Taking Steps Toward Practical THz Technology

The potential for terahertz waves is enormous for imaging and communications applications—if practical semiconductor THz detectors and generators can be developed.

Jan 4, 2016Jack Browne | Microwaves and RF

http://mwrf.com/mixed-signal-semiconductors/taking-steps-toward-practical-thz-technology

As “lower-frequency” applications, such as wireless communications, continue to consume bandwidth, researchers of imaging systems look beyond even the millimeter-wave range for available spectrum. For many applications, including materials research, medical diagnostics, and homeland-security systems, terahertz (THz) technology offers great promise. Located in that mysterious part of the electromagnetic (EM) spectrum where millimeter-wave EM energy makes the transition to infrared (IR) optical energy, THz imaging can provide greater focus and control than x-ray radiation.

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Known as the “THz gap,” this band of the EM spectrum between about 300 and 3000 GHz (0.3 to 3 THz) contains signal wavelengths that are particularly useful for detecting dielectric differences in materials. It can be applied to a wide range of applications, from early detection of tooth decay to detection of hidden weapons and explosives. THz technology may even support high-data-rate, short-range wireless communications one day (see “Is Terahertz Li-Fi in Your Future?"). One key to realizing this promise will be the practical fabrication of semiconductor devices that can generate energy at THz frequencies. 

Much research has been conducted on this portion of the EM spectrum due to the versatility of these small-wavelength electro-optical signals for material analysis and medical diagnostic applications, including for early detection of cancer (Fig. 1). A great deal of progress has been made in the development of passive components, such as antennas, needed for THz systems through the application of microelectromechanical-systems (MEMS) technology and small-wavelength circuit transmission-line techniques like substrate-integrated-waveguide (SIW) technology.

1. THz technology offers great promise in medical diagnostics, including for early detection of cancers. (Courtesy of the University of Leeds)

THz Research

Still, lots of work must be done in the areas of generating and detecting electro-optical THz energy. The trend of decreasing power with increasing frequency that’s common to the millimeter-wave EM portion of the frequency spectrum continues into the THz range, with signal power hard to come by at THz frequencies.

Organizations such as the University of Leeds (Leeds, UK) and the Rensselaer Polytechnic Institute (Troy, N.Y.) and its RPI Center for THz Research have devoted much effort to the study of THz technologies and the development of practical semiconductor solutions for the generation of THz energy. Device developers for THz frequencies typically look to high-speed switching semiconductors, such as Impatt diodes, based on semiconductor substrates long associated with high-frequency analog and high-speed digital circuitry, including gallium arsenide (GaAs) and indium phosphide (InP).

In contrast to X-rays, researchers at RPI, with numerous patents on THz generation and detection, refer to THz energy as T-rays. With funding from a diverse group of investors, including the National Science Foundation, the U.S. Army Research Laboratory (ARL), and the Defense Advanced Research Projects Agency (DARPA), RPI’s research focuses on generating, measuring, and recording THz waves.

THz signal generation has included exploration of plasma-wave excitation in submicron field-effect transistors (FETs), including those based on GaAs substrates. The goal is to allow the THz laboratory to develop tunable, solid-state THz devices that will make many of the potential applications for THz technology possible and practical.

Not Out of GaAs

Sources of THz energy are not plentiful, although some suppliers of millimeter-wave components and equipment also extend their engineering efforts into the THz range. They include Insight Product Co. with THz frequency synthesizers and TeraSense with Impatt-diode THz generators (Fig. 2). Although solid-state devices for generation of THz energy are limited in availability, a number of firms offer commercial THz-based test and diagnostic equipment.

2. Many currently available THz sources are based on discrete semiconductor diodes, such as this Impatt-diode THz generator. (Courtesy of TeraSense)

For example, TeraView Ltd. developed three-dimensional (3D) THz-pulsed-imaging (TPI) technology that operates at room temperature. Products such as the firm’s TPS Spectra 3000 use high-speed lasers along with photoconductive semiconductor switches to generate and detect THz pulses without need of superconductors or cryogenic liquids to high-speed/high-frequency operation. A femtosecond laser operating at a wavelength of 800 nm and 100-fs pulse widths excites GaAs semiconductor substrate material to generate THz photon energy. Detection of the photon energy is performed by another GaAs semiconductor device excited by the same laser pulses.

Systems such as the TPS Spectra 3000 can measure the amplitude and phase of THz signals independently, to determine the absorption and refractive index of different materials in order to calculate the complex permittivity of those materials. This capability has clear benefits for materials analysis, such as analysis of semiconductor substrates and printed-circuit-board (PCB) laminates. However, it can also be used to find small defects in materials, like those mentioned earlier.

In addition, Advantest offers a number of THz imaging systems with coverage to 7 THz. The firm’s model TAS7400SU, for example, is a wideband system capable of operating from 0.5 to 7.0 THz. It generates and detects THz radiation, holding a sample for analysis within a sealed chamber. The system works with an external personal computer (PC) for control and data analysis. Two versions are available, each handling different operating temperature ranges (within the sample chamber): –10 to +80°C and +25 to +300°C. 

Zomega Terahertz Corp. enters the fray with a number of THz-based diagnostic tools, including its compact Mini-Z time-domain spectrometer. The spectroscopic material measurement system is compact enough to be transported to any research or industrial site for nondestructive analysis of samples. It’s designed to fit within small equipment cases about the size of a notebook computer. The firm offers standard and high-speed models for different measurement requirements, bringing portability to high-precision THz analysis.

Many THz test and diagnostic systems employ discrete devices rather than ICs. Wider application of cost-effective THz technology will depend on the development of more integrated THz transceiver options. Use of nanoscale fabrication methodologies with existing semiconductor technologies, such as GaAs FET and silicon biCMOS processes, could help realize the small circuit dimensions required for THz wavelengths.

