Optical Countermeasures Research Articles

Investigation of Chaotic and Spiking Dynamics in Mid-Infrared Quantum Cascade Lasers Operating Continuous-Waves and Under Current Modulation

This study investigates chaotic and spiking dynamics of mid-infrared quantum cascade lasers operating under external optical feedback and emitting at 5.5 $\mu {\text{m}}$ and 9 $\mu {\text{m}}$ . In order to deepen the understanding, the route to chaos is experimentally studied in the case of continuous-wave and current modulation operation. The non-linear dynamics are analyzed with bifurcation diagrams. While for quasi-continuous wave operation, chaos is found to be more complex, pure continuous wave pumping always leads to the generation of a regular spiking induced low-frequency fluctuations dynamics. In the latter, results show that by combining external optical feedback with periodic forcing and further induced current modulation allows a better control of the chaotic dropouts. This work provides a novel insight into the development of future secure free-space communications based on quantum cascade lasers or unpredictable optical countermeasure systems operating within the two transparency atmospheric windows hence between 3 $\mu {\text{m}}$ –5 $\mu {\text{m}}$ and 8.5 $\mu {\text{m}}$ –11 $\mu {\text{m}}$ .

Chaotic optical power dropouts driven by low frequency bias forcing in a mid-infrared quantum cascade laser

Mid-infrared quantum cascade lasers operating under external optical feedback and external periodic bias forcing are shown to exhibit a deterministic chaotic pattern composed of frequencies which are linked to the one of the forcing. Results also show that both the amplitude and the frequency of the forcing play a key role in the number of retrieved spikes per modulation period. These findings are of paramount importance for chaotic operation of quantum cascade lasers in applications such as optical countermeasure systems and secure atmospheric transmission lines, as well as for simulating neuronal systems and the communication between neurons due to sudden bursts.

ZnGa2Se4, a nonlinear material with wide mid infrared transparency and good thermomechanical properties

During the last decades, mid-infrared (3–12 μm) laser sources using crystals with nonlinear optical properties have attracted a particular attention due to their potential applications in different fields such as optical counter-measures and remote chemical sensing. As transparency of common oxide crystals is limited to about 4 μm, many researches have been focused on chalcopyrite compounds because of their wide transparency in the mid-IR range and their strong nonlinear optical coefficients. There is a need of such crystals able to convert efficiently the near infrared wavelengths from commercially available lasers into wavelengths higher than 5 μm through Optical Parametric Oscillators (OPO) systems. This paper presents a new compound: ZnGa2Se4 (ZGSe). Measurements made on dense polycrystals show a high thermal conductivity value in comparison with other selenides (2.9 W m−1 K−1), a wide transparency from visible to beyond the band III of the mid IR (0.6 μm–17 μm) and a coefficient of thermal expansion inferior to 10−5 K−1. These results are very encouraging and improvements of the growth process are now undertaken to obtain single crystals with the required optical quality.

Low-frequency fluctuations of a mid-infrared quantum cascade laser operating at cryogenic temperatures

This work demonstrates that mid-infrared quantum cascade lasers operating under external optical feedback can output a chaotic dynamics through low-frequency fluctuations close to 77 K. Results also show that the birth of chaotic dynamics is not limited to near-threshold pumping levels. In addition, when the semiconductor material is cooled down from room temperature to 77 K, it is found that laser destabilization takes place at a lower feedback ratio, proving that quantum cascade lasers are sensitive to temperature, likely due to changes in the upper state lifetime. These investigations are meaningful for the chaotic operation of quantum cascade lasers in secure atmospheric transmission lines and optical countermeasure systems.

High-intensity light sources as optical countermeasures against human operators

Simulated test protocols are used to investigate the effectiveness of a novel and non-lethal approach for the degradation of human performance.

光电对抗用激光器技术

The development of laser technology is very fast in recent years.A variety of laser sources have been regarded as the key component in many optoelectronic devices.For directed energy weapon,the progress of laser technology has greatly improved the tactical effectiveness,such as increasing the range and strike precision.At the same time,the modern solid-state laser has become the ideal optical source for optical countermeasure,because it has high photoelectric conversion efficiency and small volume or weight.However,the total performance is limited by the mutual cooperation between different subsystems.The optical countermeasure is a complex technique after many years development.The key factor to evaluate the laser weapon can be formulated as laser energy density to target.The technical review for laser used in optical countermeasure is briefly introduced in this paper.Especially the essential techniques are discussed for the laser used in the optical countermeasure system,so that the laser has a better compatibility to total system.In this way,the maximum energy emitted by the laser source can be utilized.

