Emerging Imaging and Sensing Technologies for Security and Defence VII

Long range 3D imaging is a key technology for future target acquisition and ID. Dstl have demonstrated high resolution 3D image acquisition of representative vehicle targets at a range of 1.4km in daylight, using currently available visible band technology. With modern GPS timing capabilities, it should also be possible to separate laser and camera by some considerable distance, enabling long baseline bistatic lidar or distributed sensing to be achieved. Preliminary results from an exploration of this concept will also be shown.

Time-correlated single-photon counting (TCSPC) has been established as the preferred choice of detection for high resolution depth profiling due to its excellent surface to surface resolution and high optical sensitivity. This presentation will describe an underwater transceiver system based on a planar CMOS silicon single photon avalanche diode (Si-SPAD) detector array, and interfaced with a graphics processing unit (GPU) for real time processing capabilities with video rates up to 25 Hz. Depth and intensity profiles of stationary and moving targets were acquired with the transceiver fully submerged in scattering water, equivalent up to 7.5 attenuation lengths.

Translating a low pixel-count focal plane array sensor horizontally and vertically in the image plane of a system, in steps that are less than the pixel pitch, is a relatively simple way of using the sensor to acquire a more detailed image. With this approach, an image is acquired at each location, and all the images are then combined into a single, more detailed composite image. In the work reported here, we applied this technique to a light detection and ranging (LiDAR) system, based on the time-correlated single-photon counting technique. This time-of-flight system used a 32 × 32 InGaAs/InP single-photon avalanche diode (SPAD) detector array (with the elements on a 100 µm square pitch) that was mounted on a pair of computer-controlled translation stages capable of sub-micron steps. A λ = 1550 nm pulsed fiber laser source was used to flood-illuminate the scene, and operated at eye-safe, low average optical output power levels, typically below 5 mW. Operating in the short-wave infrared meant that the system could work in daylight over standoff distances of hundreds of meters, as the effect of solar background was reduced compared to visible and near-infrared wavelengths. The high sensitivity and picosecond timing resolution of the SPAD detector array, along with the translating of the detector array, enabled us to create more detailed intensity images, and depth maps, of distant targets. This paper presents an analysis of measurements taken, in daylight, from a variety of scenes at ranges of up to 325 meters.

The recent development of single-photon avalanche diode (SPADs) arrays as imaging sensors with both picosecond binning capabilities and single photon sensitivity has led to the rapid development of time-of-flight imaging systems however, simulations of SPAD systems outside of the Poisson regime remain rare. Here we present a model for SPAD systems which combines single photon counting statistics with computational parallelization which together enable the efficient generation of photo-realistic SPAD data. We confirm the accuracy of out model by experimental verification. Further, we apply this simulator to the problem of drone identification, orientation, and, segmentation. The proliferation of semi-autonomous aerial multi-copters i.e. drones, has raised concerns over the ability of existing aerial detection systems to accurately characterize such vehicles. Here, we fuse the 3D imaging of SPAD sensors with the classification capabilities of a bespoke convolutional neural network (CNN) into a system capable of determining drone pose in flight. To overcome the lack of publicly available training data we generate a photo-realistic dataset to enable the training of our network. After training, we are able to predict the roll, pitch, and yaw of the several different drone types with an accuracy greater than 90%.

An image feature-based approach for reconstructing SPAD LiDAR images of a single target is proposed. Geometric characteristics of the target are used in the algorithm to differentiate between target and background photon returns. Combinations of different features such as Fourier shape descriptors and apparent target size are used to improve performance. To validate the algorithm, a 32x32 silicon SPAD array Flash LiDAR system operating at 532nm is used for collecting images through fog. Simple geometric shapes are placed indoors in a dark tunnel 44.6m from the sensor with fog decreasing the visibility down to 12m.

In recent years, due to the demand of cheap proximity sensors, the development of silicon based single photon counting diode (SPAD) detectors has initiated an almost unnoticed revolutionary development and paradigm shift in sensor technology. Classical electro-optical sensing focused on the detection of light intensities and their representation in gray scale images through sensor characteristics which converts light intensities into digital gray scale values. EO system design was focusing on the trade space about signal-to-noise ratio, integration time and frame rate. In contrast to that, SPAD sensors are capable to sense a single photon event as a binary and noise free intensity. Furthermore, the occurrence of these photon events can be determined very precisely in time, allowing access to the picosecond time scale and application in precise distance measurement. The measurement procedure is subject to quantum mechanical probabilities and can be evaluated by statistical methods. Combined with computational imaging, i.e., linking the acquisition process to a strong mathematical model, it is possible to obtain information that was previously inaccessible and extend the perceptual range of EO sensors. In this talk, we will give an overview of different active and passive imaging approaches that use SPAD detectors with special laser illumination and the use of ambient light, respectively. The talk summarizes, but is not limited to, our own results in areas of vision through scattering media, range imaging, indirect vision concepts and passive imaging.

Accurate object tracking or target identification are key requirements in the automotive, consumer, and defence industries. These tasks require hardware to provide good quality images and accurate analysis routines to interpret the data. Here we will report on the use of next-generation single-photon avalanche detector (SPAD) array sensors combined with neural networks for high-speed three-dimensional imaging and object tracking. Such detectors enable three-dimensional imaging at high speeds and low light levels, and they can operate in a wide range of conditions and at large standoff distances. We will discuss the use of such detectors for tracking and monitoring airborne objects, such as drones. We will also discuss our recent work on human pose estimation, achieved from a low-cost SPAD time-of-flight sensor with only 4x4 pixels. Here we use neural networks to first increase the resolution of the data and then reconstruct the skeletal form of multiple humans in three dimensions. It is clear that the next generation of technology for object tracking and identification will use a combination of advanced imaging hardware and data fusion approaches. We will discuss our group's recent research in this area.