As this technology’s potential becomes more apparent for applications in the medical-diagnostics and materials-analysis fields, among others, demand will take off. Strong efforts from research organizations around the world will continue to improve integrated THz device solutions, creating a more practical technology that’s destined to become widespread.

Seven New Tools That Can Stop a Bomb in a Backpack

 

A researcher straps a bomb-sniffing honey bee into a custom-designed harness before a training session sniffing out explosives.

http://www.cnbc.com/id/100665014

The resources deployed since 9/11 to stop terrorist attacks have worked on a variety of levels—better human intelligence, additional cameras, more electronic snooping, and more alert citizens. But part of ending the kind of mayhem that happened at the Boston Marathon last Monday will involve better high-tech systems for detecting explosives.

Despite billions spent every year by the Pentagon's Joint Improvised Explosive Device Defeat Organization to develop better bomb detection, when it comes to sensitivity in ferreting out bomb-making material, there's still nothing better than well-trained dogs, say experts. But a number of companies are trying to do better, since people's best friend comes with several disadvantages: they get tired, become distracted, need to eat and sleep regularly, and suspects or suspicious packages have to be within range of a dog's nose.

The gains possible through easier and cheaper bomb detection go beyond U.S. borders.—unexploded landmines, for example, kill 15,000 to 20,000 people a year, according to the United Nations. There's also big money involved, with millions in government contracts up for grabs for companies that develop the next generation of anti-explosives detection systems.

All of that makes bomb detection a growth industry, with more resources likely coming its way since last week. Here are seven new tools and technologies that could stop the next terrorist with a bomb in a backpack.

1. Laser scanners: Remote laser scanners are designed to detect explosives from dozens of yards away. Currently used on the battlefield to identify improvised explosive devices, these work by directing pulses of light at suspicious objects or areas and then reading the resulting vibrations—explosives emit unique patterns. Researchers at Oak Ridge National Laboratory say they're developing a laser-based device that can detect explosives residues from up to a football field away. It will be ready for commercial development within one to two years, they say.

2. Fluorescent explosives detectors: These use "amplifying fluorescence polymers" —which go dim in the presence of explosives because the explosives bind with the polymers—to indicate the presence of bomb materials like TNT in the air. The company FLIR Systems makes handheld machines weighing 2.5 pounds that provide explosives detection levels similar to what a dog can offer, according to the company. They're already used by U.S. troops, but the unit has to get close to the target or suspect to detect the threat.

3. Terahertz (THz) spectroscopy equipment: THz detectors, being developed by researchers at Rensselaer Polytechnic Institute and NASA's Jet Propulsion Laboratory, can be pointed at suspicious objects or people from 10 or more meters away and send a short pulse of harmless radiation toward the suspicious material. The detector uses the result of the interaction between the radiation and the material to identify the atomic "signature" present. This is then matched against a library of signatures for explosives. One developer of the technology says a THz detector is so sensitive that tiny detectors could be mounted above the front doors of an airport to identify anyone entering who has even a trace amount of explosives on their clothes—likely for anyone making and transporting bombs.

Ingrid Wilke's terahertz (THz) and ultra-fast Spectroscopy lab at Rensselaer

http://www.rpi.edu/terahertz/res_time_ultra_spectro.htm

Terahertz Spectroscopy: Time-domain and
Ultra-fast Spectroscopy

Overview:
Ingrid Wilke's terahertz (THz) and ultra-fast Spectroscopy lab is focused on biological and medical applications of time-domain THz methods; applications of time-domain THz methods in accelerator physics; single-shot femtosecond electron beam bunch length measurements; and dielectric and superconducting THz properties of transition metal oxide thin films.

In the last decade time-domain terahertz transmission spectroscopy (TDTTS) has become a powerful method for studying properties of various materials from dielectrics to semiconductors and superconductors. TDTTS operates with sub-picosecond pulses of electromagnetic radiation, which in the frequency domain implies the coverage of a very broad range spanning from tens of gigahertz to a few terahertz. Thus, explains Wilke, TTDTS bridges a large frequency gap between microwave and conventional infrared spectroscopy.

Technical Description:
A time-domain THz-transmission spectrometer is typically powered by a femtosecond Ti:sapphire laser and operates according to the pump-probe scheme. A schematic of the experimental arrangements is displayed in Fig. 1. The pump-probe principle is characterized by the splitting of the initial Ti:sapphire laser beam into two parts – the pump beam and the probe beam. The pump beam hits an emitter, which in response to the optical pulse releases a sub-picosecond pulse of THz-radiation. The probe beam gates the detector whose response is proportional to the amplitude and the sign of the electric field of the THz-pulse. By varying the delay between pump and probe pulses the whole time profile of the THz-pulse is traced. The complex transmittance of a sample is then placed in the focus of the THz-beam and given as the ratio of the Fourier transforms of a THz-pulse transmitted through the sample and a reference, for example a freely propagating THz-pulse.

Wilke's lab employs time-domain Thz-spectroscopy to investigate the electro-magnetic properties – electrical conductivity, dielectric properties – of thin films and bulk materials. A recent focus of the lab's research has been the investigation of superconducting thin films. TDTTS measurements of superconducting thin films are motivated by a basic understanding of quasi-particle excitations and pairing mechanisms as well as an assessment of the performance of high-temperature superconductors in passive electronic devices operating at microwave and THz-frequencies.

