New terahertz device could strengthen security

 

November 21, 2014

Northwestern University

We are all familiar with the security hassles that accompany air travel. Now a new type of security detection that uses terahertz radiation is looking to prove its promise. Researchers have developed a room temperature, compact, tunable terahertz source that could lead to advances in homeland security and space exploration. Able to detect explosives, chemical agents and dangerous biological substances from safe distances, devices using terahertz waves could make public spaces more secure than ever.

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We are all familiar with the hassles that accompany air travel. We shuffle through long lines, remove our shoes, and carry liquids in regulation-sized tubes. And even after all the effort, we still wonder if these procedures are making us any safer. Now a new type of security detection that uses terahertz radiation is looking to prove its promise. Able to detect explosives, chemical agents, and dangerous biological substances from safe distances, devices using terahertz waves could make public spaces more secure than ever.

But 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," said Manijeh Razeghi, Walter P. Murphy Professor of Electrical Engineering and Computer Science at Northwestern University's McCormick School of Engineering and Applied Science.

Director of Northwestern's Center for Quantum Devices, Razeghi and her team have been working to develop such a device. 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.

The device has applications in medical and deep space imaging as well as security screening.

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Story Source:

The above story is based on materials provided by Northwestern University. Note: Materials may be edited for content and length.

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Journal Reference:

1. Q. Y. Lu, S. Slivken, N. Bandyopadhyay, Y. Bai, M. Razeghi. Widely tunable room temperature semiconductor terahertz source. Applied Physics Letters, 2014; 105 (20): 201102 DOI: 10.1063/1.4902245

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Universal Hybrid Photodetector

 

Thu, 11/20/2014 - 9:55am

 

Leica Microsystems has introduced the Leica HyD SMD universal hybrid photodetector with characteristics for single-molecule detection, which allows precise measurement of concentration and observation of fast cellular processes. The photodetector combines the characteristics of the classic photomultiplier tube (PMT) with highly sensitive avalanche photodiodes, resulting in high sensivity and a large dynamic range combined with rapid detection speed and low dark noise. The photodetector is fully integrated into the spectral detection system of the Leica TCS SP8 confocal microscopy platform. An active cooling system comprised of built-in Peltier cooling and additional external cooling reduces the specified dark noise of the Leica HyD SMD, resulting in high-quality SMD data. The absence of detector afterpulsing give precise and reliable particle concentrations in FCS experiments, which short living dyes can be used to observe fast live-cell processes due to the fast instrument response time of the detector.

Leica Microsystems - www.leica-microsystems.com

 

What Are the Nitrogen Purity Specifications & Grades?

 

By John DeMerceau, eHow Contributor

-last updated April 17, 2014

99.998 percent pure zero grade nitrogen is used in research laboratories as well as in industry.

Nitrogen gas is available in several grades that represent different degrees of purity. Nitrogen that is used in welding contains the highest amount of impurities, whereas the gas used in research experiments is the purest. Typical impurities in nitrogen include oxygen, carbon dioxide and hydrocarbons as well as hydrogen gas and water. Even the purest scientific-grade nitrogen may contain trace amounts of these impurities.

Scientific or Research Grade

• Scientific or research-grade nitrogen is intended for use in scientific experiments where even a slight presence of other gases or water can skew results. The specifications for this grade of nitrogen gas allow for less than five parts per million of oxygen, less than one part per million of water, less than two parts per million of carbon monoxide and carbon dioxide and less than one part per million of hydrogen. Total hydrocarbons cannot exceed one part per million. Overall purity cannot be less than 99.9995 percent.

Ultra High Purity Grade

• Ultra high purity grade nitrogen is also usually used in scientific applications. No more than two parts per million of oxygen gas are permitted in this grade of nitrogen. Total hydrocarbons cannot exceed one-half of one part per million and water cannot exceed one part per million.

Zero Grade

• Zero grade nitrogen is the most commonly used of the higher grades of nitrogen gas. Its minimum purity is 99.998 percent and its total hydrocarbon content is from less than one-half of one part per million to one part per million, depending on the manufacturer and lot. Two parts per million of carbon monoxide and carbon dioxide and one part per million each of oxygen and hydrogen gas are acceptable.

Specialized Zero Grade Nitrogen

• CEM zero grade nitrogen and VOC zero grade nitrogen are special forms of zero nitrogen that meet U.S. Environmental Protection Agency standards for use in testing pollution levels. The CEM grade can contain up to one-half ppm each of carbon monoxide and oxygen gas, up to one part per million of carbon dioxide, up to four parts per million of water and up to one-tenth of a part per million each of noxious gases, sulfur dioxide and hydrocarbons. VOC zero grade nitrogen contains less than 0.05 part per million each of carbon monoxide and hydrocarbons and less than one-half of one part per million of carbon dioxide, water and oxygen gas.

Oxygen Free Grade

• Oxygen free nitrogen is intended for scientific and calibration requirements where the presence of oxygen will cause incorrect results. It refers to any nitrogen gas that is at least 99.998 percent pure and is certified as including no more than one-half of one part per million of oxygen gas.

Pre-Purified and High Pressure Grade

• Pre-purified nitrogen is at least 99.998 percent pure. It can contain up to five parts per million of water and oxygen gas. This grade of nitrogen is used in precision welding applications. High pressure grade nitrogen is nitrogen of at least 99.998 percent purity that is intended for use in industrial processes and equipment that require gas to be dispensed at 3,500 to 6,000 pounds per square inch of pressure.

Industrial and Welding Grade

• Nitrogen gas for typical industrial and welding use is at least 99.5 percent pure. It is the least expensive and most commonly available grade of nitrogen gas. This type of nitrogen is often used along with another gas such as argon or acetylene for welding; purity is not as great a concern as it is with nitrogen that is used for other purposes.