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Page 8 of 14: Prev << 1 2 3 4 5 6 7 8 9 10 11 12 13 14 >> Next (343 Items)
176.
| Researchers Develop Simplified Approach for High-Power, Single-Mode Lasers
McCormick News Article - August 23, 2012
When it comes to applications like standoff sensing—using lasers to detect gas, explosives, or other materials from a safe distance—the laser’s strength is of the utmost importance. A stronger and purer beam means devices can sense danger more accurately from a greater distance.
Northwestern University researchers have developed a new resonator that that controls both wavelength and beam quality, creating the purest, brightest, and most powerful single-mode quantum cascade lasers yet at the 8-12 micron range. The feat is achieved through the use of a new type of “distributed feedback†mechanism called Β-DFB, a simple diffractive feedback in an angled laser cavity.
A paper describing the findings, “Angled Cavity Broad Area Quantum Cascade Lasers,†was published August 21 in the journal Applied Physics Letters ( DOI:10.1063/1.4747447). ... [read more]
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177.
| Improved LEDs and photovoltaics by hybridization and nanostructuring
SPIE Newsroom - June 15, 2012
There has been rapid industrial development for optoelectronic devices based on III-Nitrides, which span a direct bandgap from deep UV to IR, and are currently widely used in commercial white, UV, blue, and green LEDs. This alloy system is now projected to provide a platform for the development of novel multi-junction photovoltaics (PVs) with an unprecedented fit to the solar spectrum. However, improving the efficiency of InGaN-based p-n junctions is a very complex and multifaceted task for a number of reasons.
Zinc oxide (ZnO) is a remarkable, multifunctional, and biocompatible direct-, wide-bandgap semiconductor, with a distinctive property set and a unique potential for nanostructuring. Recently, there has been a surge of activity surrounding ZnO to the point where the number of publications now rivals that for GaN. Due to their similar crystal structures and bandgaps, ZnO and GaN can be combined in new ways, which opens up the prospect of novel optoelectronic devices and has the potential to solve many of the issues with existing III-Nitride devices. ... [read more]
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178.
| Superlattice sees colder objects in two colors and high resolution
SPIE Newsroom - February 10, 2012
The capabilities of IR sensing, commonly used for night vision, have been extended to see colder objects at high speed and potentially made cheaper by using a semiconductor material called the type II superlattice. The wavelength tunability and material robustness of type III-V superlattice have generated much attention in recent years. This is especially true with respect to the performance of the material in narrow-energy-gap detectors, and specifically in a part of the electromagnetic spectrum between 8 and 12 μm, called the long-wavelength IR (LWIR). The benefits of this
technology have enabled us to push type II superlattice to its logical next step: a camera capable of seeing distinct wavebands
or colors in an all-in-one package, a feat not previously demonstrated by this material system in the LWIR. Our group engineered the detection energies on the cameras to be extremely narrow, with cutoff wavelengths at 9.5 and 13 μm, in the range of roughly 0.1eV in energy. Realizing the camera was a difficult task because the light-absorbing layers are prone to surface leakage effects due to the size of the pixels, which are 30μm wide. We first reported a dual-band LWIR 320256 pixel-sized type II superlattice in July 2011.
More recently, we also demonstrated a large-format 640 x 512 pixel type II superlattice camera based on the same material design. The 4x increased resolution is necessary for many advanced applications. ... [read more]
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179.
| Compact terahertz device could improve security screening
Photonics Spectra magazine, Vol. 45, Issue 12, p. 19-20 - December 31, 2011
Using two mid-infrared laser beams, researchers have finally generated single-chip terahertz radiation at room temperature. The technology could speed up and improve a range of processes, including high-sensitivity biological and chemical analysis, astronomical study, security screening, border protection and agricultural inspection.