The recent development of single-photon avalanche diode (SPAD) based sensors has completely revolutionized the field of advanced imaging and contributed to the rapid increase of "computational imaging". A lot of scientific fields have shown significant improvements in their performances by using these sensors: medical imaging and advanced microscopy, 3D and tomographic imaging, light-in-flight recording and non-line-of-sight (NLOS) imaging. In this paper, we show that it is possible to visualize the transient propagation wave when a laser pulse is entering into an integrating sphere. The photon time-signatures at the opening port of the sphere depend on the diameter of the sphere and on its spectral reflectance. Possible applications of this technic for a quick cavity volume determination could be applied to the search and classification of cavities and caves. By using ultra-short pulses, we demonstrated that the temporal observation of the reflected waves at the skylight of such cavity can give a very quick information on its volume and shape.

The multiplication region material in an APD has to have a very large difference between the electron and hole impact ionization coefficients (α and β respectively). Materials with a small β/α ratio (defined as k) give rise to low ‘excess’ avalanche noise and have a better gain-bandwidth product, translating to higher sensitivity APDs that are capable of operating at higher speeds. In the last few years, significant advances have been made in the development of Avalanche Photodiodes (APDs) capable of detecting light at 1550nm based on the presence of antimony (Sb) in the avalanching material. Initial work on AlInAsSb p-i-n structures grown as a digital alloy on GaSb substrates showed a k as low as 0.015. This was followed by work on AlAsSb and Al0.85Ga0.15As0.56Sb0.44 on InP where the excess noise was found to equate to a k=0.005 – 0.01 in thick multiplication layers. It turns out that AlInAsSb can also be grown lattice matched to InP and this material also provides a small value of k. This presentation will review some of the material properties in these alloys, results from work done on SAM-APDs using these alloys to date and the challenges to improving their performance further.

Semiconductor based single-photon avalanche diode (SPAD) detectors are widely used in quantum technology applications, which focus on the arrival time of single photons. Using germanium as the absorption region in a Separate Absorption and Multiplication design solves the operating limitation beyond the spectrum range of silicon, i.e. typically at a wavelength of ~ 1000 nm. Our first-generation planar geometry Ge-on-Si single-photon avalanche diodes utilised a 1000 nm Germanium absorption region and showed extremely low noise-equivalent-power of 7.7 × 10−17 WHz−½ at a wavelength of 1310 nm. We demonstrate new structures designed to achieve high single-photon detection efficiency at a wavelength of 1550 nm.

Single Photon Avalanche Diodes (SPADs) are the enabling device for different kind of applications in which low noise, high photon detection efficiency, and compactness are required. They are capable of providing high photon count rate and picosecond timing precision. Furthermore, they can be fabricated in arrays, unlocking very high-count rates and the possibility to retrieve also incident photon’s spatial information. For these reasons, SPADs are the sensors of choice in many applications such as Light detection and ranging (LiDAR), Time Correlated Single Photon counting (TCSPC) and quantum key distribution (QKD). Whether the SPAD is implemented in a custom technology, allowing detector tailoring on specific application constraints, or in a CMOS process, with great benefits in terms of large-scale integration and compactness, a quenching circuit is always required, and it sets the ultimate performance that can be extracted from this sensor. The custom approach for SPAD fabrication poses a challenge in the design of the external quenching circuit mainly due to the parasitics (capacitance, wire-bonding inductance, etc.) that intrinsically come with having the detector and the circuit on two separate silicon dies, which is potentially a limiting factor for speed and timing precision. In this work, we present a fully-integrated active quenching circuit capable of driving external custom SPADs up to 250 Mcps. The circuit has been fabricated exploiting a 150nm high voltage technology and extensively tested with a custom SPAD.

Time-Correlated Single Photon Counting (TCSPC) represents a fundamental tool for the investigation of biological light signals. Unfortunately, due to pile-up distortion the photon acquisition rate must be kept below few percents of the laser rate, thus increasing the acquisition time. Recently, we proposed a single-channel TCSPC system allowing us to overcome pile-up by matching the detector dead time to the laser period. In this work, we perform on-field fluorescence measurements with this system showing that an acquisition speed of 32 Mcps can be reached without significant distortion. Thanks to the promising results, we are now developing a multi-channel module based on the same acquisition technique.

The German Research Center for Geosciences also known as GFZ-Potsdam has a long history in the definition and development of new spaceborne sensors such as for gravity and optical Earth Observation missions with GRACE, GRACE-FO, MOMS, and very recently with the launch of EnMAP on 1st April 2022. The Environmental Mapping and Analysis Program (EnMAP) is the first German spaceborne hyperspectral satellite mission. EnMAP aims at monitoring and characterizing the Earth’s environment on a global scale. Core science objectives are toward studying environmental changes, ecosystem responses to human activities, and management of natural resources. The EnMAP mission consortium is composed of the DLR Space Administration in Bonn that is responsible for the overall project management, OHB is responsible of the space segment, DLR Earth Observation Center is responsible of the ground segment, and GFZ Potsdam is responsible for the science related activities and science mission support. In particular, EnMAP is accompanied by an extensive scientific exploitation preparation program that has been run for more than a decade to support industrial and mission development, and scientific exploitation of the data by the user community. In the current EnMAP phase, this program includes mission support during the current commissioning phase and the start of the nominal phase planned toward end of October, supported by the EnMAP Science Advisory Group. In that frame, large activities in the GFZ remote sensing group are dedicated to a) hyperspectral sensor simulation, data quality and validation of EnMAP data products, b) development of methods and open softwares toolboxes such as in the QGIS EnMAP-Box for the pre-processing of radiance to reflectance, and for the retrieval of geo- and bio-physical parameters, c) user community training and workshops, development of new educational resources such as in the EnMAP online learning initiative HYPERedu, opening of a Massive Open Online Course (MOOC) on the basics of imaging spectroscopy, d) mission support and development of validation and background mission plan, and EnMAP announcement of opportunities.

