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The Sensor Development
Group advances photonic systems and methods for environmental,
industrial and biological sensing applications. Our goal
is to promote new scientific discoveries beyond the laboratory
and into applications with scientific and commercial benefits.
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Development
and use of APDs and APD arrays
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One of the key focuses of
the sensor development group is the use of avalanche photodiode
(APD) and APD arrays. Using our in-house fabrication capabilities,
we are exploring new applications for these highly sensitive
photodetectors. In addition, we continue to explore new
fabrication approaches for enhanced wavelength response,
speed and sensitivity.
A particular research area of interest has been the enhancement
of the near-infrared sensitivity of the APDs. The Advance
Sensor engineers have developed a reliable procedure to
produce APD arrays with responsivities at 1064 nm over 200
A/W. This is the highest reported responsivity for a silicon-based
device at 1064 nm. In collaboration with scientists at Harvard
University, this work is made possible by an innovative
technique to microtexture the front surface of the APD using
high power ultra-short laser pulses (100 fs) (see fig.
1, fig. 2). Using this laser microtexturing a high speed,
high gain, low noise APD array sensor module with significantly
improved near-IR response was developed. Such an array sensor
is an extremely valuable tool for long distance optical
communication and for LIDAR/LADAR and other applications.
The Advance sensor group is also evaluating lateral-effect
APDs (LEAPs) and quadrant arrays for a range of applications.
Using these position-sensitive photodetectors, our work
is focused on meeting the requirements of high sensitivity
and spatial resolution for long-range optical communications
and tracking needs. Additional applications being explored
included laser ranging and fluorescent spectroscopy.
See also:
RMD's Quadrant Array Detector
Roughing
Up Silicon Improves Near-Infrared Performance - Femtosecond
laser helps boost efficiency of avalanche photodiodes.
Photonics.com, February, 2007.
Richard A. Myers, Richard Farrell and Arieh M. Karger,
"Enhancing Near-IR Avalanche Photodiodes Performance by
Femtosecond Laser Microstructuring," Appl. Opt. 45, 8825-8831
(2006).
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Laser Induced Breakdown Spectroscopy
(LIBS)
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RMD's researchers are working on ways to improve upon and
utilize laser-induced breakdown spectroscopy (LIBS). LIBS
is an extremely simple and powerful tool for stand-off elemental
analysis of soil, water and gases. The formation of laser-induced
plasma produces a localized blackbody source of atomic emissions.
Collection of the plasma's spectral signature with a lens
or optical fiber allows examination for elemental components
of numerous materials.
Using extremely sensitive Geiger-mode APDs coupled to an
echelle spectrometer (fig. 3), RMDs scientist have
been exploring ways to make LIBS more commercially viable
for analysis on remote platforms. Matching the GPD array
format with the output from an echelle spectrometer provides
simultaneous monitoring of the major and minor elements
of greatest interest, while eliminating the need for a scanning
or multiple grating system (fig. 4).
Reference: Richard A. Myers, Arieh M. Karger and David
W. Hahn, "Geiger Photodiode Array for Compact, Lightweight
Laser-Induced Breakdown Spectroscopy Instrumentation," Appl.
Opt. 42, 6072 (2003).
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Diffuse Optical
Tomography
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The area of breast cancer imaging and tumor characterization
has experienced rapid growth over the past decade. RMD's
scientists are using recent developments in the areas of
contrast agents and diffuse optical tomography (DOT) to
help bring new clinical technology to market. Our primary
target is improvement of breast cancer screening accuracy.
Other applications include brain imaging to monitor cerebral
function or cerebral hemorrhage, and monitoring tissue and
muscle oxygenation.
Researchers in the Advance Sensor group are studying the
use of low oxygen content in tumors as a marker of radiation-resistant
tumor regions. A laboratory prototype, based on frequency
DOT was developed to demonstrate the imaging of luminescent
antibody complex with a good resolution in phantom tissues.
It employed a near-infrared excitation-detection system
using a high gain avalanche photodiodes. We also employed
an image reconstruction algorithm developed by our collaborator,
Prof. Brian Pogue of Dartmouth College.
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Laser-based
research including LADAR and LIDAR
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The Sensor Development group has a long history of laser-based
research ranging from the study and development of novel
laser systems to the use of lasers as active components
in novel LADAR instrumentation.
