Operationally significant infrared search and track (IRST) systems have been primarily second-generation thermal imager technology with scanned time-delay-integration (TDI) detector operation. The benefit of the scanned technology provides for large aperture, gimbal-scanned sensors with extremely wide field of regard, but with low revisit rates. Dramatic progress in large format staring arrays has provided the possibility of higher performance systems with lower complexity. These large format infrared staring arrays may be able to provide systems with higher performance (due to detector count) with less complexity (fewer gimbal scan limitations). In fact, lower performance IRST systems may satisfy operational requirements without scanning or stare-step operation in a “strap-down” architecture. The first step in a full capability staring system IRST design requires a thorough knowledge of staring array IRST performance. This knowledge includes a basic understanding of signal to noise (SNR) in both undersampled and well-sampled systems, with and without a matched filter. For undersampled systems, unresolved targets result in low SNR in both the average case and worst-case scenarios. We assess (using SNR as our primary metric) how the staring IRST system benefits from typical staring operations, such as dither and stare step. We provide a comparison of staring IRST system performance in the midwave infrared (MWIR) and longwave infrared (LWIR) with three modes of operation: basic staring (no sensor movement), dither, and stare step. In addition, we introduce a metric that allows comparison of different types of IRST systems. We use this metric to compare the performance of MWIR and LWIR as well as staring, dither, and stare-step systems. In the future, we will compare scanned systems to staring IRST systems.
Proc. SPIE. 9820, Infrared Imaging Systems: Design, Analysis, Modeling, and Testing XXVII
KEYWORDS: Infrared search and track, Long wavelength infrared, Signal to noise ratio, Infrared sensors, Mid-IR, Point spread functions, Sensors, Optimization (mathematics), Performance modeling, Systems modeling
The mission of an Infrared Search and Track (IRST) system is to detect and locate (sometimes called find and fix) enemy
aircraft at significant ranges. Two extreme opposite examples of IRST applications are 1) long range offensive aircraft
detection when electronic warfare equipment is jammed, compromised, or intentionally turned off, and 2) distributed
aperture systems where enemy aircraft may be in the proximity of the host aircraft. Past IRST systems have been
primarily long range offensive systems that were based on the LWIR second generation thermal imager. The new IRST
systems are primarily based on staring infrared focal planes and sensors.
In the same manner that FLIR92 did not work well in the design of staring infrared cameras (NVTherm was developed to
address staring infrared sensor performance), current modeling techniques do not adequately describe the performance of
a staring IRST sensor. There are no standard military IRST models (per AFRL and NAVAIR), and each program
appears to perform their own modeling. For this reason, L-3 has decided to develop a corporate model, working with
AFRL and NAVAIR, for the analysis, design, and evaluation of IRST concepts, programs, and solutions. This paper
provides some of the first analyses in the L-3 IRST model development program for the optimization of staring IRST
Performance models for infrared imaging systems require image quality parameters; optical design engineers need image quality design goals; systems engineers develop image quality allocations to test imaging systems against. It is a challenge to maintain consistency and traceability amongst the various expressions of image quality. We present a method and parametric tool for generating and managing expressions of image quality during the system modeling, requirements specification, design, and testing phases of an imaging system design and development project.
The capacity to measure nanoscale features rapidly and accurately is of central importance for the monitoring of manufacturing processes in the production of computer integrated circuits. Parameters of interest include, for example, trench depth, duty cycle, wall angle and oxide layer thickness. The measurement method proposed here uses focused beam scatterometry, in which the illumination consists of a focused field with a suitably tailored spatially-varying polarization distribution. In an analysis that is analogous to classical off-null measurements as well as weak measurements in quantum mechanics, we predict that four or more parameters can be measured and distinguished with an accuracy consistent with the needs laid out in the semiconductor roadmap.
Point spread function engineering is usually accomplished by controlling the amplitude, phase and/or polarization of the pupil fields. We analyze and test an optical design for full amplitude, phase, and polarization control of the pupil fields using a single spatial light modulator. In our scheme, the beam is spatially split into four components whose relative phases provide the four degrees of freedom necessary for amplitude, phase, and polarization control.
It is known that far-field scattered light requires <i>a priori</i> sample information in order to reconstruct nm-scale information such as is required in semiconductor metrology. We describe an approach to scatterometry that uses unconventional polarization states in the pupil of a high NA objective lens. We call this focused beam scatterometry; we will discuss the sensitivity limits to this approach and how it relates to micro-ellipsometry as well as low-NA scatterometry.
We describe an investigation of the polarimetric properties of suspended gallium doped silicon (Si:Ga) nanowires.
Wire fabrication has been done with a combined gallium implantation (using a focused ion beam) and subsequent
reactive ion and wet etches. A polarimetric microscope has been built and calibrated. Measurement of the
polarimetric response shows a high reflectivity and strong retardance on reflection, with some samples showing
low diattenuation, in contrast to conventional wire grid polarizers.