In the past, bolometer-based imagers have been used for earth observation. Uncooled-bolometer based imagers are especially well suited for this due to their low power consumption. NIRST (New Infra-Red Sensor Technology), an example of an imager based on uncooled bolometers, monitors high temperature events on the ground related to fires and volcanic events, and will measure their physical parameters and takes measurements of sea surface temperatures mainly off the coast of South America as well as other targeted opportunities. NIRST has one band in the mid-wave infrared centered at 3.8 um with a bandwidth of 0.8 um, and two bands in the thermal infrared, centered respectively at 10.85 and 11.85 um with a bandwidth of 0.9 um.
A software application, SIST, has been developed for the simulation of the video at the output of a thermal imager. The approach offers a more suitable representation than current identification (ID) range predictors do: the end user can
evaluate the adequacy of a virtual camera as if he was using it in real operating conditions. In particular, the ambiguity in the interpretation of ID range is cancelled. The application also allows for a cost-efficient determination of the optimal design of an imager and of its subsystems without over- or under-specification: the performances are known early in the development cycle, for targets, scene and environmental conditions of interest. The simulated image is also a powerful method for testing processing algorithms. Finally, the display, which can be a severe system limitation, is also fully
considered in the system by the use of real hardware components. The application consists in Matlabtm routines that
simulate the effect of the subsystems atmosphere, optical lens, detector, and image processing algorithms. Calls to
MODTRAN® for the atmosphere modeling and to Zemax for the optical modeling have been implemented. The realism of the simulation depends on the adequacy of the input scene for the application and on the accuracy of the subsystem
parameters. For high accuracy results, measured imager characteristics such as noise can be used with SIST instead of
less accurate models. The ID ranges of potential imagers were assessed for various targets, backgrounds and atmospheric conditions. The optimal specifications for an optical design were determined by varying the Seidel aberration coefficients to find the worst MTF that still respects the desired ID range.
The detection of concealed weapons in crowd situations is a critical need and solutions are being sought after by security agencies at the federal, state and municipal levels. Millimeter waves have been evaluated for these kinds of applications, but the currently available technologies are typically too large and bulky to allow for widespread deployment. Alternatively soft X-rays have been considered but safety issues hinder their acceptance. Terahertz technology is ideally suited for such an application as it has the ability to see through clothing, and offers higher resolution than in the millimeter band, also being more compact. THz photons have lower energy than infrared and do not show the ionizing properties of X-ray radiation. The longer Terahertz waves penetrate deeper into various materials then their visible and infrared counterparts. Though the wavelength is longer it has been shown that high resolution in a small form factor can be obtained in the THz wavebands thanks to the use of small pixel pitch detectors. In this paper, a case study for the use of a compact THz camera for active see-through imaging at stand-off distances is presented. More specifically, the cases of seeing through packages and clothing are analyzed in the perspective of concealed weapons detection. The paper starts with a review of the characteristics of a high resolution THz camera exhibiting small pixel size and large field-of-view. Some laboratory results of concealed object imaging along with details of a concept for live surveillance using a compact see-through imaging system are reviewed.
Terahertz is a field in constant expansion. Multiple applications are foreseen including see-through imaging. To develop deployable systems, real-time two-dimensional cameras are needed rather than monopixel detectors or linear arrays that require mechanical scanning systems. INO has recently developed a real-time (video rate) 384x288 THz camera exhibiting excellent sensitivity and low noise levels. The core of the THz imager is the 35 μm pitch detector array that is based on INO’s uncooled VOx microbolometer technology and fabricated in INO’s clean room. A standard ceramic package is used for final packaging. The detector FPA is finally sealed with a high resistivity float zone silicon (HRFZ-Si) window having an anti-reflective coating consisting of thick Parylene, which the thickness of which depends on the required optimization wavelength. The FPA is mounted on an INO IRXCAM core giving a passive THz camera assembly. The additional THz objective consists of a refractive 44 mm focal length F/1 THz lens. In this paper, a review of the characteristics of the THz camera at is performed. The sensitivity of the camera at various THz wavelengths is presented along with examples of the resolution obtained with the IRXCAM-384-THz camera core. See-through imaging results are also presented.
The recent arrival of TeraHertz large format focal plane arrays has opened the door for numerous applications not
previously available for this exciting technology. Video-rate imaging is now a reality and little or no scanning is
required. INO has a proven microbolometer based focal plane array that shows good sensitivity over a large THz
bandwidth and videos have been successfully acquired of objects hidden behind barrier materials. While these videos
successfully proved the real-time capabilities of the INO imager, the quality of the images required substantial system
level improvement to be useful for detection and identification purposes in various applications. To this end, INO has
designed and fabricated optical components for its active imaging set-up that allows for superior quality real-time
images. This paper discusses the concepts and techniques used to create these components. A comparison of images taken using
the same THz camera with and without these innovative techniques is presented. In addition, as stand-off detection and
imaging is the ultimate objective, an analysis of the atmospheric attenuation over the THz wavelength region is also
discussed.
