In this paper we seek to assess the potential impact of microstructured fibres for security and defence applications. Recent literature has presented results on using microstructured fibre for delivery of high power, high quality radiation and also on the use of microstructured fibre for broadband source generation.
Whilst these two applications may appear contradictory to one another the inherent design flexibility of microstructured fibres allows fibres to be fabricated for the specific application requirements, either minimising (for delivery) or maximising (for broadband source generation) the nonlinear effects.
In platform based laser applications such as infrared counter measures, remote sensing and laser directed-energy weapons, a suitable delivery fibre providing high power, high quality light delivery would allow a laser to be sited remotely from the sensor/device head. This opens up the possibility of several sensor/device types sharing the same multi-functional laser, thus reducing the complexity and hence the cost of such systems.
For applications requiring broadband source characteristics, microstructured fibres can also offer advantages over conventional sources. By exploiting the nonlinear effects it is possible to realise a multifunctional source for applications such as active hyperspectral imaging, countermeasures, and biochemical sensing.
These recent results suggest enormous potential for these novel fibre types to influence the next generation of photonic systems for security and defence applications. However, it is important to establish where the fibres can offer the greatest advantages and what research still needs to be done to drive the technology towards real platform solutions.
A simple scheme for efficient generation of mid-IR laser radiation is demonstrated. Using a 25 W thulium fibre laser to pump a Q-switched Ho:YAG laser 15.3 W of average output power is achieved with an M2 of 1.3. The holmium laser is used to pump a ZGP OPO generating 7.2 W of average output power in the 3-5 μm waveband with an M2 of 1.8.
We present an efficient, high-power mid-infrared laser source using a Thulium fiber laser as pump source. The CW fiber laser pumps a Q-switched Ho:YAG laser which in turn pumps a ZnGeP2-based OPO. We have built a semi-ruggedized version of the laser for countermeasure field trials, and using a 15 W fiber laser we obtained 5.2 W output power in the 3-5 μm band. We also present work on scaling up the power by using a 65 W fiber laser as the pump. Simulations and initial experiments suggest that the scaled-up version could produce more than 25 W in the mid-IR.
A laser diode end-pumped Q-switched Nd:YVO4 laser operating over a 25% to 100% duty cycle range has been built and characterised. A maximum average output power of 24.5 W has been achieved at an optical-to-optical conversion efficiency of 43%, with a beam quality factor M2 of 1.1.
Peak optical power from single 1-cm diode laser bars is advancing rapidly across all commercial wavelengths. Progress
to date has allowed us to demonstrate > 400-W peak output from single 1-cm diode laser bars at emission wavelengths
from 800-nm to 980-nm. The available range of emission wavelengths has also been increased, with 90-W bars shown at
660-nm, 37W at 1910-nm and 25W at 2070-nm, complementing the 100-W bar previously demonstrated at 1470-nm.
Peak power is seen to correlate closely peak power conversion efficiency. Further advances in diode laser efficiency and
low thermal resistance packaging technology continue to drive these powers higher. The most critical improvements
have been the reduction in the diode laser operating voltage through optimization of hetero-barriers (leading to 74%
efficient 100-W bars on micro-channel at 975-nm) and a reduction in packaging thermal resistance by optimizing microchannel
performance (leading to < 0.2-°C/W thermal resistance). We have also recently extended our high efficiency
designs to shorter wavelengths, now delivering over 70% efficiency at 790-nm. Ever-increasing power levels (projected
to eventually exceed 1-kW per bar) reduce the cost in Euro per W of diode laser systems, enabling broader application in
military, industrial and medical markets. In addition, increasing availability of high powers at new wavelengths is
enabling many new applications.
We report on the liquid phase epitaxy (LPE) growth of an optimized double heterostructure (DH) 3-4 μm laser and the use of linear rapid slider boat technology for the production of quantum well (QW) structures based on InAsSb/InAsSbP. Typical characteristics of some of these prototype sources are presented and analyzed, including the results of SEM, X-ray diffraction, photo- and electro-luminescence characteristics of prototype DH & QW devices. The optimized 5 epi-layer diode lasers operate readily in pulsed mode at elevated temperatures and emit near 3.45 μm at 170 K with a threshold current density as low as 118 A/cm2 at 85 K. Coherent emission was obtained up to 210 K. LPE growth of InAsSb QW has been successfully obtained experimentally. The QW structure has been confirmed by SEM and electroluminescence measurements at different temperatures.
