In this paper we discuss recent work at the Advanced Technology Centre of BAE Systems on photonic technology, in particular photonic crystal fibres, applied to infra-red and electro-optic countermeasure systems. The use of Photonic Crystal fibres or holey fibres in countermeasure systems could significantly simplify platform integration by enabling remote location of laser sources, the generation of multiple wavelengths or continuum generation from a single pump source .The paper will describe the development of these fibres, drawing examples from recent civil collaborative research projects such as PFIDEL and LAMPS.

Efficient generation of high average power mid-IR laser radiation is reported. Using a 50 W thulium fibre laser to pump a Q-switched Ho:YAG laser 27.3 W of average output power is achieved with an M² of 1.5. The holmium laser is used to pump a ZGP OPO generating 12.6 W of average output power in the 3-5 μm waveband with a worst case M² of 2.7.

Efficient laser sources in the 3 - 5 μm wavelength range are needed for directed infrared countermeasures, but also have applications in remote sensing, medicine and spectroscopy. We present results and discuss the possibilities of a tandem optical parametric oscillator (OPO) scheme for converting the radiation from a 1.06 μm Nd³⁺-laser to the mid-infrared. Our setup uses type I quasi phase-matched (QPM) crystals in a near degenerate OPO to generate 2.13 μm radiation. The QPM crystal provides higher nonlinearity and longer interaction lengths, because walk-off is avoided, compared to conventional bulk crystals. This is an advantage especially in low pulse energy applications. To make the 2.13 μm radiation usable for pumping a second OPO a volume Bragg grating is used as a cavity mirror to limit the bandwidth, which in a conventional QPM OPO at degeneracy can be several hundred nanometers. The acceptance bandwidth for efficient OPO operation of a 14 mm long ZnGeP₂ (ZGP) crystal is approximately 5 nm, which makes the need for bandwidth limiting clear. The majority of the signal energy from a periodically poled KTiOPO₄ (PP KTP) OPO with a volume Bragg grating output coupler was found to be in a single longitudinal mode, whereas the idler bandwidth was measured to 19 GHz (FWHM). A volume Bragg grating resonant near 2124 nm was chosen so that the signal and idler were separated by 9 nm. This OPO output has been used as a pump source for a conventional ZGP OPO demonstrating efficient conversion and providing broadband tunable output in the mid-infrared.

In this paper, we briefly review optically pumped type-II "W" quantum-well semiconductor lasers that emit in the midinfrared wavelengths. In addition, we demonstrate on-chip unstable resonator cavity devices that exhibit excellent lateral beam quality.

This paper describes the characteristics of a separate confinement heterostructure laser design based on type-I InAsSbP/InAsSb multiple quantum wells (MQW). An 8×8 band k.p method was used to calculate the band structure. The optical gain of the active region containing InAsSb QW was calculated using a free carrier gain model. Other properties such as behavior of the fundamental optical TE mode and refractive index profile were also determined. These were used for simulation of the resulting device properties and to estimate the threshold modal gain and threshold current density for the InAsSb MQW laser. Suitable InAsSbP cladding layer and waveguide/barrier materials have been determined. The strain, critical thickness, band offset, optical gain, Auger coefficient and threshold current density have been calculated at various Sb contents (x). The lowest current density is found for the composition range between 0.12-2.

Brightness is one of the most important criteria for diode laser applications beside reliability and efficiency. In this paper results were given for different approaches of high power nearly fundamental mode diode lasers. It will be shown that the technological implementation of spatial and spectral mode selection can lead to output powers up to 10 W from in narrow line passively cooled monolithic device at 980 nm.

Concepts and markets of semiconductor diode lasers are introduced in the context of Defense and Security applications. Specific, high profile applications are reviewed and current and future diode laser technology is discussed. Advanced diode laser technology as it pertains to Infrared Countermeasures applications is reviewed in detail along with recent 2μm diode laser results and advanced packaging product architectures from nLIGHT.

