The contribution of the thermal infrared (TIR) camera to the Earth observation FUEGO mission is to participate; to discriminate the clouds and smoke; to detect the false alarms of forest fires; to monitor the forest fires.
Consequently, the camera needs a large dynamic range of detectable radiances. A small volume, low mass and power are required by the small FUEGO payload. These specifications can be attractive for other similar missions.
In this paper, a first part will present the mechanical properties of the chalcohalide glass system GeS2-Ga2S3-CsCl. The hardness, Young’s modulus, shear modulus and toughness of a series of glasses (0.8 GeS2 - 0.2 Ga2S3)100-x CsClx with x = 0, 5, 10, 15 have been investigated and compared with other glasses. Two particular compositions 75 GeS2 - 15 Ga2S3 - 10 CsCl and 65 GeS2 - 20 Ga2S3 - 15 CsCl are compared with existing industrial chalcogenide glasses. In a second part, two multispectral antireflective coatings are presented. These coatings, developed for a multispectral application, enhanced the transmissions in specific bands.
The thermal imaging market has experienced a strong growth during the recent years due to continued cost reduction of night vision devices. The development of uncooled focal plane detector arrays is the major reason for the cost reduction. Another reason is the continuous improvement of the optical solution. In this paper, we present a new multispectral material which responds to the increasing demand for optics operating simultaneously in the visible/SWIR (Short Wave InfraRed) and the thermal infrared region. The most important properties of some glasses from the GeS2-Ga2S3- CsCl system are highlighted in this study. A stable composition 15Ga2S3-75GeS2-10CsCl allowed the synthesis of a large glass without crystallization. The refractive index of this glass was precisely measured from 0.6 to 10.4μm by using the Littrow method. The chromatic dispersion was then calculated and compared with other multispectral materials.
The military uncooled infrared market is driven by the continued cost reduction of the focal plane arrays whilst maintaining high standards of sensitivity and steering towards smaller pixel sizes. As a consequence, new optical solutions are called for. Two approaches can come into play: the bottom up option consists in allocating improvements to each contributor and the top down process rather relies on an overall optimization of the complete image channel. The University of Rennes I with Thales Angénieux alongside has been working over the past decade through French MOD funding’s, on low cost alternatives of infrared materials based upon chalcogenide glasses. A special care has been laid on the enhancement of their mechanical properties and their ability to be moulded according to complex shapes. New manufacturing means developments capable of better yields for the raw materials will be addressed, too. Beyond the mere lenses budget cuts, a wave front coding process can ease a global optimization. This technic gives a way of relaxing optical constraints or upgrading thermal device performances through an increase of the focus depths and desensitization against temperature drifts: it combines image processing and the use of smart optical components. Thales achievements in such topics will be enlightened and the trade-off between image quality correction levels and low consumption/ real time processing, as might be required in hand-free night vision devices, will be emphasized. It is worth mentioning that both approaches are deeply leaning on each other.
Thales Anenieux has been manufacturing for two decades flexible light intensifier goggles that have been popular over numerous countries: thanks to the advent of uncooled microbolometer arrays, further outlooks are settled. Army Forces can have now at their command a multi-purpose and cost effective set of devices that answer most of the battlefield mission profiles. Thales Angenieux move from light intensifier goggles to low cost infared imagers and this smooth change is sketched out: our erlier experience on compact and user-friendly L.I equipment, especially in the field of the opto-mechanical design, has helped us to push forward the best compromises. Our product line policy is displayed: really, we have made a point of addressing many potential customers demands by singling out a modular approach. Further developments are now going on.
We report on the design fabrication and characterization a 3-period grating composed of subwavelength ridges of progressively varying widths for operation at 10.6 µm. The grating is blazed into the first transmitted order (an efficiency of 80% is measured) under TM polarization and over a broad range of angles of incidence. The fabrication involves contact photolithography, reactive-ion etching, and an evaporation deposition over the etched structure. The result validates the use of photolithography, a low-cost technology, for the manufacture of efficient blazed binary diffractive elements for thermal imaging (the 8- to 12-µm IR band).