This presentation will give a general introduction to the space debris problem, current state of the environment and currently defined mitigation measures. It will then concentrate on the space debris-related aspects of ESA’s ambitous Space Safety programme and provide details on ESA’s plans to develop sensor technology for debris monitoring in the area of laser, ground- and space-based optical telescopes and radar. In addition to this, the presentation will also address current technology developments towards collision avoidance, space-traffic management and onboard technology to improve European compliance with such requirements in an economically viable way. Finally, the presentation will address the first ever active debris removal mission as an enabler of European industrial capability to conduct in-orbit servicing.

High performance imaging sensors are a fundamental requirement for many defense and security applications. The usually high cost of such sensors, however, prevents their broad deployment. Modern Computational Imaging approaches like Compressed Sensing (CS) promise cost efficient sensor architectures that might enable a wider usage of some sensor technologies. However, the technological potential for military applications still has to be verified. In order to test the capabilities of a CS-system for threat detection, a software framework for automated testing was implemented. The code contains different methods for scene modulation and image reconstruction. In our previous work, we studied the classic iterative optimization methods for image reconstruction with promising, but not completely satisfactory results. Therefore, we implemented another method. This CS video method is the ‘Fourier domain regularized inversion’ (FDRI) which promises real time single pixel video imaging. In the study presented here, we compare the rather new method with the already implemented optimization approaches regarding runtime, conventional image quality metrics and suitability for threat detection applications in different spectral bands.

We exploit micro-nano structuration to achieve multifunctional windows offering outstanding optical and fluidic properties to enhance the operation of surveillance or detection devices under rainy conditions. These windows are based on synthesis of an artificial index gradient for antireflection properties and improvement of their water repellency property thanks to their structuration at a subwavelength scale with controlled conical geometries. We demonstrate the realization of multifunctional germanium windows for LWIR camera, using two approaches: nanoimprint lithography, well-known for its very high resolution enabling applications from visible to thermal infrared domain, followed by etching techniques, and 3D direct laser writing based on Two-Photon Polymerization (TPP), which is of interest thanks to its ability to manufacture complex 3D structuration directly. Optical characterization shows the ability of such windows to improve optical transmission within 8-14µm spectral range, as compared to non-structured window. In terms of water repellency, the structured windows enable an increase of the contact angle up 160° with a very low hysteresis. To evaluate the advantage of the multifunctional windows for imaging devices, the windows are integrated in front of a thermal infrared camera and images analysis shows that the camera sensitivity is increased for the nanoimprint window thanks to the multifunctional window and high water repellency in presence of water.

Compared to frame-based visual stream, event-driven visual stream offers very low bandwidth needs and high temporal resolution, making it an interesting choice for embedded object recognition. Such visual system is seen to overcome standard cameras performances but has not yet been studied in the frame of Homing Guidance for projectiles, with drastic navigation constraints. This work starts from a first interaction model between a standard camera and an event-camera, validated in the frame of unattended ground sensors and situational awareness applications from a static position. In this paper we propose to extend this first interaction model by bringing a higher-level activity analysis and object recognition from a moving position. Event-based terminal guidance system is studied firstly through a target laser pointing scenario and the optical flow computation to validate guidance parameters, and secondly with Machine Learning techniques adapted to the address-event stream. Real-time embedded processing technics are evaluated preparing the design of a future demonstrator of a very fast navigation system. The first results have been obtained using embedded Linux architectures with multi-threaded features extractions. This paper shows and comments these first results.

We present a novel force sensor based on plasmonically modulated upconversion luminescence. The sensor is made of upconversion nanoparticles (UCNPs), gold nanodisk and flexible polymer layer. When compressed, the flexible polymer layer changes the coupling between UCNP and gold disk, resulting in a change in luminescence intensity. In this paper, we present the design and fabrication of the sensor as well as experimental observation of force induced luminescence intensity modulations accompanied with extensive analysis by numerical simulations that clearly demonstrate the high sensitivity force sensing.

This paper introduces the field of metamaterials, details various optical uses of metasurfaces and demonstrates their suitability for imaging with single-photon avalanche diode (SPAD) detector arrays as an integrated optical component. A design for a metasurface-based color filter array (CFA) is presented, the fabrication methodology detailed, and a sample is integrated with a SPAD array. Examples of imaging applications using the integrated assembly are demonstrated, including passive and fluorescence imaging microscopy. The limitations of current metasurface color filtering techniques are highlighted and directions for future advances and applications discussed.

Finite-difference time-domain simulations have been made of a security screening polarimetric radar over the band 18 GHz to 26 GHz, comparing the results with a proof-of-concept system operating over the same band. The proof-of-concept radar is presented together with its calibration and measurement set-up. Measurements indicate the cross-polarisation returns from a human subject are approximately 10 % to 25 % of the co-polarisation returns. A simulation model has been built using the openEMS software to simulate the body of a human, using realistic primitive shapes and electrical properties appropriate for these frequencies, indicating cross-polar returns are in the region of 15 % of the co-polar responses, with the duration of the reflections lasting around 2 ns. The comparisons between the measurements and simulations are good and provide a qualitative understanding of what happens when security screening radar radiation impinges on the human body. The simulation is extended to two simple enclosures, a cubic box and a short cylinder having dimensions of 300 mm and wall thicknesses of 5 mm, which could be made of wood, cardboard, paper or plastic. Results indicate the cross-polar reflection ranges from 3 % to 75 % of the co-polar and bursts of reflections are commensurate with reflections from the front and back surfaces, these being separated in time by 2 ns.