Fig. 1

Relativistic electron beam diagnostics
Time-domain THz methods are also a unique new method to measure the length and shape of single relativistic electron bunches in linear accelerators. Accelerators employed in next generation TeV linear electron-positron colliders for high energy physics, or used as drivers for new femtosecond X-ray free electron lasers (FELs), require dense relativistic electron bunches with bunch lengths shorter than a picosecond. Precise measurements of the electron bunch length and its longitudinal charge distribution are necessary to monitor the preservation of the beam quality while the electron bunch train travels through the beam pipe, as well as to tune and to operate a linear collider or a FEL (Fig.2).

Fig. 2. Experimental arrangements for electron bunch length measurements by electro-optic sampling with chirped optical pulses. The electron bunch length is measured by using an electro-optic crystal of ZnTe placed inside the vacuum pipe at the entrance of the undulator. The shaded parts indicate the vacuum housing of the electron beam.

Ultra-fast spectroscopy
A new area of research underway in Wilke's lab is the interaction of femtosecond optical laser pulses with biological cells, in particular the generation of pores in the cell membrane as well as the basic understanding of this process. Femtosecond optoporation offers great potential for targeted transfection of cells with high transfection efficiency, opening up possible applications in drug delivery and genetic engineering fields.

Contact Information:
Ingrid WilkeAssistant Professor of Physics
Rensselaer Polytechnic Institute
110 8th Street
Troy, NY 12180-3590

(518) 276-6318
wilkei@rpi.edu

Scientists at Rensselaer Polytechnic Institute employ Nanowiggles: graphene nanomaterials with 'tunable functionality in electronics'

Troy, N.Y. – Electronics are getting smaller and smaller, flirting with new devices at the atomic scale. However, many scientists predict that the shrinking of our technology is reaching an end. Without an alternative to silicon-based technologies, the miniaturization of our electronics will stop. One promising alternative is graphene - the thinnest material known to man. Pure graphene is not a semiconductor, but it can be altered to display exceptional electrical behavior. Finding the best graphene-based nanomaterials could usher in a new era of nanoelectronics, optics, and spintronics (an emerging technology that uses the spin of electrons to store and process information in exceptionally small electronics).

Scientists at Rensselaer Polytechnic Institute have used the capabilities of one of the world's most powerful university-based supercomputers, the Rensselaer Center for Nanotechnology Innovations (CCNI), to uncover the properties of a promising form of graphene, known as graphene nanowiggles. What they found was that graphitic nanoribbons can be segmented into several different surface structures called nanowiggles. Each of these structures produces highly different magnetic and conductive properties. The findings provide a blueprint that scientists can use to literally pick and choose a graphene nanostructure that is tuned and customized for a different task or device. The work provides an important base of knowledge on these highly useful nanomaterials.

The findings were published in the journal Physical Review Letters in a paper titled "Emergence of Atypical Properties in Assembled Graphene Nanoribbons."

"Graphene nanomaterials have plenty of nice properties, but to date it has been very difficult to build defect-free graphene nanostructures. So these hard-to-reproduce nanostructures created a near insurmountable barrier between innovation and the market," said Vincent Meunier, the Gail and Jeffrey L. Kodosky '70 Constellation Professor of Physics, Information Technology, and Entrepreneurship at Rensselaer. "The advantage of graphene nanowiggles is that they can easily and quickly be produced very long and clean." Nanowiggles were only recently discovered by a group led by scientists at EMPA, Switzerland. These particular nanoribbons are formed using a bottom-up approach, since they are chemically assembled atom by atom. This represents a very different approach to the standard graphene material design process that takes an existing material and attempts to cut it into a new structure. The process often creates a material that is not perfectly straight, but has small zigzags on its edges.

Meunier and his research team saw the potential of this new material. The nanowiggles could be easily manufactured and modified to display exceptional electrical conductive properties. Meunier and his team immediately set to work to dissect the nanowiggles to better understand possible future applications.

"What we found in our analysis of the nanowiggles' properties was even more surprising than previously thought," Meunier said.

The scientists used computational analysis to study several different nanowiggle structures. The structures are named based on the shape of their edges and include armchair, armchair/zigzag, zigzag, and zigzag/armchair. All of the nanoribbon-edge structures have a wiggly appearance like a caterpillar inching across a leaf. Meunier named the four structures nanowiggles and each wiggle produced exceptionally different properties.

They found that the different nanowiggles produced highly varied band gaps. A band gap determines the levels of electrical conductivity of a solid material. They also found that different nanowiggles exhibited up to five highly varied magnetic properties. With this knowledge, scientists will be able to tune the bandgap and magnetic properties of a nanostructure based on their application, according to Meunier.

Meunier would like the research to inform the design of new and better devices. "We have created a roadmap that can allow for nanomaterials to be easily built and customized for applications from photovoltaics to semiconductors and, importantly, spintronics," he said.

By using CCNI, Meunier was able to complete these sophisticated calculations in a few months.

"Without CCNI, these calculations would still be continuing a year later and we would not yet have made this exciting discovery. Clearly this research is an excellent example illustrating the key role of CCNI in predictive fundamental science," he said.

Graphene Foam Sensors Cheaply Detect Trace Particles in Air Ten Times Better Than Current Tech

Military //http://www.popsci.com.au/technology/military/graphene-foam-sensors-cheaply-detect-trace-particles-in-air-ten-times-better-than-current-tech

Nanotechnology as a discipline is bleeding-edge cool, but so often we hear more about its amazing potential than its practical application. So it's always refreshing to catch wind of a story like this: Researchers at Rensselaer Polytechnic Institute in New York have developed and demonstrated a small, relatively inexpensive, and reusable sensor made of graphene foam that far outperforms commercial gas sensors on the market today and could lead to better explosives detectors and environmental sensors in the very near future.

