Browsing by Autor "Gazeas, Kosmas"

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    Imaging LIDAR performance model development and simulation
    (Revista Boliviana de Física, 2012) Gazeas, Kosmas; Pereira do Carmo, João
    LIDARS involved in space applications are mainly used as atmospheric monitoring sensors or as altimeters (i.e. ALADIN, ATLID, LOLA, MOLA or BELA). In future exploration missions, like the Mars Sample Return mission, LIDARs shall be implemented as imaging and ranging devices for different applications: in the support of the autonomous landing of a spacecraft on a planetary surface; during the deployment of rovers provided with autonomous navigation and hazard avoidance capabilities; and for the support of rendezvous and docking operations between spacecrafts in orbit. The ability to rapidly derive 3-D topographic information is vital for the realization of these missions. We present a recently developed Imaging LIDAR (IL) performance model, which was created in order to simulate and optimize Imaging LIDAR instruments, under various scenarios and applications. The IL performance model is based primarily on the LIDAR equation and takes into account all basic parameters of a LIDAR device, which apparently affect the overall instrument performance, such as the laser power, telescope aperture, detection method, background illumination, range gating etc.
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    Optical study of the laser beam propagation on Nd:YAG crystal slab for space LIDAR missions
    (Revista Boliviana de Física, 2012) Gazeas, Kosmas; Tzeremes, George; Armandillo, Errico
    The present paper reports on the development of a simulation and modeling tool which allows to estimate the propagation effects on a laser beam passing through a laser-diode-pumped Nd:YAG slab amplifier. This in-house research work is motivated by current ESA spaceborne LIDAR programs (ADM, Earth Care) as a mean to provide understanding of the LIDAR beam pointing stability as results of thermal and mechanical stresses. A dynamic model has been generated that can simulate the optical characteristics of the laser beam propagation, as a result of the various thermal and mechanical processes occurring inside the laser Pumping Unit and the thermal lensing occurring along the crystal slab. The simulation results and their comparison with actual laboratory tests are being presented and discussed. The model developed is based on the Finite Element Model (FEM) methodology, where the slab as an active element is "broken" down into interdependent segments, each simulated as being heated by an individual LD source. The light beam is propagated along the slab using dynamically varying boundary conditions, to the next so to account for the cumulated thermal and mechanical loads.