and these are then used as inputs to the neural network. The neural network is trained on these features to recognise the difference between ships and decoys. Examples of the performance of the tracking algorithm will also be shown.
The proliferation of a diversity of capable ManPADS missiles poses a serious threat to civil and military aviation.
Aircraft self protection against missiles requires increased sophistication as missile capabilities increase. Recent
advances in self protection include the use of directed infrared countermeasures (DIRCM), employing high power
lamps or lasers as sources of infrared energy. The larger aircraft self-protection scenario, comprising the missile,
aircraft and DIRCM hardware is a complex system. In this system, each component presents major technological
challenges in itself, but the interaction and aggregate behaviour of the systems also present design difficulties
and performance constraints. This paper presents a description of a simulation system, that provides the ability to model the individual components in detail, but also accurately models the interaction between the components, including the play out of the engagement scenario. Objects such as aircraft, flares and missiles are modelled as a three-dimensional object with a physical body, radiometric signature properties and six-degrees-of-freedom kinematic behaviour. The object’s physical body is modelled as a convex hull of polygons, each with radiometric properties. The radiometric properties cover the 0.4–14 μm spectral range (wider than required in current technology missiles) and include reflection of sunlight, sky radiance, atmospheric effects as well thermal self-emission. The signature modelling includes accurate temporal variation and spectral descriptions of the object’s signature. The object’s kinematic behaviour is modelled using finite difference equations. The objects in the scenario are placed and appropriately orientated in a three-dimensional world, and the engagement is allowed to play out. Low-power countermeasure techniques against the missile seekers include jamming (decoying by injecting false signals) and dazzling (blinding the sensor). Both approaches require knowledge of the missile sensor and/or signal processing hardware. Simulation of jamming operation is achieved by implementing the missile-specific signal processing in the simulation (i.e. accurate white-box modelling of actual behaviour). Simulation of dazzling operation is more difficult and a parametric black-box modelling approach is taken. The design and calibration of the black-box dazzling behaviour is done by heuristic modelling based on experimental observations. The black-box behaviour can later be replaced with verified behaviour, as obtained by experimental laboratory and field work, using the specified missile hardware. The task of simulating a DIRCM system is scoped, by considering the threats, operational requirements and detailed requirements of the respective models. A description is given of the object models in the simulation, including key performance parameters of the models and a brief description of how these are implemented. The paper closes with recommendations for future research and simulation investigations.
The development of modern imaging and non-imaging infrared missile signal processing and countermeasure techniques strongly relies on high quality simulated imagery of target and countermeasure signatures. Likewise, the development of an effective countermeasure technique or system for aircraft self-protection requires accurate missile behaviour modelling. The development of these algorithms and protocols can be done most effectively in an accurate infrared imaging simulation. This paper investigates the requirements for such a simulation system, supporting the evaluation of the missile behaviour in the missile-aircraft engagement scenario. The development and evaluation of target detection and tracking algorithms, or countermeasure systems, requires a comprehensive simulation environment where thousands of missile flights can be simulated, covering a wide variety of scenarios and signature conditions. The missile seeker algorithms generally detect and classify targets based on intensity, spatial and dynamic characteristics. The key considerations identified for such an imaging infrared simulation system are: 1) radiometric accuracy in all spectral bands, i.e. sunlight and thermal radiance to provide correct colour ratios; 2) accurate emitting source surface temperature behaviour, be it by aerodynamic or thermodynamic heating; 3) high fidelity geo- metrical and spatial texture modelling to provide shape of targets and countermeasures; 4) true dynamics and kinematic behaviour in six degrees of freedom; 5) detailed modelling of signatures and backgrounds; 6) accurate atmospheric transmittance and path radiance models; 7) realistic rendering of the scene image in radiometric, spatial and temporal terms; and 8) comprehensive sensor modelling to account for primary and second order imaging effects. This paper briefly analyses the broader framework of requirements for an imaging simulation system, in the 0.4 to 14 μm spectral bands. An existing imaging simulation system, OSSIM, is used to evaluate the identified key requirements for accurately simulating the missile-aircraft engagement scenario. Parameters considered include signature spectral colour ratio, spatial shape, kinematics, temporal behaviour, as well as the effect of the atmosphere and background. From this analysis the significance and relevance of the modelled signature elements are reviewed, thereby confirming the key requirements for simulating the missile-aircraft engagement.