The improvement of the security of platforms (aircrafts) with countermeasure techniques in the mid-IR especially in the take-off or landing phase is nowadays more stringent due to upcoming threats. We report on the development of a Tm:YLF-fiber laser (1.908 μm) pumped Ho:YAG (2.09 µm) high energy laser system with pulse energies up to 100 mJ at pulse lengths close to 20 ns and repetition rates of 100 Hz. A high quality laser beam leaving a platform through a variable-index-of-refraction airflow will experience wave-front aberrations and consequently lose its ability to be perfectly focused in the far field. Two main causes of laser beam degradations are issued in this investigation. First, there is the degradation immediately around the fuselage, referred to aero-optic problems and second the atmospheric propagation influence via air turbulence. The aero-optic influence on the laser beam degradation will be investigated in a laboratory experimental approach with a mid-IR laser beam traversing a transonic free air stream relevant to a real air flow around a fuselage. The propagation characteristics of a laser beam passing turbulent air will be numerically simulated with a multiple phase-screen method and a Fourier propagation technique. Different turbulence degrees relevant to propagation directions especially behind aircrafts will be considered.

We report on the development of a compact laser source devoted to airborne countermeasures. Several spectral lines are emitted simultaneously by the use of optical parametric oscillators (OPOs) pumped by a high repetition rate near-IR pulsed laser. The general architecture of the source is designed to locate the pump laser inside the aircraft while the conversion stages are positioned close to the orientation turret. In this purpose, OPOs whose typical volume is less than 100 cm³ are optimized to produce the required average power under high repetition rate pumping and the emitted output beam quality is typically 1.5 diffraction limited. The selection of the proper nonlinear material for each OPO is also a critical issue. ZnGeP₂ (ZGP) is currently the material of choice to operate where conventional nonlinear materials strongly absorb. In this context, the ZGP crystal growth has been investigated. The first samples with a good optical quality have been obtained and the preliminary results are discussed. In addition to countermeasure applications, we also discuss other Defence & Security issues that can be addressed by miniature OPOs such as biological and chemical detection.

A high power, efficient, and tunable laser source in the 8-10 µm wavelength range, based on a ZnGeP₂ (ZGP) optical parametric oscillator (OPO) pumped by a hybrid 2-micron-laser, is demonstrated. Tuning to 9.8 μm was achieved, and with 8.9 W of 2.1 µm pump power we obtained 0.95 W at 8 μm with an M² value of 2.7 from an OPO with two walk-off compensating crystals. More than 40% quantum efficiency was achieved.

We present a rugged and reliable real-time laser beam tracking system operating with a high speed, high resolution piezo-electric tip/tilt mirror. Characteristics of the piezo mirror and position sensor are investigated. An industrial programmable automation controller is used to develop a real-time digital PID controller. The controller provides a one million field programmable gate array (FPGA) to realize a high closed-loop frequency of 50 kHz. Beam tracking with a root-mean-squared accuracy better than 0.15 μrad has been laboratory confirmed. The system is intended as an add-on module for established mechanical mrad tracking systems.

Micro-lens arrays of large formats are well suited for agile laser beam steering. State-of-the-art beam steering devices comprise three microlens arrays which are distributed among two cascaded substrates. The substrates are decentered laterally by piezoelectric transducers. This arrangement acts like a blazed grating structure with variable blaze angle. Beam steering with blazed grating micro-lens arrays suffers from non-uniformity of the optical parameters across the aperture which leads to a reduction of the spatial coherence between the interfering beamlets and an increase in the beam divergence. This disadvantage can be resolved by combining the blazed grating beam steerer with an array of phase shifting elements. If the number of phase shifting elements (pixels) is sufficiently large, several pixels cover one subaperture of the blazed grating and phase piston as well as higher wavefront errors (tip/tilt, defocus) may be corrected. In the VIS and NIR spectral range large format liquid crystal spatial light modulators (SLM) are available for adaptive correction of the wavefront of each subaperture of the blazed grating beam steerer. Spatial light modulators based on micro-mirrors or electro-optical ceramics which cover a broader spectral range up to the MWIR are under development. This paper outlines the concept of adaptive compensation of the wavefront error of each subaperture in a blazed grating beam steerer. The combination of micro-lens arrays with large format spatial light modulators for the NIR and the MWIR spectral ranges will be described. Investigations and measurements at component level (micro-lens arrays and a commercially available liquid-crystal-on-silicon spatial light modulator) at 1.5 μm will be presented in order to support the theory.