The next generation of sUAS (small Unmanned Aircraft Systems) for automated navigation will have to perform in challenging conditions, bad weather, high and low temperature and from dusk-to-dawn. The paper presents experimental results from a new wide-angle vision camera module specially optimized for low-light. We present the optical characteristics of this system as well as experimental results obtained for different sense and avoid functionalities. We also show preliminary results using our camera module images on neural networks for different scene understanding tasks.

We present work on versatile, compact optical components for waveguided atom interferometry with rotation sensing in mind. These diffractive optical elements: static Fresnel zone plates (FZPs), paired with a dynamic spatial light modulator, expand on the previous design and construction in our group of FZPs for smooth, red-detuned optical waveguides, allowing a wider range of functionality such as dark trapping with blue-detuned light and the generation of multiple, distinct waveguides from single FZPs. Our experiment utilises Bose-Einstein condensates of Rb-87 for interferometry, currently in a free-space configuration, by introducing such waveguides we can reduce the scale of this apparatus while increasing sensitivity to rotation.

We describe simple quantum lidar and show it provides the best, most rapid identification of high reflectivity nearby targets. For lower reflectivities or more distant targets quantum lidar is impractical so we describe a protocol that mimics the relevant feature of quantum lidar via random intensity modulation of a classical beam. This provides a degree of covertness together with many of the other useful properties of a quantum lidar without the complication of producing quantum states and crucially, without the limit on mean photon number. Hence it is useful for identifying much lower reflectivity targets than is practical with quantum states.

GaN laser diodes have the potential to be a key enabler for many quantum technologies, including quantum sensing & timing, precision meteorology and quantum computing, since the AlGaInN material system allows for laser diodes to be fabricated over a wide range of wavelengths from ultra-violet to visible. Furthermore, GaN allows the development of very high specification laser diode sources that are portable, robust and provide practical solutions that are otherwise unobtainable using more conventional laser sources. Novel applications for quantum technologies include GaN laser sources for cold-atom interferometry, such as next generation optical atomic clocks, quantum sensors and quantum computing. Several approaches are taken to achieve the required line-width, wavelength and power for cold-atom interferometry, including an extended cavity GaN laser diode (ECLD) system, and a distributed feedback (DFB) GaN laser diode with side-wall etched nano-gratings. We report our latest results on a range of AlGaInN diode-lasers targeted to meet optical atomic clock and quantum sensor applications. This includes the [5s2S1/2-5p2P1/2] cooling transition in strontium+ ion optical clocks at 422 nm, the [5s21S0-5p1P1] cooling transition in neutral strontium clocks at 461 nm and the [5s2s1/2 – 6p2P3/2] transition in rubidium at 420 nm.

We give an overview of our research programme on the use of atomic magnetometers to detect and image concealed conductive objects via electromagnetic induction. The extreme sensitivity of atomic magnetometers at low frequency, several orders of magnitude higher than a coil-based system of similar size, allows for their operation in such a frequency range, thus permitting deep penetration through different barriers. This overcomes the limitations usually associated with electromagnetic detection. Applications in security and surveillance are discussed.

This study rationalizes the polarization effects on surface plasmon polariton modes in plasmonic waveguides under a high-intensity radiation via the Floquet engineering methods. First, we describe the behavior of dressed metal fermion system using Floquet states. Then, we examine the impurity scattering effects on electron transport in disordered plasmonic metals using the generalized Floquet-Fermi golden rule. We show that we can diminish the losses in plasmonic materials using the dressing field using detailed numerical calculations. Moreover, this study presents a particular figure of merit to compare the performance of popular plasmonic metals, assessing their performance enhancements under the different dressing field polarizations. These results thus corroborate to achieve high-efficiency SPP propagation in practice. Our study can be applied to accurately interpret the usage of strong external radiation as a tool in quantum plasmonic circuits.

We report on results of a proof-of-principle experiment that exposes the potential side channel in a system that uses an optical in-phase and quadrature modulator to implement a single sideband encoding scheme in the coherent-state continuous-variable quantum key distribution protocol. Such a side channel occurs due to limited sideband suppression during the modulation of the quantum signal, and leaks the information regarding the state preparation. Theoretical analysis of the experimental results confirmed the vulnerability, showed the overall impact on the performance of the protocol, including the reduction of the secure key and identified conditions for a security breach.

Continuous Variables Quantum Key Distribution (CV-QKD) tackles the problem of the generation and distribution of cryptographic keys without assuming any computational limitations while employing standard telecom equipment. Gaussian Modulation (GM) theoretically maximizes the information a CV-QKD system is capable of transmitting while exhibiting a higher resistance to excess channel noise. However, GM-CV-QKD protocols put an extreme burden on the transmitter’s random number source and tend to be more susceptible to imperfect state preparation. Due to these difficulties, most experimental implementations of CV-QKD have used Discrete Modulation (DM). The closer the DM constellation approaches a GM one, the closer the theoretical performance of the associated system will be to the optimum value. To achieve this, high-cardinality constellations, coupled with probabilistic shaping, can be explored. However, choosing a too complex constellation will cause the modulation stage imperfections to again become apparent. Thus, the choice of the constellation format is not direct and is of high importance. In this work we present a methodology to determine the optimum constellation for a given DM-CV-QKD system, taking into account the limitations of the modulation stage, choosing from a variety of M-QAM and M-APSK constellations coupled with probabilistic shaping. Our obtained methodology will allow for the optimum modulation format for each specific system to be selected.