The new sensor dispenses with a lot of the limitations that have been holding back sensors in this space. In the last several years, many strides have been made in the science of manipulating nanostructures to be excellent detectors of very fine trace elements of chemicals on the air. But these sensors, while great in theory, are impractical in actual service.
Current sensor designs are complex, often relying on an individual nanostructure that must be carefully manipulated and even more carefully analysed. They are often not reusable and must be deployed at specific temperatures or pressures, making a handheld sensor device unreliable, very expensive, and impossible to use repeatedly.
Enter graphene foam. The new postage-stamp-sized sensor developed at RPI involves growing graphene - one-atom-thick layers of carbon - on a structure of nickel foam. Removing that nickel foam leaves behind a structure of foam-like graphene with unique electrical properties that can be tuned to the task of sensing.
When exposed to air, particles absorb to the foam's surface. And each of these particles affects the graphene foam in a different way, slightly modifying its electrical resistance. Run a current through it, and a measurement of the change in resistance tells you what's sticking to the foam. Moreover, by running a roughly 100-milliampere current through the foam the RPI team found they could cause the particles to desorb - that is, they unattached themselves from the sensor, cleansing it so it can be used again and again.
Tweaked to detect ammonia (a key ingredient in homemade explosive ammonium nitrate - think: fertiliser bombs), the graphene foam sensor managed to detect the offending particle at just 1,000 parts per million in just five to 10 minutes - making it ten times more effective than the best detectors on the market today. A second demo involving nitrogen dioxide (another trace element given off by explosives as they degrade) showed nearly identical results - effective at 100 parts per million, or ten times better than current commercial sensors.
Given that graphene foam is fairly easy to handle and manipulate given its larger size and room-temperature-ready performance, that's pretty remarkable. It also drastically lowers the barrier to a practical handheld devices for atmospheric sensing

Researching graphene nanoelectronics for a post-silicon world

MY POST: ALTHOUGH THIS ARTICLE TALKS OF THE CHANGES GRAPHENE WILL HAVE IN THE WORLD OF COMPUTING, YOU CAN ANTICIPATE A SIMILAR IMPACT IN THE WORLD OF SCANNING TECHNOLOGY

http://www.physorg.com/news/2011-11-graphene-nanoelectronics-post-silicon-world.html
As new generations of computer chips continue to shrink in size, so do the copper pathways that transport electricity and information around the labyrinth of transistors and components. When these pathways—called interconnects—grow smaller, they become less efficient, consume more power, and are more prone to permanent failure.
To overcome this hurdle, industry and academia are vigorously researching new candidates to succeed traditional copper as the material of choice for interconnects on computer chips. One promising candidate is graphene, an atom-thick sheet of carbon atoms arranged like a nanoscale chicken-wire fence. Prized by researchers for its unique properties, graphene is essentially a single layer of the graphite found commonly in our pencils or the charcoal we burn on our barbeques.
Led by Rensselaer Professor Saroj Nayak, a team of researchers discovered they could enhance the ability of graphene to transmit electricity by stacking several thin graphene ribbons on top of one another. The study, published in the journal ACS Nano, brings industry closer to realizing graphene nanoelectronics and naming graphene as the heir apparent to copper.
"Graphene shows enormous potential for use in interconnects, and stacking up graphene shows a viable way to mass produce these structures," said Nayak, a professor in the Department of Physics, Applied Physics, and Astronomy at Rensselaer. "Cooper's limitations are apparent, as increasingly smaller copper interconnects suffer from sluggish electron flows that results in hotter, less reliable devices. Our new study makes a case for the possibility that stacks of graphene ribbons could have what it takes to be used as interconnects in integrated circuits."
The study, based on large-scale quantum simulations, was conducted using the Rensselaer Computational Center for Nanotechnology Innovations (CCNI), one of the world's most powerful university-based supercomputers.


Copper interconnects suffer from a variety of unwanted problems, which grow more prominent as the size of the interconnects shrink. Electrons travel through the copper nanowires sluggishly and generate intense heat. As a result, the electrons "drag" atoms of copper around with them. These misplaced atoms increase the copper wire's electrical resistance, and degrade the wire's ability to transport electrons. This means fewer electrons are able to pass through the copper successfully, and any lingering electrons are expressed as heat. This heat can have negative effects on both a computer chip's speed and performance.
It is generally accepted that a quality replacement for traditional copper must be discovered and perfected in the next five to 10 years in order to further perpetuate Moore's Law—an industry mantra that states the number of transistors on a computer chip, and thus the chip's speed, should double every 18 to 24 months.
Nayak's recent work, published in the journal ACS Nano, is titled "Effect of Layer Stacking on the Electronic Structure of Graphene Nanoribbons." When cut into nanoribbons, graphene is known to exhibit a band gap—an energy gap between the valence and conduction bands—which is an unattractive property for interconnects. The new study shows that stacking the graphene nanoribbons on top of each other, however, could significantly shrink this band gap. The study may be viewed online at: http://dx.doi.org/10.1021/nn200941u
"The optimal thickness is a stack of four to six layers of graphene," said Neerav Kharche, first author of the study and a computational scientist at CCNI. "Stacking more layers beyond this thickness doesn't reduce the band gap any further."
The end destination, Nayak said, is to one day manufacture microprocessors—both the interconnects and the transistors—entirely out of graphene. This game-changing goal, called monolithic integration, would mean the end of the long era of copper interconnects and silicon transistors.
"Such an advance is likely still many years into the future, but it will certainly revolutionize the way nearly all computers and electronics are designed and manufactured," Nayak said.
Provided by Rensselaer Polytechnic Institute (news : web)

Rensselear Polytechnical Institute (RPI) and EMCORE Developing Handheld Terahertz (THz) Spectrometer (RPI)