This paper describes the options available for a Man-Portable Air-Defence (MANPAD) weapon. The strengths and weaknesses of the options are quickly discussed and this highlights the choice of the Infrared Surface-to-Air Missile (IRSAM) as the most likely external threat to civil aircraft. The paper then looks at the signature aspects of the aircraft which drives the choice of the operating waveband of the IR seeker. The paper then illustrates how early generation IRSAMs work and finally sets this in the context of platform survivability.

As part of mass transportation systems, commercial aircraft are a potential target for terrorists because they represent one of the best achievements of our society. As a result, an attack would have a large psychological impact on people and economic activity. Several European Commission-funded Research and Technology programs, such as SAFEE and PALMA, are dedicated to technologies and systems that will be implemented onboard aircraft in the near future to increase the security of commercial flights. One of these programs, CASAM, is focusing on a potential solution to reduce aircraft vulnerability against Man Portable Air Defense Systems (MANPADS) during takeoff, ascent and landing. A specific onboard jamming system will be developed, meeting stringent yet competitive requirements that deal with high reliability, low cost and minimal installation constraints. The overall objective of the CASAM Project¹ is to design and validate a closed-loop, laser-based DIRCM (Directed IR Countermeasure) module for jamming fired missiles. It will comply with commercial air transportation constraints, including the normal air traffic control rules. For example, the following aspects will be considered: - Environmental friendliness for ground objects and inhabitants close to airports, aircraft safety (maintenance, handling and usage) and high efficiency against the recognized threats; - Upgradability for further and future disseminated threats - Adherence to commercial operation budgets and processes

Imaging systems are widespread observation tools used to fulfil various functions such as detection, recognition, identification and video-tracking. These devices can be dazzled by using intensive light sources, e.g. lasers. In order to avoid such a disturbance, dazzling effects in TV-cameras must be better understood. In this paper we studied the influence of laser-dazzling on the performance of pattern recognition algorithms. The experiments were performed using a black and white TV-CCD-camera, dazzled by a nanosecond frequency doubled Nd:YAG laser. The camera observed a scene comprising different geometrical forms which had to be recognized by the algorithm. Different dazzling conditions were studied by varying the laser repetition rate, the pulse energy and the position of the geometrical forms relative to the laser spot. The algorithm is based on edge detection and locates areas with forms similar to a reference symbol. As a measure of correspondence it computes the degree of correlation of the different areas. The experiments show that dazzling can highly affect the performance of the used pattern recognition algorithms by generating lots of spurious edges which mimic the reference symbol. As a consequence dazzling results in detrimental effects, since it not only prevents the recognizing of well defined symbols, but it also creates many false alarms.

High performance fibre lasers are now well established as an extremely robust and reliable technology enabling a growing and diverse number of demanding industrial and medical and applications. Compared to rival technologies, such as carbon-dioxide (CO₂), Lamp/Diode-Pumped Solid-State (L/DPSS) and disk lasers, fibre lasers offer a number of unique characteristics that have resulted in their wide adoption in an increasing number of industrial sectors. In addition to replacing conventional lasers in existing applications, fibre lasers have been very successful in enabling new applications, both factors which explain their increasing market share. In this paper we describe the basic features of fibre lasers, and discuss their generic advantages compared with other laser technologies and consider how these may translate to defence applications. We explain our proprietary cladding-pumping technology (GTWave^TM) and the laser architectures we use to implement our commercial products. We present parametric performance data that show the vast range of pulse waveforms that can be produced and discuss some new industrial applications that they have recently enabled. Finally, we reference some of the leading research results for multi-kW continuous-wave (CW) fibre lasers and summarise SPIE's published work in this field.

