Special Coverage


High-Performance Processor of Hyperspectral Images

Efficient algorithms analyze pixel spectra to estimate abundances of materials. The Remote Sensing Hyperspectral Engine (RSHE) is a special-purpose, portable computer that performs high-performance processing of hyperspectral image data collected by a remote-sensing optoelectronic apparatus. Typically, the remote-sensing apparatus is airborne or spaceborne, the images are of terrain, and the purpose of collecting and analyzing the image data is to estimate the spatially varying abundances of materials of interest. Remote-sensing applications in which the RSHE could prove beneficial include assessment of crops, exploration for minerals, identification of military targets, urban-planning studies, environmental assessment, and large-area search-and- rescue operations.

Posted in: Photonics, Briefs, Tech Briefs, Photonics


Hand-Held Optoelectronic Particulate Monitors

Data on concentrations and sizes are obtained from diffraction of light. Optoelectronic instruments are being developed for use in measuring the concentrations and sizes of microscopic particles suspended in air. The instruments could be used, for example, to detect smoke, explosive dust in grain elevators, or toxic dusts in industrial buildings. Like some older, laboratory-bench-style particulate monitors, these instruments are based on diffraction of light by particles. However, these instruments are much smaller; exploiting recent advances in optics, electronics, and packaging, they are miniaturized into compact, hand-held units.

Posted in: Briefs, TSP, ptb catchall, Tech Briefs, Photonics


Laser Scanning Improves Dimensional Accuracy of Automotive Gas Tanks

In the past, one of the world’s leading manufacturers of fuel tanks used coordinate measuring machines (CMMs) to inspect first articles. The geometry of the tanks is so complex, however, that it was difficult to fully inspect the surface one point at a time. Inergy Automotive Systems has achieved significant improvements in quality by switching to laser scanning, which “paints” the surface of the tank with a laser and then uses a sensor to capture all the points in the laser’s path. The new approach generates a solid model of the as-built part that can be compared to the design intent to highlight the full extent of any differences between the two. As a result, Inergy can make required tooling changes with a higher level of confidence and ensure that production parts meet customer specifications.

Posted in: Articles, Features, ptb catchall, Photonics


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


Electroform/Plasma-Spray Laminates for X-Ray Optics

Properties of lightweight components can be optimized. Goddard Space Flight Center, Greenbelt, Maryland Electroform/ plasma-spray laminates have shown promise as lightweight, strong, low-thermal-expansion components for x-ray optics. The basic idea is to exploit both (1) the well-established art of fabrication of optical components by replication and (2) plasma spraying as a means of reinforcing a thin replica optic with one or more backing layer(s) having tailorable thermomechanical properties. In x-ray optics as in other applications, replication reduces the time and cost of fabrication because grinding and polishing can be limited to a few thick masters, from which many lightweight replicas can thereafter be made.

Posted in: Photonics, Briefs, ptb catchall, Tech Briefs, Photonics


Preventing Raman Lasing in High-Q WGM Resonators

Raman-lasing threshold power is increased through suitable choice of dimensions. NASA’s Jet Propulsion Laboratory, Pasadena, California A generic design has been conceived to suppress the Raman effect in whispering-gallery-mode (WGM) optical resonators that have high values of the resonance quality factor (Q). Although it is possible to exploit the Raman effect (even striving to maximize the Raman gain to obtain Raman lasing), the present innovation is intended to satisfy a need that arises in applications in which the Raman effect inhibits the realization of the full potential of WGM resonators as frequency-selection components. Heretofore, in such applications, it has been necessary to operate high-Q WGM resonators at unattractively low power levels to prevent Raman lasing. (The Raman-lasing thresholds of WGM optical resonators are very low and are approximately proportional to Q–2.)

Posted in: Photonics, Briefs, TSP, ptb catchall, Tech Briefs, Photonics


Procedures for Tuning a Multiresonator Photonic Filter

A desired high-order filter function can be established and maintained. NASA’s Jet Propulsion Laboratory, Pasadena, California Two procedures have been devised for tuning a photonic filter that comprises multiple whispering-gallery-mode (WGM) disk resonators. As used here, “tuning” signifies locking the filter to a specific laser frequency and configuring the filter to obtain a desired high-order transfer function.

Posted in: Photonics, Briefs, TSP, ptb catchall, Tech Briefs, Photonics