Informational Signage Increases Awareness of a Rattlesnake in a Canadian Urban Park System

Human–snake conflict results in negative outcomes for people and snakes, and if left unmanaged, could undermine conservation efforts. One approach to managing conflict between people and snakes is to use signage to inform members of the public on the presence of venomous snakes and measures to prevent snakebites. To be an effective tool, however, signs must first be noticed, then read and understood by the target audience. As part of conservation efforts targeting eastern massasauga rattlesnakes (Sistrurus catenatus) in southwestern Ontario, Canada, we tested the effectiveness of signage at increasing awareness of its presence, status and threats, and snakebite prevention. We installed 6 informational signs at trailheads in a park occupied by massasaugas and conducted a random questionnaire survey of visitors during a 3-week period before (n = 51) and after (n = 54) sign installation. Awareness of the presence of massasauga habitat increased significantly after sign installation, whereas awareness of status, threats, and snakebite prevention methods did not change. Our results suggest that informational signs were effective, to some degree, at short-term information sharing with recreationists in the context of venomous snake conservation. This cost-effective approach warrants consideration as part of an overall strategy to mitigate human–snake conflict

Quantum Noise and Polarization Fluctuations in Vertical Cavity Surface Emitting Lasers

We investigate the polarization fluctuations caused by quantum noise in quantum well vertical cavity surface emitting lasers (VCSELs). Langevin equations are derived on the basis of a generalized rate equation model in which the influence of competing gain-loss and frequency anisotropies is included. This reveals how the anisotropies and the quantum well confinement effects shape the correlations and the magnitude of fluctuations in ellipticity and in polarization direction. According to our results all parameters used in the rate equations may be obtained experimentally from precise time resolved measurements of the intensity and polarization fluctuations in the emitted laser light. To clarify the effects of anisotropies and of quantum well confinement on the laser process in VCSELs we therefore propose time resolved measurements of the polarization fluctuations in the laser light. In particular, such measurements allow to distinguish the effects of frequency anisotropy and of gain-loss anisotropy and would provide data on the spin relaxation rate in the quantum well structure during cw operation as well as representing a new way of experimentally determinig the linewidth enhancement factor alpha.Comment: 16 pages and 3 Figures, RevTex, to be published in Phys. Rev.

Antiresonances and Ultrafast Resonances in a Twin Photonic Oscillator

We consider the properties of the small-signal modulation response of symmetry-breaking phase-locked states of twin coupled semiconductor lasers. The extended stability and the varying asymmetry of these modes allows for the introduction of a rich set of interesting modulation response features, such as sharp resonances and anti-resonance as well as efficient modulation at very high frequencies exceeding the free running relaxation frequencies by orders of magnitude.Comment: 6 pages, 5 figure

Exceptional Points in Two Dissimilar Coupled Diode Lasers

We show the abundance of Exceptional Points in the generic asymmetric configuration of two coupled diode lasers, under nonzero optical detuning and differential pumping. We pinpoint the location of these points with respect to the stability domains and the Hopf bifurcation points, in the solution space as well as in the space of experimentally controlled parameters.Comment: 5 pages, 4 figure

Temperature-dependent characteristics and single-mode performance of AlGaInP-based 670-690-nm vertical-cavity surface-emitting lasers

Includes bibliographical references.We report on temperature dependent characteristics and single mode performance of one-wave cavity, planar implanted, AlGaInP-based vertical-cavity surface emitting lasers. By optimizing the overlap between the gain peak and the cavity mode of the structure, we demonstrate record device performance, including 8.2 mW maximum output power and 11% power conversion efficiency for multimode operation and 1.9 mW and 9.6% power conversion efficiency for single mode operation at 687 nm. Improved performance at elevated temperatures is also achieved, with 1.5 mW output power demonstrated at 50 °C from a 15-μm-diameter device.This letter was supported by the US Department of Energy under contract no. DE-AC04-94AL85000

Index guiding dependent effects in implant and oxide confined vertical-cavity lasers

Includes bibliographical references.Implant and oxide confined vertical-cavity surface-emitting lasers are compared in terms of properties dependent upon the nature of index guiding in the two structures including CW threshold current scaling with size, light-current linearity, pulsed operation delay, and beam profiles. The oxide confined lasers, fabricated by wet thermal oxidation, have a built-in index guide and thus exhibit substantially better properties than do lasers from the same wafer fabricated by proton implantation which rely on a thermal lens to reduce diffraction losses.This work was supported by the U.S. Department of Energy under Contract DEAC04-94AL85000

Gain-dependent polarization properties of vertical-cavity lasers

Includes bibliographical references.We show that the partitioning of power into the two orthogonal eigen polarizations of infra-red gain-guided vertical-cavity lasers depends upon the relative spectral overlap of the nondegenerate polarization cavity resonances with the laser gain spectrum. Furthermore, at the condition where the polarization resonances and the peak laser gain are aligned, abrupt switching of power between the eigen polarizations is observed as the gain sweeps through the polarization resonances. The gain-dependence of the polarization requires spectral splitting between the eigen polarizations, which is found to be strongly influenced by local strain. The polarization of the fundamental and higher-order spatial modes can be selected and maintained for all InGaAs vertical-cavity lasers in a wafer simply by employing a 20 nm or greater blue-shift offset of the peak laser gain relative to the cavity resonances.The work performed at Sandia National Laboratories is supported by the U. S. Department of Energy under contract No. DE-AC04-94AL85000

Photonic Crystal Vertical Cavity Lasers

Photonic crystal confinement in vertical cavity surface-emitting lasers (VCSELs) is a robust and reliable technology for achieving operation in the fundamental lateral mode and is potentially applicable to a variety of materials systems and operating wavelengths. We demonstrate photonic crystal VCSELs operating in a single transverse mode with over 30 dB side mode suppression and over 1 mW of output power. These lasers have been subjected to a post-process technique to introduce the etched holes making up the photonic crystals that surround a centralized defect in which lasing occurs. We also show that coupling between adjacent defects in a photonic lattice is possible, further increasing the power available in the devices