Low Threshold Two-Dimensional Annular Bragg Lasers

Lasing at telecommunication wavelengths from annular resonators employing radial Bragg reflectors is demonstrated at room temperature under pulsed optical pumping. Sub milliwatt pump threshold levels are observed for resonators with 0.5-1.5 wavelengths wide defects of radii 7-8 mm. The quality factors of the resonator modal fields are estimated to be on the order of a few thousands. The electromagnetic field is shown to be guided by the defect. Good agreement is found between the measured and calculated spectrum.Comment: 8 pages, 4 figure

Collapsar Jets, Bubbles and Fe Lines

In the collapsar scenario, gamma ray bursts are caused by relativistic jets expelled along the rotation axis of a collapsing stellar core. We discuss how the structure and time-dependence of such jets depends on the stellar envelope and central engine properties, assuming a steady jet injection. It takes a few seconds for the jet to bore its way through the stellar core; most of the energy output during that period goes into a cocoon of relativistic plasma surrounding the jet. This material subsequently forms a bubble of magnetized plasma that takes several hours to expand, subrelativistically, through the envelope of a high-mass supergiant. Jet break-through and a conventional burst would be expected not only in He stars but possibly also in blue supergiants. Shock waves and magnetic dissipation in the escaping bubble can contribute a non thermal UV/X-ray afterglow, and also excite Fe line emission from thermal gas, in addition to the standard jet deceleration power-law afterglow.Comment: Ap.J. Letters, accepted 6/20/01, first subm 4/24/01; aaspp4, 9 pages, no figures; minor revision

Reliability growth during a development testing program

Binomial and trinomial mathematical models for reliability growth studies - statistical analysis of system failure

Vertically emitting annular Bragg lasers using polymer epitaxial transfer

Fabrication of a planar semiconductor microcavity, composed of cylindrical Bragg reflectors surrounding a radial defect, is demonstrated. A versatile polymer bonding process is used to transfer active InGaAsP resonators to a low-index transfer substrate. Vertical emission of in-plane modes lasing at telecom wavelengths is observed under pulsed optical excitation with a submilliwatt threshold

Band splitting and Modal Dispersion induced by Symmetry braking in Coupled-Resonator Slow-Light Waveguide Structures

We study the dispersion relations in slow-light waveguide structures consisting of coupled microdisk resonators. A group theoretical analysis of the symmetry properties of the propagating modes reveals an interesting phenomenon: The degeneracy of the CW and CCW rotating modes is removed, giving rise to two distinct transmission bands. This effect induces symmetry-based dispersion which may limit usable bandwidth of such structures. The properties of this band splitting and its impact on CROW performance for optical communications are studied in detail

Perspectives of High School and Community College Instructors on College Readiness

The preparation students need to complete college successfully is important to many stakeholders, including students, educators, and the community. Colleges struggle with enrollment and retention while high school teachers and community college instructors focus on the preparation of students to succeed in college. High school teachers and community college instructors are uniquely qualified to inform the determinants of college readiness across the continuum of education. This research study explored the perceptions of high school teachers and college instructors on the skills and behaviors required of students to be successful in college. This qualitative descriptive study was based on the conceptual framework of Conley\u27s 4 keys to college readiness and used interviews from 4 high school teachers and 5 community college instructors to explore the research question. The data were open coded multiple times to construct categories that revealed 3 major themes of college readiness: preparation, engagement, and personal characteristics. High school teachers and college instructors identified similar skills and behaviors displayed by college ready students. The information gleaned from the interviews about college readiness informed the creation of a professional development project to provide college faculty with strategies to facilitate the skills and abilities needed for college success within the context of college courses. This research and project development are a move towards positive social change in improving student success in college. Given the need for college completion and the rising cost of education, the social impact of ongoing work to improve college readiness and college success is imperative for students, colleges, and teachers at all levels

Observations of Arctic haze from the NCAR C-130 during TOPSE(2000) and evidence of nitric acid uptake and redistribution by cirrus clouds during TC4(2007) obtained from the NASA DC-8

The use of large aircraft is an invaluable tool for the study of chemical and physical processes in the atmosphere. In this thesis, some findings from two different major aircraft campaigns are reported. Part I examines measurements of fine aerosol sulfate in the Arctic made aboard the National Center for Atmospheric Research (NCAR) C-130 aircraft during the Tropospheric Ozone Production about the Spring Equinox Experiment (TOPSE) in 2000. Measurements highlighted the seasonal evolution of the Arctic haze phenomenon. Part II reports on measurements of nitric acid and various cloud microphysical properties made aboard the NASA DC-8 aircraft during Tropical Composition, Cloud, and Climate Coupling Experiment (TC4) in 2007. Results presented further our understanding of the role of tropical cirrus clouds in the redistribution of nitric acid which is an important component in upper tropospheric ozone production

Assessment of lithographic process variation effects in InGaAsP annular Bragg resonator lasers

Optical microresonators based on an annular geometry of radial Bragg reflectors have been designed and fabricated by electron-beam lithography, reactive ion etching, and an epitaxial transfer process. Unlike conventional ring resonators that are based on total internal reflection of light, the annular structure described here is designed to support optical modes with very small azimuthal propagation coefficient and correspondingly large free spectral range. The effect of lithographic process variation upon device performance is studied. Laser emission wavelength and threshold optical pump power are found to vary between similar devices given different electron doses during electron-beam lithography. As the resonance wavelength and quality factor of these resonators are very sensitive to environmental changes, these resonators make ideal active light sources that can be integrated into large arrays for gas and liquid sensing applications and are easily interrogated

Radiative Efficiencies of Continuously Powered Blast Waves

We use general arguments to show that a continuously powered radiative blast wave can behave self similarly if the energy injection and radiation mechanisms are self similar. In that case, the power-law indices of the blast wave evolution are set by only one of the two constituent physical mechanisms. If the luminosity of the energy source drops fast enough, the radiation mechanisms set the power-law indices, otherwise, they are set by the behavior of the energy source itself. We obtain self similar solutions for the Newtonian and the ultra-relativistic limits. Both limits behave self similarly if we assume that the central source supplies energy in the form of a hot wind, and that the radiative mechanism is the semi-radiative mechanism of Cohen, Piran & Sari (1998). We calculate the instantaneous radiative efficiencies for both limits and find that a relativistic blast wave has a higher efficiency than a Newtonian one. The instantaneous radiative efficiency depends strongly on the hydrodynamics and cannot be approximated by an estimate of local microscopic radiative efficiencies, since a fraction of the injected energy is deposited in shocked matter. These solutions can be used to calculate Gamma Ray Bursts afterglows, for cases in which the energy is not supplied instantaneously.Comment: 28 LaTeX pages, including 9 figures and 3 table