MY NOTE: STOCK MESSAGE BOARD POSTER bucktailjig05, BROUGHT THIS VERY INTERESTING LINK AND INFORMATION TO MY ATTENTION. IT APPEARS THAT IN ADDITION TO THE HAND-HELD THz, SYSTEM BEING DEVELOPED BY ADVANCED PHOTONIX, (WHICH IS TO BE DELIVERED TO THE TSA), AND IN CONJUNCTION WITH CIA, SPINOFF IQT, THAT SIMILAR DETECTION SYSTEMS ARE ALSO BEING DEVELOPED FOR THE DEPARTMENT OF DEFENSE, BY RPI AND EMCORE. 
DIFFERENT TARGET APPLICATIONS OR MARKETS WOULD APPEAR TO BE ENVISIONED BUT YOU HAVE TO WONDER ABOUT HOW THEY ALL OVERLAP. I'VE ASKED FOR COMMENTARY AND HOPE TO SHARE WITH YOU, WHAT I AM ABLE TO FIND OUT.  

***UPDATE: AN UNNAMED (BUT RELIABLE SOURCE, AT A MAJOR UNIVERSITY), HAS ADVISED ME THAT:
Although this may be classified as a “security” device, it is not meant for personnel or baggage screening.
It is essentially a THz analog to some of the “first responder” devices that are out there (like http://www.ahurascientific.com/chemical-explosives-id/index.php).
It is meant to identify a substance that is found while in the field.  I do not believe that it will be able to do that identification through anything but a thin sheet of something (like a plastic).



http://www.acq.osd.mil/ncbdp/nm/pseag/capabilityareas/DA/HHTHz.html
The purpose of this project is to develop a handheld (less than 10 lbs) THz Spectrometer to detect and identify explosives. The identified signatures are then matched to the database within the system. This project has two performers, Rensselear Polytechnical Institute (RPI) and EMCORE. The two phase RPI project will develop a handheld THz explosive detector. Phase I was a 12-month effort to develop and test an optical THz fiber laser that weighs less than 10 lbs. After satisfactory completion of Phase I, Phase II has been funded to gather spectroscopy measurements and integrate all electronics into a lightweight handheld explosive detector. The Explosive Detection Equipment (EDE) Program has been concurrently testing the developed systems. At the end of Phase II, three prototype handheld spectrometers will be delivered, along with the design documents, to undergo full testing (lab and field). EMCORE is developing a second Handheld Spectrometer that differentiates from RPI in the techniques by which the system works; emphasizing Frequency Domain Spectrometry (FDS) instead RPI's Time Domain Spectrometry (TDS).

Requirements:

• Integrated Unit, Base Installation Protection Joint Capabilities Document (JCD), 13 July 2007
• Joint Urgent Operational Needs Statement CC-0255, 26 September 2007
• Improvised Explosive Device Defeat Initial Capabilities Document (ICD), 23 February 2006
• Portable Chemical, Biological, Radiological, Nuclear and High Explosive (CBRNE) / Weapons of Mass
• Destruction Detector, Navy Urgent Operational Needs Statement, 31 December 2006
• Integrated Base Defense Security System Capability Development Document (CDD), 17 February 2005
• Joint Service Explosive Ordnance Disposal ICD, 1 June 2005
• CBRNE Sense ICD, 8 June 2005

Accomplishments:

RPI:

• Developed and demonstrated a light weight THz optical system
• Performed spectroscopy measurements of explosives and created a database
• Integrated the optics and the database to produce an entire handheld system weighing less than 10 lbs

Emcore:

• Collected spectroscopy on explosives at Naval Explosive Ordnance Disposal Technology Division (NEODTD)
• Designed and built an inexpensive, portable, battery operated, high speed, THz spectrometer
• Integrated fiber-based optics with phase control ability
• Demonstrated both transmission and reflection measurement modalities

Key Dates / Milestones:

RPI:

• Deliver Ruggedized Prototypes: March 2011

Emcore:

• Deliver Prototype: January 2011
• Conduct T&E on Both Systems: April 2011

The information located on the project pages of the PSEAG website does not necessarily show endorsement from or the approval of the Department of Defense. All information pertaining to the PSEAG programs contained on this website are published for informational purposes only. 

Listening to terahertz electromagnetic waves

http://thznetwork.net/index.php/archives/1287                                                                                                           A technique for detecting short bursts of terahertz radiation through the use of laser plasma-induced acoustic waves should enable the detection of hazardous materials at a safe distance.
Terahertz (THz) electromagnetic waves have remarkable and unique abilities for imaging, chemical identification, and penetration of many optically opaque barriers. Photon energies at these frequencies are relatively small (meV), which means the radiation is non-ionizing and therefore considered biologically innocuous. With the growing list of applications and demand for THz technology, THz sources and detectors have improved significantly, creating opportunities for realizable commercial and national defense related devices.

Figure 1. Plasma acoustic wave enhancement when a THz pulse interacts with a bichromatic field-induced plasma. Free electrons have acquired a net drift velocity through the laser field that is either antiparallel, symmetric, or parallel to the applied THz field. The THz pulse is scanned in time relative to the plasma formation while the acoustic emission is monitored for each scenario. Curves are offset for clarity. arb: Arbitrary.
Despite its advantages, THz radiation also presents several challenges. First, absorption of THz waves in the atmosphere at habitable altitudes can be greater than 100dB/km due to fundamental vibrational and rotational resonant modes of water molecules that absorb the waves’ energy. In comparison, visible light is attenuated about 0.02dB/km. For this reason, THz radiation is only operated at either extremely short distances (several centimeters), or under dry nitrogen-purged laboratory environments. Second, with traditional measurement techniques, it is only possible to obtain THz wave information in the forward propagating direction, which is impractical for remote applications. Third, existing detection methods require either electro-optic crystals or electrodes at the point of detection, meaning they must be performed on a very local scale. Therefore, there is a need to use the powerful yet non-invasive material and vapor identification abilities of THz waves while extending the effective distances over which the technology can be used.

