The quantum cascade laser is a semiconductor light source based on resonant tunnelling and optical transitions between quantised conduction band states. In these devices the principles of operation are not based on the physical properties of the constituent materials, but arise from the layer sequence forming the heterostructure. The quantum design and the control of the layer thickness, down to an atomic mono-layer, allows one to ascribe into a semiconductor crystal, artificial potentials with the desired electronic energy levels and wavefunctions. In recent years the performance of quantum cascade lasers has improved markedly and this semiconductor technology is now an attractive choice for the fabrication of mid-far infrared lasers in a very wide spectral range (3.5-160 μm). At present, the best performances are reached at wavelength between 5-10 μm, but recent results on new material systems with deeper quantum wells are indicating that this technology will be soon available also in the 3-5 μm spectral region.
Countermeasures against heat seeking missiles require access to efficient laser sources, which should emit wavelengths at band I, II and IV. Efficient diode pumped solid-state lasers, combined with efficient non-linear wavelength shifters, allow the development of practical tuneable mid-IR countermeasure sources. The paper describes the requirements and the development of a tabletop laser source for study of DIRCM techniques. Jamming laser systems must be able of creating pulse sequences in the frequency range between 100 Hz and 10,000 Hz, including the capability to mix and sweep the jam frequency. A Nd:YVO4 pump laser with maximum pump power of 3 Watt and pulse length of 10 ns, and a maximum modulation frequency of 100 kHz was selected. A linear single resonant OPO cavity with 30 mm long, 1mm thick PPLN crystals was build. With the tabletop laser system we were able to generate wavelengths from 1.5 to 4 micron. In band I, at 2 micron we can generate between 400-550 mW, and in band II, from 3-4 micron we can generate 130-160 mW laser jam power. The beam quality (M2) is approximately 2.5. The power efficiency for the idler was 8.8%, while the slope power efficiency was 15%. Jam patterns are generated by use of an acousto-optic modulator.
This paper presents the design and construction of a photonic fibre pumped OPO. The photonic fibre is used to provide high-energy pump power to an optical parametric oscillator (OPO) from a remotely sited pump laser source. Delivery of the high power radiation required for these systems is not possible using conventional fibre, as the fibres would need to be highly multimode to handle the high intensities without damage. Photonic fibres are a disruptive technology for power transmission and light manipulation/control. The fibres have the potential for supporting high irradiation powers and can operate with robust singlemode guidance. The OPO is to be used to provide a 3-5 μm wavelength source for active sensor applications. The integration of high power lasers into air platforms for remote sensing applications would therefore be facilitated, as the fibre delivery would enable the laser to be sited remotely from the sensor head and open up the possibility of several sensor types sharing the same multi-functional laser. This could reduce the complexity and hence the cost of such sensors systems leading to the potential for an affordable, robust system for military platforms.
There is currently considerable interest from the military and civil authorities in defences against man portable air defence systems. One such approach utilizes directing in-band modulated mid-infrared lasers at missile seekers to disrupt the missile tracking. The work presented here discusses some of the engineering issues associated with the development of such a laser system. The laser system is based on the MURLIN (Multi-band Research Laser INfrared). A prototype system has been developed based on a highly efficient diode laser pumped Nd: YAG co-planar folded slab laser that is frequency converted by cascaded optical parametric oscillators and an optical parametric amplifier. The water-cooled system produces up to 1.4 W of modulated power which is distributed across 3-lines in the 2-5 mm spectral region. The potential countermeasure utility of this system is enhanced by the single beam multi-line output and capability to directly modulate the pump diodes with a range of waveforms. The follow-on air-cooled version currently under development has recently achieved 8 W of modulated average power at the 1.064 mm pump wavelength. Measured beam quality is twice the diffraction limit.
A unique and cost effective measurement facility called the Reusable Aerodynamic Flare Ejection Capability (RAFEC) has been developed at the Defence Science and Technology Organisation (DSTO), Australia. The RAFEC system involves the use of a reusable, carrier projectile that is launched from a 10 inch, nitrogen driven gas gun. The IRCM flare is loaded in the carrier projectile and the gas gun launches the carrier projectile with a known velocity of between approximately 350 to 650 knots. At a pre-determined time after firing and in the field of view of the measuring instrumentation, the flare is ejected from the carrier projectile for performance measurements to be undertaken. The temporal, spatial and spectral quantities were accomplished with the instruments fielded around the gas gun line of fire and the trajectory is derived from the spatial measurements. The data will be used for hardware in the loop simulations and modelling. Further improvements such as; (1) multiple (maximum of three) flare ejection, (2) 1”x1”x8” format flares made to the carrier projectile, and (3) design and manufacture of the puston, a new item of firing hardware to obtain lower muzzle velocities have enhanced the RAFEC capability. Thus the RAFEC system provides a more realistic IRCM performance measurement capability as it incorporates the deceleration effects experienced by the flare on deployment.
