Thermal imaging cameras are widely used in military contexts for their night vision capabilities and their observation range; there are based on passive infrared sensors (e.g. MWIR or LWIR range). Under bad weather conditions or when the target is partially hidden (e.g. foliage, military camouflage) they are more and more complemented by active imaging systems, a key technology to perform target identification at long range. The 2D flash imaging technique is based on a high powered pulsed laser source that illuminates the entire scene and a fast gated camera as the imaging system. Both technologies are well experienced under clear meteorological conditions; models including atmospheric effects such as turbulence are able to predict accurately their performances. However, under bad weather conditions such as rain, haze or snow, these models are not relevant. This paper introduces new models to predict performances under bad weather conditions for both active and infrared imaging systems. We point out their effects on controlled physical parameters (extinction, transmission, spatial resolution, thermal background, speckle, turbulence). Then we develop physical models to describe their intrinsic characteristics and their impact on the imaging system performances. Finally, we approximate these models to have a “first order” model easy to deploy for industrial applications. This theoretical work will be validated on real active and infrared data.
Within the EC funded international project OPTHER (OPtically Driven TeraHertz AmplifiERs) a considerable
technological effort is being undertaken, in terms of technological development, THz device design and integration. The
ultimate goal is to develop a miniaturised THz amplifier based on vacuum-tube principles
The main target specifications of the OPTHER amplifier are the following:
- Operating frequency: in the band 0.3 to 2 THz
- Output power: > 10 mW ( 10 dBm )
- Gain: 10 to 20 dB.
The project is in the middle of its duration. Design and simulations have shown that these targets can be met with a
proper device configuration and careful optimization of the different parts of the amplifier. Two parallel schemes will be
employed for amplifier realisation: THz Drive Signal Amplifier and Optically Modulated Beam THz Amplifier.
Most of optoelectronic semiconductor devices, especially quantum well based ones, make use of a grating to
couple the active layer to free space. To go beyond the simplistic coupling role of the grating we propose a
specifically designed metal-dielectric corrugated interface that squeezes normal incidence light in subwalength
scale, taking advantage of the very active work achieved over the last few years in near field electromagnetism.
This structure coherently combines three surface plasmon engineering tools: Bragg reflection, microcavity, and
grating coupling. These electromagnetic properties are demonstrated experimentally in the gigahertz regime, as
a function of design parameters. Light squeezing is observed down to a quarter of a wavelength.
We present the first steps for the validation of the concept of a new optically driven field emission cathode. The
approach relies on the interaction of surface plasmons with vertically aligned multi-wall carbon nanotubes or metallic
nanowire arrays. The objective is to modulate the field emission current by using the optical field component at the
emitter apex through antenna coupling. Thanks to metallic surface gratings, surface plasmons will be generated and
localized in the vicinity of nanoemitters to increase the interaction. First simulations and preliminary experimental
measurements are presented jointly with perspectives for the wideband modulation of electronic beams up to THz.