Quantum key distribution (QKD) technologies are evolving from laboratory experiments to real-word implementations over optical networks. Nowadays, those cryptographic systems are implemented using discrete variables or continuous variables (CV), differing mainly on the detection strategy used to recover the information. We investigate, theoretically and experimentally, the impact of random polarization drifts imposed by optical fiber channels on quantum coherent states used for the implementation of CV-QKD systems. Besides that, we propose a polarization diversity scheme based on a polarization diversity true heterodyne scheme, capable of passively overcoming the impact of those drifts on the performance of a CV-QKD system

This paper presents the demonstrator of a fully polarimetric ultra-wideband (UWB) multistatic imaging system working in the FCC UWB frequency band from 3.6 GHz to 10.6 GHz. The low frequency range is chosen to reduce the influence and clutter of clothes to a minimum. This is important for the screening in public places because the scanner needs to identify threats even under thick and heavy jackets with a low false alarm rate. Furthermore, the effect of motion blurring in the reconstructed radar images is enormously reduced. To further improve the detection of threats a fully polarimetric radar frontend was chosen for the imaging system. Radar polarimetry is a well-established technique in remote sensing to characterize different scattering mechanisms like single and double bounce or volumetric scattering. This offers the opportunity to classify different terrain properties or manmade objects in remote sensing. The investigated antenna arrangement is a roof-like geometry which can be installed on ceilings or archways in public areas. This approach doesn't disturb the ow of walking persons and even could enable a hidden installation of the screening device. Furthermore, this arrangement reduces shadowing risk, i.e. that a terrorist hides himself between closely walking neighbors.

With regards to composites materials, the need for noninvasive evaluation of their structures, components, or systems they form continuous to rise. This is connected with the fact that the most frequently used methods, based on X-rays, ultrasound, thermography, eddy current or optics, have some limitations, especially when it comes to structural analysis of selected materials such as fiber-reinforced plastics, and hollow or sandwich structures. This forces new experimental methods to be developed. One of such method being a promising candidate for contactless inspection of composites materials is based on the use of terahertz radiation. Terahertz (THz) radiation band includes electromagnetic waves in the range from 0.1 THz to 10 THz what corresponds to wavelength from 3 mm to 30 µm. They may deeply penetrate nonconductive materials such as ceramics, semiconductors, and polymer composites. It allows for higher spatial resolution detecting of defects such as delaminations, voids or uneven reinforcement. In comparison to X-ray radiation, THz radiation is unharmful for people and may penetrate clothes. This special property can be potentially used for safe inspection of people e.g., at airports or in biomedical applications e.g., skin diseases detection and treatment. In presented work, the investigations with the use of THz radiation in transmission mode was performed on samples imitating soft ballistic inserts of bulletproof vests. The samples had intentionally introduced defects. Overall, the phenomenon of non-destructive evaluation and the selected application of Terahertz-based noninvasive system was presented.

Improving the security screening requires good knowledge and understanding of human skin signatures. Our previous publications indicate that the signature of the human skin varies from person to person under a dry and wet state. Human skin is a very sensitive organ and not all material can be applied or attached directly to the skin. Therefore, it is an essential requirement to find a close surrogate i.e. (animal tissue) and characterise similarities in signature between human and animal skin. The importance of this is that it will allow us to investigate more easily signatures of the human skin under different materials and conditions. This paper investigates signatures for the human skin and ex-vivo porcine skin samples using the 90 GHz calibrated radiometer. The paper aims to compare and show similarities and differences in the signature between human and ex-vivo porcine skin samples for the first time using millimetric wave radiometry. To this end, water and different types of cream were applied to the palm of the hand and porcine skin samples namely: skin with water jel, skin with silver sulfadiazine cream, and skin with betadine cream. The reflectance of the skin was measured before and after the application, with and without the presence of a clothing layer. Reflectance measurements on human skin were applied on six participants in the palm of the hand region for comparison with reflectance measurements of porcine skin from six samples taken from the back region of different animals. Reflectance measurements for the palm of the hand skin show that the mean reflectance values for all six participants are: 0.458, 0.618, 0.578, 0.548, and 0.488 for normal skin, skin with water, skin with water jel, skin with silver sulfadiazine cream, and skin with betadine cream respectively. For porcine skin samples, the mean reflectance values for all six samples are: 0.438, 0.608, 0.598, 0.558, and 0.508 for normal skin, skin with water, skin with water jel, skin with silver sulfadiazine cream, and skin with betadine cream respectively. These measurements indicate the similarities between the palm of the human hand and the back region of swine. The measurements also show that the difference in the mean reflectance values between the palm of the hand region and porcine skin for all cases is ~0.02. After adding a clothing layer made of textiles on the palm of the hand skin and porcine skin samples; the reflectance measurements for the palm of the hand skin become 0.408, 0.545, 0.498, 0.488, and 0.458 for normal skin, skin with water, skin with water jel, skin with silver sulfadiazine cream, and skin with betadine cream respectively. For porcine skin samples the mean reflectance values are: 0.388, 0.518, 0.488,0.488, and 0.478 respectively. These measurements indicate that textiles are relatively transparent over the frequency band (80 -100) GHz and the signature of the skin can be observed through clothing. The increased understanding of these measurements brings means research into the medical applications of millimetre wave imaging to assess wounds under dressings. More specifically, subjects bearing bandaged wounds could be screened more reliably using imagers. In addition to the security screening applications and anomalies detection.