We present a method based on an orthonormal vector space basis representation to detect camouflaged targets in natural environments. Because the method is intensity invariant we detect camouflage targets independently of the illumination conditions. The detection technique does not require knowing the exact camouflage pattern, but only the class of patterns (foliage, netting, woods...). We used nonlinear filtering based on the calculation of several correlations. Moreover, the nonlinearity of the filtering process allows a high discrimination against false targets. Several experiments confirm the target detectability where strong camouflage might delude even human viewers.
TACSI (TACtical SImulation) is an existing simulator used as a tactical environment for manned simulators at Saab Aerosystems. TACSI can also be used as a stand-alone desktop development and simulation tool. TACSI simulates a large number of entities and functions such as platforms, sensors, weapons, signatures, communication, multisensor fusion, decision support etc. TACSI has a rule based pilot model and uses High Level Architecture (HLA) for interfacing with other simulation models. This model, a development of TACSI, simulates the flight dynamics, IR-signature and IR-seeker operation. The dynamic behaviour of the aircraft, the IRCM, the missile and the IR-seeker are modelled. The IR-contrast seen by the seeker through the atmosphere in front of the aircraft and the IRCM are spectrally and dynamically modelled. The seeker operation behaviour and function are also modelled. To implement this in a real-time simulation system simplifications are necessary. This paper describes the simplifications to model the IR-contrast and the seeker function. This model is used to analyse the effect of IR countermeasures (IRCM) on a missile IR-seeker.
Directed infrared countermeasure (DIRCM) systems are being developed in several configurations ranging from open loop, closed loop (CLIRCM) and lately for preemptive use (PIRCM). Critical performance parameters, from an atmospheric propagation point of view, include attenuation as well as turbulence effects on target detection, tracking and the capability to deliver enough power to the target (power in bucket). In order to evaluate the performance of DIRCM and other laser applications in a naval environment we have performed laser beam propagation studies over the Baltic Sea during June to October 2003. The experimental data were used to derive atmospheric attenuation, irradiance fluctuation parameters for different beam offsets relative to the beam centre, temporal and amplitude signal distributions, probability and mean time of fade and tracking performance. Results from simultaneous single and double-ended paths were obtained. This paper will shortly summarize the results from this campaign, and discuss and exemplify how the results can be used for prediction of DIRCM system performance.
IR decoys can be an effective countermeasure against IR guided anti ship missiles. However, it's not so easy to determine how the decoys should be deployed to get maximum effectiveness. A limitation of trials is that results are obtained for the specific trial condition only. Software tools have been developed to solve these problems. One solution uses recorded IR imagery from a decoy deployment trial, while the other solution generates IR imagery and is thus independent of trials. In the first solution, a combination of hardware and software is used that allows recording of a scene with an infrared camera, and simulating a missile seeker. A pre-processing algorithm corrects the recorded images before they are fed into the seeker algorithm of the simulated missile. To perform this correction the pre-processing uses the speed, distance to the target and field of view of the IR camera as fixed parameters and the speed and starting distance of the simulated missile as variable parameters. Modtran and the Navy Aerosol Model are used to calculate the atmospheric transmission effects in the pre-processing. The second solution generates artificial IR images that are subsequently fed into the seeker algorithm. This solution also allows variation of those parameters that are fixed when recorded IR imagery is used. Examples are among others: the signature of the target ship, the orientation, size and speed of the target ship, the type of decoy, the timing of the decoy sequence, atmospheric conditions etc. With these tools the effectiveness of decoy deployment in various scenarios can be evaluated.
The threat to aircraft from missiles with imaging infrared seekers has developed more rapidly and in more countries independently than the original infrared missile threat. This is, in part, a consequence of the civil sector's demand for high-resolution infrared imagers and the development of computer processors capable of implementing complex image-processing algorithms im real time. Dstl has developed the Fly-In model to analyse the potential effectiveness of existing countermeasures (CM) to imaging infrared seekers and to test new CM approaches before trialling them against surrogate imaging seekers.
The validation of the Fly-In model is extremely important, particularly as the newness of the imaging infrared threat, means that actual examples of the threat are not available for study. Extensive measurements have been carried out on the appearance of flare CM in different infrared wavebands, and on the effects of lasers on the optics and detector of an surrogate imageing seeker. Other parts of the model are derived from other Dstl models, including the NATO Infrared Airborne Target Model (NIRATAM) and HADES (missile dynamics) that are validated against trials' data.
Initial studies have shown that existing CM, and those under development, can be very effective against imaging infrared seekers, by defeating the seeker's image-processing algorithms. It is already clear that laser CM will play an increasing role in the defence of aircraft, thereby enhancing aircraft survivability. Moreover, this model will aid the military planner in determining the best mix of CM and the tactics for using them.
A digital watermark is a visible, or preferably invisible,
identification code that is permanently embedded in digital media,
to prove owner authentication and provide protection for security
or defence documents. In this paper, we present an approach for
the generation of watermarks using a logistic chaotic function.
