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Page 7 of 14: Prev << 1 2 3 4 5 6 7 8 9 10 11 12 13 14 >> Next (336 Items)
151.
| New Terahertz Device Could Strengthen Security
McCormick Press Release - November 20, 2014
current terahertz sources are large, multi-component systems that sometimes require complex vacuum systems, external pump lasers, and even cryogenic cooling. The unwieldy devices are heavy, expensive, and hard to transport, operate, and maintain. A single-component solution capable of room temperature and widely tunable operation is highly desirable to enable next generation terahertz systems. In a recent paper in Applied Physics Letters, they demonstrate a room temperature, highly tunable, high power terahertz source. Based on nonlinear mixing in quantum cascade lasers, the source can emit up to 1.9 milliwatts of power and has a wide frequency coverage of 1 to 4.6 terahertz. By designing a multi-section, sampled-grating distribution feedback and distributed Bragg reflector waveguide, Razeghi and her team were also able to give the device a tuning range of 2.6 to 4.2 terahertz at room temperature. ... [read more]
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152.
| View from... IQCLSW 2014: Frequency comb cascade
NATURE PHOTONICS | NEWS AND VIEWS - October 31, 2014
This year marks the 20th anniversary of the first experimental demonstration of QCL, but rather than looking back on the history of QCLs the workshop was focused on leading-edge research. It featured about 150 presentations, including both oral and poster, and attracted more than 200 researchers from 15 countries. An emerging topic of discussion at the conference was ultrabroadband tunable QCLs. Manijeh Razeghi of Northwestern University, USA, reported broadband tuning over 5.7–9.3 μm using a heterogeneous structure. She is now trying to extend the tunability even further. “Imagine having a QCL source that is electrically tunable across the entire mid-infrared range of 3–12 μm,” she said. “This would revolutionize mid-infrared spectroscopy and perhaps enable new applications as well.” ... [read more]
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153.
| New Technology Illuminates Colder Objects in Deep Space
McCormick Press Release - July 8, 2014
“High performance infrared cameras are crucial for space exploration missions,†said Manijeh Razeghi, the Walter P. Murphy Professor of Electrical Engineering and Computer Science in the McCormick School of Engineering and Applied Science. “By studying the infrared waves emitted by cool stars and planets, scientists are beginning to unlock the mysteries of these cooler objects.â€
Published in the June 23 issue of Applied Physics Letters, Razeghi and her collaborators describe a new technology, which uses a novel type II superlattice material called indium arsenide/indium arsenide antimonide (InAs/InAsSb). The technology shows a stable optical response in regards to very long wavelength infrared light. By engineering the quantum properties of the type II superlattice material, the team demonstrated the world’s first InAs/InAsSb very long wavelength infrared photodiodes with high performance. The new detector can be used as an inexpensive and robust alternative to current infrared technologies.
... [read more]
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154.
| Team Demonstrates Continuous Terahertz Sources at Room Temperature
McCormick Press Release - June 4, 2014
Imagine a technology that could allow us to see through opaque surfaces without exposure to harmful x-rays, that could give us the ability to detect harmful chemicals and bio-agents from a safe distance, and that could enable us to peer so deeply into space that scientists could better understand the formation of the universe.
All of these scenarios are possible with terahertz radiation, electromagnetic waves with lengths that fall between microwaves and infrared light. However, the potential of terahertz waves has yet to be reached because they are difficult to generate and manipulate. Current terahertz sources are large, multi-component systems that require complex vacuum electronics, external pump lasers, or cryogenic cooling. It’s an expensive and cumbersome process.
Manijeh Razeghi and her team are the first to produce terahertz radiation in a simplified system, making it easier to harness the power of these elusive waves. They have developed the first room-temperature, compact, continuous terahertz radiation source, and it’s six times more efficient than previous systems.