A new type of optical resonator gyroscopes based on systems with parity-time-symmetry properties is considered. A system with parity-time-symmetry properties is composed of two direct coupled waveguides, one of which is characterized by losses, and the second one – by amplification, and a passive ring resonator connected to them. The influence of the characteristics of the parity-time-symmetry system on the optical resonator gyroscope parameters is investigated. Attention is paid to the influence of the gain, losses and coupling coefficients of the waveguides that make up the system with the parity-time-symmetry properties. The influence of the gain coefficient instability caused by a change in the pumping power on the angular velocity measurement results is also considered. The advantages and disadvantages of this approach are compared with a conventional optical resonator gyroscope. The main advantage of using systems with parity-time-symmetry properties is the increase of accuracy of registration of passive ring resonator eigenfrequencies by several orders of magnitude and, as a result, the maximum sensitivity to angular velocity.

A sample of a ring confocal resonator designed to operate as a sensitive element of an optical resonator gyroscope is studied. The sample has a monoblock design - the resonator is a single block (prism) with reflective surfaces operating on the effect of total internal reflection. The optical contour of the resonator has the shape of a square with a side length of 10 mm and is formed by four reflective surfaces. Three reflecting surfaces are flat, and one is toroidal with curvature radii in the meridional and sagittal planes that satisfy the confocality condition. The resonator is designed to operate at wavelengths of about 1.55 µm. The advantages of using a of a ring confocal resonator as a sensitive element of an optical resonator gyroscope are analyzed. In particular, it is shown that the reduction of the angular velocity measurement error caused by the optical Kerr effect becomes possible (compared to the use of a waveguide cavity and a whispering gallery mode cavity). The resistance of the system to external influences also improves.

The paper considered the possibility of using communication lines already existing at urban development sites based on such information transfer technologies as fiber to the office and fiber to the desk in relation to the tasks of physical protection of objects. The aspects of using distributed acoustic sensors based on a phase-sensitive optical time domain reflectometer for localizing sources of acoustic impact in real time, that is, for determining the location of an intruder on a protected object, are considered. An assessment was made of the sensitivity of optical paths of various configurations to acoustic influences corresponding to the speech signals of the alleged intruder. Optical paths based on optical fiber in a dry optical cable and optical fiber in an optical module with hydrophobic filling are considered.

The geometric parameters of sharpening the rake surface are very important for the efficient use of the drill. Therefore, it is important to know the correct sharpening angle of the drill in the radial direction. This is especially important at the stage of regrinding the drill, due to the incorrect installation of the drill into the fixture. In this paper, a new image processing algorithm is proposed that allows you to set indicators and factors that determine the correct choice of the angular position of the drill after regrinding. This algorithm can be of great industrial use due to the simplicity of implementation and minimization of the necessary equipment for setting up the measuring station. The presented model has an important application value and differs from the existing ones in that it can be applied for regrinding of drills with curvilinear cutting edges. This advantage is achieved by using a simpler construction of the drill’s flank surfaces. The proposed design ensures a rational distribution of the clearance angle value along the cutting part regardless of the original shape of the flank surface before the regrinding. Taking into account the limitations of the image processing algorithm and the theoretical model of the cutting part of a tri-flute drill, a rational ratio of the rake and clearance angles obtained by simulating the edge movement in cutting process. This approach allows a radical revision of the traditional recommendations for regrinding process of tri-flute drills. This is becomes possible to solve problems associated with regrinding drills with involute and multi-level flat flank surface. However, the validity of our work still needs to be carefully checked.

Modern methods of control geometry parameters of cutting tools often incorporate measuring operations per- formed using high-precision CCD cameras which work on the contrast-detection method. The key advantages of this method are the high speed of measurements, the simplicity of using general method on modern CNC measuring systems and a wide range of possibilities for controlling pro􏰇le locations of surfaces. However, using this method largely depends on the resolution of the camera's ability and the size of the controlled area, which in turn imposes signi􏰇cant restrictions on the measurement of surface areas which are less than 10% of the frame area. This paper proposes a new way to measure the area of pro􏰇le section of microtool surfaces, based on the identifying of a focused area throughout the entire frame area. This method makes it possible to recognize the nature of the focus distribution at di􏰆erent camera positions, which in turn makes it possible to measure the area of pro􏰇le section of microtool surfaces when the size of the controlled area is less than 10% of the frame size to use the contrast autofocus method to incomparably increase.

The modern world is saturated with information parameters. The formation of knowledge about the surrounding space allows you to secure the world and predict the impact of external factors on the ecosystem and humans in it. An analysis of the movement of air flows in real or close to real time makes it possible to secure aircraft control, analyze precipitation, analyze the origin of tornadoes, etc. Formation of airspace data is possible using local measuring systems that record the wind effect on the local point (at a ground station or weather balloon). The use of RF scanning and analysis of Doppler reflections from particles floating in the air mass makes it possible to form a three-dimensional cloud of points and analyze their general movement. The procedure for scanning space, as well as the formation of a volumetric matrix, is a difficult task. The analysis and identification of persistent traits is the problem under consideration in this study. The paper proposes an approach to improve the visibility of sections of vortex structures and wind currents recorded by radio frequency stations using the analysis of the Doppler effect. The analysis is performed on the basis of the generated two-dimensional data portraits. The paper proposes the use of a multicriteria method with variable local parameters and selection of local stationarity areas to identify areas with speed drops and concentration of suspended particles in an air stream. Формирование локальных границ и выделение границ осуществляется с использование локального оценивания и анализа изменений локальных градиентов с уменьшением их размаха. The formation of local boundaries and the selection of boundaries is carried out using local estimation and analysis of changes in local gradients with a decrease in their range. As natural data used to evaluate the effectiveness, test multidimensional arrays are used in the form of local mappings of the Doppler estimation divided by heights. The generated data is represented by images of 4000x4000 characters (8 bits, color image, high-speed flow is marked with color).

