The ongoing development of High Energy Laser (HEL) weapon systems is leading to a new suite of potential anti-satellite (ASAT) capabilities among both spacefaring and non-spacefaring nations. Powerful ground-based HEL systems may be used to dazzle or damage sensors or disable entire satellites. Such uses offer several advantages over other counterspace capabilities. HEL weapons could be used both in an offensive and a defensive manner and may be difficult to attribute to a specific actor. Furthermore, in some cases the physical effects are reversible, and the use of HEL may significantly limit the creation of space debris compared to other ASAT capabilities. The very long slant-paths through the turbulent atmosphere, coupled with the necessity to track and engage fast-moving objects in Low Earth Orbit (LEO) makes this particular application an interesting cross-over between typical HEL technology, astronomical instrumentation, satellite and space debris laser ranging, and laser satellite communication. In this paper we will review some of the scenarios and physical effects that may be expected from HEL systems used as an ASAT capability. We show that HEL systems of even moderate powers may pose severe risks to the sensors of imaging satellites passing overhead. We also find that the laser fluence delivered to a satellite on a single passage could easily reach the damage thresholds of many of the components that a satellite needs in order to function. A fourth scenario in which HEL is used to provide a negative impulse to alter the orbit or even de-orbit a small LEO satellite seems unlikely but merits some attention as a potential future capability.
We investigate in what turbulent conditions and propagation geometries conventional adaptive optics (AO) can provide improvement in laser applications. Characterizing the optical aberrations is essential to provide the input required for a conventional AO system. In this parametric study we characterize these aberrations by numerically propagating a beacon from an effector into the far field and back using a split-step method involving turbulent phase screens. The beacon’s aberrated field at the location of the effector is sensed assuming a perfect wavefront sensor and subsequently used to pre-correct the effector for its turbulent propagation into the far field. In the far field, beam metrics such as spot size, Strehl ratio and power-ratio-in-the-bucket (PRIB) with and without AO correction applied to the effector are investigated. By varying propagation geometries and turbulent conditions, the dependence of the beam metrics on the propagation scheme is analyzed in detail. Additionally, the dependence of the beam metrics on assumptions in the AO system such as number of Zernike modes taken into account in the correction are studied. The results can be used to identify when AO should be considered given the broader operational context in which a laser system is expected to operate and give insight in accompanying AO considerations.
We present a new analysis of laser propagation experiments carried out with the Laser Propagation Testbed (LPT) developed by TNO. A major goal of these experiments is to validate and improve atmospheric propagation models that are essential to applications such as laser communication, high energy laser weapon systems and remote sensing. The data were obtained during a field campaign with a 1W 1556 nm laser beam deployed over a 3.6 km maritime path in The Netherlands. The measurements consist of intensity profiles of the propagated laser beam and local meteorological and atmospheric conditions (visibility, refractive index structure parameter and aerosol data) obtained during a ten day period under varying weather conditions. We use the locally measured atmospheric conditions and numerical weather prediction to constrain a turbulent laser propagation model developed by TNO, and compare the results with the time series measurements of the laser beam profile.
An over-water propagation link of 3.6 km was set up between the Dutch city of Den Helder and the island of Texel. For 6 days in November 2021, a laser beam was propagated along this path. An analysis of the beam wander resulted in an estimate of the strength of optical turbulence C2n. Estimates compare quite well with independent measurements of C2n by two boundary layer scintillometers. Regional maps of C2n were produced by a numerical tool consisting of the WRF model coupled to a micrometeorological module. Regional differences in C2n could be explained in terms of surface conditions, and acceptable agreement was found between the numerical values of C2n for the trial site and the values provided by the scintillometers.
TNO has expanded its 30 kW HEL research facility with the capability to monitor specular and diffuse reflections of the laser beam. A capture screen and high-speed camera focus on dynamic specular reflections, while 15 individually placeable probes monitor the diffuse component under different angles. This paper introduces the reflection measurement capability and discusses the behaviour of steel and aluminium coupons under high-energy laser irradiation. Laser-material interaction was found to be rather predictable in thermal behaviour up to the perforation event. Reflections, however, showed a highly dynamic pattern, varying in magnitude and direction and depending on bulk material, material surface condition, phase state of the material (solid or liquid) and geometry. The difficulty of assessing proper stand-off distances for laser safety is illustrated.
Fielding TNO’s LPT (Laser Propagation Testbed) for the first time in an international trial, a 3.6 km optical propagation path was created in a maritime environment between the city of Den Helder and the island of Texel in the Netherlands. Using a 1 W, 1556 nm laser beam, atmospheric propagation was investigated by capturing the resulting beam profile on a capture plate, which was imaged with a high-speed SWIR camera. Meteorological conditions were monitored using standard meteo stations, two visibility meters, two scintillometers and aerosol equipment. Over two weeks of measurements, propagation conditions varied from windy with clear, blue skies to significantly limited visibility. In this paper, the setup is introduced and a first discussion of the relation between beam behaviour and meteorological conditions is presented.