Figure 2. THz pulses retrieved through acoustic detection and traditional methods using an electro-optic crystal. a.u.: Arbitrary units.
Recently, we demonstrated that two intense optical beams focused into the air can generate intense broadband THz radiation at distances up to 30m and with pulse energies up to 250nJ through the photoionization process. While this is a step towards realizing remote THz sensing, obtaining information on the wave from these distances is still a problem. It is well known that when a laser plasma is formed through photoionization, it releases energy in the form of acoustic waves. After photoionization, the remaining portion of the laser pulse accelerates freed electrons inside the plasma. Collisions between hot electrons and their surrounding air molecules produce an increase in localized gas temperature that results in the release of a shock wave that quickly relaxes into a broadband acoustic pulse. What is less known is that THz wave information, on the picosecond time scale, can be encoded into these acoustic waves, making it possible to retrieve this information from any direction without electro-optic crystals, electrodes, or the penalty of high water vapor attenuation of the encoded signal.
To encode THz information into acoustic waves, it is first necessary to create asymmetric electron motion inside the plasma by introducing a second optical field at twice the frequency. By carefully selecting the phase between these two optical pulses, a dominant electron motion parallel or antiparallel to the laser pulse polarization can make the electron drift velocity asymmetric. Figure 1 shows the acoustic amplitude of the plasma as the THz pulse is scanned in time relative to the plasma formation for the three aforementioned scenarios of electron motion relative to the THz electric field.
When a pulse is introduced into each respective scenario for which the freed electrons have acquired antiparallel, symmetric, or parallel drift in relation to the THz field before the first collision event, electrons are either slightly accelerated, unaltered, or decelerated by the field, respectively. Taking the difference in acoustic emission for parallel and antiparallel scenarios eliminates acoustic enhancement contributed by electron kinetic energy transfer after the first collision event (for which electron trajectory is randomized and no longer coherent). The resulting information reveals this energy transfer, which is directly proportional to the field. Ultimately, this means we can recover a coherent waveform by ‘listening’ to the interaction between THz waves and an asymmetric laser-induced plasma. Figure 2 shows the pulse retrieved through acoustics and through traditional methods for comparison.
In conclusion, our acoustic technique uses the powerful capabilities of THz radiation for non-invasive imaging and chemical identification, and it uncovers new opportunities for overcoming some of the greatest limitations of THz wave technology. In the future, we hope to gain a deeper understanding of the collisional energy transfer process by imaging the photoacoustic shock wave using a gated, intensified, charge-coupled device that will allow us to visualize the evolution of the pressure waves under the influence of high-field THz radiation.
Benjamin Clough, Jingle Liu, X.-C. Zhang
Rensselaer Polytechnic Institute (RPI)
Source: SPIE.org.

Xi-Cheng Zhang of Rensselaer Receives Distinguished IEEE Award for Influential Terahertz Research

Xi-Cheng Zhang, the J. Erik Jonsson ’22 Distinguished Professor of Science and director of the Center for Terahertz Research at Rensselaer Polytechnic Institute, has received the William Streifer Scientific Achievement Award from the IEEE Photonic Society. The award honors Zhang for his exceptional contributions in the past 10 years to the field of lasers and electro-optics.
“Dr. Zhang’s work is literally changing the way in which we can see the world and all that it is made of,” said Rensselaer Acting Dean of Science David Spooner. “His research and development of terahertz technology has broken new ground in the field of photonics time and again and has implications for science, industry, law enforcement, and even counter-terrorism efforts. We are exceptionally proud of his many achievements.”
The award is given for a single, recent contribution to photonics that has greatly influenced the research community. Zhang was cited “for the exceptional contribution of terahertz air photonics, especially free-space coherent detection of ultra-broadband terahertz waves.”
Terahertz (THz) waves occupy a segment of the electromagnetic spectrum between the infrared and microwave bands. As such, they can be used for imaging and sensing in ways that are not possible with conventional technologies such as X-ray and microwave. Because THz radiation transmits through almost anything that is not metal or liquid, the waves can “see” through most materials that might be used to conceal explosives or other materials, such as packaging, corrugated cardboard, clothing, shoes, backpacks, and book bags. They are also safer than X-rays and microwaves for human tissue.
The vast potential of terahertz-based technology has been understood for years, but the development of practical applications of THz was greatly limited by something as simple as air. Ambient moisture in the air outside of a highly regulated lab environment blocks THz wave transmission. This made it nearly impossible to apply THz technology outside the controlled lab setting up until now.
Zhang’s development of THz air photonics has resulted in the discovery of several important THz techniques:

• THz Air-Biased-Coherent-Detection (THz ABCD). Instead of fighting with the properties of the air, the technology developed by Zhang works with it. This technique uses air and selected gases as the THz wave emitter. A focused optical pulse creates atmospheric plasma, which produces very strong and ultra-broadband THz waves.
• THz-Enhanced Acoustics (TEA) and THz-Enhanced Fluorescence (TEF). The development of remote, spectroscopic sensing technologies for THz waves are lagging behind important real-world needs such as the detection of explosives in airport baggage. Zhang and his students have developed THz-enhanced acoustic (TEA) and THz-enhanced fluorescence (TEF) techniques with standoff sensing capability. By “hearing” THz-enhanced acoustics (TEA), or “seeing” THz-enhanced-fluorescence (TEF), coherent detection of THz waves at standoff distance has been achieved.
• Control of THz Wave Polarization. Zhang and his team developed a unique method to harness THz wave polarization. The polarization of THz pulses emitted from a laser-generated air-plasma can be rotated by changing the relative delay between ultra-short two color (red and blue) pulses.