... [read more]
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155.
| Accelerating adoption of GaN substrates for LED manufacture
Compound Semiconductor Magazine - June 1, 2014
COMMERCIALISATION of the GaN LED can be traced back to the development of p-type doping of this wide bandgap semiconductor in the early 1990s. Since then, the performance of this device has improved exponentially, enabling it to progress from use in the backlighting of mobile screens to providing a source for solid-state lighting. However, although LED lighting is now commonplace, its cost-performance profi le has a long way to go untill the incumbent vacuum-tubebased lighting technologies will cease to dominate. One of today’s key bottlenecks is the requirement to use a ‘non-native’ substrate. A new substrate option that has attracted a signifi cant amount of attention is ZnO, which not only has the same crystal structure as GaN, but also very similar lattice parameters and comparable thermal expansion coefficients. ... [read more]
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156.
| Razeghi Authors Technical Article in International Society for Optics and Photonics (SPIE)
EECS Newsroom - January 10, 2014
Razeghi1-oct3 2Manijeh Razeghi, Walter P. Murphy Professor, Director, Center for Quantum Devices (CQD) wrote a featured technical article, titled, "Quantum Cascade Lasers for IR and THz Spectroscopy," that was published December 16, 2013, on the International Society for Optics and Photonics (SPIE) website for her recent research on demonstrating increased power, spectral coverage, and tunability of quantum cascade lasers.
Prof. Razeghi's recent publication, focuses on how developing quantum cascade lasers (QCLs) with the highest power, efficiency, and tunability. Unlike traditional diode lasers, the QCL has a series of quantum wells, which split the usual electron bands into subbands. The QCL emits over several intersubband transitions in this structure. Her CQD team can engineer its optical response using quantum size effects, to achieve a highly variable emitting wavelength based on nanometer-scale control of the quantum well thickness. They demonstrated room-temperature QCLs covering both the 3–16μm and 65–300μm wavelength ranges using an indium phosphide (InP) material system. ... [read more]
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157.
| Quantum cascade lasers for IR and THz spectroscopy
SPIE Newsroom - December 22, 2013
Terahertz spectroscopy is widely used for chemical detection, and has applications in quality control for manufacturing, security screening, and astronomy. Most chemicals absorb in the mid-IR and THz spectral regions, which cover a wavelength range of 3–300 microns. During our research1 we developed quantum cascade lasers (QCLs) with the highest power, efficiency, and tunability. Unlike traditional diode lasers, the QCL has a series of quantum wells, which split the usual electron bands into subbands. The QCL emits over several intersubband transitions in this structure. We can engineer its optical response using quantum size effects, to achieve a highly variable emitting wavelength based on nanometer-scale control of the quantum well thickness. We demonstrated room-temperature QCLs covering both the 3–16μm and 65–300μm wavelength ranges. ... [read more]
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158.
| Researchers Develop World’s Highest Quantum Efficiency UV Photodetectors
McCormick Press Release - December 3, 2013
Manijeh Razeghi, Walter P. Murphy Professor of Electrical Engineering and Computer Science at McCormick, and her group have brought this AlxGa1-xN-based dream device closer to reality by developing a compact photodetector with the world’s highest quantum efficiency. This was achieved by refining the low-pressure metal-organic chemical-vapor-deposition growth as well as the UV photodetector p-i-n structure. A paper describing the results, “AlxGa1-xN-Based Back-Illuminated Solar-Blind Photodetectors with External Quantum Efficiency of 89%,†was published November 5 in the journal Applied Physics Letters.
Although sapphire is the most common choice for back-illuminated devices, researchers also developed alternative low-cost UV photodetectors grown on silicon substrate. Razeghi’s group used a novel maskless Lateral Epitaxial Overgrowth (LEO) technique for the growth of a high-quality aluminum nitride (AlN) template layer on silicon substrate. Following the template growth, a p-i-n structure is grown and processed. This low-cost approach eventually led to the world’s first successful implementation of UV-PD structure grown on a silicon substrate. A paper describing the findings, “AlxGa1-xN-Based Solar-Blind Photodetector Based on Lateral Epitaxial Overgrowth of AlN on Si Substrate,†was published October 30 in the journal Applied Physics Letters. ... [read more]
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159.
| CQD Research Highlighted on the Cover
Physica Status Solidi C - October 14, 2013
Self-forming, vertically-aligned, arrays of black-body-like ZnO moth-eye nanostructures were grown on Si(111), c-Al2O3, ZnO and high manganese austenitic steel substrates using Pulsed Laser Deposition. X-ray diffraction (XRD) revealed the nanostructures to be well-crystallised wurtzite ZnO with strong preferential c-axis crystallographic orientation along the growth direction for all the substrates. Cathodoluminescence (CL) studies revealed emission characteristic of the ZnO near band edge for all substrates. Such moth-eye nanostructures have a graded effective refractive index and exhibit black-body characteristics. Coatings with these features may offer improvements in photovoltaic and LED performance. Moreover, since ZnO nanostructures can be grown readily on a wide range of substrates it is suggested that such an approach could facilitate growth of GaN-based devices on mismatched and/or technologically important substrates, which may have been inaccessible till present. ... [read more]
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160.