The project got its start in an unscientific place: the airport security lineup. Like most travelers, Manijeh Razeghi, a professor at Northwestern University's McCormick School of Engineering and Applied Science, was concerned with both the delays in the process and its accuracy. The technology to safely and easily inspect items for hazardous substances is expensive and bulky, so much of it is underused, Razeghi said. The same concerns — time, reliability and cost — are found in medical diagnostics, tumor detection and package inspection. She wanted to come up with "something useful that can overcome these basic limitations and allow terahertz technology to truly become pervasive in order to make everyone's life a little safer and easier."
Coherent terahertz radiation historically has been very difficult to generate, and the search for a compact easy-to-use source continues today. Existing terahertz sources are large multicomponent systems that may require complex vacuum electronics, external pump lasers and/or cryogenic cooling. A single-component device that does not have these limitations could enable next-generation terahertz systems.
... [read more]
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180.
| 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]
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181.
| 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]
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182.
| 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]
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183.
| 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]
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184.
| 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]
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185.
| 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]
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186.
| 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]
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187.
| 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]
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188.
| 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]
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189.
| 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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190.
| Researchers Create High-Power Single Mode Quantum Cascade Lasers
Northwestern University McCormick News Article - November 8, 2010
New laser technology developed by researchers at the Center for Quantum Devices may soon allow long-distance chemical analysis that could potentially be used in spills and warfare. Because chemicals absorb light in the infrared, it is possible to detect specific chemicals by using a laser and analyzing the returned light. But this long-distance mapping of chemicals by laser isn’t yet possible because researchers haven’t created a suitable laser source.
Manijeh Razeghi and her group have created new laser technology that combines the high-power output of a broad area mid-infrared quantum cascade laser (QCL) with a two-dimensional diffractive resonator design that controls both the wavelength and beam quality with the laser. This led to the demonstration of up to 34 watts of peak power at room temperature and near-diffraction-limited beam quality at 4.3 μm, which is near the absorption frequency of several important chemicals. That represents almost a significant improvement in output power for this type of laser source. ... [read more]
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191.
| European Semiconductor Laser Workshop at Pavia University in Italy
La Provencia - September 22, 2010
Among the invited speakers, in particular, there will be Manijeh Razeghi, one of the first scientists to develop semiconductor lasers in Europe in the
'80s ... [read more]
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192.
| Two Named Boeing Engineering Student of the Year
McCormick News Magazine - April 5, 2010
Two McCormick graduate students from the Center for Quantum Devices recieved first- and second-place awards in the 2009 Engineering Student of the Year competition sponsored by Boeing Company and presented by the aerospace publisher Flightglobal. Can Bayram (second from left) was one of two first place winners and Pierre-Yves Delaunay (second from right) won second place. Both are PhD canidates in electrical engineering and computer science working under the guidance of Profesor Manijeh Razeghi. John Tracy, Boeing's Chief technology officer and senior vice president of engineering, opperations, and technology (far right), presented the awards with Warren McEwan, Flightglobal's North American sales director (far left). ... [read more]
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193.
| Quantum Cascade Lasers Gain Efficiency
Optics and Photonics News (OPN) magazine, Vol. 21, Issue 4, p. 6 - April 2, 2010
Quantum cascade lasers (QCLs) have much potential in the mid-infrared spectral region, but their low energy efficiency has limited their application prospects. Two separate U.S. research teams have fabricated QCLs that significantly boost “wall plug efficiency,†or the ratio of the power the laser emits to the power that the device consumes.
At Northwestern University, OSA Fellow Manijeh Razeghi and her colleagues made a 4.85-µm-wavelength pulsed QCL with a wall plug efficiency of 53 percent at an operating temperature of 40 K. The authors wrote in their abstract, “In other words, we demonstrate a quantum cascade laser that produces more light than heat.†... [read more]
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194.
| Imaging Advances Boost Defense
Advanced Imaging magazine, p. 12-15 - March 31, 2010
New materials and new detector architectures pave the way for lighweight, high-sensitivity IR imagers. For years MCT has been the material of choice for imagin in the MWIR and LWIR spectral regions. However, recent advances in III-V-based Type-II superlattices (T2SLs) grown on gallium antimonide (GaSb) substrates promise to change all that. A team at Northwestern University, led by seminal T2SL researcher Manijeh Razeghi is making impressive strides in the development of MWIR and LWIR focal plane arrays. ... [read more]
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195.
