Application Briefs

Nanotechnology’s Role in Mid-Infrared Laser Development

Progress in developing improved semiconductor lasers with emission in the mid-IR spectral region (≈3 μm to ≈15 μm) has depended heavily on the use of nanometer-scaled structures. Mid-IR quantum cascade lasers (QCLs), for example, represent a “tour de force” of semiconductor nanotechnology where large band gap GaAs and InP based III-V semiconductor multiple quantum well (MQW) structures are used to engineer intersubband transition energies that enable mid-IR photon emission. First developed at Bell Labs and now demonstrated by many other groups, QCLs have offered great hope as a new mid-IR light source for applications such as trace gas sensing [1] and isotope ratio measurement [2]. However, from their first use [3], QCL operation has been complicated by high power inputs, typically a minimum of 5 watts, and associated high heat load in packaged systems. Considering the significant resources devoted to QCL development and the apparent lack of progress in reducing high power consumption levels over the last ten years, it is likely that this problem is fundamental to QCL design. QCLs require high applied voltages (>8 volts) to achieve the necessary band alignment and the cascade effect, so focusing on this contribution is not expected to be fruitful. The other contribution, high threshold current (≈300 mA), appears to be fundamental to all intersubband lasers where there are parallel energy versus momentum dispersion relationships for electrons associated with intraband laser transitions. Figure 1, which depicts E vs. k subband dispersion for a three-level QCL gain medium, shows that there is an efficient competing non-radiative relaxation pathway for excited electrons when they scatter with non-zone-center optical or acoustic phonons. Since low energy subband separation is required for mid-IR light emission and the sub-band dispersions are parallel, such electron-phonon scattering will always be an efficient upper laser state depopulation mechanism thus necessitating high electron currents to achieve population inversion. Note, as indicated in Figure 1, the deliberate use of electron-phonon resonance with longitudinal optical (LO) phonons in QCL designs to depopulate the lower laser transition subband states. Exploitation of such electrophonon resonance effects in reducing laser threshold currents will be discussed below within the context of interband IV-VI mid-IR lasers.

Posted in: Application Briefs, Applications, ptb catchall, Photonics

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Spectroscopy of Planetary Systems Made Possible by Focal Plane Detector

NIRSpec STM Focal Plane Detector ITT Corp. White Plains, NY 914-641-2000 www.itt.com The James Webb Space Telescope (JWST) is scheduled for launch in 2013 with the goal of discovering the first galaxies that formed in the early Universe. On board the JWST is ITT Corp.’s Near Infrared Spectrometer (NIRSpec) Structural Thermal Model (STM) focal-plane detector packaging that will allow scientists to perform spectroscopy on planetary systems and further the studies on the origins of life.

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New Testing Equipment Helps NASA Prepare for Telescope Launch

LabVIEW FPGA National Instruments Austin, TX 888-280-7645 www.ni.com NASA’s next-generation successor to the Hubble Space Telescope, the James Webb Space Telescope (JWST), features the Near Infrared Spectrograph (NIRSpec), which is equipped with more than 250,000 microshutters designed to observe thousands of distant galaxies to better understand the origins of the universe. The microshutters are microelectromechanical system (MEMS) devices that physically open and close for light exposure, similar to shutters on a camera. Engineers at NASA’s Goddard Space Flight Center in Maryland have tested the microshutters using National Instruments' LabVIEW FPGA to control the shutters in a test chamber.

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Magnetostrictive Sensor System Helps High-Performance Car Brake Quickly

The Bugatti Veyron is the world’s fastest street-legal motor vehicle, a high-end passenger car that can reach speeds of more than 200 miles per hour. These high speeds require extra braking power, which comes from raising an aerodynamic rear wing and generating additional braking forces. The Veyron can decelerate from 230 mph to 0 in only 7.5 seconds, largely due to the extra down force achieved with the rear wing, which is raised within 0.4 seconds to a 55° angle.

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Creating Motion Control and Drive Electronics With an FPGA-based System

Complex machines in semiconductor manufacturing often have tough performance requirements for motion control. When traditional PLCor PC-based motion controllers fail to meet these requirements, machine builders turn to custom board development — a time-consuming and expensive process. Recent advances in embedded technologies have made it possible to use FPGA-based COTS platforms to not only meet those requirements, but also to get to market faster by using graphical system design.

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Simulation Software Enables Development and Validation of NASA Probe Bus and Probe Carrier

MSC Nastran and MSC Adams Enterprise Simulation Software MSC.Software Corp. Santa Ana, CA 714-540-8900 www.mscsoftware.com NASA’s MIDEX Mission THEMIS (Time History of Events and Macroscale Interactions during Substorms) aims to resolve one of the oldest mysteries in space physics: namely, to determine what physical process in near-Earth space initiates the violent eruptions of the aurora that occur during substorms in the Earth’s magnetosphere. THEMIS is a 2-year mission consisting of five identical probes that will study the violent colorful eruptions of Auroras.

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Imaging Software Provides Access to Critical Mission Images Across NASA

Presto Imaging Software Inmagic Woburn, MA 781-287-6277 www.inmagic.com With every space shuttle mission, hundreds of individuals across NASA need to access extensive photographs, video footage, and other imaging assets in order to monitor launch results, review design decisions, and ensure mission safety. Additional video footage and still images shot on orbit enables NASA engineers to compare pre-flight and in-flight images in order to assess functionality and highlight areas that warrant further scrutiny. Until recently, only the Image Analysis Team (IAT) staff could view these baseline images, and sometimes with delays due to the complexity of accessing them.

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