| SOLID-STATE DEEP UV EMITTERS/DETECTORS: Zinc oxide moves further into the ultraviolet
Laser Focus World - October 10, 2013
Zinc oxide (ZnO) is a remarkable, multifunctional semiconducting material with a direct, wide bandgap energy (Eg ~ 3.4 eV), intrinsically high transparency over the whole visible range, and a resistivity that can be tuned from semi-insulating right through to semi-metallic by doping. In photovoltaics, ZnO is currently displacing indium tin oxide for use as a transparent conducting electrical contact due to recent improvements in conductivity obtainable with aluminium-doped ZnO, combined with processing, cost, and toxicity advantages. Alloys of ZnO with magnesium (MgxZn1-xO) have been explored as an alternative to (Al)GaN for UV LED applications. For fabricating (Mg)ZnO-based solar-blind photodetectors, Mg content should be at least 45%, but many studies have found that phase segregation of rock-salt phase MgO appears when Mg content is over 36 at %. Recently, however, single-phase wurtzite layers with Mg concentrations over 49 at % were prepared through strain engineering at the substrate interface by means of buffer layers (ZnO and strontium tin oxide—SrTiO3—or bulk ZnO substrates). ... [read more]
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161.
| Northwestern Researchers Develop Compact, High-Power Terahertz Source at Room Temperature
News from McCormick - October 3, 2013
Terahertz (THz) radiation — radiation in the wavelength range of 30 to 300 microns — is gaining attention due to its applications in security screening, medical and industrial imaging, agricultural inspection, astronomical research, and other areas. Traditional methods of generating terahertz radiation, however, usually involve large and expensive instruments, some of which also require cryogenic cooling. A compact terahertz source — similar to the laser diode found in a DVD player —operating at room temperature with high power has been a dream device in the terahertz community for decades. ... [read more]
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162.
| Stress-reduced solar-blind AlGaN-based FPA is crack-free
Laser Focus World, Vol. 49, No. 4, p. 14 - April 30, 2013
Focal-plane arrays (FOAs) that operate in the solar-blind spectral region (created by the absorption of light below 290 nm by atmospheric ozone)have uses in covert non-line-of-sight other forms of free space communications as well as UV spectroscopy, flame detection,and many other applications. With their extremely high rejection of the non-solar-blind spectrum , aluminum gallium nitride (AlGaN) -based structures are potentially excellent photodetecting candidates for solar blind FPAs. However this type of structures is difficult to fabricate without the formation of cracks. ... [read more]
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163.
| Imager combines SWIR and MWIR sensitivity
Laser Focus World, Vol. 49, No. 2, p. 24-25 - February 27, 2013
Manijeh Razeghi and her group at Northwestern University have created High performance infrared (IR) image that combines detection in both the shortwave and midwave IR(SWIR and MWIR) in one device-a quality particularly valuable for tracking and reconnaissance. The device is based on a III-V semiconductor-based type-II indium arsenide/gallium antimonide (InAs/GaSb) superviously had only been implemented for MWIR and longwave IR (LWIR). Each pixel is made of an MWIR single heterodiode grown on top of a p-i-n SWIR homodiode, all fabricated on a GaSb substrate, which is subsequently removed for backside illumination (meaning the SWIR layer is on top). Crucially, the residual InAsSb etch-stop layer is also removed, using a citric-acid-based solution that etches away a specially inserted GaSb layer, eliminating the problem of the 4 µm InAsSb absorption-band edge. The prototype focal-plane array (FPA) has 320 256 pixels. ... [read more]
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164.
| Northwestern tunes mid-infrared QCLs
SPIE Photonics West Show Daily, p. 29 - February 6, 2013
The ongoing challenge of developing short-wavelength QCLs were described by Neelanjan Bandyopad hyay of Northwestern University in an OPTO Session on the topic. “Wave-lengths of 3 to 3.5 microns are important for several different spectroscopy applications, because it coincides with many hydrocarbon absorbtion bands,†he said. Of the candidate semiconductor system, InGaAs-InAlAs on InP is the best choice on balance for short wavelength QCLs according to Northwestern research. Using it has allowed the development of the first room-temprature continuous wave QCLs in the target wavelength band, although the same system can additionally cover the entire 3-16 micron range under appropriate conditions. Daylight Solutions has demonstrated a broadly-tunable high-resolution CW laser based on its QC devices. “Broad tuning capability allows the identification of multiple chemical species in spectroscopy applications, while narrow linewidth facilitates the high spectral resolution that spectroscopy requires, “commented Leigh Bromely. The company’s external-cavity system, called ECqcl, uses a grating to tune the QCL output and control the tuning performance, and a unique cavity geometry that enforces one mode during operation. ... [read more]
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165.