Thales Angenieux has been developing for almost two decades, compact and flexible light intensifier goggles that are in service through numerous countries. More recently, a new product line, called Elvir, has been launched which is based upon uncooled sensitive arrays: as a consequence, Thales Angenieux has now at command a full set of night vision equipment's, answering most of the operational purposes. A 'blocks' policy has been used to cut the non-recurring expenses: the thermal camera re-uses some upgraded sub-assemblies of the previous IL goggles. This paper reviews the main trades off, showing how we relied on earlier and successful designs to meet the best compromises between performances, costs and compactness. Some issues, such as the front infrared optics set up, will be emphasized later on. The choices that have ruled the visualization unit design will be outlined. Future prospects backing the latest technologies breakthroughs wil be sketched out: topics such as new infrared materials and hybrid lenses made of subwavelength features are addressed.
Uncooled LWIR technology yields now an attractive alternative within the thermal sights area: TAGX launched one year ago, a new product line ELVIR, promoting cost-efficient solutions whilst meeting performances that are likely to suit most hand-held military purposes.
We backed on our earnest skills on previous in-house made equipment such as light intensifier goggles, to reach the best trends, both complying with operational demands and current market prices.
The very first step which is aiming at settling the main device characteristics will be emphasized thought typical requirements upon current customer’s requests: quick and flexible range computations models should answer that purpose and we will rely on operational feed back. ELVIR is built around micro- bolometer arrays that are available in France: a very best effort was done on each cost budget contributor, involving mechanics, electronics and optics. As detailed hereafter, many improvements were steered up by the latest research outcomes, partly sponsored by the French DGA, as, for instance, low cost LWIR lenses already off-the-shelves in France thanks to the UMICORE IR Glass Company. All these compromises will be displayed
Blazed-binary optical elements are diffractive components, composed of subwavelength ridges, pillars or other simple geometries carefully etched in a dielectric film, that mimic standard blazed-echelette diffractive elements. Recent experimental results in the visible showed that, blazed-binary optical elements offer high diffraction efficiencies and unique properties that cannot be achieved by standard echelette diffractive elements. Meanwhile, the manufacture of these optical elements for operation in the visible represents a challenge for today’s technologies since they involve both sub-micron sizes and high aspect ratios. In this paper, we extend the study to the thermal infrared, where the fabrication constraints are compatible with simple manufacture process such as photolithography. A 3λ-period blazed-binary grating etched into a silicon substrate, implementing an antireflection function (zinc sulphide deposition over the etched structure), was designed for operation under TM polarization at 10.6 μm. Its fabrication involved contact photolithography, reactive ion etching and an evaporation deposition over the etched structure. A first-order transmitted diffraction efficiency of 80 % was measured under TM polarization at 10.6 μm. This result validates the use photolithography, a low-cost technology, and an antireflection deposition, for the manufacture of efficient blazed-binary diffractive elements operating for thermal imaging (8-12μm infrared band).
This paper deals with diffractive surfaces used in optical designs: fabricated devices operating over the infrared wavebands are detailed, and the means of manufacture within the Thomson Optronic Group are described.
Diffractive optics five a means of decreasing the number of components in infrared devices, while meeting the current performances of conventional designs. The testing of such lenses needs two steps: the first one deals with MTF evaluations. The corresponding measurement tool will be briefly presented. An optical bench dedicated to diffraction efficiencies assessments for hybrid lenses is described: the main principles are addressed including the tolerance budget of such a means and experimental results are sketched out.
This paper deals with illumination assessment for IR devices: a skill software has been developed to predict image non-uniformities, including Narcissus effect. Built upon real raytraces, special algorithms have been carried out to reduce the computation time and to increase the accuracy. Some tutorial examples are provided.