The paper summarizes laser beam steering techniques for power beaming, sensing, and communication applications. Principles and characteristics of novel mechanical, micro-mechanical and non-mechanical techniques are compiled. Micro-lens based coarse beam steering in combination with liquid crystal or electro-optical phase control for fine steering is presented in more detail. This review addresses beam steering devices which modulate the phase distribution across a laser beam and excludes intra-cavity beam steering, beam steering based on combining tuneable lasers with dispersive optical elements, active optical phased arrays, and optical waveguides.
An increasing interest in lasers placed on aircrafts for active countermeasures and active imaging is observed. There remain unsolved issues regarding the propagation effects close to the jet engine exhaust and the possibilities of compensating them with adaptive optics. Laser beam propagation experiments parallel to the exhaust of a downscaled jet engine test rig have been performed. The experiments were carried out with nanosecond laser pulses at 1.6 and 3.5 μm wavelength. The laser spots were projected on a screen and the centroid motion were imaged by cameras. Root mean square magnitudes of the beam wander between 50 and 150 μrad were observed for different engine conditions and geometries. The 3.5 μm system had a frame rate of 607 Hz and could partly resolve the time variation of the beam wander. A correlation time (50 %) of 3.5 ms was observed for the beam wander. Deflections of several hundred μrad due to the average gradients in temperature and pressure were also found when the engine was turned on. In addition to beam wander intensity scintillations has been studied.
Atmospheric propagation experiments for active and passive EO systems were performed over a 2 and 8 km path.
Single and double path propagation effects were studied using retroreflectors and hot point targets. The systems used
include laser systems at 1.5 and 3.5 μm wavelength as well as imaging systems in the visible, 1-2 and 8-9 μm regions.
A scintillometer operating at 0.8 μm wavelength was also used for the shorter path. Experimental data will be
presented and evaluated concerning statistics. The results will be discussed mainly from a laser countermeasure point
We present results from a numerical study on heating in Hg0.72Cd0.28Te induced by 4.2 μm laser pulses in the μs regime. A number of highly nonlinear mechanisms contribute to the heating process, their relative importance being dependent on the instantaneous irradiance and the material temperature. The mechanisms include one- and two-photon absorption across the band gap, inter-valence band absorption between the light- and heavy hole bands, electron-hole recombination, free-carrier absorption, hot-carrier generation, and refractive index changes. A special feature of this material is the fact that the direct band gap increases with temperature. This eventually terminates one-photon absorption processes from the valence to the conduction band. The varying band gap also introduces changes in the electron- and light hole masses and thereby in the separation between the light- and heavy hole bands, thus strongly affecting inter-valence band absorption. Therefore first principles electronic structure calculations were used to determine the band structure and the inter-valence band absorption. The simulations also show that hot carrier effects can have a significant influence on the amount of energy the material can absorb.
With the proliferation of lasers for ranging and atmospheric studies, satellite system operators have become concerned about the possibility of laser illumination on their vehicles. This paper contains the results of a risk analysis involving the inadvertent laser illumination of satellites from ground-based lasers. The methodology used for the probability analysis is discussed and specific examples are provided. The methodology begins with a discussion of the assumptions used; the principles involved; and then details four specific cases using the methodology. The final case is for a notional low-earth orbiting, earth resource satellite with a steering optical sensor against a diverse, globally dispersed laser network. The author proposes this methodology be used for the systematic analysis of the probability of inadvertent laser illuminations against specific scenarios for satellite operations. For the notional cases examined in the paper, the probability of an inadvertent laser strike ranges from 10-4 to 10-6 for a single satellite lifetime of a decade. These extremely low probabilities imply an accidental illumination of a satellite is very unlikely. If a satellite is suspected of having been illuminated, the satellite operator may want to examine the problem further for causes other than an accidental lasing.
