Hans Kariis

Countering laser pointer threats to road safety

The market demand for bright laser pointers has led to the development of readily available devices that can pose a threat to road safety. Laser pointers can be involved in accidents caused by laser users who do not realise the dangers involved, but laser pointers can also enable deliberate criminal activity. There are technologies available that can counter the threat in different ways. A number of protective principles are outlined below. Some technologies built upon Liquid Crystal Devices are described in greater detail. Without any knowledge of what laser pointers a potential aggressor has access to, a frequency agile filter seems to be the most promising way to avoid the most severe consequences of dazzle from laser pointers. Protective systems incorporating suitable glasses or visors holding frequency agile filters of this kind however, are not commercially available today.

Scattering and polarization properties of the scarab beetle Cyphochilus insulanus cuticle

Optical properties of natural photonic structures can inspire material developments in diversified areas, such as the spectral design of surfaces for camouflage. Here, reflectance, scattering, and polarization properties of the cuticle of the scarab beetle Cyphochilus insulanus are studied with spectral directional hemispherical reflectance, bidirectional reflection distribution function (BRDF) measurements, and Mueller-matrix spectroscopic ellipsometry (MMSE). At normal incidence, a reflectance (0.6-0.75) is found in the spectral range of 400-1600 nm and a weaker reflectance <0.2 in the UV range as well as for wavelengths >1600  nm. A whiteness of W=42 is observed for mainly the elytra of the beetle. Chitin is a major constituent of the insect cuticle which is verified by the close similarity of the measured IR spectrum to that of α-chitin. The BRDF signal shows close-to-Lambertian properties of the beetle for visible light at small angles of incidence. From the MMSE measurement it is found that the beetles appear as dielectric reflectors reflecting linearly polarized light at oblique incidence with low gloss and a low degree of polarization. The measured beetle properties are properties that can be beneficial in a camouflage material.

Polymer based devices with adaptable infrared reflection and transmission

In the present work the infrared-transmission of PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(styrensulfonat)) is being investigated using three different kind of electrochromic devises. PEDOT:PSS is an electrochromic conducting polymer able to change its optical properties when it is doped and undoped. The doping is achieved by a voltage applied across the cell. The optical properties are reversible if the polarity of the voltage is changed. We report here, to our knowledge, the first cell with adaptive transmission in the infrared wavelength range. The issue for this type of cell is that all the layers in the device must be transmissive in the whole relevant wavelength range. The results were further verified by construction of similar cells with different configuration giving adaptable reflectivity.

Optical polarization and the dependence of angle of incidence for different surfaces: comparison between different wavelengths from UV to IR

As the sensor technology for polarimetric imaging is advancing into more robust commercial systems such sensors could soon be expected for, e.g., military surveillance and reconnaissance applications in addition to more conventional sensor systems. Thus, there might be an upcoming need to understand limitations on present camouflage systems to meet this new sensor threat. Some of the reasons why polarimetric imaging has drawn attention is the ability to achieve a higher contrast for artificial surfaces against natural backgrounds, by analyzing the degree of linear polarization, which in this work has been analyzed for different types of surfaces as a function of wavelength. We also compare with the polarimetric vision of horse-flies and other aquatic insects via the polarization properties of different colors of horse coat hair in order to give some further insight into polarimetric vision techniques developed by nature. In this work we have used different measurement techniques, such as angle dependent polarimetric spectral directional hemispherical reflectance and polarimetric imaging.

Optical polarization: background and camouflage

Polarimetric imaging sensors in the electro-optical region, already military and commercially available in both the visual and infrared, show enhanced capabilities for advanced target detection and recognition. The capabilities arise due to the ability to discriminate between man-made and natural background surfaces using the polarization information of light. In the development of materials for signature management in the visible and infrared wavelength regions, different criteria need to be met to fulfil the requirements for a good camouflage against modern sensors. In conventional camouflage design, the aimed design of the surface properties of an object is to spectrally match or adapt it to a background and thereby minimizing the contrast given by a specific threat sensor. Examples will be shown from measurements of some relevant materials and how they in different ways affect the polarimetric signature. Dimensioning properties relevant in an optical camouflage from a polarimetric perspective, such as degree of polarization, the viewing or incident angle, and amount of diffuse reflection, mainly in the infrared region, will be discussed.

Camouflage in Thermal IR-Spectral Design

In this work a spectral designed coating from SPECTROGON is evaluated. Spectral design in this case means that the coating has a reflectivity equal to one at 3-5 and 8-12 microns were sensors operate and a much lower reflectivity in the other wave length regions. Three boxes are evaluated: one metallic, one black-body and one with a spectral designed surface, all with a 15 W radiator inside the box. It is shown that the box with the spectral designed surface can combine the two good characteristics of the other boxes: low signature from the metallic box and reasonable inside temperature from the black-body box. The measurements were verified with calculations using RadThermIR.

A systems approach to stealth on the ground revisited

This new security development is expected to increase interest from Northern European states in supporting the development of conceptually new stealthy ground platforms, incorporating a decade of advances in technology and experiences from stealth platforms at sea and in the air. The scope of this case study is to draw experience from where we left off. At the end of the 1990s there was growing interest in stealth for combat vehicles in Sweden. An ambitious technology demonstrator project was launched. One of the outcomes was a proposed Systems Engineering process tailored for signature management presented to SPIE in 2002.(Olsson et.al, A systems approach…, Proc. SPIE 4718 ) The process was used for the Swedish/BAE Systems Hägglunds AB development of a multirole armored platform (The Swedish acronym is SEP). Before development was completed there was a change of procurement policy in Sweden from domestic development towards Governmental Off-The-Shelf, preceded by a Swedish Armed Forces change of focus from national defense only, towards expeditionary missions. Lessons learned, of value for future development, are presented. They are deduced from interviews of key-personnel, on the procurer and industry sides respectively, and from document reviews.

Microwave properties of thermochromic metal oxide surfaces

Thermochromic metal oxides with a Mott transition, such as vanadium dioxide (VO2) exhibit an extensive alteration in their infrared reflectivity when heated above the transition temperature. For VO2 the infrared reflectivity increases as the material becomes more metal-like above the transition temperature at 68°C. Given these dynamic electromagnetic properties in the IR-range, it is interesting to study the reflection of the material also in other wavelength ranges. The microwave properties of VO2 as a function of temperature have been investigated here. Measurements were made with an automated network analyzer combined with an electrical heating unit. Reflection properties of VO2 in the microwave region were determined. Above the transition temperature, an increase in the reflection of the surface was observed. The VO2 became more metal-like in the whole measured microwave frequency range, as in the infrared region. It is concluded that VO2 not only can be used to adapt the thermal emissivity of a surface but also to control the microwave reflectivity. Possible applications are switchable radomes, switchable radarabsorbers and heat protection for antenna apertures.