Imaging systems are widespread observation tools used to fulfil various functions such as detection, recognition, identification and video-tracking. These devices can be dazzled by using intensive light sources, e.g. lasers. In order to avoid such a disturbance, dazzling effects in TV-cameras must be better understood. In this paper we studied the influence of different parameters on laser-dazzling. The experiments were performed using a black and white TV-CCD-camera, dazzled by a nanosecond frequency doubled Nd:YAG laser. Different dazzling conditions were studied by varying for instance the laser repetition rate, the pulse energy or the settings of the camera. We proceeded in two steps. First the different dazzling effects were analyzed and classified by their mainspring. Pure optical phenomena like multiple reflections, scattering and diffraction were discriminated from electronics effects related to charge transfer processes. Interactions between the laser repetition rate and the camera frequency or the camera exposure time were also observed. In a second step, experiments were carried out for different dazzling conditions. It was then possible to assess the weight of each experimental parameter on dazzling effects. The analysis of these quantitative results contributes to the better understanding of laser-dazzling, useful to design efficient means to protect imaging systems.

The problem set of battlefield helicopters and related photonics in asymmetric scenarios is addressed with emphasis on survivability and electronic warfare. The problem set is identified starting from an operational perspective, asking how different the asymmetric battlefield is from the traditional Cold War scenario, and by identifying relevant characteristics of battlefield helicopters. Based on this information requirements for photonics are deduced. It is concluded that the shift to asymmetric conflicts brings evolutionary-but not revolutionary-challenges for photonics, mostly so for the laser community. Main causes for the evolutionary drive are shortened engagement ranges, increased threat from ballistic and CBRE weapons, stringent ROEs, and assassination operations.

Optical range profiling with high resolution can be accomplished using single-photon counting time-of-flight techniques. Detection of optical surfaces with high resolution is of importance for several remote sensing applications. The use of laser pulses in the picosecond regime, single-photon detectors and acquisition electronics with high timing resolution provides the tools for improving the range accuracy. In this work a system based on time-of-flight range profiling using time-correlated single-photon counting techniques is described. The system is intended to be used for optical range profiling in field experiments. Experimental results from measurements on test targets are presented. Schemes for extraction of range information from the experimental temporal profile and results from performance modelling are briefly discussed.

Laser countermeasures against infrared focal plane array cameras aim to saturate the full camera image. In this paper we will discuss the results of dazzling experiments performed with MWIR lasers. In the "low energy" pulse regime we observe an increasing saturated area with increasing power. The size of the saturated area can be explained by an expression derived from the point spread function of the optics. The experimental results for short "high energy" pulses show a strong non-linear response of the detector arrays. Physical processes potentially responsible for these effects are described. Possible consequences of this non-linear detector behaviour for the effectiveness of laser countermeasures applying short high energy pulses are discussed. A better understanding of the response of infrared detectors to short high energy laser pulses, will allow changing the laser design in order to mitigate these effects.

With the ever-growing demand for increased realism in defence modelling and simulation, smoke modelling, which is computationally expensive, must be conducted on graphics hardware to enable execution at fast rates with good fidelity. Visual smoke simulation has been successfully implemented by many authors over recent years, but infrared smoke modelling adds new requirements with additional challenges. This paper discusses the introduction of a Navier-Stokes staggered grid model into CounterSim, our countermeasures simulation software, highlighting the problems and benefits of using PC commodity graphics hardware for infrared applications and detailing the methodology used to control mass loss and to model thermal cooling. Additionally, the need to use an adaptive grid is explained, with the implications for both the simulation equations and the management of data storage, particularly when mixtures of smoke products with widely differing properties may be present. The focus is then shifted to rendering, highlighting the requirements for greater accuracy than the standard eight bits per channel of visual applications. Problems with alpha blending on graphics hardware are also discussed, and examples are presented that illustrate how changes in pixel format give rise to sometimes startlingly different end results.