Novel Wavelength Standards in the Near Infrared

The goal of this work was to develop a new class of portable optical frequency references based on sub-Doppler spectroscopy inside gas-filled, hollow-core photonic bandgap (PBG) optical fiber. The change in line width with core size, and narrower transitions inside a new “kagome” structured optical fiber, were demonstrated. A simplified and more compact method for observing saturated absorption spectroscopy in half-sealed photonic bandgap fibers, called the “reflected pump technique,” was realized. Two systems, each consisting of a narrow-line fiber laser locked to the P(13) transition in acetylene, were constructed. By comparing those two systems, it was possible to obtain stability data on the fiber-filled references.

A mode-locked Cr:forsterite laser was developed and stabilized to a GPS-disciplined Rb clock with which to characterize the gas-filled, hollow-fiber optical frequency references. It was found that these lasers offer noisier “f0” beats than Ti:sapphire lasers, but a method was found to dramatically reduce the f0 beat width. A study was initiated into the source of the noise and the exact explanation for the narrowing. In the meantime, absolute frequency measurements of the fiber laser locked to the hollow fiber references are in progress.

A generally useful technique was developed for splicing the photonic bandgap fibers to solid-core fibers using an arc fusion splicer, which makes PBG fibers easier to use in the laboratory. Toward making a completely sealed photonic bandgap fiber cell, PBG was spliced to solid-core fibers inside a vacuum system using a CO2 laser. Efforts to reproduce this in an acetylene vapor proved unsuccessful, most likely due to the thermal properties of acetylene.

This work was done by Kristan L. Corwin of Kansas State University for the Air Force Research Laboratory. For more information, download the Technical Support Package (free white paper) at under the Photonics category. AFRL-0132

Posted in: Briefs, Photonics, Fiber optics, Lasers, Spectroscopy

Power Enhancement of a Rubidium Vapor Laser with a Master Oscillator Power Amplifier

The concept of alkali lasers was first suggested by Schalow and Townes in the late 1950s. In the 1970s, photo-dissociation of several of the alkali salts produced lasers with wavelengths ranging from the visible to the far infrared. Thirty years later, diode-pumped alkali lasers (DPAL) started rapidly gaining attention as highly efficient lasers as well as brightness converters. These systems partly owe their high efficiencies to the very small energy differences between the pump and lasing levels. Due to recent technological advances in the field of solid-state lasers, direct-diode pumping has provided the efficient, yet compact method for excitation.

Posted in: Briefs, Photonics, Amplifiers, Lasers, Thermal management

Real-Time Intelligent Chemical and Biological Nanosensors on a Flexible Platform

The objectives of this research are to examine the feasibility of real-time sensing of chemical and biological species by using the unique materials and electronic properties of carbon nanotubes, and to demonstrate the multi-agent sensing and information processing capabilities of such devices.

Posted in: Briefs, Materials, Sensors and actuators, Biomaterials, Chemicals, Nanotechnology

Templated Synthesis of Aluminum Nanoparticles for Stable Energetic Materials

Reactive nanoparticles as energetic materials have received much recent attention for a variety of existing and/or potential applications. Among more extensively investigated are nanosized (sub-100-nm) aluminum (Al) particles. Their large specific surface area and energy density, when coupled or mixed with oxidative species, make them unique combustible additives in propellant formulations. Nanoscale Al particles are also studied as high-capacity hydrogen storage materials. Therefore, significant effort has been made in the development of synthetic methodologies for Al nanoparticles of desired properties.

Posted in: Briefs, Materials, Hydrogen storage, Propellants, Fabrication, Aluminum, Nanomaterials

Performance and Operability of a Dual-Cavity Flame Holder in a Supersonic Combustor

Supersonic combustion has been of interest for many years in order to support future Air Force hypersonic missions. The current generation of hydrocarbon-fueled scramjet combustors typically requires a flame-holding device to facilitate flame ignition and stable combustion. The amount of time available for fuel injection, fuel-air mixing, and combustion is very short — on the order of 1 millisecond. This short dwell time, along with the relatively long ignition delay times of hydrocarbon fuels, makes the flow path and flame holder design extremely important. This study investigates the perormance and operability of using a symmetric dual-cavity flame holder flow path to stabilize and enhance supersonic combustion.

Posted in: Briefs, Physical Sciences, Hydrocarbons, Scramjet engines, Performance tests, Hypersonic and supersonic aircraft, Military aircraft

Gesture-Directed Sensor-Information Fusion Gloves

Current chemical-protection gear for warfighters on the ground inhibits electronic communication via keyboards, cell phones, and remote-control devices. To improve communications capabilities for the warfighter wearing protective gear in hazardous environments, a series of eGloves has been developed with a view toward freeing the warfighter of the need to type on a keyboard while wearing a Mission-Oriented Protective Posture (MOPP) suit. The eGloves can help the warfighter transmit gestures with the hands and fingers from within the protective gear, or they can be used to transmit encoded ASCII characters.

Posted in: Briefs, Physical Sciences, Communication protocols, Human machine interface (HMI), Product development, Protective clothing, Military vehicles and equipment

GigE Advanced Imaging Sensor

The Wide-Field Dynamic Range (WFDR) camera is a high-sensitivity, wide-field-of-regard sensor of importance to future military surveillance and survivability systems. It is intended to be used in harsh, noisy military platforms with multiple camera streams simultaneously gathered. By developing a Gigabit Ethernet (GigE) video transport solution for multiple cameras with low latency and high data reliability, a flexible processing architecture will be developed that allows optimization of processor throughput for real-time imaging in defense applications.

Posted in: Briefs, Physical Sciences, Architecture, Optics, Sensors and actuators, Surveillance, Military vehicles and equipment

Liquid-Crystal-Based Optical Phased Array for Steering Lasers

A paper describes the basic design and concepts of tunable liquid-crystal polarization gratings with a nematic liquid crystal (LC) optical phase plate, with a large, continuous in- plane gradient that is variable, and its application to a beam steering device with high efficiency.

Posted in: Briefs, Physical Sciences, Calibration, Lasers, Waveguides

Channel Modeling for a Wireless Transmission System

A wireless transmission system provides high-quality video transmission over severely impaired wireless links between nodes that are connected within airborne networks. The target bit rate for the proposed video communication can be in the range between 24 Kbps and 384 Kbps with relatively high visual quality. However, the system may operate at extreme low bit rates down to 10 Kbps and at high bit rates up to 1.5 Mbps. To accommodate the large range of the data rate for heterogeneous wireless links and devices, the H.264 SVC standard for video coding and decoding was adopted.

Posted in: Briefs, Information Technology, Mathematical models, Cryptography, Imaging, Wireless communication systems

Clock Oscillator

Crystek Crystals (Fort Myers, FL) has released the CCSO- 014-1090, a 1.090-GHz surface acoustic wave (SAW) clock oscillator that produces low-noise, low-jitter performance with true SineWave output, and -138 dBc/Hz phase noise at 10 kHz offset. It comes in a 14 PIN DIP hermetically sealed package, features a 12V input voltage, and generates a true sinewave with +12 dBm minimum output power. It has no sub-harmonic, and the second harmonic is -40 dBc max. Operating temperature is -55 °C to 105 °C.

Posted in: Products, RFM Catchall