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161. | Focal-Plane Arrays: Northwestern develops solar-blind, deep-UV FPA Laser Focus World magazine - November 2, 2011 In the solar-blind region, the ozone layer in our atmosphere absorbs nearly 100% of the Sun’s energy for wavelengths shorter than 285 nm. Within this region, 254 nm—the dominant ultraviolet (UV) emission line of low-pressure mercury lamps used in germicidal disinfection—can cause damage to the human cornea, making it an especially important wavelength to monitor and control in clinical environments. Current detection methods for this deep-UV spectral range include photocathode and microchannel-plate combinations or silicon-photodetector arrays with bandpass filters. However, these options are fragile (vacuum-tube based) and require high-voltage power supplies or are not intrinsically solar blind and become complex and inefficient due to filtering requirements, respectively.
Progress in back-illuminated, aluminum-gallium-nitride (AlGaN)-based photodetectors has eliminated many of these drawbacks. Low quality of the AlGaN layers—hindered by the need for high Al content to make the detectors truly solar blind—has limited this progress. By refining the metal-organic chemical-vapor-deposition (MOCVD) growth process, researchers at Northwestern University (Evanston, IL) have improved the quality and increased the Al content of the AlGaN layers and successfully fabricated the first deep-UV focal-plane array (FPA). ... [read more] |
162. | Superlattice cameras add color to night-vision imaging Laser Focus World magazine - November 2, 2011 In addition to their recent development of a narrowband terahertz source, Manijeh Razeghi’s group at Northwestern University’s Center for Quantum Devices have built an infrared camera that can see more than one optical waveband or “color†in the dark. The semiconducting material used in the camera--a type-II superlattice--can be tuned to absorb a wide range of infrared wavelengths, and now, a number of distinct infrared bands at the same time.
The idea of capturing light simultaneously at different wavelengths is not new. Digital cameras in the visible spectrum are commonly equipped with detectors that sense red, green, and blue light to replicate a vast majority of colors perceived by the human eye. Multi-color detection in the infrared spectrum, however, offers unique functionalities beyond color representation. The resonant frequencies of compounds can often be found in this spectral range, which means that chemical spectroscopy can be relayed in images real-time. ... [read more] |
163. | Type II superlattice enables high operating temperature SPIE Newsroom - October 25, 2011 Currently, commercial technologies for MWIR detection and imaging are based on indium antimonide (InSb), mercury cadmium telluride (HgCdTe or MCT), or quantum-well IR photodetector systems. However, these materials are fundamentally limited. We recently developed a novel variant of Type-II superlattices, the M-structure superlattice with large effective mass and tunability of band-edge energies. This M-structure has been incorporated in a novel photodiode architecture for operation at high temperatures. A focal plane array based on this new material and detector architecture with improved electrical performance provides mid-wavelength-IR imaging of a human being at 170K. ... [read more] |
164. | New Generation of Superlattice Camera Add More Color to Night Vision McCormick News Article - October 19, 2011 Recent breakthroughs have enabled scientists from the Northwestern University’s Center for Quantum Devices to build cameras that can see more than one optical waveband or “color†in the dark. The semiconducting material used in the cameras – called type-II superlattices – can be tuned to absorb a wide range of infrared wavelengths, and now, a number of distinct infrared bands at the same time.
The idea of capturing light simultaneously at different wavelengths isn’t new. Digital cameras in the visible spectrum are commonly equipped with detectors that sense red, green, and blue light to replicate a vast majority of colors perceived by the human eye. Multi-color detection in the infrared spectrum, however, offers unique functionalities beyond color representation. The resonant frequencies of compounds can often be found in this spectral range, which means that chemical spectroscopy can be relayed in images real-time.
Razeghi’s group engineered the detection energies on the cameras to be extremely narrow, close to one-tenth of an electron volt, in what is known as the long-wave infrared window. Creating the cameras was difficult, however, because the light-absorbing layers are prone to parasitic effects. Furthermore, the detectors were designed to be stacked one on top of another, which provided spatially coincident pixel registration but added significantly to the growth and fabrication challenges. Nevertheless, a dual-band long-wave infrared 320-by-256 sized type-II superlattice camera was demonstrated for the first time in the world, the results of which were published in the July 2011 issue of Optics Letters.
... [read more] |
165. | Razeghi and group develop small, narrowband room-temperature terahertz source Laser Focus World magazine - October 2, 2011 A chip containing two mid-IR quantum-cascade (QC) lasers is at the heart of a small room-temperature terahertz-radiation source developed by researchers at Northwestern University.1 Using intracavity difference-frequency generation, the chip emits 4 THz radiation with a linewidth of only 6.6 GHz and an output power of up to 8.5 μW.
The research was headed by a scientist well-known for her work on QC lasers -- Manijeh Razeghi, a professor at Northwestern University's McCormick School of Engineering and Applied Science.
As is well-known to Laser Focus World readers, terahertz radiation can be used for security screening, terahertz-absorption spectroscopy for detecting biological and chemical compounds, and, through mixing, detection of weak terahertz signals from deep space.
