Phase-locked arrays of unstable resonator semiconductor lasers

A phase-locked array of several unstable resonator semiconductor lasers is demonstrated. Single lateral mode was obtained for currents I<2.5Ith, and partial spatial coherence for I<=5Ith, with an optical output power of 0.95 W

Low-gravity liquid-vapor interface configurations in spheroidal containers

Determining liquid-vapor interface configuration in oblate spheroids in low-gravity environment

Foreword: Making Sense of Information for Environmental Protection

Despite the ubiquity of information, no one has proposed calling the present era the Knowledge Age. Knowledge depends not only on access to reliable information, but also on sound judgment regarding which information to access and how to situate that information in relation to the values and purposes that comprise the individual\u27s or the social group\u27s larger projects. This is certainly the case for wise and effective environmental governance. A regulator needs accurate information to understand the nature of a problem and the consequences of potential responses. Likewise, the regulated community needs information to decide how best to comply with adopted rules, and the public needs information in order to accept the credibility and legitimacy of the regulatory regime. But governance also requires judgment regarding how to manage information itself - how to structure burdens of proof in light of goals such as public safety or promotion of economic growth, how to balance the public\u27s interest in disclosure against competing aims such as national security or the protection of trade secrets, whether to withhold information in the belief that it may actually be harmful to the recipient, and so on. This paper, written as a foreword for the Texas Law Review\u27s symposium issue, Harnessing the Power of Information for the Next Generation of Environmental Law, provides a model to understand the role of information in environmental law - how it is generated, utilized, and disseminated within regulatory processes. Drawing on the diverse and significant insights of the symposium articles, the paper attempts both to make sense of the role of information in environmental protection and to highlight significant questions and concerns

A comparison of measured and calculated upwelling radiance over water as a function of sensor altitude

A comparison is made between remote sensing data measured over water at altitudes ranging from 30 m to 15.2 km and data calculated for corresponding altitudes using surface measurements and an atmospheric radiative transfer model. Data were acquired on June 22, 1978 in Lake Erie, a cloudless, calm, near haze free day. Suspended solids and chlorophyll concentrations were 0.59 + or - 0.02 mg/1 and 2.42 + or - 0.03 micrograms/1 respectively throughout the duration of the experiment. Remote sensor data were acquired by two multispectral scanners each having 10 bands between 410 nm and 1040 nm. Calculated and measured nadir radiances for altitudes of 152 m and 12.5 km agree to within 16% and 14% respectively. The variation in measured radiance with look angle was poorly simulated by the model. It was concluded that an accurate assessment of the source of error will require the inclusion in the analysis of the contributions made by the sea state and specular sky reflectance

Lateral coupled cavity semiconductor laser

We report the fabrication and operation of a lateral coupled cavity semiconductor laser that consists of two phase-locked parallel lasers of different lengths and with separate electrical contacts. Mode selectivity that results from the interaction between the two supermodes is investigated experimentally. Frequency selectivity and tunability are obtained by controlling the current to each laser separately. Highly stable single mode operation is also demonstrated

Frequency selectivity in laterally coupled semiconductor laser arrays

A longitudinal-mode analysis of a system of laterally coupled waveguided resonators is presented in the coupled-mode approximation. It is shown that variations in the mirror reflectivity of the individual channels result in coupling between the supermodes of the structure. This may lead to mode suppression by modulation of the threshold gain of different Fabry-Perot modes

Lateral coherence properties of broad-area semiconductor quantum well lasers

The lateral coherence of broad-area lasers fabricated from a GaAs/GaAlAs graded index waveguide separate confinement and single quantum well heterostructure grown by molecular-beam epitaxy was investigated. These lasers exhibit a high degree of coherence along the junction plane, thus producing a stable and very narrow far field intensity distribution

Confocal unstable-resonator semiconductor laser

GaAs/GaAlAs heterostructure lasers with a monolithic confocal unstable resonator were demonstrated. The curved mirrors satisfying the confocal condition were fabricated by etching. Close to threshold, the lasers operate in a single lateral mode with a nearly collimated output beam. A single-lobe far-field intensity distribution as narrow as 1.90 full width at half maximum was measured

Atmospheric temperature measurements, using Raman lidar

The Raman-shifted return of a lidar system had been used to make atmospheric temperature measurements. The measurements were made along a horizontal path at temperatures ranging from -30 to 30 C and at ranges of about 100 meters. The temperature data were acquired by recording the intensity ratio of two portions of the rotational Raman spectrum, which were simultaneously sampled from a preset range. These tests verified that the theoretical predictions formulated in the design of the system were adequate. Measurements were made to an accuracy of + or - 4 C with 1-minute temporal resolution

Concept for advanced satellite communications and required technologies

The advanced communications technology satellite (ACTS) program of NASA is aimed at the development of high risk technologies that will enable exploiting higher frequency bands and techniques for improving frequency reuse. The technologies under development include multiple beam spacecraft antennas, on-board switching and processing, RF devices and components and advanced Earth stations. The program focus is on the Ka-band (30/20 GHz) as the implementing frequency since it has five times the bandwidth of either the C- or Ku-bands. However, the technology being developed is applicable to other frequency bands as well and will support a wide range of future communications systems required by NASA, other Government agencies and the commercial sector. An overview is presented of an operational 30/20 GHz satellite system that may evolve. How the system addresses service requirements is discussed, and the technology required and being developed is considered