This article describes the fiber-optic Bragg grating sensor which is encapsulated by using 3D print and polylactic acid material. This FBG sensor is designed for heart rate monitoring of the human body. In this article, we describe the complete process consisting of creating, encapsulating, and experimental verification of the sensor. This sensor we compared with the conventional ECG monitoring system. Measurement was performed with a group of 5 volunteers in the laboratory conditions. The measured data were compared by the Bland-Altman method.

One of the new important directions in the development of the manufacturing industry is the use of cutting tools with a textured front surface. These technical solutions were used on prefabricated cutting tools, which is explained by the difficulty of access when exposed to a nano-textured surface. In this paper, a technological possibility is proposed to carry out nano-texturing by various controlled methods that cause different features of the helical surface. The proposed solution is to form classes of nano-textured surfaces that meet the requirements of manufacturability (grinding, electroerosion, laser ablation and additive technologies). This solution will increase the tool life of end mills and improve cutting conditions.

A new wave front phase sensor is introduced that is based on acquiring two or more intensity images at two different optical distances away from the reflective surface or transparent material to be measured. The technique, Wave Front Phase Imaging (WFPI), acquires millions of data points in just seconds with phase information in ever pixel in the image sensor array. As high-resolution wave front sensors can be advantageous in many industries ranging from opthalmology20 to lens characterization21, the industry with a need for ever higher resolution due to its continuous shringing features is the semiconductor industry. On product overlay (OPO) is one of the most critical parameters for the continued scaling according to Moore’s law. Without good overlay between the mask and the silicon wafer inside the lithography tool, yield will suffer1. As the OPO budget shrinks, non-lithography process induced stress causing in plane distortions (IPD) becomes a more dominant contributor to the shrinking overlay budget2. To estimate the process induced in-plane wafer distortion after cucking the wafer onto the scanner board, a high-resolution measurement of the freeform wafer shape of the unclamped wafer with the gravity effect removed is needed. Measuring both intra and inter die wafer distortions, a feed-forward prediction algorithm, as has been published by ASML, minimizes the need for alignment marks on the die and wafer and can be performed at any lithography layer3. Up until now, the semiconductor industry has been using Coherent Gradient Sensing (CGS) interferometry or Fizeau interferometry to generate the wave front phase from the reflecting wafer surface to measure the free form wafer shape3,4. In this paper, we present a new method to generate a very high-resolution wave front phase map of the reflected light from a patterned silicon wafer surface that can be used to generate the free form wafer shape. We show data using a WFPI patterned wafer geometry tool to acquire 3.4 million data points on a 200mm patterned silicon wafer with 96µm spatial resolution with a data acquisition time of 5 seconds.

Within the last decade, new threats like UAV’s and loitering ammunition have appeared on the battlefield and have revealed to be difficult to defend by conventional effectors. Hence, High Energy Laser Effectors have proved to be an efficient counter to these threats. As one of the leading defence companies in Germany, Rheinmetall Waffe Munition GmbH (RWM) is pushing the Directed Energy program to respond to these new threats. Diode pumped fiber lasers (DPFL) are now available as a robust technology for military applications. HighEnergy Laser Effectors containing DPFL offer a high power transmission in the near infrared region. Also, high power in a combination with best beam quality, integration into a small volume through reduced weight and low costs per engagement. Since 15 years, RWM has developed DPFL based HEL systems for the military environment. Rheinmetall supplies the laser source for both actual national Laser Demonstrator Programs in Germany the 10kW mobile testbed and the 20kW Navy demonstrator. Both laser sources are based on DPFL modules in combination with spectral beam coupling (SBC) units. Concepts for scaling towards 100kW with best beam quality are under investigation. SBC power scaling and unique combining elements are developed in cooperation with the Fraunhofer Institute for Applied Optics and Precision Engineering. Besides the development program for the laser source, Rheinmetall is conducting intensive target interaction experiments in the laboratory and on the laser test range of the company. The results of these experiments will be the basis on defining the parameters of Laser Weapon Effectors for an efficient engagement. Based on these parameters, Rheinmetall develops complete HEL effectors with the main components, as there is the laser weapon station, beam forming unit (BFU), laser source and C² in order to realize the full-kill chain form target detection, course tracking and fine tracking, as well as defeating the target up to the target assessment. Rheinmetall performed first steps to demonstrate the capabilities of High-Energy Laser technology in live-firing trials. Thus, the laser technology increased its technological readiness level from 4 (lab tests) to 6/7 (prototype in relevant environment). The presentation will explain these steps from the first demonstrators using military weapon stations like Mantis or MLG 27 for coarse tracking up to the current Army and Navy High Energy Laser Weapon Demonstrator.

Collecting and exploiting optronic information is more than ever of increasing importance in security and defense, thus a growth in the number of optronic systems on various platforms worldwide is taking place. This trend is accelerated by an increasing performance and simultaneous cost reduction of optronic systems and their components. Laser sources – as part of optronic systems or as a countermeasure – therefore become increasingly relevant in that context. Research and development thus is pushing limits of laser sources to enhance efficiency, output power and wavelength coverage, especially in the SWIR and MWIR bands. Based upon these efforts and achievements power scaling of fiber laser sources in the SWIR range – albeit originally investigated mainly in the optronic context – have reached power levels now compatible with directed energy applications when suitably combined. This allows for new scenarios exploiting the reduced eye hazard of two-micron lasers while significantly increasing interaction effects with some optronic systems or materials like plastics. The presentation will discuss recent achievements in pulsed thulium- and thulium-holmium-doped solid-state and fiber lasers in the two-micron range allowing for significant average-power and pulse-energy scaling for direct applications or in mid-IR OPOs based on conversion crystals like ZnGeP2, CdSiP2 or OP-GaAs, thereby broadening the scope of various optronic applications. In addition, continuous-wave (cw) sources in the two-micron range are addressed, which are important for materials processing, communication and high-energy lasers. Therein, a focus is put on all-fiber designs and robust, if possible self-aligning, laser resonators, which allow for stable and ruggedized embodiments for (industrial and defense) applications under harsh environments. Where possible, the context of the underlying applications is also discussed.