Zhang joined Rensselaer in 1992. He received his bachelor’s in physics from Peking University in China and both a master’s and doctoral degree in physics from Brown University. He is a fellow of the American Physics Society, the Institute of Electrical and Electronic Engineers, and the Optical Society of America. He is an NSF CAREER Award winner who has been featured in more than 80 magazines, 28 books and book chapters, and 300 journal papers. He holds 26 U.S. patents.
The Technology Review listed Zhang’s work in as one of “10 Emerging Technologies That Will Change World” in 2004. The History Channel and Discovery Channel have interviewed Prof. Zhang for their Modern Marvels and The Greatest Gadgetprograms. Zhang’s instrument development was also selected as one of the “Scientific American 50” in 2008.
More information of the Center for Terahertz Research can be found at http://thz.phys.rpi.edu/.

T-rays triumph over X-rays in bomb detection

MY NOTE: I'VE HAD A VIDEO RELATED TO THIS STORY ON THE BLOG FOR A FEW DAYS.  
http://www.punemirror.in/article/26/201103112011031101432792152d7a50c/Trays-triumph-over-Xrays-in-bomb-detection.html

New York: Benjamin Clough, a student of Rensselaer Polytechnic Institute in New York, has demonstrated a promising, cost-effective technique that employs sound waves for bomb detection, physorg .com has reported.

With his project, titled Terahertz Enhanced Acoustics, Clough has developed a method in which sensors using terahertz waves can penetrate packaging materials or clothing and identify the unique terahertz ‘fingerprints’ of many hidden materials. 

Terahertz waves, or T-rays, occupy a large segment of the electromagnetic spectrum between the infrared and microwave bands. Unlike X-rays and microwaves, T-rays pose no known health threat to humans.

Benjamin Clough

The problem
A major limitation of T-rays is that they work over short distances. Moisture in air absorbs them, weakening the signal and sensing capabilities.

This is not ideal for applications in bomb or hazardous material detection, where the human operator wants to be away from the potential threat.

The solution
Clough’s patent-pending solution to this problem is using sound waves to remotely ‘listen’ to terahertz signals from a distance.

Focusing two laser beams into air creates small bursts of plasma, which create terahertz pulses. Another pair of lasers is aimed near the target to create a second plasma for detecting the terahertz pulses after they have interacted with the material.

This detection plasma produces acoustic waves as it ionises the air. Using a sensitive microphone to ‘listen’ to the plasma, one can detect terahertz wave information embedded in these sound waves.

This audio information can be converted into digital data and instantly checked against a library of known terahertz fingerprints, to determine the chemical composition of the material.

Distance covered

So far, Clough has demonstrated the ability to use acoustics to identify the terahertz fingerprints from several metres away. He has separately demonstrated plasma acoustic detection from 11 metres, limited only by available lab space.

Along with the increased distance from the potentially hazardous material, an additional advantage is that his system does not require a direct line of sight to collect signals, as the microphone can still capture the audio information.

Rensselaer Spaces: The Terahertz Cleanroom

My Note: I enjoy getting a peak at the inside of the Rensselaer THz cleanroom, and thought some of you that had not seen this story, might too. 

by GABRIELLE DEMARCO on JANUARY 4, 2011

An optics quiz: What is between microwaves and infrared light on the electromagnetic spectrum? Something very special sits in that electromagnetic gap – terahertz wave radiation, or T-rays.

Welcome to the cleanroom of the Center for Terahertz Technology. Yes, that is actually me in the stunning cleanroom hat talking to researcher Jianming Dai. This post is part of a continued effort of The Approach to bring you into the sophisticated research spaces that are housed at Rensselaer, but few of us ever get the chance in poke around in. Except you might not want to poke around in this lab too much. A small amount of dust or one badly placed elbow could damage one of the hundreds of piece of optics equipment in the lab. You could also burn your retina if you look at one of the ultra powerful lasers the wrong way. Needless to say, I stepped around very lightly.

The cleanroom is just one of the laboratory facilities within the center. It is a very large space, which is solely dedicated to producing and studying T-rays, which have historically been very difficult to produce even in the lab. Those large grey curtains can be pulled across at various spots to block off different sections of the lab. There are several large optical tables that are resistant to vibration. This is important so that the laser beams used to generate T-rays hit the correct targets. On each table is an array of lasers, lenses, and mirrors that produce, shape, and direct the laser beam respectively to produce and manipulate the T-rays. Various spectrometers and oscilloscopes throughout the lab measure the properties of the light and voltage produced.

The team of researchers within the Center for Terahertz Technology are among the top terahertz scientists in the world. Their breakthroughs in developing T-ray emitters and detectors are providing researchers and companies around the world with important new technologies. Their research has even been used by NASA to study damage to the hulls of space shuttles.  

Why go to all this trouble and set up some many mirrors and lasers to produce these rays? Many materials are transparent to terahertz radiation. They also offer many advantages over conventional imaging and material detection techniques. Unlike x-rays, terahertz radiation is safe for human cells, which make them ideal for security checks and medical imaging. They also go further than x-rays by producing something akin to a material’s fingerprint or signature. The unique responses of different materials within the THz range provide information generally absent in optical, X-ray and NMR images. This fingerprinting of materials has important potential for use in uncovering explosive materials or even drugs without opening or even getting near a potentially dangerous object.

Learn more about the center here. Also, Check out this recent article on remote sensing using terahertz.