| QCL peak power record smashed
Photonics Spectra magazine, February 2010, p. 19-20 - February 28, 2010
Only a year ago, the peak output power of a quantum cascade laser (QCL) was only 34W. Today, thanks to research at the Center for Quantum Devices (CQD), peak power of 120 W from a single device at room temperature has been achieved. This "breakthrough is particularly attractive for sensing chemicals at a distance and for infrared countermeasures," Professor Razeghi said, "because power is a luxury that defines range, speed, and sensitivity for targeting remote applications." ... [read more]
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196.
| Producing more light than heat from quantum cascade lasers
Semiconductor Today magazine, Vol. 5, Issue 1 - February 28, 2010
Two separate groups have reported increased wall-plug efficiency (WPE) for quantum cascade lasrs (QCLs) in Nature Phtonics: Manijeh Razeghi et. al at the Center for Quantum Devices (CQD) and Peter Liu et. al from Princeton and John Hopkins Universities. The CQD team uses a single-well injector to achieve 53% WPE at 40K with an emitting wavelength of 5 μm. In other words, they "Produce a quantum cascade laser that prduces more light than heat." ... [read more]
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197.
| Quantum Cascade lasers, a glass half full
NATURE PHOTONICS | NEWS AND VIEWS - February 15, 2010
Since the first report of its successful operation in the mid-1990s1, the quantum cascade laser (QCL) has evolved to become an important source of mid-infrared and terahertz radiation. However, it has historically been labelled as a device with a relatively poor efficiency of operation. This view may finally be about to change, thanks to the report in Nature Photonics by the Center for Quantum Devices of mid-infrared QCLs that provide wall-plug efficiencies reaching 50% for the first time. ... [read more]
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198.
| New Quantum Cascade Lasers Emit More Light Than Heat
Northwestern University McCormick News Article - January 11, 2010
Northwestern University researchers have developed compact, mid-infrared laser diodes that generate more light than heat — a breakthroughs in quantum cascade laser efficiency. The results are an important step toward use of quantum cascade lasers in a variety of applications, including remote sensing of hazardous chemicals. The quantum cascade laser (QCL) is a diode laser that is designed on the quantum mechanical level to produce light at the desired wavelength with high efficiency. Unlike traditional diode lasers, the device is unipolar, requiring only electrons to operate. A significant effort has been spent trying to understand and optimize the electron transport, which would allow researchers to improve the laser quality and efficiency.
“This breakthrough is significant because, for the very first time, we are able to create diodes that produce more light than heat,†says Razeghi. “Passing the 50 percent mark in efficiency is a major milestone, and we continue to work to optimize the efficiency of these unique devices.†... [read more]
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199.
| CQD Students Receives 1st and 2nd Place Boeing Engineering Award
Boeing press release - December 2, 2009
Can Bayram, a fifth-year PhD student in electrical engineering and computer science and member of the Center for Quantum Devices, was selected as the Boeing Company’s 2009 Engineering Student of the Year. Pierre Yves-Delaunay, another 5th year PhD student also from the Center for Quantum Devices was the runner-up. ... [read more]
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200.
| Researchers Demonstrate 100-Watt-Level Mid-infrared Lasers
Northwestern University Press Release - December 1, 2009
Northwestern University researchers from the Center for Quantum Devices have achieved a breakthrough in quantum cascade laser (QCL) output power, delivering 120 watts from a single device at room temperature. In this work, Professor Razeghi’s team demonstrated that the ridge width of a broad-area QCL can be increased up to 400 microns, without suffering from filiamentation. As a result, room temperature peak output power as high as 120 watts was obtained from a single device, which is up from 34 watts only a year ago. ... [read more]
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Address: Center for Quantum Devices; 2220 Campus Drive RM 4051; Evanston, IL 60208-0893
Phone: (847) 491-7251
Email: razeghi@northwestern.edu