The investigation of transmission, refraction, and turbulence over the False Bay in South Africa and their influence on wave propagation was the main topic of First European South African Transmission ExpeRiment (FESTER). It yielded a 9-month continuous dataset of turbulence (Cn2) data, acquired by three Boundary Layer Scintillometers (BLS) and one ultrasonic anemometer. The data is analysed in terms of atmospheric stability, and relations are sought between the atmospheric state and the power spectrum of turbulence on the one hand, and the vertical gradients of turbulence strength on the other hand. This allows us to test various parameterizations of the z/L function, not only against experimental data, but also against numerical weather prediction (NWP) data. This work extends our previous analysis of specific case studies of the FESTER dataset.
A 1.55µm Laser Propagation Testbed (LPT) has been deployed over a 3.5 km stretch of open water between the port of Den Helder and the island of Texel in The Netherlands. The laser intensity and beam profile have been measured after propagation and reflection off a capture plate. Supplementing data was provided by large-aperture scintillometers, aerosol counters, visibility meters and standard meteorological equipment. The LPT will be presented, as well as a selection of data to demonstrate the potential of this setup. The LPT is expected to validate and verify laser propagation models and thereby to contribute in the field of atmospheric propagation, optical communication and high energy laser systems.
This paper will report on a first series of experiments of High Energy Laser effects on drones and drone components at TNO. After a description of the 30kW L3O laser facility at TNO, the experimental results will be discussed. The experiments were performed in an indoor facility and some considerations will be given on how to set up the experiments to enable “translation” of the experimental results to outdoor operational scenarios. The results illustrate that there can be large variations in the illumination time of the High Energy Laser on the target before fatal damage is observed, depending on the specific drone component selected as target. This illustrates that target aimpoint selection is critical for the result and a good understanding of the weak spots of drones is required to enable High Energy Laser systems to be effective against drones.
Infrared imaging of the sea surface is used for many purposes, such as remote sensing of large oceanographic structures, environmental monitoring, surveillance applications and platform signature research. Many of these studies rely on determining the contrast of a target feature with its background and therefore benefit from accurately predicting the signature of the underlying sea surface background. We here present a model that synthesizes infrared spectral images of sea surfaces. This model traces explicitly the behaviour of the sea wave structure and light propagation. To self-consistently treat spatial and temporal correlations of the clutter, geometrical realizations of sea surfaces are built based on realistic sea wave spectra and their temporal behaviour is subsequently followed. A camera model and a ray tracer are used to determine which parts of the sea surface are observable by individual camera pixels. Atmospheric input elements of the model, being sky dome, path radiance and transmission, are computed with MODTRAN for a chosen atmosphere.
In the framework of a NATO research group Fraunhofer IOSB and partners conducted a field trial in an arid shrub land environment in southern New Mexico (USA). The group investigates environmental limitations of fielded EO-TDAs (Electro-Optical Tactical Decision Aids). Main objective of the trial was to study the impact of the atmosphere on imaging sensor performance with a focus on the effects of atmospheric extinction and near surface turbulence. An overview of the trial will be given, as well as an overview on EO-TDA development. Results of efforts to forecast the refractive index structure parameter using numerical weather prediction (NWP) models will be described, as well as the results of a perception study on the influence of turbulence on target acquisition ranges using MWIR imagery.
In performance prediction of IR sensor systems for missile detection, apart from the sensor specifications, target signatures are essential variables. Very often, for velocities up to Mach 2-2.5, a simple model based on the aerodynamic heating of a perfect gas was used to calculate the temperatures of missile targets. This typically results in an overestimate of the target temperature with correspondingly large infrared signatures and detection ranges. Especially for even higher velocities, this approach is no longer accurate. Alternatives like CFD calculations typically require more complex sets of inputs and significantly more computing power.
The MATLAB code Hyperheat was developed to calculate the time-resolved skin temperature of axisymmetric high speed missiles during flight, taking into account the behaviour of non-perfect gas and proper heat transfer to the missile surface. Allowing for variations in parameters like missile shape, altitude, atmospheric profile, angle of attack, flight duration and super- and hypersonic velocities up to Mach 30 enables more accurate calculations of the actual target temperature. The model calculates a map of the skin temperature of the missile, which is updated over the flight time of the missile. The sets of skin temperature maps are calculated within minutes, even for >100 km trajectories, and can be easily converted in thermal infrared signatures for further processing.
This paper discusses the approach taken in Hyperheat. Then, the thermal signature of a set of typical missile threats is calculated using both the simple aerodynamic heating model and the Hyperheat code. The respective infrared signatures are compared, as well as the difference in the corresponding calculated detection ranges.