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Terahertz Trailblazing by Advanced Photonix (API) is the leading story/ trend of 2010

What an exciting year in the continuing emergence of THz, as a scientifically, and commercially viable technology! This blog, has also evolved from a "lark"  which was  put together by me,  simply to try to bring attention  and greater public awareness to this amazing virgin technology.  THz's development is increasing at a geometric pace, in private and public laboratories, while this blog now attracts, 50-100+ visitors from all over the world, each day because of the worldwide excitement for THz's development.

As I noted at the outset, in starting this blog, I am an unlikely candidate for such a role, because I have no real scientific, engineering, computer, or blogging experience. Many times, that lack of knowledge has shown through, but  I believe the quality of the blog, has improved over the last year, as reflected by a number of comments I have received both publically, and privately.

 So today, at year's end, and after a hundred posts,  I thought it would be fun to post my picks for the 5 top- trends, stories, and/or advances I observed here this year, albeit from a layman's perspective. (Please share your thoughts, comments and disagreements about my selections-Also please note, that it's no secret that I am a long-time investor in Advanced Photonix, (API) but I believe the selection of API, as this year's trailblazer for the development of THz, would be shared by most objective observers).

HERE ARE MY TOP 5 BLOG ARTICLES/TRENDS AND/ OR ADVANCES FOR 2010.

1. Advanced Photonix, starts and ends 2010, with multiple contracts, cutting-edge developments and is the clear leader in the commercial development of THz, heading into 2011.
On January 7th, 2010, this blog posted the first article of the new year announcing a 3 million dollar SBIR contract with the USAF, to develop a THz, quality control system for use on the F-35 fighter jet.

http://terahertztechnology.blogspot.com/2010/01/advanced-photonix-wins-3-million-dollar.html
The article for the first time,  also discussed the development of a hand-held scanner, to be used as a plug-in device for the T-Ray 4000, forecasting an application which would play a prominent role, in a series of later contract announcements.

On January 11th, 2010, Advanced Photonix unveiled it's  hand-held THz scanning application,  on Detroit Television as a candidate to address airport security issues highlighted by the efforts of Umar Farouk Abdulmut to use the chemical PETN, (which could not be detected either by backscatter or x-ray security devices at airports) to blow up an airplane.

http://terahertztechnology.blogspot.com/2010/01/advanced-photonix-featured-in-detroit.html

On June 30th, 2010, Advanced Photonix, announced that the THz contract for use on the F-35, had been finalized and noted the contract would provide the foundation for future systems, and revenue over the next decade. API also noted additional sales to NASA,  a radome scanning system to Hill AFB, and continuing pilot trial testing of the T-Ray 4000, on the factory floors of two  prospective  commercial users.

http://terahertztechnology.blogspot.com/2010/06/advanced-photonix-announces-major.html

On August 12th, 2010, Advanced Photonix announced the sale of the T-Ray 4000, to the C2RMF, at the Louvre for a variety of uses in art restoration.

http://terahertztechnology.blogspot.com/2010/08/advanced-photonix-sells-t-4000-to.html

On Novermber 5th, 2010, Advanced Photonix announced that the Transportation Security Administration, (TSA), had agreed to fund IQT, to contract with API, to develop a low cost anomaly device, in the form of a hand-held device or wand to be used for "multiple systems" intended to scan persons without the need for timely imaging or "pat-downs".

http://terahertztechnology.blogspot.com/2010/11/advanced-photonix-to-engineer-low-cost.html

The November 5th  contract announcement was followed in "quick succession", by contracts dated November 11th, and December 9th, the first with the Department of Homeland Security (DHS), and the second with NASA.

http://terahertztechnology.blogspot.com/2010/11/another-contract-win-for-advanced.html

http://terahertztechnology.blogspot.com/2010/12/picometrix-advanced-photonix-subsidary_98.html

Each of these contracts reflect divergent governmental agencies funding the development of smaller, more  powerful, THz units for use in diverse applications and areas, all making use of the T-Ray 4000, as the neuxus or starting point for development. One may reasonably surmise that the research being conducted will be synergistic and complementary, with each advance in one program leading to improvements in the others.


These contracts were followed  in the last few weeks by yet another announcement of a new  affilation with NASA, in computed tomoography at the Glenn Research facility.

http://terahertztechnology.blogspot.com/2010/12/terahertz-computed-tomography-studies.html

Year ends close leaves many of us in the API community awaiting news of the first commercial sale of the T-Ray 4000, to a  private, commercial OEM.  "Any day" is the unofficial word of when this will occur.

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2. Readers of this blog helped me select the number two  story of the year which was the announcement by Bridge12 that it awas awarded an SBIR  contract for development of the first commercial application of Dynamic Nuclear Polarization,  (DNP), which will have a number of uses for THz especially in the medical imaging area.  This was the most viewed story of the year.
http://terahertztechnology.blogspot.com/2010/12/bridge12-awarded-first-sbir-grant-for.html

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3.  Dr. Daniel  Mittleman shared his insights on this blog, helping to refute wide-spread blogging found on the net, claiming  that THz damages DNA.
http://terahertztechnology.blogspot.com/2010/12/dr-mittleman-at-rice-university.html
It's my number 3 story on this blog, having been picked up and rerun on the  well-known, Virtual Journal of Thz Science & Technology
http://thznetwork.net/index.php/archives/1140

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4. My pick for the single most interesting story of the year goes to the THz developments  at the Rensselaer institute.
http://terahertztechnology.blogspot.com/2010/07/someone-may-soon-be-able-to-tell-what.html

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5. For the investor I thought the news release regarding the affiliation of T-Ray Science and Teraview to be the 5th most significant story of the year.
http://terahertztechnology.blogspot.com/2010/07/t-ray-science-signs-sub-licensing.html

These are my picks for this year. Thanks for reading and please share your comments about the most significant story & your viewpoint.