NATO-SCI-139 and its predecessor groups have more than a decade of history in the evaluation and recommendation of EO and IR Countermeasures against anti-aircraft missiles. Surrogate Seekers have proven to be a valuable tool for this work. The use of surrogate seekers in international co-operations has several advantages over the use of an operational seeker, which is in service or in development: 1) the system is flexible, allowing both hardware and software modifications to be made in order to test the effectiveness of specific IRCM techniques; 2) the seeker design is open - every last parameter is available to the science team, allowing detailed, end-to-end validation of software models and simulations; 3) the availability of an unclassified seeker facilitates open discussions on CM issues between the participants in the NATO-group.
Testing of high intensity countermeasures (for example based on lasers) needs a system with realistic seeker optics, with proper representation of optical scatter in seeker optics, which differs from scatter in commercial infrared camera optics.
A technical description of the ISS is given: an overview of the optical design and the detector, the principle of the tracking software and the possibilities to implement alternative tracking algorithms in order to represent different threat CCM techniques. The ISS is built for use both in the laboratory and in the field. Finally, some experimental results will be presented.
Anti-aircraft infrared (IR) guided missile systems, such as man-portable air defence systems (MANPADS), may be equipped with a variety of counter-countermeasure techniques. One such technique could be to look at the trajectory differences of a fast moving jet aircraft and a deployed flare countermeasure (this is often known as relative kinematics). This paper investigates, via simulation, what improvement in aircraft protection against MANPADS might be achieved by modifying these trajectory differences through the use of advanced flare decoys and forward firing techniques.
Self-protection systems using expendable pyrotechnics have been in operational service for several decades, and still
enjoy a significant popularity on military platforms, due to potentially high efficiency, low cost and versatility. Recent
developments in advanced materials as well as spatial and temporal behaviour optimization using advanced simulation
tools also contribute to continued success against threat systems of ever-increasing sophistication.
One of the most significant drawbacks of these systems is the limited capacity of the countermeasures dispensers of
such a system. The risk of emptying the countermeasures dispensers leads to restrictions in the acceptable false-alarm-rate,
again leading to a reduced detection probability. The approaches for optimization known to the author have been
either one of Monte-Carlo simulations or a functional threat countering analysis. Neither of these brings insight into the
parameters relating the overall performance of the self-protection system against one missile attack and the overall
platform survivability on a mission.
In this work, a new model is presented where an overall survivability probability can be calculated and optimized,
including the effect of a limited dispenser capacity versus countermeasures program size as well as missile approach
warning systems key parameters, such as detection probability and false-alarm-rate. The model is extended to allow
independently variable missile attack- and false-alarm probabilities. Criteria for choosing optimal flare programs are
presented. It is shown that a dynamic update of the self protection system can enhance the performance of self protection
systems deploying expendable countermeasures. Monte-Carlo-simulations are shown to be in good
agreement with the model.
This paper describes a method where it is possible to configure and simulate an entire dynamic scenario with several platforms in a network and where electronic warfare (EW) is an integrated part. The method utilizes a multispectral (radio, radar, electro-optics) framework, EWSim (Electronic Warfare Simulation interface model), for distributed EW simulations. In the framework it is possible to design dynamic scenarios which can assess the few-against-few duel, in a single user mode or in an assessment duel where teams can compete against each other. The EWSim method is also compared to simpler methods where events on a timeline is studied to draw conclusions about EW systems in a network and also to more advanced methods where system specific models are used with a high level of fidelity.
We compare active optical elements based on different technologies to accomplish the requirements of a 2-dim. fine tracking control system. A cascaded optically and electrically addressable spatial light modulator (OASLM) based on liquid crystals (LC) is used for refractive beam steering. Spatial light modulators provide a controllable phase wedge to generate a beam deflection. Additionally, a tip/tilt mirror approach operating with piezo-electric actuators is investigated. A digital PID controller is implemented for closed-loop control. Beam tracking with a root-mean-squared accuracy of Δα=30 nrad has been laboratory-confirmed.