Single-shot 3-D imaging matrix offers stealth capabilities
GRENOBLE, France – Researchers have demonstrated a single-pulse
active 3-D imaging matrix operating in the infrared. The imaging matrix can produce
a three-dimensional image of a distant object with only a single laser pulse, said
the investigators, who work with the Laboratory for Electronics & Information
Technology (CEA-Léti), a public research and technology organization.
Development of the imaging matrix was initially driven by military
applications, said Gérard Destéfanis of CEA-Léti – specifically,
the need to identify a distant object with good stealth, with a single shot. But
the device also could contribute to a range of civilian applications, including
aerial surveying and mapping the Earth from planes. It offers a spatial resolution
of 30 cm.
A view, visible to the eye, of the scene used to demonstrate laser
detection and ranging imagery (left). Intensity image expressed in number of photoelectrons
per pixel (middle) and relative range color-coded image after nonuniformity correction
and intensity correction (right). Because the integration time for 2-D was longer
(~1 μs) than the duration of the voltage ramp (200 ns), the depth of field
is wider in the 2-D image than in the 3-D. Courtesy of CEA-Léti.
Currently, for eye safety reasons, the 320 x 256 imaging matrix
operates at a wavelength of 1.55 µm. It can also operate with infrared lasers at
wavelengths up to 5 µm.
CEA-Léti reports that the 3-D imaging matrix is the result
of two major technical innovations by its researchers. The first of these is the
manufacture of an avalanche photodiode matrix created in the HgCdTe semiconductor.
Operating in the nanosecond range, the matrix imitates the characteristics of a
perfect amplifier, the organization said. It can obtain very high gains (more than
100) at low polarization voltages (less than 10 V), without any excess noise.
The second innovation is the design and manufacture of a readout
circuit combining a time-of-flight measurement with a three-dimensional radiometric
CEA-Léti performed the work in conjunction with the French
company Sofradir. The researchers reported some details of the technical innovations
at the SPIE Defense, Security and Sensing meeting in Orlando last April, and at
the SPIE Security and Defense meeting in Toulouse last September.
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