Using this function, in conjunction with seed management, it is
possible to generate chaotic sequences that may be used to create
highpass or lowpass digital watermarks. A slight change in the
initial conditions will quickly lead to a significant change in
the subsequent states of the system, and thus will generate
substantially different watermarks. This technique has been shown
to offer an added security advantage over the more traditionally
generated watermarks created from pseudorandom sequences, in that
only the function seed needs to be stored. We have previously
presented a study where an optical correlator was suitable for the
detection of chaotically generated watermarks. We have also
studied the impact of shot noise present in an optical detector
for watermarks generated using the logistic function. The logistic
function presented in this paper is ill-defined for certain seed
values and has not been fully investigated for the purpose of
watermark generation. We consider the impact of the theoretical
properties of the logistic function on watermark generation and
their highpass and lowpass properties, which when embedded in
digital media, are suitable for optical detection.
Marking of documents by means of a laser beam is a secure and efficient personalization method. The marking is based on a carbonization process, which is caused by a focused laser beam. The process of gray scale laser marking is today's standard on ID documents e.g. driver's licenses, passports. - Now it is possible to personalize these documents with colored lettering, company logos or images in photo quality, using a new laser marking method: CYMart. This development offers the possibility of a more flexible layout arrangement and increased information content. In addition, CYMart provides a new, active security feature for preventing forgeries, particularly in the ID market. The CYMart technology enables the document to be marked inside the multilayer structure, as opposed to a color print on the surface of a document. In combination with other security features e.g. Kinegram or security printing a very high level of protection against forgery is possible. The generation of color is based on a wavelength sensitive process. Multicolor is achieved by the combination of RGB laser beams and photosensitive materials which are integrated into the card layer structure.
Laser beam propagation in severe environment such as a jet engine exhaust may influence performance of e.g. laser countermeasure and active imaging systems located on airborne platforms. Beam propagation in close vicinity to the engine plume causes performance degradation due to beam wander and beam broadening effects. In this study beam propagation effects were studied experimentally using a downscaled jet engine. Beam wander and broadening effects were studied directing a 1.55 μm laser beam parallel to the jet exhaust. The beam centroid motion increased significantly during onset of the engine. Perturbation effects were registered imaging a blackbody source using a fast infrared camera. The geometrical set-up and thrusts were altered during the experimental registrations to examine various flow conditions. A comparison of experimental results with simplified theoretical models describing propagation close to jet engine plumes will be presented. Limitations in existing models will be discussed and methods for refinements proposed.
Directed infrared countermeasures (DIRCM) play an increasingly important role in electronic warfare to counteract threats posed by infrared seekers. The usefulness and performance of such countermeasures depend, for example, on atmospheric conditions (attenuation and turbulence) and platform vibrations, causing pointing and tracking errors for the laser beam and reducing the power transferred to the seeker aperture.
These problems make it interesting to simulate the performance of a DIRCM system in order to understand how easy or difficult it is to counteract an approaching threat and evaluate limiting factors in various situations. This paper describes a DIRCM model that has been developed, including atmospheric effects such as attenuation and turbulence as well as closed loop tracking algorithms, where the retro reflex of the laser is used for the pointing control of the beam.
The DIRCM model is part of a large simulation framework (EWSim), which also incorporates several descriptions of different seekers (e.g. reticle, rosette, centroid, nutating cross) and models of robot dynamics. Effects of a jamming laser on a specific threat can be readily verified by simulations within this framework. The duel between missile and countermeasure is simulated in near real-time and visualized graphically in 3D. A typical simulation with a reticle seeker jammed by a modulated laser is included in the paper.
The method for evaluation of holographic security effectiveness has been developed. The use of the Wiener filter based method allows the holograms patterns to be identified from a printed page. Due to elimination of background influence on a correlation function of two analysed images it is possible to estimate a quality factor of a holographic device. The Wiener filter algorithm for numerical analysis of digital images has been proposed. On the basis of correlation analysis the quantitative quality coefficient of the holographic security has been defined.
The optical method for document protection against counterfeit has been proposed. It is based on the use of optically variable graphics. For the security device design the numerical computation algorithm has been formulated. The algorithm is founded on the coupled-waves theory of the light diffraction by gratings. The computation example for the holographic foil design is demonstrated.
In this article is presented an application of synthetic hologram as fragile watermarking. The proposed technique is a frequency domain watermarking, based on computer generated hologram. Our technique, named Fragile Synthetic Holographic Watermarking (F-SHW), is suitable for ID Cart image authentication. In this paper, the F-SHW is applied to Color Images as well as to Gray Scale ones. The proposed schema is based on the knowledge of original mark from the Authentication Entity, for applying Image Correlation between this and the extracted one. Due to the application the mark is encrypted using a private key (symmetric schema).
Optical countermeasures have been used for several millenia to provide a defensive capability capability. The fundamental approach is to use an intense optical source to dazzle a sensor or distract an operator or target tracking system causing a weapon to miss its intended target. The development of the laser has provided a stimulus for anumber of soft-kill weapon systems used to enhance platform survivability and anti-air missile applications; in this case the laser may cause dazzle, or if the beam is sufficiently intense it may cause damage. Laser technology is also crucial for an aspect of directed energy weapons.
The various aspects of optical countermeasures are considered in this paper, including defeat mechanisms of active and passive techniques. The review includes a historical perspective through to prospects for the future.