Nanofibers based on polymers are widely used in different fields, including cosmetics, electronics, sensing, medicine, phtonics, energy and filtration. These materials have a 1D character and exhibit tailorable physico-chemical properties which enables their use in multifunctional devices. They are characterized by properties such as, high surface to volume ratio, large area coverage and low-cost manufacturing which makes their use already widespread in industry. Here I report on our research on nanofibers made by spinning technologies assisted by electric fields, which exhibits photonic functions and energy harvesting/sensing capabilities1. An additional exploited application relies on their use as photoprogrammable material, based on an epoxy-based negative photoresist. Intelligent, flexible, paper-based labels, capable to operate by visual contrast and indicate inappropriate time-temperature exposure of perishable food and drugs are demonstrated2. The research leading to these results has received funding from the European Research Council under the European Union’s Horizon 2020 Research and Innovation Programme (Grant Agreement no. 682157, “xPRINT”) and the Italian Minister of University and Research PRIN 2017PHRM8X and 20173L7W8K projects. References 1 L. Persano et al., Advanced Materials 2017, 29, 1701031, 10.1002/adma.201701031. 2 L. Romano et al. Nature Communications 2020, 11, 5991, https://doi.org/10.1038/s41467-020-19676-y.

We report on nanoimprint and plasma etching technologies development for high-density sub-wavelength surface structuration at a scale from 1.5µm to 200nm or below, to get multifunctional windows (of size ~2”-3”) offering both outstanding optical and fluidic properties. Such windows are of interest for outdoor surveillance systems, which need to operate whatever the environmental conditions. We demonstrate the realization of multifunctional surfaces enabling antireflection and water repellency properties on different optical materials, i.e. glass/silica, silicon and germanium, for applications from visible to longwave infrared domains. Illustration of such multifunctional window advantages for imaging is provided thanks to its integration in front of a MWIR camera and image analysis in presence of water droplet.

Recently the authors proposed a new angle measurement technology based on the use of the two-dimensional scales. The rotation angle measurement is based on measuring the rotation of the pattern image on the sensor of a digital camera. The report presents the results of generalization of the developed earlier technology of angular measurements using a two-dimensional scale to measurements of linear displacements. It is shown that using a simple optical-digital system with a physical resolution, for example, of the order of several micrometers, it is possible to measure angles with an error of one thousandth of an arc second and linear displacements with an error of a fraction of a nanometer.

Brain modulation achieved with biophysical approaches has a huge potential in order to enhance, rescue and modulate cognitive functions. On this regards, the brain modulation approaches has been always focused on neurons. However, studies over the past four decades have lighten-up the attention of neuroscientist towards the role of astrocytes in brain functions at multiple spatio-temporal scales and raised questions on the limits of the classical Neurocentric vision of the brain function. Accordingly, the role of ions, water and structural dynamics of astrocytes is assuming relevance for brain communication processes, typically univocally assigned to neurons. A major obstacle in studying astrocytes is that most of the technologies used to probe and sense them are derived from those developed to study neurons. In this presentation, I will review the results from my laboratory for Glial Interfaces and Engineering obtained by highly collaborative, truly multidisciplinary, international EU and non-EU countries research effort enabled by the support of AFOSR-Biophysics Program, and more recently, leveraging funding from EU-MSCA. I will overview insight on mechanism underpinning the ability of astrocytes to sense, transduce and respond to chemo-physical stimuli and to communicate with neurons, achieved by pioneered use of materials interface, technologies and approaches ad hoc tailored to stimulate, monitor and modulate the structure and function of astrocytes.

We report on a series of novel experimental results based on new electrically conductive nanoparticle-electrically insulating, guest-host, electromagnetic interference shielding (EMIS) composites. An EMIS effectiveness in excess of -10dB was achieved over a frequency range of 8 to 12 GHz. Film thicknesses were ~150 m. Material processing, thin film fabrication and EMIS effectiveness are presented.

Tunability is an important aspect of lasers. Nowadays there are many possible ways to achieve this advantageous property; however, dynamic tuning is limited. Red to InfraRed emissive dyes allow a direct visualization of molecular interactions, through deep tissue penetration, along with minimal tissue damage. In our studies we use simple systems based on a single dye-doped polymeric thin films for distributed feedback (DFB) and random lasing (RL) investigations. As active compounds we have applyed novel push-pull luminescent diphenylaminofluorene and tiophene derivatives, with different acceptor groups. Integration of such luminescent dyes with transparent polymeric medium allows fabricating real-time lasing tunability in the visible region and first biological window (650-950 nm). The observed spectral tuning of 150 nm is a groundbreaking value obtained in a single-dye system. Also Excited-State Intramolecular Proton Transfer (ESIPT) compounds, have attracted our considerable attention, due to their unique optical properties. In this contribution we show a novel bis-trimethylsilyl substituted 2-(2’hydroxyphenyl)benzothiazole (HBT) derivatives functionalized with a trifluoromethyl - a strong electron-withdrawing group. Such structure enabled real-time red-green-blue (RGB) switching of emission, both in solution and solid-state, providing white laser light emission. We show strong dependence on environment polarity, as well as Aggregation-Induced Emission Enhancement (AIEE) properties, and successful implementation of ESIPT molecules in DFB lasing, both in solution and solid-state.