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Porter C.,University of Notre Dame | Porter C.,Kratos Defense and Security Solutions | Rennie M.,University of Notre Dame | Jumper E.,University of Notre Dame
AIAA Journal | Year: 2015

A fast low-order computational approach is presented for estimating the aero-optic effect of the rotor tip vortex system on helicopter-borne optical systems. The approach employs prescribed-wake methods that have been developed by the helicopter design community to rapidly generate realistic approximations to the vortex-wake systems of helicopters in hover and forward flight. With the geometry of the vortex-wake system defined, an experimentally validated computational method that employs the isentropic assumption is then used to compute pressure, temperature, density, and index-of-refraction fields in the selected computational domain. Predictions determined using the computational approach for the spatially and temporally resolved aero-optic aberrations on an optical system mounted on a helicopter in hover and forward flight are presented. Copyright © 2014 by Chris O. Porter, R. Mark Rennie, and Eric J. Jumper. Source

Chua S.-L.,Massachusetts Institute of Technology | Caccamise C.A.,Deloitte | Phillips D.J.,Kratos Defense and Security Solutions | Joannopoulos J.D.,Massachusetts Institute of Technology | And 4 more authors.
Optics Express | Year: 2011

We investigate laser emission from optically-pumped rotationally excited molecular gases confined in a metallic cavity. To this end, we have developed a theoretical framework able to accurately describe, both in the spatial and temporal domains, the molecular collisional and diffusion processes characterizing the operation of this class of lasers. The effect on the main lasing features of the spatial variation of the electric field intensity and the ohmic losses associated to each cavity mode are also included in our analysis. Our simulations show that, for the exemplary case of methyl fluoride gas confined in a cylindrical copper cavity, the region of maximum population inversion is located near the cavity walls. Based on this fact, our calculations show that the lowest lasing threshold intensity corresponds to the cavity mode that, while maximizing the spatial overlap between the corresponding population inversion and electric-field intensity distributions, simultaneously minimizes the absorption losses occurring at the cavity walls. The dependence of the lasing threshold intensity on both the gas pressure and the cavity radius is also analyzed and compared with experiment. We find that as the cavity size is varied, the interplay between the overall gain of the system and the corresponding ohmic losses allows for the existence of an optimal cavity radius which minimizes the intensity threshold for a large range of gas pressures. The theoretical analysis presented in this work expands the current understanding of lasing action in optically-pumped far-infrared lasers and, thus, could contribute to the development of a new class of compact far-infrared and terahertz sources able to operate efficiently at room temperature. © 2011 Optical Society of America. Source

Yagla J.J.,Kratos Defense and Security Solutions
Proceedings - 28th International Symposium on Ballistics, BALLISTICS 2014 | Year: 2014

When a high pressure gas is suddenly released from a pressure vessel through a valve, port, or piping sy stem, the rapid gas dynamic process is called a "blow down." When this process can be assumed isentropic, a set of equations can be found for the pressure in the vessel versus time. These equations appear in various textbooks and papers. The blow down equation contains the pressure, the initial pressure, the gas constant, the temperature, the port area, and the ratio of specific heats, and time. The usual equation can be rearranged to use the speed of sound rather than the temperature as a thermodynamic state variable. Then a dimensionless pressure and a dimensionless time group can be found. The time group contains the vessel volume, initial speed of sound, free area of the port, and the ratio of specific heats. The equation is very simple and applies to all blow downs. Examples of results of the equation and experimental data are shown for the discharge of burned propellant from an air bag gas generator and a 30mm cannon, and the discharge of compressed air from a bank of SCUBA tanks through a gun muzzle device. Source

Wellenius P.,North Carolina State University | Smith E.R.,Kratos Defense and Security Solutions | Leboeuf S.M.,Valencell, Inc. | Everitt H.O.,U.S. Army | And 2 more authors.
Journal of Applied Physics | Year: 2010

Europium gallium oxide (Eux Ga1-x) 2 O3 thin films were deposited on sapphire substrates by pulsed laser deposition with varying Eu content from x=2.4 to 20 mol %. The optical and physical effects of high europium concentration on these thin films were studied using photoluminescence (PL) spectroscopy, x-ray diffraction (XRD), and Rutherford backscattering spectrometry. PL spectra demonstrate that emission due to the D5 0 to F7 J transitions in Eu3+ grows linearly with Eu content up to 10 mol %. Time-resolved PL indicates decay parameters remain similar for films with up to 10 mol % Eu. At 20 mol %, however, PL intensity decreases substantially and PL decay accelerates, indicative of parasitic energy transfer processes. XRD shows films to be polycrystalline and beta-phase for low Eu compositions. Increasing Eu content beyond 5 mol % does not continue to modify the film structure and thus, changes in PL spectra and decay cannot be attributed to structural changes in the host. These data indicate the optimal doping for optoelectronic devices based on (Eux Ga1-x) 2 O3 thin films is between 5 and 10 mol %. © 2010 American Institute of Physics. Source

Smith E.R.,Kratos Defense and Security Solutions | Gruber J.B.,University of Texas at San Antonio | Wellenius P.,North Carolina State University | Muth J.F.,North Carolina State University | And 2 more authors.
Physica Status Solidi (B) Basic Research | Year: 2010

In pulsed laser deposition of the sesquioxide semiconductor Gd2O3, adjusting the chamber oxygen pressure controls the crystalline structure of the host. This technique was used to deposit thin films of nominally 1.6% by weight europiumdoped, cubic phase Gd2O3 using 50 mTorr of oxygen. Structural measurements using high-resolution transmission electron microscopy and selected area electron diffraction confirm the films were polycrystalline, cubic phase Eu:Gd2O3. The spectroscopic assignment of emission lines to specific radiative transitions within the trivalent Eu ion is confirmed by theoretical analysis of the appropriate crystal field Hamiltonian. Detailed crystal-field splittings are presented for the 5DJ=0-2 and 7FJ=0-5 multiplet manifolds of Eu3+ in this host material. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

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