INO has developed infrared camera systems with microscanning capabilities in order to increase image resolution. It has
been shown in previous works that the image quality may be improved even if the pixel pitch is smaller than the point
spread function.
This paper introduces a catadioptric optics system with fully integrated microscan for improved resolution in the THz
band. The design, inspired by the INO's HRXCAM infrared camera core and adapted for terahertz wavelengths, includes
two mirrors and one refractive element. It has a 11.9 degree full field of view and an effective F-number of 1.07 over a
wide spectral range, from 100 μm to 1.5 mm wavelength. This diffraction limited optics is used to provide video rate
high quality THz images. A THz camera, with 160 x 120 pixel and 52 μm pitch detector, is combined with the microscan
objective to provide a 320 x 240 pixel image with a 26 μm sampling step.
Preliminary imaging results using a THz illumination source at 118 μm wavelength are presented. A comparison
between standard and microscanned images is also presented.
Conventional guidelines and approximations useful in macro-scale system design can become invalidated when applied
to the smaller scales. An illustration of this is when camera pixel size becomes smaller than the diffraction-limited
resolution of the incident light. It is sometimes believed that there is no benefit in having a pixel width smaller than the
resolving limit defined by the Raleigh criterion, 1.22 λ F/#. Though this rarely occurs in today's imaging technology,
terahertz (THz) imaging is one emerging area where the pixel dimensions can be made smaller than the imaging
wavelength. With terahertz camera technology, we are able to achieve sub-wavelength pixel sampling pitch, and
therefore capable of directly measuring if there are image quality benefits to be derived from sub-wavelength sampling.
Interest in terahertz imaging is high due to potential uses in security applications because of the greater penetration depth
of terahertz radiation compared to the infrared and the visible. This paper discusses the modification by INO of its
infrared MEMS microbolometer detector technology toward a THz imaging platform yielding a sub-wavelength pixel
THz camera. Images obtained with this camera are reviewed in this paper. Measurements were also obtained using
microscanning to increase sampling resolution. Parameters such as imaging resolution and sampling are addressed. A
comparison is also made with results obtained with an 8-12 μm band camera having a pixel pitch close to the diffractionlimit.
Infrared and terahertz are two imaging technologies that differ fundamentally in numerous aspects. Infrared imaging is
an efficient passive technology whereas terahertz technology is an active technology requiring some kind of illumination
to be efficient. What's more, the detectors are also different and yield differences in the fundamental physics when
integrated in a complete system. One of these differences lies in the size of the detectors. Infrared detectors are typically
larger than the infrared wavelengths whereas terahertz detectors are typically smaller than the wavelength of
illumination. This results in different constraints when designing these systems, constraints that are imposed by the
resolution capabilities of the system.
In the past INO has developed an infrared imaging camera core of 1024×768 pixels and tested some microscanning
devices to improve its sampling frequency and ultimately its resolution. INO has also engineered detectors and camera
cores specifically designed for active terahertz imaging with smaller dimensions (160×120 pixels). In this paper the
evaluation of the resolution capabilities of a terahertz imager at the pixel level is performed. The resolution capabilities
for the THz are evaluated in the sub-wavelength range, which is not actually possible in the infrared wavebands. Based
on this evaluation, the comparison between the resolution limits of infrared detectors and the terahertz detectors at the
pixel level is performed highlighting the differences between the wavebands and their impact on system design.
A THz camera based on an uncooled microbolometer 160X120 pixel array with nominal pitch of 52 μm has been
developed at INO and initial transmission and reflection images showed promise. In the present paper, the
characterization of both standard infrared and THz-optimized uncooled microbolometer pixel arrays are presented at
both infrared and THz wavelengths. Measurements in the THz region has been performed using non-uniform low-power
quantum-cascade laser (QCL) and uniform high-power far-infrared laser (FIR laser) beams at 3 THz and 4.25 and 2.54
THz, respectively. A measurement comparison has been achieved in the infrared using a blackbody radiation. Different
methods for noise-equivalent power (NEP) measurements have been investigated. These characterization methods are
promising especially for non-uniform laser beams irradiated on pixel arrays. The NEP results obtained from the different
methods are in good agreement independent of the method used in the experiments. The results show a high sensitivity
of the THz-optimized pixel array in the THz region. Large beam area reflection imaging of obscured materials at 2.54
THz have been performed at video rates of 30 frames per second using the THz-optimized pixel array equipped with a
semi-custom fast THz objective, proving that the INO THz camera provides a promising solution for stand-alone
imaging systems.
A novel technique, was developed to implant gaseous ions into the surface of metallic objects with arbitrary geometry. A system presenting a pulsed ECR plasma and a constant voltage of the target has the advantage of monoenergetic implantation. Depth distribution and chemical interactions were investigated by AES and XPS. Surface microstructure and friction forces on the nanometric scales were evaluated by AFM. We found that the depth of implantation can be controlled by the sample position relative to the extraction grid, which may have benefits for certain applications. The evolution of the implantation indicates that, at room temperature, the chemical reactions involved lead to sub-stoichiometricor composite products. In the nitriding case, an increase in microroughness and a reduction of local friction forces on the nanometric scale were found.
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