Coherent terahertz radiation has historically been very difficult to generate, and the search for an easy-to-use, compact source continues today. Existing terahertz sources are large, multi-component systems that may require complex vacuum electronics, external pump lasers, and/or cryogenic cooling. A single-component device without any of these limitations is highly desirable for next-generation terahertz systems. ... [read more] |
166. | Researchers Realize High-Power, Narrowband Terahertz Source at Room Temperature McCormick News Article - September 27, 2011 Researchers at Northwestern University have developed a simpler way to generate single-chip terahertz radiation, a discovery that could soon allow for more rapid security screening, border protection, high sensitivity biological/chemical analysis, agricultural inspection, and astronomical applications. Coherent terahertz radiation has historically been very difficult to generate, and the search for an easy-to-use, compact source continues today. One possible avenue toward achieving a robust single component terahertz source is to create and mix two mid-infrared laser beams within a single semiconductor chip in the presence of a giant nonlinearity. The researchers at the CQD have incorporated a novel dual-wavelength diffraction grating within the laser cavity to create single mode (narrow spectrum) mid-infrared sources, which in turn has led to very narrow linewidth terahertz emission near 4 terahertz. The initial device yielding powers of 10 microwatts, but Razeghi said her group will continue in hopes of reaching higher power levels: “Theory says that it is possible, and we have all of the tools necessary to realize this potential.â€
... [read more] |
167. | FlightGlobal Engineering Student Of The Year: Where are they Now? FlightGlobal Magazine - September 15, 2011 Bayram, a graduate student at the Center for Quantum Devices at Northwestern University in Ilinois, shared the 2009 award with Michael Grant after his work developing semiconductor-based energy-efficient high performance optoelectronic device technologies impressed the judges. Originally from Turkey, Bayram came to Northwestern after graduating with a batchelor of science degree in electrical engineering from Bilkent University in Ankara, and chose the centre because of the reputation of its director, Manijeh Razeghi, “a world-leading authority†in that field, he says.
Bayram now works as a research scientist at IBM TJ Watson Research Centre at Yorktown Heights, New York. The Boeing award, he says, “has brought world-wide exposure to my work and enabled broadening my vision. After the Boeing award, I have established strong collaborations including those with Boeing, Dow Chemical, and IBM extending my contributions into terahertz wavelength technologies.†... [read more] |
168. | Efficient laser arrays for infrared spectroscopy SPIE Newsroom - June 13, 2011 All molecules absorb infrared radiation at characteristic frequencies, with most substances preferring the mid-infrared band (roughly, the 3–16μm wavelength range). Hence, infrared spectroscopy can be applied to the study and identification of chemicals. Recently, there have been tremendous improvements in mid-infrared QCL technology in terms of output power and
efficiency. In addition, we continue to explore possibilities of combining high power capability with tunable single mode (single wavelength) devices since a laser array with these characteristics is particularly attractive for chemical sensing applications. We have recently demonstrated the first DFB QCL array working in continuous-wave mode at room temperature that covers a wide spectral range from 4.5 to 4.7μm. This chip can deliver up to 150mW continuous-wave output power with low fidelity thermal packaging
(see Figure). ... [read more] |
169. | CQD ICDD Poster Draws a Crowd; will be on long-term display Northwestern University McCormick News Article - March 16, 2011 The Center for Quantum Devices (CQD) team designed a poster for the 2011 International Centre for Diffraction Data (ICDD) Spring Meeting, held March 14-18, 2011 in Newton Square, PA. The poster, entitled "Ultraviolet Towards Terahertz III-Nitrode Optoelectronic Devices," was such a success that the ICDD president requested the poster be kept on display throughout the year. The team consists of PhD students Can Bayram, and Yinjun Zhang; Research Scientists Dr. Zahra Vashasi and Dr. Ryan McClintock; Collaborators Dr. Ferechteh Teherani, Dr. Dave Rogers, and Principal Investigator Prof. Manijeh Razeghi. ... [read more] |
170. | Researchers Create World’s First High Performance Infrared Camera Based on Type-II InAs/GaSb Superlattices Northwestern University McCormick News Article - November 15, 2010 Researchers from the Center for Quantum Devices at Northwestern University have created a new large-format infrared camera based on Type-II InAs/GaSb superlattices that produces much higher resolution images than previous infrared cameras.
Created by Manijeh Razeghi and her group, the long wavelength infrared focal plane array camera provides a 16-fold increase in the number of pixels in the image. Their results were recently published in the journal Applied Physics Letters, Volume 97, Issue 19, 193505 (2010).
The goal of the research is to offer a better alternative to existing long wavelength infrared radiation (LWIR) cameras, which, with their thermal imaging capabilities, are used in everything from electrical inspections to security and nighttime surveillance. Current LWIR cameras are based on mercury cadmium telluride (MCT) materials, but the Type-II superlattice is mercury-free, more robust, and can be deposited with better uniformity. This will significantly increase yield and reduce camera cost once the technology goes commercial. ... [read more] |
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