| Light or no light-this new infrared camera captures images
Medill Reports-Chicago / Medill News Service - January 29, 2013
The center has developed detectors that are a complex quantum structure. The devices are expected to be valuable for military, medical and civilian purposes.
http://news.medill.northwestern.edu/chicago/news.aspx?id=214663
... [read more]
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166.
| Researchers Develop Integrated Dual-mode Active and Passive Infrared Camera
R&D Magazine - January 16, 2013
High-performance infrared cameras are crucial for civilian and military applications such as night-vision goggles and search-and-rescue operations. Existing cameras usually fall into one of two types: active cameras, which use an invisible infrared source to illuminate the scene, usually in the near or short-wavelength infrared; and passive cameras, which detect the thermal radiation given off by a warm object, typically in the mid- or long-wavelength infrared, without the need for any illumination. Both camera types have advantages and disadvantages in the field.
Read more at http://www.rdmag.com/news/2013/01/researchers-develop-integrated-dual-mode-active-and-passive-infrared-camera?et_cid=3044524&et_rid=54751184&linkid=http%3a%2f%2fwww.rdmag.com%2fnews%2f2013%2f01%2fresearchers-develop-integrated-dual-mode-active-and-passive-infrared-camera ... [read more]
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167.
| Researchers Develop Integrated Dual-mode Active and Passive Infrared Camera
News from McCormick - January 14, 2013
In a move that may change the way we look a two-color imaging, researchers at the Northwestern University’s Center for Quantum Devices have now found a way to integrate active and passive infrared imaging capability into a single chip. This opens the way to lighter and simpler dual-mode active/passive cameras with lower power dissipation.
A paper about the findings, “Active and Passive Infrared Imager Based on Short-Wave and Mid-Wave Type-II Superlattice Dual-Band Detectors,†was published January 1 in the journal Optic Letters. The work was led by Manijeh Razeghi, Walter P. Murphy Professor of Electrical Engineering and Computer Science in Northwestern’s McCormick School of Engineering and Applied Science.
The researchers achieved this feat by engineering the quantum properties of novel semiconductor materials called the indium arsenide/gallium antimonide (InAs/GaSb) type-II superlattices. Researchers at the center have been pioneering the development of type-II superlattices as a superior replacement of aging mercury-cadmium-telluride (HgCdTe) infrared camera technology in terms of both performance and cost.
Using the unique band-structure engineering capabilities of type-II superlattices, they have developed a new structure incorporating two different superlattices with different layer spacings, thus enabling detection with a cutoff wavelength of either 2.2µm (active mode) or 4.5µm (passive mode). This new device can simply switch from passive to active mode by a very small change in bias.
The work was funded by the Defense Advanced Research Projects Agency.
... [read more]
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168.
| Lasers improved for standoff sensing
Photonics Spectra - November 1, 2012
A new resonator design that controls both wavelength and beam quality enables the purest, brightest and most powerful beams ever from a single-mode infrared quantum cascade laser. Manijeh Razeghi, the Walter P. Murphy Professor of Electrical Engineering and Computer Science at Northwestern University’s McCormick School of Engineering and Applied Sciences, and colleagues developed the resonator using a new type of distributed feedback mechanism called B-DFB, a simple diffractive feedback in an angled laser cavity. The work improves the accuracy of the devices, critical for boosting the standoff detection of gas, explosives or other hazardous materials to even greater distances.
The findings appeared in Applied Physics Letters (doi: 10.1063/1.4747447). ... [read more]
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169.
| 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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170.
| 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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171.
| 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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172.
| 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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173.
| 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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174.
| 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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175.
| 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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Address: Center for Quantum Devices; 2220 Campus Drive RM 4051; Evanston, IL 60208-0893
Phone: (847) 491-7251
Email: razeghi@northwestern.edu