Physical Sciences

Handheld Imaging Device for Security Applications

Intelligent radar core provides three-dimensional, through-wall imaging capabilities.A standalone, handheld, through-wall radar unit is under development to provide three-dimensional feedback on the location and movement of people inside buildings. Applications include military and emergency service such as hostage situations and search and rescue. The unit, which can be held against a wall or mounted on a tripod located up to 2 meters away, transmits low-frequency ultrawideband (UWB) radar pulses that pass through building materials over 40 cm thick and detects activity over a range of up to 15 meters.

Posted in: Physical Sciences, Briefs

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Broadband External-Cavity Diode Laser

This relatively simple, inexpensive device is suitable for use in survey spectroscopy.A broadband external-cavity diode laser (ECDL) has been invented for use in spectroscopic surveys preparatory to optical detection of gases. Heretofore, commercially available ECDLs have been designed, in conjunction with sophisticated tuning assemblies, for narrow- band (and, typically, single-frequency) operation, as needed for high sensitivity and high spectral resolution in some gas-detection applications. However, for preparatory spectroscopic surveys, high sensitivity and narrow-band operation are not needed; in such cases, the present broadband ECDL offers a simpler, less-expensive, more-compact alternative to a commercial narrowband ECDL.

Posted in: Physical Sciences, Photonics, Briefs

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High-Efficiency Solar Cells Using Photonic-Bandgap Materials

Energy-conversion efficiencies exceeding 50 percent may be possible.Solar photovoltaic cells would be designed to exploit photonic-bandgap (PBG) materials to enhance their energy- conversion efficiencies, according to a proposal. Whereas the energy-conversion efficiencies of currently available solar cells are typically less than 30 percent, it has been estimated that the energy- conversion efficiencies of the proposed cells could be about 50 percent or possibly even greater.

Posted in: Physical Sciences, Photonics, Briefs

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High Peak Power Fiber Amplifiers Operating at Eye-Safe Wavelengths

PM-clad fibers enable scaling with single transverse mode beam quality.Recent advances in fiber technology have enabled a dramatic increase in the power delivered from fiber based amplifiers and lasers. This is particularly true at the 1060-nm wavelength where ytterbium (Yb)-doped fibers operate, with state-of-the-art peak powers now approaching 1 MW (1 mJ and 1 ns) delivered with single-mode, near diffraction limited beam quality. However, progress on scaling fiber-based eye-safe devices, such as those operating around the 1550-nm wavelength regime, based on Er:Yb (erbium:ytterbium) co-doped fibers has been much slower. The progress at this wavelength range hampered by the lack of suitable large mode area (LMA) fibers.

Posted in: Physical Sciences, Photonics, Briefs

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Improved Thermal Matching of Materials for Hermetic Optical Windows

A wider range of glass materials can be bonded when custom alloys are used to create the frame. A family of iron-nickel and ironnickel- cobalt alloys made using metal injection technology (MIT) has been designed to match the coefficient of thermal expansion (CTE) of select optical glass materials more closely than commonly available wrought alloys of similar composition. Using these glass and metal combinations, custom windows can be developed with improved optical properties, greater hermeticity levels, and lower residual stress.

Posted in: Physical Sciences, Photonics, Briefs

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Spectral Beam Combining Architecture for Diode Laser Bars

Individual laser controls are not necessary.A new Spectral Beam Combining (SBC) architecture is currently being developed to address the limitations diode laser bars in applications requiring high output power and excellent beam quality. The architecture features an external resonant cavity with a dispersive element to automatically control the wavelength of each laser, thereby eliminating the need for individual laser controls.

Posted in: Physical Sciences, Photonics, Briefs

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Adding GaAs Monolayers to InAs Quantum-Dot Lasers on (001) InP

Modifications enable long-wavelength lasing at higher temperatures. In a modification of the basic configuration of InAs quantum-dot semiconductor lasers on (001)lnP substrate, a thin layer (typically 1 to 2 monolayer thick) of GaAs is incorporated into the active region. This modification enhances laser performance: In particular, whereas it has been necessary to cool the unmodified devices to temperatures of about 80 K in order to obtain lasing at long wavelengths, the modified devices can lase at wavelengths of about 1.7 μm or more near room temperature.

Posted in: Physical Sciences, Photonics, Briefs

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