光电对抗技术研究进展

The optical countermeasure technique is a complex technology after many years development.Especially,laser which has the properties of monochromaticity,high brightness and directional transmission,has been applied to optical countermeasure.The laser dazzling,laser blinding and even damaging detector was focused in the field of optical countermeasure,which had been paid a great attention by many nations.The development of the optical countermeasure was presented in this paper.Furthermore,the challenge for future high-power laser applied in the optical countermeasure was forecasted.

The development of an imaging infrared surrogate seeker

Optical techniques have been developed to provide a relatively simple but effective homing heads for guided weapons over the last five decades. The original approaches tended to use single detectors operating around "two microns" in the infrared. Improvements in detector technology have enabled significant enhancements to the performance of such seekers.Development of focal-plane array technology provided an opportunity to design and develop imaging seeker technology. This type of seeker technology appears to be resilient to conventional optical countermeasure techniques. This paper describes the development of an imaging infrared seeker to investigate potential infrared countermeasure techniques to defeat mechanisms.

Application of laser technology to optical countermeasures

Optical sensors of one form or another have been used on the battlefields for millennia in order to collect information about adversaries. Many techniques have been used throughout history to defeat these sensors. The original approaches tended to attempt to use the sun to dazzle the sensors. The development of laser technology has provided many opportunities to defeat a vast range of sensors operating in various wavebands of the electromagnetic spectrum.This paper considers how laser technology may be used to defeat sensors. The high radiant intensity of laser emissions that are feasible from such devices enables various scales of phenomena to be generated in the sensors, ranging from temporary effects to permanent damage. These mechanisms are considered in this paper.

Facilitation of Aircraft Recognition by Selective Attentional Allocation

When attempting to recognize a potential airborne target in a tactical setting, a field commander is confronted with a variety of variables that may affect the quality of the recognition process. Many of these variables; such as target distance, contrast, and optical countermeasures, are perceptual in nature. Others, like command and control oriented information, are more cognitively based. The present experiments explored the effects of selective attentional allocation on aircraft target recognition. This was done by manipulating a variety of factors that one might expect to be present in a tactical command and control scenario. The major intent of these experiments was the achievement of insight into the nature of the internal representation upon which aircraft recognition is based and the degree to which subjects can alter attentional algorithms in order to faciliate stimulus processing. Two alternative accounts of the nature of the internal representation were evaluated. The template model assumes that the representation consists of a template of the target to be recognized. When exposed to a display, the subject maps the display elements onto the template and responds on the basis of the degree of similarity between the display and the internal template. Proponents of this global view assume that processing takes place in a top-down manner (Navon, 1977). The feature model, on the other hand, assumes that recognition is based on a scan through a list of criterial features. Upon encountering a display the subject extracts a list of such features and compares these to a list held in memory. Evidence for such a bottom-up processing algorithm has been advanced by Hoffman (1980). The experiments were carried out within the context of a two alternative forced-choice paradigm. Subjects viewed a series of displays consisting of silhouettes of two aircraft. One of these was designated as the target (either a MIG-23 or an FB-111). The other silhouette served as a distractor (A-10, F-14, MIG-25 or SU-20). All stimuli were presented on a three channel tachistoscope and subject's responses were recorded with respect to both recognition accuracy and reaction times. Several variables were manipulated over the course of several experiments; for instance, the contrast of the displays, the presence and type of cue preceeding a stimulus display, the orientation of the silhouettes in each display, and the stimulus onset asynchrony of cue and display. The specific effects of each of these variables on aircraft silhouette recognition performance will be discussed. Briefly, data indicated that recognition performance degrades under reduced contrast conditions; performance differs depending on from which orientation the display is viewed; and the type of pre-exposure cueing affects the speed of recognition. In addition to this, several interesting interactions among these variables occurred. These variables, and their effects on aircraft recognition, will be discussed within the context of the nature of the internal representation and the use of selective attentional algorithms by the subject. Subjects apparently were not limited to a single attentional algorithm. Rather, several strategies were potentially available (Dixon, 1981). Subjects altered these processing strategies depending on target orientation, the nature of pre-exposure cueing, and the time available for selection and preparation of an algorithm.