This paper compares in-situ and path-averaged measurements of the electro-optical transmission, with emphasis on
aerosol effects. The in-situ sensors consisted of optical particle counters (OPC) and a visibility meter, the path-averaged
data was provided by a 7-wavelength transmissometer (MSRT) and a scintillometer (BLS). Data was collected at a test
site in Northern Germany. A retrieval algorithm was developed to infer characteristics of the aerosol size distribution
(Junge approximation) from the MSRT data. A comparison of the various sensors suggests that the optical particle
counters are over-optimistic in their estimate of the transmission.
This paper compares in-situ and path-averaged measurements of the electro-optical transmission, with emphasis on
aerosol effects. The in-situ sensors consisted of optical particle counters (OPC), the path-averaged data was provided by
a 7-wavelength transmissometer (MSRT) and scintillometers (BLS). Data were collected at two sites: a homogeneous
test site in Northern Germany, and over the inhomogeneous False Bay near Cape Town, South Africa. A retrieval
algorithm was developed to infer characteristics of the aerosol size distribution (Junge approximation) from the MSRT
data. A comparison of the various sensors suggests that the optical particle counters are over optimistic in their estimate
of the transmission. For the homogeneous test site, in-situ and path-averaged sensors yield similar results. For the
inhomogeneous test site, sensors may react differently or temporally separated to meteorological events such as a change
in wind speed and/or direction.
A long term field trial called FESTER (First European South African Transmission Experiment) has been conducted by an international collaboration of research organizations during the course of almost one year at False Bay, South Africa. Main objectives of the experiment are a better insight into atmospherical effects on propagation of optical radiation, a deeper understanding of the effects of (marine) aerosols on transmission, and the connection of the mentioned effects to the general meteorological and oceanographic conditions/parameters. Modelling of wakes and possible infrared-radar synergy effects are further points of interest. The duration of one year ensures the coverage of most of the relevant meteorological conditions during the different seasons. While some measurements have been performed by permanent installations, others have been performed during intensive observation periods (IOP). These IOPs took place every two to three months to ensure seasonal changes. The IOPs lasted two weeks. We will give an overview of the general layout of the experiment and report on first results. An outlook on the planned analysis of the acquired data, which includes linkage to the Weather Research and Forecasting model (WRF), will be given.
Most models that predict the infrared signature of an object are based on steady-state equilibrium conditions and do not model the dynamic nature of the real world. To gain more understanding of the dynamic infrared signatures of an object, several outdoor experiments were performed, using a CUBI and a small vessel as an object. Dynamic changes were (intentionally) made to the object, while the temperatures of the facets, the meteorological parameters, and the infrared signature were being monitored. The influence of environmental parameters on the dynamic infrared signature of an object is discussed in this paper. A first attempt to model the decrease in object temperature is made.
An overview is given of the First European – South African Transmission ExpeRiment (FESTER), which took place in South Africa, over the False Bay area, centered around Simon’s Town. The experiment lasted from April 2015 through February 2016 and involved continuous observations as well as periodic observations that took place during four Intensive Observation Periods (IOPs) of 2 weeks each, which were spread over the year. The continuous observations aimed at a characterization of the electro-optical propagation environment, and included standard meteorology, aerosol, refraction and turbulence measurements. The periodic observations aimed at assessing the performance of electro-optical sensors in VIS / SWIR / MWIR and LWIR wavebands by following a boat sailing outbound and inbound tracks. In addition, dynamic aspects of electro-optical signatures, i.e., the changes induced by variations in the environment and/or target orientation, were studied. The present paper provides an overview of the trial, and presents a few first results.
KEYWORDS: Luminescence, Bacteria, Spectroscopy, Data acquisition, Camera shutters, Signal to noise ratio, Diode pumped solid state lasers, Fiber couplers, Ocean optics, Charge-coupled devices
Accurate monitoring of microbial viability plays an essential role in pharmacodynamic studies such as in
estimating the efficiency of antimicrobial agents. Traditionally, bacterial viability is determined by their ability
to form colonies on solid growth medium or to proliferate in liquid nutrient broths but, with these culture-based
methods, the live bacterial population can only be estimated retrospectively.
To address this challenge, we have employed differential fluorescence staining and an all-fiber optical system
developed by our group. The detection is based on the collection of the fluorescence from commercial dyes that
produce a substantially increased signal upon binding with bacterial nucleic acids. The dyes allow
discrimination between alive and dead cells through differential membrane permeability and fluorescence
wavelength. The respective fluorescence signal is correlated to the number of bacterial cells present in the
sample.
Our setup uses DPSS lasers and a sensitive CCD-based spectrometer over the 400-800 nm wavelength range. A
laser shutter allows the sample exposure time and acquisition time to be synchronized to minimize the effect of
photobleaching.
As a model, bacteria (Escherichia coli or Staphylococcus aureus) killed with isopropyl alcohol were mixed with
live cells at different ratios. The population ratios of alive and dead cells were accurately quantified by our
optical setup providing a rapid method for the estimation of bactericidal treatments.
In summary, our optical system may offer a robust, accurate and fast alternative for detection of dead/alive
bacteria in turbid solution opening the new avenues for pharmacodynamic studies.
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