Remote sensing systems based upon Light Detection and Ranging
(LIDAR) are very promising for standoff detection of various
pollution gasses (fig. 5). The advance sensor group
at RMD has experimentally demonstrated the capabilities
of Raman LIDAR under laboratory conditions and developed
the design of a prototype Compact UV Raman LIDAR. The results
indicate an excellent ability to identify and quantify the
test species. We estimate that the Compact UV Raman LIDAR
system will be capable of achieving better than 40 parts-per-million
(PPM) sensitivity. Further optical design of a compact UV
Raman LIDAR using a linear array of APD, indicated that
the smokestack pollution monitoring system will be capable
of detecting various pollutants with better than 100 PPM
sensitivity at a ranges of 100-200 m. This LIDAR system
is expected to result in a variety of commercial environmental
monitoring products, including automobile pollution monitoring.
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Polymer based
olfactory sensing including landmine detection
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Scientist in the advance sensor group, in collaboration
with research from Tufts University Medical School are working
on the development of optical-based olfactory sensors. By
integrating a robust and sensitive optical design with newly
developed polymer based sensor, targeted odors can be monitored
through fluorescence. While a preliminary prototype was
assembled for remote sensing of the signature emissions
from landmines, clinical applications for early diagnostics
of disease are also being pursued.
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Single molecule
detection and identification instrument and improved
substrates for single molecule detection
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The Advance Sensor group is exploring ways to improve and
utilize instrumentation for single-molecule fluorescence
correlation spectroscopy (FCS). Our target application is
the study of the detailed behavior of individual molecules
in their surroundings. We are exploring instrumentation
that employs FCS and two color fluorescence cross-correlation
(TC-FCCS) principles in combination with other techniques
to increase its usefulness as an analytical tool for studying
individual biomolecules. Because a very small number of
optical photons are detected from individual molecules,
the majority of this work utilizes Geiger-mode APDs (fig.
6a & 6b). In addition, we are working with other
scientist and companies to use utilize new nanotechnology
for surface-enhancement signals.
Additional single-molecule detection research by the Advance
Sensor group includes the designed and implemented of an
optical system to study Raman optical activity (ROA) of
biomolecules. Using an advanced optical design, we are able
to detect signals at the shot noise level to achieve detection
of the very weak ROA signals in a relatively compact design.
To further utilize the capabilities of this effort, we are
seeking ways to further enhance the ROA effects using nanotechnology.
Our primary goal for this technology is to elucidate structural
and stereochemical information of biomolecules and chiral
molecules in general.
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Development
of radiation imaging instruments
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The Advance Sensor group is also involved in the development
of radiation imaging systems utilizing RMD's large area
APDs and APD arrays. The group has assembled and tested
an X-ray/gamma ray imaging telescope for NASA. The telescope
consisted of two Fresnel zone plates, a 64-element avalanche
photodiode (APD) array coupled to a matching CsI (Tl) scintillator
array along with readout electronics and software (fig.
7). Angular resolutions as fine as 30 arc-seconds has
been achieved with the prototype system (fig. 8).
The development of a compact 64-channel readout unit was
a significant feat that has the potential to enable other
applications including high-energy physics, scintillating
fiber readout, X-ray astronomy, medical imaging, nondestructive
testing, LIDAR, LADAR, and laser induced fluorescence.
Reference: Michael R. Squillante, Richard A. Myers, Mitchell
Woodring, James F. Christian, Frank Robertson, Ruchard Farrell,
Alexander I. Kogan, Timothy Tiernan, and Gerald Entine,
"APD-based x-ray imaging telescope using Fresnel zone plates
for extremely high resolution," Proc. SPIE 5923, 179-186
(2005).
The Sensor Development group has developed an APD-based
probe for monitoring contamination of Tritium (3H) on surfaces
(fig. 9). This unit can be operated from the battery
power of a laptop computer (fig. 10). A very low
energy radiation emitter, tritium is historically very challenging
to detect, however, it can be an extremely hazardous material
when attached to airborne particles. Facilities at the DOE
are in dire need of an improved instrument that can provide
them with knowledge of the location and magnitude of tritium
contamination prior to decommission and demolition.
Reference: R. Scott Willms, Rick Myers, David Dogrue, and
Richard Farrell, "A New Solid State Tritium Surface Monitor,"
Fusion Science and Technology, 48, 409 (2005).
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