Aircraft self-protection against heat seeking missile threats is an extremely important topic worldwide, recently even more so with the instability in the Middle East region due to, for example, the large number of man-portable air defense systems (MANPADS) that were stolen from army arsenals. A fundamental step in successfully achieving self-protection is the ability to capture and identify aircraft infrared signatures. This work discusses some of our efforts and results in creating an asset database for infrared signatures. The database was designed in a way that will feed an image processing engine to allow for automated feature and signature extraction. A common failing in the handling of target signature raw data is the fact that raw data files can become unreadable because of changes in technology, software applications or weak media archiving technology (e.g. corrupt DVD media). A second shortcoming is often the fact that large volumes of raw or processed data are stored in an unstructured manner, resulting in poor recall later. A third requirement is the portability of data between various processing software packages, legacy, current and future. This paper demonstrates how the challenge of future-proofing measured data is met with reference to the archiving and analysis of data from a recent measurement campaign. Recommendations for future work are given, based on the experience gained.
A radiance inversion technique, in which in-flight aircraft plume radiance recordings are exploited to construct a three dimensional (3D) radiance model of the plume, is presented. The recordings were done with a mid-wave infrared (3 – 6 μm) camera at different altitudes. The algebraic formulation of this inversion technique, also known as an emission-absorption technique, is stated for the ideal case of spectral radiance measurements of a high spatial sampling resolution over the plume area, as would be obtained from a hyperspectral imager. The non-ideal case of having only broad-band (mid-wave) image measurements and only one spectral measurement of the plume, is then investigated. It is shown that from this incomplete information set, an effective spectral absorption coefficient can be calculated for which the associated plume spectral transmittance and spectral emissivity calculations exhibit the correct qualitative behaviour. It is also shown that, by using this effective absorption coefficient, an optimization procedure can be used to determine the temperatures and/or spectral radiance values within the plume. This optimization procedure consists of minimizing the difference between the observed line of- sight (LOS) radiance in the image (i.e. a pixel radiance value in the image) and its theoretical projected radiance. After the temperature values within the plume were determined, the observer LOS radiance is parameterized so that it can be described for an arbitrary angle with respect to the main axis of the plume. The inferred temperature, spectral transmittance and spectral emissivity are then used in calculating the expected spectral radiance at this arbitrary angle. The spectrally integrated/mid-wave broad-band radiances and intensities for aspect angles other than those used during the inversion process, are then calculated and compared with actual measurements in order to determine the adequacy of this model for incorporation into existing infrared imaging system simulation software used in the training of infrared seekerhead missiles.
In asymmetric warfare scenarios, a major threat is caused by hostile attacks using mortars and artillery rockets
(RAM). Existing air defence weapons use missiles or cannons as effectors. These systems are well suited for
engagements against large air targets, such as aircraft, but they have strong drawbacks for the defence against attacks
of small targets, such as mortar grenades or artillery rockets.
High-energy laser weapons possess the abilities to be used successfully against such targets: i.e. a short reaction
time, a high accuracy, a strong impact on the target. Further, the costs per shot are low and they cause no collateral
damages. To counter such a RAM-threat by an effective laser weapon, only a short time scale is available. We
developed a laser-matter interaction simulation model to dimension the laser weapon. The main mechanisms of the
laser neutralisation of explosive devices are the conversion of the laser source photonic energy into heat on the shell
surface and the heat transfer to the explosive. The European consortium of the Air Defence – High-Energy Laser
Weapon Project (AD-HELW), composed of French, German, Polish and Portuguese specialists developed a system
layout of a complete air defence high-energy laser weapon system.