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Arisholm G.,FFI Norwegian Defence Research Establishment
Frontiers in Optics, FIO 2012

Simulation can be useful for design of OPCPAs and to improve the understanding of the underlying physics. Methods for efficient simulation of realistic systems will be presented. © OSA 2012. Source

Advanced numerical simulations show that the performance of high pulse energy optical parametric oscillators (OPOs) based on quasi phase matched materials can be significantly improved by the use of a non-collinear pumping scheme in a RISTRA geometry. For a PPLNbased RISTRA OPO with a 4 mm diameter pump beam, the output beam quality was improved from M2 ~ 25 to M2 ~ 1.5 with 150 mrad external pump angle, while the decline in output energy was small. © OSA 2013. Source

Nysaeter A.,FFI Norwegian Defence Research Establishment | Iwe H.,Radar Sensor AS
2016 IEEE Radar Conference, RadarConf 2016

In a practical colocated MIMO radar design case, there will often not be a free choice of locations for single element antennas. Antenna parts may be available as rectangular arrays of antenna elements located on tiles, and multiple TX/RX modules may be assembled on TX/RX boards to be attached to the antenna tiles from the backside. The first part of the paper focuses on optimum attachment of transmit/receive modules to antenna tiles for a non-Adaptive MIMO radar. The main lobe width and the maximum side lobe level have been minimized using genetic algorithms (GA). In the second part of the paper, transmit beamforming has been optimized using semidefinite relaxation with 4 orthogonal beams from the optimized array antenna. The antenna and processing performance using 64 active TX/RX channels have been compared to a conventional 256 elements array antenna. © 2016 IEEE. Source

Jo H.K.,FFI Norwegian Defence Research Establishment
25th International Symposium on Ballistics, ISB 2010

Fragments from a VBIED fall into two categories; pre-formed and thin- plate fragments. Thin-plate fragments are deformed and may not be described using existing drag coefficient curves. Using high-speed video footage from full-scale experiments, key fragment variables are determined and used to examine the applicability of existing drag coefficient curves to such fragments. To improve predictions of the throw distance, new drag coefficient curves are developed through finite-element simulations using ANSYS AUTODYN. The new drag coefficient curves and better area estimation techniques enable us to improve predictions significantly. Source

Seidel M.,Max Planck Institute of Quantum Optics | Arisholm G.,FFI Norwegian Defence Research Establishment | Brons J.,Max Planck Institute of Quantum Optics | Pervak V.,Ludwig Maximilians University of Munich | Pronin O.,Max Planck Institute of Quantum Optics
Optics Express

Spectral broadening in bulk material is a simple, robust and low-cost method to extend the bandwidth of a laser source. Consequently, it enables ultrashort pulse compression. Experiments with a 38 MHz repetition rate, 50 W average power Kerr-lens mode-locked thin-disk oscillator were performed. The initially 1.2 μJ, 250 fs pulses are compressed to 43 fs by means of self-phase modulation in a single 15 mm thick quartz crystal and subsequent chirped-mirror compression. The losses due to spatial nonlinear effects are only about 40 %. A second broadening stage reduced the Fourier transform limit to 15 fs. It is shown that the intensity noise of the oscillator is preserved independent of the broadening factor. Simulations manifest the peak power scalability of the concept and show that it is applicable to a wide range of input pulse durations and energies. © 2016 Optical Society of America. Source

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